Detail Practice: Photovoltaics : Technology, Architecture, Installation 9783034615709, 9783034603690

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Photovoltaics Technology Architecture Installation

Bernhard Weller Claudia Hemmerle Sven Jakubetz Stefan Unnewehr

Edition Detail

∂ Practice

Photovoltaics Technology Architecture Installation

Bernhard Weller Claudia Hemmerle Sven Jakubetz Stefan Unnewehr

Birkhäuser Edition Detail

This book was produced by a team consisting of construction engineers, one architect and one engineer specialised in renewable energies at the Building Design Institute, Faculty of Civil Engineering, Dresden TU www.bauko.bau.tu-dresden.de in conjunction with the Institut für internationale Architektur-Dokumentation GmbH & Co. KG www.detail.de.

Authors: Bernhard Weller, Prof. Dr.-Ing. Claudia Hemmerle, Dipl.-Ing. Sven Jakubetz, Dipl.-Ing. Stefan Unnewehr, Dipl.-Ing. Architect Drawings: Heiko Mattausch, Dipl.-Ing.

Editor: Project Management: Steffi Lenzen, Dipl.-Ing. Architect Editorial services: Melanie Weber, Dipl.-Ing. Architect Editorial assistants: Nicola Kollmann, Dipl.-Ing. Architect; Petra Sparrer; Florian Köhler; Peter Popp, Dipl.-Ing.; Eva Schönbrunner, Dipl.-Ing. Drawings: Nicola Kollmann, Dipl.-Ing. Architect; Simon Kramer, Dipl.-Ing.; Elisabeth Krammer, Dipl.-Ing.; Melanie Denys, Dipl.-Ing.; Ralph Donhauser, Dipl.-Ing. Translators (German/English): Gerd H. Söffker, Philip Thrift, Hannover © 2010 Institut für internationale Architektur-Dokumentation GmbH & Co. KG, Munich An Edition DETAIL book ISBN: 978-3-0346-0369-0 Printed on acid-free paper made from cellulose bleached without the use of chlorine. This work is protected by copyright. All rights are reserved, specifically the right of translation, reprinting, citation, re-use of illustrations and tables, broadcasting, reproduction on microfilm or in other ways, and storage in databases of the material, in whole or in part. For any kind of use, permission of the copyright owner must be obtained. Typesetting & production: Simone Soesters Printed by: Aumüller Druck, Regensburg 1st edition, 2010 This book is also available in a German language edition (ISBN 978-3-920034-25-6). A CIP catalogue record for this book is available from the Library of Congress, Washington D.C., USA. Bibliographic information published by Die Deutsche Bibliothek Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliographie; detailed bibliographic data is available on the internet at http://dnb.ddb.de.

Institut für internationale Architektur-Dokumentation GmbH & Co. KG Hackerbrücke 6, D-80335 München Telefon: +49/89/38 16 20-0 Telefax: +49/89/39 86 70 www.detail.de Distribution Partner: Birkhäuser GmbH PO Box 133, 4010 Basel, Switzerland Tel.: +41 61 2050707 Fax: +41 61 2050792 e-mail: [email protected] www.birkhauser.ch

∂ Practice Photovoltaics

Contents

7

Introduction

11 14 19 22 25 26 29 32

Generating and using solar electricity The sun as a source of energy Solar cells – turning light into electricity Modules Performance Photovoltaic systems System technology Yields and economics Ecology

35 36 39 40 41 46

Designing with photovoltaics Features of crystalline photovoltaics Differences between traditional and PV materials and products Photovoltaics and its relationship with the building Design strategies Design options Transparency and design potential

50 52 55 62 66

Construction and integration Designing with photovoltaics Fixing Roof installations Facade installations Sunshade installations

71 72 73 76 77 79

Technical rules and building legislation Type approval of PV modules – Electrical installation and safety An overview of building legislation Building products and forms of construction Non-regulated building products and forms of construction Experimental testing Fire protection

82 84 87 90 92 94 97 100

103 106 107 108 109 111

Photovoltaics case studies Federal Environment Agency offices in Dessau Institute premises in Beijing Local government offices in Ludesch Paul Horn Arena in Tübingen Sports hall in Burgweinting Mixed commercial and residential building in Munich Additional residential storeys and new office building in Darmstadt Private house in Hegenlohe Appendix Glossary Standards, directives, statutory instruments and recommendations (selection) Bibliography Manufacturers, companies and trade associations (selection) Index Picture credits

Introduction

Life without energy is impossible. Plants and some species of bacteria are able to convert sunlight into chemical energy and thus form a source of food for other living organisms. Plants and animals, together with their habitats, form an ecosystem that consumes only so much energy as the sun supplies continuously. Part of the solar radiation is converted into chemical energy in the form of biomass, which is stored permanently, sealed off from the atmosphere. Millions of years ago this material was transformed into the fossil fuels coal, oil and natural gas. It is those fuels that we currently consume to meet about 80 % of our energy requirements [4]. But the extremely long periods taken to form such materials can in no way keep pace with the consumption, which means that our planet’s fossil resources will either become exhausted or their recovery uneconomical. And as their conversion into usable energy leads to the emission of carbon dioxide, which in turn damages our climate, suitable measures must be taken to achieve a balance between renewable and non-renewable energy sources.

Oceanic energy water power Geothermal energy Biomass Wind power

170 2400

Global primary energy consumption

1

Solar radiation

Elec. gen. from renew. energy [TWh/a]

1

100 80 60 40 20 0

1990

1995

2000

2005

2008

Gross electricity consumption 2008: 617 TWh Elec. gen. from renew. energy: 93.0 TWh = 15.1 % Thereof…

2

Photovoltaics 4.3 % Bioenergy 30.1 %

Wind power 43.2 % Water power 22.4 %

Energy can be present in many different forms: thermal, mechanical, potential, chemical, nuclear, radiation or electrical. The latter represents a special case in this list because, owing to its high propor-

tion of exergy, it is especially easy to use and to transport over power lines. However, the storage of large quantities of electrical energy does pose problems. Renewable energy In principle, renewable energy sources are available on our planet in three forms (Fig. 3): • Solar radiation • Geothermal energy • Planetary energy The availability of these three sources varies considerably, and radiation from the sun represents by far the largest source (Fig. 1). Deep within the sun, hydrogen is converted into helium in a nuclear fusion process, during which part of the mass is converted into energy. The surface of the sun radiates this energy out into space in the form of electromagnetic waves – and will continue doing this for what, on a human timescale, seems like an infinitely long time: another four to five billion years. Although only a very small proportion of the solar radiation reaches the surface of the earth, just a few hours of sunshine contain more energy than the entire population of the planet consumes in one year! If we could use just 0.04 % of the available solar radiation effectively, the sun could meet our total energy needs worldwide (Fig. 1).

The earth’s energy resources Non-renewable Nuclear energy Past radiation Atomic energy 1

2

3

The potential of renewable energy sources in relation to global primary energy consumption (2007) [1]. This potential is based on estimates according to [2]. The development of electricity generation from renewable energy sources in Germany from 1990 to 2008. Energy resources on the earth and the forms in which they appear, after [3], p. 44.

3

Coal Crude oil Natural gas

Renewable Solar radiation Current radiation Global irradiation Geothermal energy (ground coupling) Atmospheric heat Wind Oceanic thermal energy Oceanic currents Waves Hydroelectric power Biomass production

Geothermal energy

Planetary energy

Geothermal energy (borehole)

Tides

7

Introduction

Electricity price [cent/kWh]

45 40 35 30 25 20 15 2009

4

2011 EEG building up to 30 kW EEG ground-mounted array

2013

2015 Grid 3% p.a. Grid 5% p.a. Grid 7% p.a.

Solar radiation, geothermal energy and planetary energy occur on the earth as phenomena that can be exploited to different extents. This is one reason why their contributions to the total energy generation are so different. In Germany, for example, only wind and water power, biomass and photovoltaics currently contribute significantly to electricity generation (p. 7, Fig. 2); in 2008 these forms of energy already accounted for 15.1 % of gross electricity consumption. Their contribution to total final energy consumption was about 9.6 %. Photovoltaics Photovoltaics (PV) is a word that has been coined to describe the underlying physical principle of solar cells, which convert global irradiation (light – Greek: phōs, phōt-) into electricity, whose unit of measurement is the volt (V). The fact that energy is generated silently and cleanly, seemingly out of nothing, combined with the wide range of potential applications, makes this a fascinating process. From individual solar cells with outputs in the milliwatt range powering clocks or pocket calculators right up to large power plants covering several square kilometres and outputs measured in megawatts, the modular principle enables systems of any size for any electricity requirement. In all of this, the basic building block, the solar cell, is always the same. History Although the French physicist Alexandre Edmond Bequerel discovered the photovoltaic effect as early as 1839, it was not until the 1950s that the development of semiconductor technology made it possible to use this effect in practice. Owing to the extremely high production costs, the first solar cells were restricted to those applications where cables could not be used for providing an electricity supply, portable energy supplies were relatively expensive and costs were not the decid8

5

ing factor. One use that corresponded well with this specification was space travel; and it is space travel that supplies what is probably the most radical but, by the same token, most graphic example of a stand-alone energy system. In space, photovoltaics is the only sensible solution if we want to avoid heavy energy sources and at the same time wish to retain longterm energy autonomy for living and working. The most important criteria are reliability, durability and low weight, coupled with high efficiency. The advantages of this location are the low ambient temperature in space and also the comparatively high level of radiation owing to the lack of an atmosphere. Back on the earth, PV technology was initially restricted to applications remote from an electricity grid and where the provision of electrical power via batteries or fuels was uneconomic or unreliable. For example, in developing countries, at sea (e.g. marker buoys) or transmission masts in remote regions of North America or Australia. As the cost of production dropped, so too did the distance between potential applications and developed regions already provided with an electricity grid, an evolution that ended in the direct connection between photovoltaic systems and the electricity grid [5]. Economy The Basic Law of the Federal Republic of Germany states that protection of the “natural bases of life” is a national goal [6]. It was against this background that the Renewable Energies Act (EEG) came into force in 2000, the intention being the economic operation of PV systems in principle. The EEG specifies a feed-in tariff that all distribution network operators must adhere to for electricity generated in accordance with this Act. Operators subsequently pass on this “funding” paid to

6

the EEG electricity provider to the end users in the form of a charge. The remuneration for electricity generated by the installed system remains constant for 20 years, but drops annually for new installations. This principle, known as degression, increases the pressure on manufacturers to continue developing better solutions and ensures that the cost of producing PV electricity and the price for the end user are brought into line with the price of conventional electricity and will match this in the foreseeable future. Assuming an annual price rise of 5 % for grid power, this condition, known as “grid parity”, could be reached as early as 2013 (Fig. 4). Production benefits most of all from a rationalisation effect due to mass production, the “economy of scale”. It has been proved that in the past decades each doubling of the production of modules has cut the cost per unit by about 20 % [7]. Looking beyond the business and economic calculations, the long-term advantages of renewable energy for both national and global economies can hardly be overestimated. The domestic market benefits above all from stable energy prices, reliable supplies and the fact that the value creation remains within the country. Renewable energy sources reduce significantly the “external costs” that are not included in the price of electricity, which result, for example, from damage to the environment. In the case of electricity generated in lignite- and coal-fired power stations, these costs amount to about EUR 0.06 – 0.08 per kilowatt-hour; but with renewable energy these costs are mostly less than one cent [8]. And last but not least, the use of renewable energy sources gives rise to geopolitical stability on a global level due to the combination of nature conservation and climate protection plus dependable supplies over the long-term [9].

Introduction

4

5

6

7

8

Convergence of electricity prices: the feed-in tariff specified in the German Renewable Energy Act (EEG) is here plotted against various price development scenarios for grid power. The intersections represent grid parity. Vanguard I (model): the first satellite operated by PV electricity. It went into service in space on 17 March 1958. The first PV installation integrated into a facade – at the offices of an energy company. STAWAG Stadtwerke Aachen (D), 1991, Architekturbüro Georg Feinhals Architectural benefits are achieved with new technologies. On this facade the PV modules appear homogeneous. Ferdinand Braun Institute for UHF Technology, Berlin (D), 2007, msp Architekten The colour of building-integrated PV modules is also growing in importance in addition to texture. Sample modules of CIS thin-film cells with coloured/textured cover glasses, EU research project BIPV-CIS, 2004 – 2007. 7

Applications Compared with other methods of energy provision, PV technology exhibits certain features that make it particularly suitable for applications in urban environments. Only to a very small extent does the conversion efficiency of an installed solar power system depend on the size of the installation; generator area and yield remain approximately proportional to one another. This means that even very small solar power systems can be worthwhile, making them attractive for home-owners with modest budgets. The completely silent and zero-emissions PV generator can be installed exactly where the energy is needed – directly on the building. That in turn saves the cost of purchasing land and providing an infrastructure, avoids transport losses and also avoids additional soil sealing. Moreover, the electricity generated by a PV system over the course of a day correlates well with demand. However, one of the greatest challenges is the inconstancy of the energy source itself! The first grid-connected installations appeared mainly on the roofs of houses. In the meantime they are being installed increasingly on commercial buildings and public amenities such as schools or government offices, railway stations and noise barriers. In principle, virtually every type of structure is suitable for the installation of a PV system – with the solar generator either as a separate item or integrated into the roof or facade. Employing the modules as both electricity generators and building materials in the building envelope saves not only money and production energy, but also helps to integrate the systems appropriately into the urban or rural landscape. Ground-mounted arrays, e.g. on former military, industrial or landfill sites, have proved to be an important interim driver of development and practical trials for large PV power

8

plants. In densely populated Germany, however, such arrays play only a minor role. Single- or double-axis tracking systems, enabling the modules to follow the trajectory of the sun, have been attracting attention because this is one way of increasing the yield. This book focuses on building-mounted and building-integrated photovoltaics, which means that besides the numerous technical issues, architectural and constructional matters also become priorities. Each of these aspects is handled in a separate chapter. There is also a chapter on the legislation and technical rules relevant to the construction and use of PV systems, which are based on those for the use of glass in building. A glossary explains the technical terms and a bibliography and directory of manufacturers provide the reader with sources of further information. Fine examples of the different ways that photovoltaics can be incorporated into a building – roofs, facades, sunshades – complete our survey of this subject. Outlook The solar cell industry is looking forward to another decade of high growth rates of 30 – 40 % annually, albeit on a relatively low level. In 2009 PV electricity accounted for only about 1 % of the electricity generated in Germany. In the long-term, however, photovoltaics has the potential to develop into one of the fundamental pillars of energy supplies. That calls for more flexible electricity grids, which can handle large quantities of solar electricity, and also further drastic cost reductions by industry so that the predestined transition from funded market launch to independent profitability can take place. Manufacturers are responding to this pressure by introducing innovations at a fast rate: constantly rising conversion efficiencies,

the saving of expensive materials and more mass production characterise developments in cell, module and system technologies. PV modules with traditional crystalline silicon solar cells will soon achieve conversion efficiencies exceeding 20 % and will remain the dominant technology. Thin-film technology is winning a greater and greater share of the market, and their still relatively low conversion efficiencies are being improved with new materials and multi-junction cells, which can exploit an especially wide sunlight spectrum. New cell concepts are eliminating the differences between conventional and thin-film cells. Crystalline cells, for example, whose thickness has been reduced by one-third within just a few years, could in future be produced as foils peeled off a reusable wafer. And nanotechnology is providing further momentum. At the same time, the PV sector is becoming more closely involved with the glass industry, and hence the building industry. New module concepts are based on insulating glass production. For architectural applications, we can hope to see an expansion in the range of products on offer – in the direction of more flexible dimensions and colour schemes. The construction sector could contribute to appropriate solutions by integrating PV elements into standardised roof and facade products.

References: [1] BP, 2008, p. 40 [2] Fischedick, 2000, p. 17f. [3] German Renewable Energy Agency, 2009 (2) [4] Hegger, 2007, p. 45 [5] cf. Perlin, 1999, p. 57ff. [6] Basic Law for the Federal Republic of Germany, Article 20a [7] cf. Luther, 2003, p. 5f. [8] Federal Ministry for Environment, Nature Conservation & Nuclear Safety, 2008, p. 35 [9] Tänzler, 2007, p. XIff.

9

Generating and using solar electricity

Since the 1990s state-sponsored schemes have promoted the wide use of electricity generated from sunlight. Today, feed-in tariff programmes such as that of Germany’s Renewable Energy Act (EEG) stimulate not only the construction, but primarily the efficient operation of grid-connected photovoltaic (PV) installations. This is one reason why technical developments have reached a very high level. Every tiny solar cell is in fact an independent power plant that can convert sunlight directly into electricity. Normally, several cells are interconnected to form a prefabricated module, a number of which are then interconnected to form a larger power unit, the PV or solar generator (Fig. 1). The sun as a source of energy The sun supplies the energy for all life on earth. That energy reaches us in the form of electromagnetic radiation. Using that radiation passively as a source of heat and light is as old as building itself. Solar radiation and spectrum The solar energy available is generally measured on a surface of 1 m2 perpendicular to the incident radiation. Outside the earth’s atmosphere that radiation is almost constant. The so-called solar con-

1

The modular principle of photovoltaics. The elementary component, the solar cell, any number of which can be assembled to form a solar electricity system.

1 Cell

Cell string

Module

stant is approx. 1367 W/m2. In accordance with its surface temperature of about 5800 K (approx. 5500 °C), the sun’s spectrum ranges from short-wave ultraviolet light to long-wave infrared light, but high-energy visible light accounts for the largest part of the spectrum (p. 12, Fig. 2). In the atmosphere, air molecules and aerosols absorb, reflect and scatter the sunlight. This not only reduces the intensity of radiation at the earth’s surface to max. 1000 W/m2, it also changes the spectral composition. When the sun is perpendicular to the earth’s surface, i.e. directly overhead, it’s radiation has the shortest path through the atmosphere, i.e. simply the thickness of the atmosphere, with an air mass (AM) number of 1 (p. 12, Fig. 3). With the sun low on the horizon, the path of the light through the atmosphere is increased by the corresponding AM factor. Each increase in the AM value represents a weakening of the radiation. As the light spectrum has a considerable influence on the efficiency of different solar cells, an average terrestrial spectrum of AM = 1.5 has been agreed so that cells can be described and compared. The figure of 1.5 is equivalent to a solar altitude angle (elevation) of 41.8° (p. 12, Figs. 2 and 3). Outside the earth’s atmosphere AM = 0.

PV string

Generator

11

Generating and using solar electricity The sun as a source of energy

ultraviolet

visible

21 Jun, 12 noon AM 1.1 63.5°

infrared

AM 1 90°

2

Radiation intensity [W/m²nm]

AM 0 solar energy 1367 W/m2

AM 1.5 41.8° AM =

AM 1.5 solar energy 1000 W/m2

1

21 Dec AM 3.42 17°

1 sin α

Location: latitude 50° north

Upper limit of atmosphere 0

α 0

500

1000

1500

Earth’s surface

2000 2500 Wavelength [nm]

AM 0: solar energy 1367 W/m²

2

Kiel Rostock Hamburg Bremen Berlin

Hannover Münster Essen

Leipzig Dresden

Kassel Cologne

Frankfurt Trier

Nuremberg Stuttgart Passau

Ulm Freiburg

< 950 kWh/m2a > 950 kWh/m2a

Munich

> 1000 kWh/m2a > 1050 kWh/m2a

> 1100 kWh/m2a > 1150 kWh/m2a

4

0° 87 74 60 100 109 91 114 80 106 99 112 70 108 95

45° 90°

80

South

5

2

3 4 5

12

30°

15°

107 78

90

38

North

48

65

East (West)

The extraterrestrial (AM 0) and global (AM 1.5) spectra of sunlight. The energy content of the radiation depends very significantly on its wavelength. Air mass (AM) for different solar altitude angles Global irradiation map: annual solar irradiation on horizontal surfaces in Germany Relative annual incident radiation on various surface orientations in Germany in comparison to a horizontal surface

AM 1.5: solar energy 1000 W/m2

Global irradiation The level of global irradiation and the proportions of direct, diffuse and reflected light vary depending on the cloud cover. Solar cells can function with all three forms of light, although direct radiation is the form richest in energy. In contrast to diffuse light, i.e. the light that has been scattered in the atmosphere, direct light arrives uninterrupted from the direction of the sun and casts a hard shadow. Depending on surface characteristics, brightness and colour, the so-called albedo value describes the reflecting power of the environment. In built-up areas and on open ground this value is on average 20 %. By contrast, an albedo of up to 90 % is possible on snow, for example, or aluminium roofs (in a weathered condition still almost 50 % albedo), and in the vicinity of PV installations this can have a favourable effect on the system yield. Black bituminous roofing felt, on the other hand, reflects only about 7 %. Whereas the peak solar radiation values on clear, cloudless days can reach about 1000 W/m2 anywhere in the world, it can happen that the input on overcast days with exclusively diffuse radiation climbs no higher than 50 W/m2. That is still considerable when compared with very good interior lighting, which corresponds to a radiation intensity of just a few W/m2, but does explain why PV installations achieve only a fraction of their planned rated output on such days. The trajectory of the sun, which depends on the latitude of the location, and the weather conditions result in great differences in the distribution of solar radiation at different locations. In the northern hemisphere the sun travels from east via south to west and in doing so changes its elevation γS, also over the course of the year (Fig. 6). This is why, for instance, in Germany a cloudless, long summer’s day with up to 17 hours of daylight supplies

3 Air Mass (AM)

about 25 times more solar energy than an overcast day in winter, when the Germans can expect no more than about eight hours of daylight. The cumulative solar radiation for one year supplies the annual global irradiation figure in kWh/m2a. The sunbelt around the earth stretches from approximately the 40th parallel north to the 40th parallel south, and encompasses, for example, the southern part of the Mediterranean. Although this region has twice the amount of solar energy available (up to 2500 kWh/m2a) as is the case in Central Europe, it is still worthwhile exploiting this free energy source in Central European latitudes. Solar radiation in Germany The German Weather Service produces global irradiation maps on the basis of values averaged over 20 years (Fig. 4). These are valid for horizontal surfaces and can be used as the starting point for predicting energy yields from solar installations. There are also regional differences in addition to the north-south gradient. The average is about 1050 kWh/m2a but the figures range from a low of 900 kWh/ m2a in north-west Germany to a high of 1200 kWh/m2a and more in the sunniest regions south of the Danube. Unlike the availability of wind energy, solar radiation can be calculated with some reliability. It deviates by less than 10 % from the average value from year to year. Only in years with extreme meteorological events can it deviate by up to 20 %. Irradiation on inclined surfaces The energy yield per square metre rises, the more a solar module surface is turned to face the sun directly. As the sun reaches its highest elevation in the south, in our latitudes a south-facing surface inclined at about 30° to the horizontal is best for maximising the irradiation. Placing an installation at such an angle increases

Generating and using solar electricity The sun as a source of energy

West

6

Meridian

a

b 7

North Elevation γS

Solar trajectories

c

a

South c

d 8

b

Azimuth αS East

6

7e

the annual yield to 110–115 % (Fig. 5) compared to a horizontal surface (100 %). Different angles and orientations either side of this optimum result in similarly high figures; surfaces facing south-east to south-west and inclinations between 15° and 50° are basically excellent. On vertical south-facing facades the quantity of incident radiation is still about 80 %, in other words nearly 30 % less than a roof surface at an optimum angle. Even on facades facing east or west, PV modules can still achieve acceptable energy yields in some circumstances: approx. 65 % compared to a horizontal surface, or 55 % compared to an optimum south-facing module.Steep, north-facing modules are, however, generally inadvisable. Locations in southern Germany offer more potential because of the higher level of radiation available, which means that less favourable surfaces can be used as well. In contrast to the tendency in the building industry to relate everything to a north point, in solar technology the angle designation 0° stands for due south. Generators that track the trajectory of the sun can achieve an ideal yield. However, the higher cost of the mechanism, control and drive is mainly only worthwhile in southern Europe, where the level of direct

f

radiation is high, and in the case of movable sunshades. Shadows Shadows reduce the usable solar irradiation on a surface. With crystalline modules especially, even the smallest shadows can reduce the energy yield considerably. Shadows can be caused by the following: • Adjacent buildings, structures and vegetation • Other parts of the same building, e.g. chimneys, projections, ventilation and lightning protection installations, fixings • Temporary phenomena such as snow, leaves and soiling (Fig. 7) In the case of new buildings it is at least possible to design and construct to avoid shadows caused by parts of the same building. But in order to prevent subsequent shadows, e.g. caused by new planting at a later date, exact stipulations for the planners responsible are advisable. Objects that cast shadows cut out the direct sunlight, which means that only the diffuse radiation strikes the solar module surfaces. The closer the object is to the surface, the greater is this blackout effect. In an area of total shadow, the incident energy can be cut by 60 – 80 %, in semi-

70° 12 noon 11 a.m.

60°

1 p.m.

21 June

2 p.m.

10 a.m. 50°

3 p.m. 9 a.m.

40°

21 March 21 Septemb er

8 a.m.

30°

4 p.m. 5 p.m.

7 a.m. 20°

6 p.m.

21 Decemb er

6 a.m.

Solar trajectories for latitude 50° north a 21 June (summer solstice) b 21 March/21 September (spring/autumn equinox) c 21 December (winter solstice) Possible causes of shadows a Adjacent buildings b Vegetation c Building projections d Rooftop structures e Snow f Soiling Sun path diagram for latitude 49° north, with shadows caused by neighbouring buildings from south-east to west and vegetation from east to south-west.

shade, however, only by approx. 30 – 40 % [1]. Projecting fixing clips or glazing bars, and dust and dirt, can therefore have a particularly serious effect. No solar cells or modules should be positioned in areas affected by such shadows. In their in situ analysis, the planners must take into account the annual and seasonal variations of the shadows. When the sun is low on the horizon, the length of a shadow is several times the height of the object casting that shadow, a fact that is frequently underestimated. A sun path diagram helps when assessing the surroundings (Fig. 8). The diagram describes the daily path of the sun for each month in the form of a curve consisting of azimuth angle (angle between sun and due south) and elevation angle (angle between sun and horizon). Looking south from the relevant surface, it is possible to see which objects interrupt the trajectory and for how long. The horizon should be essentially unobstructed above an elevation of about 15° so that the modules can exploit the solar radiation at least over the three months either side of midsummer. Shadows in the early morning or late evening or on a few days in winter are generally accepted in practice because they cause only minimal losses. Simple silhouettes can be easily calculated geometrically from distance and difference in height. However, analyses making use of digital photographs and evaluation software are more convenient (Fig. 8). The resulting energy losses over one year are best estimated with the help of simulation programs. Some of these can reproduce complex shadows in three dimensions and assess these exactly.

7 p.m.

10° 5 a.m. 0° 8

O

SO

S

SW

W

13

Generating and using solar electricity Solar cells – turning light into electricity

– Monocrystalline

n-layer

– +

Trimming

Sawing into wafers

Phosphorus diffusion

Screen-printing the contacts

Solar cell

Cutting blocks

Sawing into wafers

Phosphorus diffusion

Screen-printing the contacts

Solar cell

+

Electrical field

p-layer

9

10 Polycrystalline

Solar cells – turning light into electricity The solar cells available commercially differ in terms of their structure and the basic materials employed. Both of these aspects influence the efficiency of the energy conversion and also the appearance of the cells (Fig. 11). Cell types are divided into two principal groups: the traditional crystalline silicon cells and the newer thin-film cells made from various semiconductor materials. The first niche products employing the third generation of solar cells – based on nanotechnology – are just appearing on the market. The secret of the invisible and completely silent energy conversion is to be found in the material of the solar cells, the semiconductors. At very low temperatures these behave like insulators and do not become electrically conductive until heat or light is applied. A solar cell is a combination of two layers with differently manipulated conductivity. In crystalline silicon, for example, the layer on the sunlight side

is negatively (n-) doped with phosphorus, i.e. is deliberately contaminated, which gives it an excess of negative charge carriers. The layer beneath this is positively (p-) doped with boron, which therefore has an excess of positive charge carriers (Fig. 9). In thin-film cells, on the other hand, the p- and n-type layers sometimes consists of different raw materials. In both types of cell, the boundary between the layers is the p-n junction. At this junction, the diffusion of excess charge carriers between the two layers gives rise to an electrical field. Outwardly, however, the solar cell is neutral in electrical terms. Sunlight striking the cell is absorbed by the semiconductor. The energy of photons releases pairs of electrical charge carriers. Influenced by the electrical field at the p-n junction, the negatively charged electrons migrate to the top side, whereas the positive charge carriers accumulate in the p-zone. This separation gives rise to a voltage between the front contact and the

Crystalline silicon cells

The photons in the spectrum of sunlight have different levels of energy. In the traditional perception, each photon can create only one electron upon absorption. A certain quantity of energy is required for this, which depends on the semiconductor material. Long-wave photons have insufficient energy for this process and are lost, just like the excess of high-energy short-wave light. Therefore, solar cells can use only a certain part of the solar spectrum, which limits the theoretical conversion efficiency of the most efficient semiconductor materials, such as gallium arsenide (GaAs) and indium phosphide (InP), to about 30 % [2]. Crystalline silicon has a theoretical conversion efficiency potential of 28.5 %. Higher conversion efficiencies can be achieved only with multi-junction cells, which have several p-n junctions.

Thin-film solar cells

Monocrystalline

Polycrystalline

Special types: • High-efficiency cells • Hybrid cells

Special types: • Ribbon silicon cells

• Wafer technology: round to square single pieces • Wafer thickness 0.2 mm, side length 100 –156 mm 11 • approx. 85 % market share, well-developed technology

14

back contact. If the circuit between the two contacts is closed, the electrons flow as an electric current.

Silicon • Amorphous • Micromorphous • Microcrystalline

Nano solar cells

Compound semiconductors

(In)organic semiconductors

• Cadmium telluride (CdTe) • Copper-indiumgallium diselenide/ copper-indium disulphide (CIS)

Organic: • Dye-sensitised solar cells • Synthetic solar cells Inorganic: • CIS

• Vacuum technology, electroplating: substrate normally fully coated • Layer thickness 0.5 – 5 μm, width of cell strips 0.5 –17 mm • approx. 15 % market share, growing

• Printing method • Nano structure • Pilot stage

Generating and using solar electricity Crystalline silicon

a

12

13

Crystalline silicon Solar cells made from crystalline silicon continue to account for about 85 % of the cells used worldwide. Silicon is not found in its pure form in nature, but only in chemical bonds, most frequently in the form of silicon dioxide in quartz sand. This sand forms the raw material for highpurity silicon, which is obtained following several costly and high-energy melting and cleaning stages. For a long time, silicon waste from the semiconductor industry was used as the raw material for solar cells. However, such residues and, in the meantime, production of electronic-grade silicon can no longer meet the incredible growth in demand. As a result of this shortage, the expanding solar industry is now setting up its own production plants for less costly solar-grade silicon because solar cells place considerably lower demands on the purity of the silicon than microelectronics. Various processes produce either monocrystalline or polycrystalline wafers from molten polysilicon (Fig. 10). These silvery grey discs with a metallic sheen serve as the blanks for solar cells. A thickness of just 0.05 mm is sufficient for light absorption. However, the discs are thicker for mechanical reasons because such thin cells would be much too fragile for the production of PV modules. Monocrystalline solar cells The first solar cells were monocrystalline. The normal method for wafer production is comparable with the technique of making a candle. A cylindrical silicon rod, several metres long, is produced through slow rotation as it is pulled out of the silicon melt. As the material consists of just one crystal, its structure is homogeneous and the potential conversion efficiency is relatively high at 15 – 21 %. This single crystal is trimmed to create an approximately square block with a side length of 100, 125 or 150 mm and then cut into

14 b

wafers approx. 0.2 mm thick with a wire saw. The kerf itself is about the same width and a considerable quantity of nonrecyclable silicon dust is lost as a result. However, the ends of the rod and the offcuts resulting from the cutting of the cylinder to form a square can be melted down again. In principle it is possible to produce untrimmed circular cells with a diameter of 125 or 150 mm, however, this method is no longer common owing to the poor utilisation of the area in the later solar module. Wet cleaning with a chemical agent and etching of the wafers removes any sawdust and adds a texture to the surface. The p-doped initial wafers are given a thin n-doping on their top side by diffusing them with a phosphorus source at high temperature, and it is this that turns the wafer into a solar cell with a p-n junction. A subsequent anti-reflection coating is applied to the front by vapour-deposition so that a maximum amount of sunlight can be absorbed. As crystalline solar cells prefer long-wave light, the coating thickness of approx. 70 nm is adjusted such that it mainly reduces the light reflection at the red end of the spectrum. This is the reason for the dark blue to black colour of such cells. In order that the electricity can be collected from the solar cells, highly conductive contacts are screen-printed on both sides. Fine contact fingers at a spacing of 2–3 mm and two or three wider busbars made from silver applied in the form of a paste result in the typical minimal coverage grid pattern on the front, sunlit side. On the back, wide bands of silver create the electrical contact and a complete coating of aluminium, as a reflector for the charge carriers, improves the conversion efficiency. Polycrystalline solar cells Owing to their simpler and cheaper production process, polycrystalline solar cells are today encountered far more frequently

c

than the monocrystalline variety. The production process involves casting the liquid silicon into square ingots which then solidify under strictly controlled temperature conditions into a multitude of crystals with different orientations. The grain boundaries – visible as a frost-like structure – behave like crystal imperfections and are responsible for the slightly lower conversion efficiency compared to the monocrystalline cells. The ingots can be sawn into exactly square blocks with the desired cross-section and thereafter into wafers ready for further processing (phosphorus doping, addition of anti-reflection coating and contacts) to form the familiar bluish solar cells. Ribbon silicon solar cells Various ribbon growth methods reduce the silicon, and hence energy requirements yet further. In such methods a 0.3 mm thick silicon foil is drawn out of the melt (Fig. 12). These ribbons are cut by a laser into square or rectangular wafers. The sawing process with its high kerf loss is therefore unnecessary. Examples are the string-ribbon process, in which the liquid silicon spans like a skin between two parallel wires drawn through the melt, and EFG cells (Edge-defined Film-fed Growth,

9 The structure and operational principle of a solar cell: it becomes a source of electrical energy when exposed to light. 10 Often, various companies are involved in the many operations required for the production of monocrystalline and polycrystalline solar cells made from high-purity silicon. 11 Typology and features of customary solar cells: monocrystalline cells have characteristic rounded corners, polycrystalline cells a distinct crystal structure, and thin-film modules a stripy appearance. 12 Drawing string-ribbon solar cells 13 Drawing and cutting EFG solar cells 14 High-efficiency solar cells: a Front view of back contact cell b View of back, with stripy, alternating positive and negative terminals c Hybrid HIT solar cells in the form of quarter cells densely packed in the module

15

Generating and using solar electricity Thin-film technology

Transparent TCO front contact

Cover glass Transparent TCO front contact

-

+

Blue-absorbent cell (p-i-n) Green-absorbent cell (p-i-n)

CdS layer (n-conducting, d = 0.3 μm)

Red-absorbent cell (p-i-n) CdTe layer (p-conducting, d > 0.3 μm) Metallic back contact

15

Fig. 13). In this latter method, the EFG silicon solidifies on an octagonal die upon being drawn out of the melt to form an octagonal tube whose walls form the later wafers. String-ribbon and EFG cells are polycrystalline, but appear almost as homogenous as monocrystalline silicon. High-efficiency cells In the laboratory there are many ways of increasing the conversion efficiency of crystalline solar cells up to record values of max. 25 %. Some of the affordable tricks and special methods are being used by some manufacturers in the industrial production of high-efficiency cells. The “Saturn” solar cell, for example, relies on a textured surface and buried contacts on the front. Its pyramid-shaped surface structure reduces reflections and retains incident light within the cell for a longer time thanks to multiple reflections. Deep, narrow, metalfilled laser-cut grooves reduce the area covered by the front contacts and the electrical resistance. Back-contact solar cells made from especially high-quality silicon are currently achieving the best conversion efficiencies (up to 22 %). The p-n junction and all contacts in such a cell are in the form of strips on the back (p. 15, Figs. 14 a and b), which means that the front contacts can be omitted completely. The textured cell surface appears homogenous, with a black velvety look. The hybrid HIT solar cell combines the absorption capacity of thin-film silicon with the good electronic properties of monocrystalline wafers. This type of cell has a thin coating of amorphous silicon on both sides (Fig. 14c), which means that HIT cells are potentially active on both sides (bi-facial solar cell). Provided with a contact grid, they are potentially useful for vertical installations in the north-south direction. In generators mounted clear of the surface, they can also convert the light reflected onto the back of the module from a light-coloured surface. 16

TCO reflector layer

+

Stainless steel backing foil

-

16 a

b

Thin-film technology Thin-film photovoltaics is classed as the second generation of solar cells, following on from crystalline wafer technology. The solar cells and their contacts are applied as thin layers to a low-cost backing material, usually a pane of glass. Thin-film silicon or compound semiconductors (i.e. made from various chemical elements) serve as the photoactive semiconductors. Whereas the production of amorphous or micromorphous silicon has undergone the most development and cadmium telluride (CdTe) promises the lowest production costs, copper-indium-gallium diselenide (CIS) achieves the highest conversion efficiencies. Thanks to the direct light absorption of the materials, a film thickness of just a few micrometres is adequate. The electrical contacts are part of the layered structure: an opaque layer of metal, e.g. molybdenum, forms the back contact, whereas a highly transparent and conductive TCO (Transparent Conductive Oxide) layer based on various metal oxides provides the contact for the front, facing the light. Zinc oxide (ZnO), tin dioxide (SnO2) or indium-tin oxide (ITO) are examples of possible TCO materials. A rough TCO surface creates additional light traps (Fig. 15). Depending on the cell technology, manufacturers coat either the transparent cover glass – starting with the front contact – or a backing material using various methods: • Vapour deposition • Sputtering • Plasma-enhanced chemical vapour deposition (PECVD) • Electroplating baths

as metallic foils or plastic films as a basis for lightweight and flexible solar modules which can be readily integrated into roof and facade systems (p. 22, Figs. 31 and 32).

Whether the front or back serves as the substrate has a considerable influence on the configuration of the later module (see “Construction and integration”, p. 51). For example, only a coating on the back enables the use of opaque substrates such

The advantages of thin-film technology over crystalline solar cells are to be found in the greater design potential (see “Designing with photovoltaics”, pp. 43 – 47) and the lower consumption of energy and materials during production. Semiconductor material is saved by the fact that the cells are about 100 times thinner. And compared to process temperatures of up to 1500°C in wafer production, the coating temperatures are considerably lower – between 150 and 600°C. The format of thin-film modules is not restricted to certain wafer sizes. Theoretically, a backing material of any size or shape can be covered with semiconductors. Practically, however, production is confined to standardised dimensions and rectangles or squares. In the majority of cases individual panes of glass pass through various coating stations on a fully automatic production line, leaving it as a basic module with ready-connected solar cells. The greater degree of automation in production and the higher throughput present the chance for significant cost-reductions in the medium-term. Synergies from the coating of glass for architectural purposes and the experience gained with thin-film coatings on large surfaces for flat-screen applications can benefit the solar industry. New production plants for the cost-effective coating of large areas and the shortage of silicon have led to the establishment of large manufacturing capacities for thin-film modules. This will help to increase their share of the market because the lower production costs can more than compensate for the disadvantage of their comparatively low conversion efficiencies.

Generating and using solar electricity Thin-film technology

Transparent TCO front contact

Transparent TCO front contact (n-conducting, d ~ 1 μm) CdS layer (n-conducting, d = 0.05 μm)

Cover glass

Cover glass

+

Transparent TCO front contact

Amorphous silicon cell (p-i-n, d ~ 0.3 μm)

p-type silicon layer (d ~ 0.01 μm)

Monocrystalline silicon cell (p-i-n, d ~ 1.5 μm)

i-type silicon layer (d ~ 0.4 μm)

TCO reflector layer

n-type silicon layer (d ~ 0.02 μm)

+

-

CIS layer (p-conducting, d = 2 μm)

Metallic back contact

-

Metallic back contact

Metallic back contact

-

+

Glass substrate

c

d

e

Thin-film cells can be produced as multispectrum, multi-junction cells with higher conversion efficiencies. Highly efficient multi-junction cells made from expensive, and in some cases toxic, semiconductors such as gallium arsenide, indium phosphide or germanium reach conversion efficiencies of more than 40 % under concentrated light. Besides space travel, however, their use is restricted to concentrator systems in very sunny regions with high levels of direct radiation. In these applications, low-cost lenses focus the sunlight onto tiny cells – often only a few square millimetres in area – that are designed to track the sun and require cooling.

The colour of this cell is blue to violet, whereas conventional amorphous silicon cells applied to glass substrates appear reddish brown.

ing CIS layer is bounded by the CdS buffer layer and the n-conducting transparent contact layer (Fig. 16e). Whereas CIS cells containing selenium achieve conversion efficiencies of up to 14 %, newer developments based on sulphur reach only 8 %. However, they can be manufactured easier and faster. The appearance of both types of cell is dark grey to black.

Amorphous, microcrystalline and micromorphous silicon solar cells In terrestrial applications, amorphous silicon cells (a-Si) represent the most common thin-film technology. During the chemical deposition from the gas phase, the silicon does not form a crystalline structure, but rather a random, amorphous network. The multitude of electronic defects results in a low conversion efficiency, which during the first weeks of exposure to sunlight drops to a stable value of 5 – 8 %. Another particular feature of amorphous solar cells is the p-i-n structure. A non-doped intermediate layer with a high electronic quality (i) partially compensates for the poorer semiconductor properties. The doping substances are included in the coating gases. Most manufacturers use the cover glass on the sunlight side as the substrate. Besides single-junction cells (Fig. 16a), tandem or triple cells with two or three active p-i-n junctions respectively, one above the other, are possible. The addition of germanium optimises the cells for different wavelengths of the solar spectrum. This concept increases the total conversion efficiency over that of single cells. One example is the “Uni-Solar” flexible triple-junction solar cell (Fig. 16b).

Microcrystalline silicon (μc-Si), consisting of tiny silicon crystals, is produced at higher deposition temperatures or by way of additional heating processes. In order to be able to absorb enough photons successfully with thin films of crystalline silicon, textured surfaces, designed as light traps, must capture the solar radiation very efficiently. The combination of microcrystalline and amorphous silicon to form “micromorphous” tandem solar cells has become successfully established in mass production (Fig. 16c). In contrast to the amorphous front cell, the microcrystalline back cell also absorbs light from the near infrared range, which enables micromorphous cells to achieve conversion efficiencies twice as high as those of amorphous cells. They are darker in colour, from dark grey to black. Cadmium telluride solar cells The naturally p-conducting semiconductor cadmium telluride (CdTe) forms the absorber in this type of solar cell. A very thin layer of n-conducting cadmium sulphide (CdS) forms the p-n junction between the two semiconductors (Fig. 16d). CdTe solar cells exhibit conversion efficiencies of between 10 and 12 % and appear black with a greenish sheen. CIS solar cells The material system CIS combines various compounds of copper (Cu), indium (In), selenium (Se) or sulphur (S) and in some cases gallium (Ga), which are characterised by high light absorption and a highly variable spectral sensivity. Commercial solar cells mainly use copper-indiumgallium diselenide or copper-indium disulphide as the absorber. The p-conduct-

Integrated electrical connections As a rule, the solar layer applied over a large area in the coating process is cut into individual cell strips 5 –17 mm wide and simultaneously interconnected electrically. In three structuring steps a laser removes a line from every contact and semiconductor layer – parallel to but slightly offset from the one before – and therefore produces a conductive connection from the back contact of one cell to the front contact of the next one (Figs. 17 and 18). It is this that gives thin-film modules their typical stripy appearance. These integrated electrical connections determine the form, size and number of cells in a module even before the production process is complete. The series connection requires cells of the same size, which in turn calls for rectangular active areas.

15 Layer structure of a CIS solar cell viewed through the scanning electron microscope 16 Typical layer structures of various thin-film solar cells on cover glasses or backing materials a Amorphous silicon cell: single solar cell b “Uni-Solar” triple-junction solar cell made from amorphous silicon. The three individual cells are successively applied to a flexible stainless steel foil. The front cell converts the blue wavelengths, the middle cell the green and yellow, and the back cell absorbs exclusively the remaining red wavelengths. c Micromorphous solar cell in the form of a tandem cell made from one amorphous and one microcrystalline p-i-n structure. The lower TCO layer, together with the metallic back contact, functions as a reflector which increases the length of the path of the light through the cell and hence the absorption. d Cadmium telluride solar cell (CdTe) e Copper-indium-gallium diselenide solar cell (CIS)

17

Generating and using solar electricity Nano solar cells

a TCO coating

b First structuring

c Solar cell coating

d Second structuring

17 e Back contact coating

f Third structuring

17 The principle of the integrated series interconnection of thin-film cells: every layer is divided into offset strips and overlapped by the one above. 18 Cell strips with interconnections complete, consisting of front contact, layer of solar cells and back contact on a glass substrate. The structuring is reversed when the cover glass is coated. 19 Integrated interconnection by means of laser. 20 CIS solar cells based on 0.1 mm thick strips of copper, which are simultaneously the substrate and part of the semiconductor: cell field made from interconnected cell strips cut to size. 21 Production of CIS nano solar cells using the rollto-roll printing method.

20

18

Removing a strip of coating about 10 – 20 mm wide from the perimeter guarantees a tight edge seal in the module and prevents electrical breakdowns. New strip, spherical and tubular cells Instead of the large-scale coating of individual module substrates, some manufacturers are turning to alternative cell concepts. Continuous roll-to-roll (R2R) processes can coat flexible substrates, mostly metal foils, with solar cells faster and more cost-effectively. With “Uni-Solar” products, the coated stainless steel foil is cut into cells measuring 356 ≈ 239 mm (p. 22, Fig. 32), and newly developed CIS solar cells, which are produced on strips of copper 10 mm wide and several kilometres long, can be cut into strips of cells of any length and combined to form the desired width. A conductive adhesive connects the cells, which overlap like shingles (Fig. 20). In the “Sunrise” concept, which is still at the research stage, tiny glass beads (0.2 mm) are coated with CIS. A perforated metal foil holds the individual solar cells and forms the electrical contact between them. Thin and flexible, in future these could be applied to any backing materials or construction elements. On the other hand, the “Solyndra” system consisting of a cylindrical tubes coated with CIS cells requires a new module concept similar to the vacuum-tube collectors of solar thermal systems. In this system a hermetically sealed outer tube of glass and an intermediate layer of oil protects the cells attached to the inner tube. Both tubular and spherical cells absorb the sunlight not only largely regardless of the angle of the modules, but also radiation reflected from the back. Nano solar cells Nano solar cells come very close to nature’s way of gaining energy from sunlight – photosynthesis. At the same time,

21

18

19

the dream of solar paint, which can be applied to any surface, seems to be almost within reach. Research into dyesensitised solar cells – also known as Grätzel cells after their inventor – has been going on since the early 1990s. Their transparency and the possibility of different colours opens up new design potential for the building envelope. However, before they can be used on large areas, problems such as the permanent sealing of the electrolytes must first be solved. The newer, also reddish, organic cells made from synthetic semiconductors (polymers) have so far failed due to their lack of stability and low conversion efficiencies. Nevertheless, the chemical industry is pursuing this avenue with great commitment because the simple production processes, e.g. inkjet printing and film application, promise an extremely interesting perspective with regard to costs. The first commercial nano solar cells are based on an ink with CIS nano particles and are printed onto a highly conductive aluminium foil in a roll-to-roll process (Fig. 21). In a similar way to crystalline silicon cells, the manufacturer is producing approx. 150 ≈ 150 mm units and laminating these on conventional modules. These, however, are intended for use in the power plants of electricity companies and not really for the building industry.

Generating and using solar electricity Modules

-

+

+

22 Electrical interconnection of crystalline cells a The shiny silvery narrow strips of solder are visible on the cells and at the connections on the edge of the module. b Junction box fitted to back, with bypass diodes and two cables with positive and negative plugs that rule out any wrong connections. 23 Module production: a Joining the cells together b Positioning the soldered cell strings on a module cover glass with EVA hot-melt film c Covering with EVA and backing foil

-

22 a

b

Modules As the voltage and power output of individual solar cells is inadequate for most applications, they are connected in series, which means that the individual voltages are added together. Crystalline cells in the form of individual pieces with a side length of 100 –156 mm can be arranged in any way within the module. However, straight and hence simple interconnection is only possible with an orthogonal grid (Fig. 22a). For reasons of electrical insulation, the minimum distance between the cells must be about 2 mm. In the majority of standard crystalline modules, 9 –12 cells form one cell string in the longitudinal direction first of all. Thin, soldered copper strips connect the front contacts (negative terminals) of a cell to the back contacts (positive terminals) of the adjacent cell. In modern module plants this is carried out automatically (Fig. 23a). Only for bespoke production are the cells still partly soldered manually. In a typical module with 36 –72 cells, between four and six of these cell strings are placed alongside each other (Fig. 23b). At one end there is the electrical connection to form one, two or three parallel PV strings with approx. 18 – 36 V system voltage.

sometimes also polyvinyl butyral (PVB), are used for the intermediate layers. In production, the cell strings are positioned on the cover glass with the EVA film, soldered together with cross-connectors and then covered with a second EVA film and a protective backing material (Fig. 23c). Upon laminating this module sandwich with the help of heat and a partial vacuum, the milky looking EVA film melts to form a transparent, hard plastic layer that provides electrical insulation for the cells and connections. The backing sheet consists of a weather-resistant combination of several Tedlar and PET films that guar- 23 a antee the electrical insulation on the back of the module. The reflective white colour ensures low temperatures and therefore optimum efficiency. Alternatively, the use of a transparent Tedlar film will allow light to pass through the gaps between the cells. In partially transparent modules for integration into glass roofs and facades or sunshading louvres, however, the film is usually replaced by a second pane of glass. If a casting resin system is used as the embedding material, custom modules of virtually any size can be produced.

Encapsulation The ensuing cell strings are embedded in a transparent material and placed between stable glass or plastic sheeting to protect them from mechanical damage, weather and moisture. The covering on the lightsensitive side of the solar cell should allow a maximum amount of solar radiation to pass through to the cells. A low-iron, toughened, clear glass pane with high transmittance is best suited to such a requirement and can withstand external actions, e.g. hail, likewise internal thermal stresses due to partial shading or overheated cells (hotspots). Hot-melt films, made from ethylene-vinyl acetate (EVA),

Connection and frame A hole in the backing sheet or a drilled hole in the backing glass enables the electrical connections to pass through to the weather-resistant, plastic module junction box glued to the module. The bypass diodes for bridging over shaded areas are also housed in this junction box (Fig. 22b). Many modules are supplied complete with connecting cables and plugs in order to simplify the interconnection of several modules. Normally, the negative and positive terminals are housed in a common junction box. However, some modules are fitted with two separate, smaller junction boxes, depending on cell layout and intended application. Although the solar cell laminate can be used with-

b

c

19

Generating and using solar electricity Modules

24 a

b

out a frame, in most instances modules are fitted into an aluminium frame, which protects the vulnerable glass edges and can be used for assembly, earthing and equipotential bonding purposes. A flat frame profile on the top side is important in order to prevent the accumulation of dust and dirt which would, over time, mask the cells. On the other hand, frameless modules are often the better choice when the modules are to be incorporated into vertical or overhead glazing. Special aspects regarding thin-film modules The assembly and soldering of individual cells is unnecessary in the production of thin-film modules because these are permanently attached to the backing material and interconnected for voltages from 40 to 100 V. Two narrow contact strips along the edge of the module lead to a junction box at the rear. Therefore, only one side with the unprotected cell surface has to be covered. As the coating temperatures would ruin a toughened glass pane, the coated substrate panes are of float glass; depending on the technology, that is either the sunlit front (a-Si, CdTe) or the back (CIS). In most cases a second pane of float glass forms the final weather protection, which is laminated to the module

25

Standard modules The vast majority of the photovoltaic modules normally available are square or rectangular elements with various standardised dimensions and ratings. The aim of such standard modules is to achieve cost-effective production, maximum system yields and rational assembly. Standard crystalline modules are usually fitted into an aluminium frame and have a cover of toughened low-iron clear safety glass 3.2 or 4 mm thick, which is also known as

26

20

“solar glass”. Some manufacturers offer modules with anti-reflection coatings or self-cleaning surfaces (Lotus effect). The backing is generally a white plastic sheet (glass/plastic laminate, Figs. 24 and 25), occasionally a pane of glass (glass/glass laminate). Thin-film modules are normally laminated glasses consisting of two panes of float glass 3.2 mm thick with an EVA or PVB interlayer and are often sold as frameless glass/glass laminates (Figs. 26 and 27). Typical crystalline solar modules are available in sizes from 0.60 ≈ 1 m to 1 ≈ 2 m and with nominal outputs of between 80 and 300 Wp. Up until recently, a format of about 0.60 ≈ 1.20 m and an output of less than 100 Wp was common for thin-film modules, but now the new production plants are producing modules up to 5.7 m2 in area. The weight of glass/ plastic laminates is approx. 12–16 kg/m2; glass/glass laminates can weigh up to 30 kg/m2.

with an EVA or PVB film in a laminator or autoclave. The second pane can be of heat-strengthened or toughened safety glass if required because the production of the cells has been completed by this stage. A plastic backing sheet may be used on amorphous and CdTe modules as an alternative. New strip-type CIS cells permit more flexibility in terms of dimensions and formats – getting away from the standard sizes – because the manufacturer can laminate bespoke cell units between cover glass and backing sheet as required (p. 22, Fig. 33). Thin-film modules without glass are also available. These have a transparent ETFE film plus EVA intermediate layer covering the laminate on the front (p. 22, Figs. 31 and 32).

Special and custom modules The range of standard products does not always cover all the needs of buildingintegrated photovoltaics (BIPV). The standard designs and the sizes available often prove to be problematic, especially when dealing with existing buildings.

27

Generating and using solar electricity Modules

28

Specialised companies therefore also build custom modules for architectural applications with bespoke formats and other materials, e.g. plastic frames or polycarbonate covers. So far, custom modules exceeding 12 m2 in area, in square, rectangular or even circular, triangular or trapezoidal form, have been installed, for instance. Injection-moulding enables the production of plastic frames made from polyurethane (PUR) with attractive designs and multiple functions, e.g. cast-in electrical connections and fixing elements (see “Construction and integration”, p. 60, Fig. 35). In theory, manufacturers can attach thin-film modules to any size of glass pane with a square or rectangular active area. However, the majority have set up their production for standard sizes and are only prepared to supply custom formats, cut from the standard elements, when very large quantities are required. Some companies fabricate patchwork modules made from multiples of the basic elements. Custom modules provide the option of varying the transparency and the configuration of the elements (see “Designing with photovoltaics”). Furthermore, they can fulfil additional building functions (see “Construction and integration”, p. 51). For example, using

29

insulating glass as the backing turns a solar module into photovoltaic low E glazing. There are also special modules in which the solar cells are already integrated into a building material, e.g. glued to metal sections or roof tiles (p. 22, Fig. 32). Deviations from the standardised mass products inevitably lead to higher costs, however. Quality and life expectancy Before the modules leave the production line, each one is individually measured and rated according to the corresponding electrical output. In addition, standard modules are thoroughly tested for output, durability and safety by independent institutes (see “Technical rules and building legislation”, p. 71). Module types that pass all tests are awarded a certificate according to the international standard IEC 61215, or IEC 61646 for thin-film modules, and are regarded as very reliable and long-lasting. Depending on their place of installation and the respective ambient conditions, solar modules can achieve a life expectancy of at least 20 years. Quality and the materials used – principally the composites – have improved in recent years, which means that today’s products will probably operate for much longer

without problems. The manufacturers base their warranties on this. In addition to the statutory minimum warranty of two years, many companies offer warranties of five years, a few even up to 30 years. In addition, the voluntary warranty guarantees the customer a certain minimum performance over a longer period. The two-stage warranty usually guarantees an output of 90 and 80 % for 10 and 20 –25 years respectively. Compared with other technical equipment, these warranties are very ambitious. But they can certainly be interpreted as a minimum lifetime because the modules have proved to be the most reliable component in PV installations. To date there have hardly been any warranty issues involving high-quality standard products.

24 Standard crystalline modules as glass/plastic laminates with aluminium frame a Monocrystalline b Polycrystalline 25 View of back of standard crystalline module complete with junction box, cables and plugs. 26 View of front and back of a frameless standard module for building-integrated photovoltaics, with amorphous silicon cells and separate terminals for positive and negative cables. 27 Framed standard CIS module. 28 Cable exit at side for building-integrated glass/ glass laminates. The small size of the connection means that it can be concealed within the supporting construction. 29 Modern production line: crystalline modules on their way to the laminator.

21

Generating and using solar electricity Efficiency

Conversion efficiency of module

Space requirement

11.5 – 20 %

11 – 21 m2/kWp

Amorphous, micromorphous

6 – 11 % 30

Cell type

Max. cell efficiency (lab.) [%]

Module efficiency (commercial) [%]

Output per m2 of module area [Wp]

Space needed for 1 kWp [m2]

Loss of output due to temp. rise [% / °C]

Monocrystalline, standard high-efficiency cells hybrid HIT cells

21.6 24.7 20.2

12 –16 16 – 20 16 –17

120 –160 160 – 200 160 –170

6.5 – 9 5 – 6.5 6 – 6.5

0.4 – 0.5 0.3 – 0.4 0.33

11.5 –15

6–9 m2/kWp

Monocrystalline, polycrystalline

5–9 %

T1: Conversion efficiencies of various solar cells and modules, space requirements and thermal behaviour

9 – 17 m2/kWp

Polycrystalline

20.3

115 –150

7–9

0.4 – 0.5

Silicon, amorphous microcrystalline micromorphous

13.2 15.2 13.0

5 –7 5 –7 7–9

50 –70 50 –70 70 – 90

15 – 21 15 – 21 11 –14

0.1 – 0.2 0.5 – 0.7 0.3 – 0.4

CIS, standard (selenium) sulphur nano solar cells

20.0 13.1 14.0

8 –11 6 –7 8 –10

80 –110 60 –70 80 –100

9 –13 15 –17 10 –13

0.3 – 0.4 0.3

CdTe

16.5

6 –11

60 –110

9 –17

0.2 – 0.3

CIS, CdTe

Performance The current and voltage of a solar cell, and those of a solar module, are not constant; instead, they depend on the momentary load. Different operating points are established depending on the loads connected. The output power of a solar cell is the product of current and voltage. There is exactly one current/voltage combination for each irradiation and temperature value at which the power output of the solar modules reaches its maximum value. This point is called the maximum power point, abbreviated to MPP. The unit of measurement for the peak output at MPP is the watt-peak [Wp]. In addition, as the illuminance, temperature, angle of incidence and the spectral distribution of the light influence the output, uniform standard test conditions (STC) have been established internationally for determining the electrical data: • 1000 W/m2 irradiation level perpendicular to surface of module • Reference air mass solar spectral irradiation distribution at AM 1.5 • 25 °C cell or module temperature

31

Rated output and conversion efficiency The specified rated output of a solar module in Wp or a solar generator in kilowatt-peak [kWp] corresponds to the peak output under laboratory conditions; such conditions are, however, hardly ever achieved in practice. After all, the high irradiation of a summer’s day and the spectrum of a clear day in spring or autumn seldom coincide with the cool cell temperatures on a winter’s day. The electricity produced by a solar cell climbs with the irradiation level. The conversion efficiency describes the percentage of the available solar energy that is converted into an electrical current by a solar cell or module. It is the ratio of the rated output to the radiation incident on the cell or module area at STC. The degree of efficiency of the module is always lower

32

33

22

than that of the cell because the former includes inactive spaces between cells and frame surfaces plus the transmittance of the solar glass. Depending on the manufacturer and the number of cells per unit area, a certain range for each cell technology is evident within the module market (Tab. T1). Compared to conversion efficiencies of 12–20 % for crystalline modules, thin-film technology supplies much lower values, although module efficiencies > 18 % are feasible with CIS in principle. Modules with amorphous or micromorphous silicon achieve 5 – 9 %, whereas cadmium telluride and CIS, currently with efficiencies of 6 –11 %, are approaching those of crystalline cells. However, in contrast to the situation with conventional power stations, the conversion efficiency often plays a minor role. As solar radiation, a primary energy source, is available to us free of charge, high conversion efficiencies are only important when space for the modules is in short supply. Otherwise, a low conversion efficiency merely means that we need a larger area to reach the same output. As the costs are not based on a module’s area, but rather on its output, the system costs per kWp can usually be compared across cell types. However, the output-related costs of thin-film modules must be lower in order to compensate for the higher specific costs of planning and installation. Where a PV system is to be integrated into a building, low conversion efficiencies can even prove to be beneficial for the economics of the system because of the lower cost of the surface area. Temperature behaviour As the temperature increases, so the efficiency of a solar cell decreases continually – up to half a percentage point per °C in the case of crystalline modules. The

Generating and using solar electricity Efficiency

100 80

Relative intensity [%]

60 Solar spectrum AM 1.5 40 20 0 300

34

Crystalline silicon (Si) Back-contact cell

500

700

900

1100

Amorphous silicon (one layer) Amorphous (triple), micromorphous Si

scale of this effect is specified by the temperature coefficient. With a high irradiation, module temperatures of up to 80 °C are possible during the summer in certain situations, which reduces their output by more than 25 % compared to the rated output. PV modules should therefore be installed in such a way that the underside is well ventilated, allowing the heat to escape quickly into the surroundings. Temperature behaviour is generally more of a problem with crystalline modules than thin-film types; the output of amorphous and CdTe modules drops by only about 0.2 % per °C temperature rise. Spectral sensitivity Owing to the selective absorption properties of the respective cell materials, solar cells exploit the different sections of the solar spectrum differently (Fig. 34). Whereas crystalline cells are particularly sensitive to long-wave solar radiation, thin-film cells are better suited to the visible part of the spectrum with its shorter wavelengths. And amorphous and micromorphous cells in particular achieve a better yield with weak and diffuse irradiation because they absorb short-wave blue light best of all. On overcast days, only this high-energy radiation is able to penetrate the cloud cover in the form of scattered light. CdTe thin-film modules, too, often exhibit a somewhat higher conversion efficiency at low light levels than is the case with the AM 1.5 spectrum, whereas the efficiency of crystalline solar modules decreases with respect to STC. Many PV installations with thin-film modules, but also those with high-efficiency cells, therefore achieve comparatively higher yields per kWp rated output. With their favourable temperature and shading characteristics, they offer further advantages for building integration projects where the ventilation and irradiation conditions are often less than optimum.

1300

1500 Wavelength [nm]

Cadmium telluride (CdTe) Copper-indium diselenide (CIS)

Shadows The solar cells in the modules are connected in series and so they react very sensitively to partial shading of a cell or module. A shadow is, in effect, severely diminished irradiation, which reduces or even stops the current flow in a cell. Without illumination, the solar cell behaves like a normal diode and becomes a passive component consuming the current from the other cells. The cell in the shadow heats up, in some circumstances to such an extent that a so-called hotspot ensues, which can damage the cell and its embedding material. Modules are therefore fitted with bypass diodes which direct the current past the shaded cell(s). The best solution would be to bridge over every individual cell. But in order to keep the wiring costs in production within reasonable limits, each group of 12 –24 cells is protected; standard modules are therefore normally fitted with between two and four bypass diodes. During normal operation these do not cause any losses, but when part of a module is in shadow, the module junction box must be able to dissipate the heat produced by the diodes. At the same time, bypass diodes reduce the yield losses in the case of partial shading. If a shadow obscures only one single cell in a module, the series wiring works like a garden hose with a kink in it. Without a bypass option, this cell, as the weakest point, would determine the current throughout the module, and in a worstcase scenario lead to the total failure of the module. Even with a bypass diode, the output drops by a disproportionately large amount, but only for the group of cells bypassed in that moment – by half or one-third, for example, depending on the number of bypass diodes fitted. Thin-film modules react less sensitively because the long, thin strips of cells are not completely covered quite so easily (Fig. 35). If the shadow runs perpendicular

30 Relationship between conversion efficiency of module and space requirement 31 Transparent, air-inflated membrane construction with integral amorphous silicon PV modules. The laminates based on flexible synthetic backing films, encapsulated in EVA, are laminated to the underside of the structural ETFE membrane. 32 Flexible special module with amorphous triple cells integrated into a roof and facade system. The cells, measuring 356 ≈ 239 mm, are interconnected via bypass diodes to create one module. That increases the tolerance with respect to shadows. 33 Trapezoidal custom module made from bonded, interconnected strips of CIS cells in a glass/plastic laminate. The cell fields can be arranged as required in the module, which permits full use of the area available and no restriction on the shape of the module, or use of the intermediate spaces for architectural purposes. 34 The efficiency of a solar cell is affected by the spectral composition of the light. Crystalline cells use long-wave red light particularly well. Thin-film cells are better adapted to the spectrum of diffuse light. High-efficiency and multi-junction cells absorb a particularly wide range of the wavelengths in sunlight.

23

Generating and using solar electricity Efficiency

35 5 %

20 %

50%

100 %

to the strips, up to a certain point the output decreases in proportion to the cell area affected. Often, thin-film modules do not require any bypass diodes, at most only one. Shadows on the area of the PV generator should therefore be avoided whenever possible. Nearby objects are particularly disadvantageous because of the dark shadows they cast. Small areas of soiling, e.g. bird droppings, leaves, are dangerous because of the risk of causing a hotspot. But dust and dirt, owing to its more even distribution, is less of a problem, causing losses in output and yield that are only as high as the reduction in irradiation caused by the soiling itself. With slopes of about 10° and more, the self-cleaning effect of rain is adequate in Germany, which means that cleaning of the module surface – apart from the aforementioned particular cases – is usually only worthwhile in the presence of severe airborne pollution.

35 Output losses in crystalline and thin-film and crystalline modules caused by shadows. The shadow effect decreases as the distance of the object from the module increases. 36 Only by way of an ingenious interconnection of the solar cells within each module and the modules within the generator was it possible to limit the shading losses due to the top chord of the roof construction and the set-back top storey to an acceptable degree. Office of the Federal President, Berlin (D), 1998, Gruber + Kleine-Kraneburg 37 Mountain refuge with autonomous energy supply and built to passive house standards. The PV system with rechargeable batteries supplies conventional household appliances via inverters and provides about 65 % of the building’s electricity requirements. PV output: 7.5 kWp. A co-generation plant cuts in as required to cover the shortfall. Mountain refuge, St. Ilgen (A), 2005, pos architekten, Treberspurg & Partner Architekten 38 Solar cells can operate small DC devices directly, here a milk frother with integral solar cells. 39 Schematic diagram of grid-connected photovoltaic installation a PV generator b DC disconnecter c Inverter d Generation meter e Supply point f Public grid g Consumer meter h Distribution board 37

24

36

From solar module to solar generator The same principles and problems experienced with the interconnection of cells to form modules also apply to the next larger unit – the solar generator, in which any number of solar modules can be combined, from a small installation mounted on the roof of a house with an output of just a few kWp to a multi-megawatt power plant consisting of hundreds of thousands of modules. Several identical solar modules connected in series form a PV string which is connected to other strings in parallel. A shadow on one module therefore has an effect on the output of the entire string. Appropriate wiring within the generator can minimise the losses caused by temporary shadows (Fig. 36). If necessary, electrically inactive dummy elements, e.g. printed glass panes, can be used to fill up any spaces. Varying radiation levels and manufacturing tolerances can cause

Generating and using solar electricity Photovoltaic systems

a

h

g kWh

b

c

d

e

f

= π

38

similar effects to partial shading, albeit to a much lower degree. Here again, the module with the lowest amperage determines the series connection and causes “mismatching” (losses due to current/voltage differences among the modules in a PV array). For this reason, only identical cells are used in a solar module, grouped together according to their exact electrical values. Sorting of the modules within the generator is, on the other hand, usually too involved and too costly. Photovoltaic systems Although solar electricity supplies do not necessarily require an existing infrastructure, their conception is very closely linked with such an infrastructure. We distinguish between stand-alone and grid-connected systems. Photovoltaic installations installed on buildings are generally grid-connected. Stand-alone systems Stand-alone systems are autonomous systems that supply one or more loads completely independently of any electricity grid. The solar energy yield must therefore be coordinated with the energy requirements. In most systems, rechargeable batteries absorb any temporary surpluses and store the electricity for periods with little sunshine. If necessary, a diesel-powered generator, wind turbine or other, additional energy source can be used to supplement the PV generator. In small systems, for mobile applications such as motorhomes or boats, stand-alone photovoltaic systems have long since established themselves as practical and economic alternatives to batteries (Fig. 38). The PV systems fitted to traffic and infrastructure facilities, e.g. parking ticket machines, traffic control systems and mobile communications transmitters, are also standalone systems. And in mountain huts or remote holiday homes it is often more costeffective for users to generate electricity

kWh

39

with photovoltaic modules than to install a new connection to the grid (Fig. 37). Many thinly populated, war-torn or poor regions of the world will remain without a comprehensive electricity grid for the foreseeable future. For example, in remote provinces of China, in Iraq, in the Himalayas or in the developing countries of Africa, South America and South-East Asia, stand-alone PV systems can raise the standard of living and promote economic development. From individual modules right up to autonomous mini-grids, they can supply lights, houses, hospitals, schools, production plants or even whole villages with electricity and operate treatment plants for clean drinking water. On islands in the Mediterranean, PV installations can form the basis for environmentally friendly electricity supplies or supplement poor networks. As interest in using electricity for powering vehicles increases, so the potential for using solar electricity as a drive energy grows. Grid-connected systems In order to avoid costly storage systems involving high losses and requiring extensive maintenance, PV installations are connected to the electricity grid whenever possible and use this as a virtual energy store. An inverter forms the interface between the solar generator and the grid, converting the direct current generated by the PV modules into the customary alternating current required in households or industry. Surplus PV electricity – perhaps all of it, depending on the particular tariff – is fed into the grid. And vice versa: at times when the solar generator cannot supply enough energy, electricity is drawn from the grid in the customary way. In the public electricity grid, an energy mix maintains a constant balance between suppliers and users. In the ideal case, PV installations make electricity generation in other power stations superfluous. Since 2000 the German Renewable Energies Act

(EEG) states that users have a legal right to a connection to the public electricity grid and a minimum remuneration for electricity generated by renewable energy. This remuneration per kilowatthour is higher than the price for conventional electricity. It is therefore worthwhile feeding all the solar electricity into the grid and covering a building’s requirements with electricity from the grid in the customary way. The so-called generation meter, fitted in addition to the standard consumer meter, records the amount of energy supplied and forms the basis for the grid operator’s accounting (Fig. 39). Every owner of a PV installation therefore becomes a power plant operator and the PV system operates completely independently of the electricity supplies within the building. In the event of a mains failure, however, the PV system is able to provide an emergency supply. So it is no longer the electricity consumption of a building that determines the size of the installation, but rather the architectural, geometrical or economically reasonable area available for the installation of solar modules, and the budget of the client. This increases the design freedoms and the solar coverage rate that can be achieved – even if this only represents a theoretical annual figure. In the future this method of operation may change again because in the meantime the EEG even remunerates solar electricity consumed within the building quite generously. In addition, as the costs of systems continue to fall, in a few years we will see the appearance of PV installations that are able to compete with the consumer prices for electricity generated conventionally without the need for grants and subsidies (see “Introduction”, p. 8). As the price of electricity increases, the direct marketing of PV electricity will become interesting, especially with a differentiated pricing policy, as is already common in 25

Generating and using solar electricity System technology

energy exchanges. Solar electricity is a valuable peak-load electricity because PV installations provide the highest output around midday – exactly when demand is highest.

40

T2: Typical output ranges (electrical) Grid-connected PV installations Detached house 1–5 kWp Larger buildings (apartment block, industry) 10 kWp – 2 MWp Systems connected to DC networks 10 kWp – 1 MWp PV power plants (solar farms) 500 kWp – 50 MW p Other power plants Co-generation plant < 10 kW – 2 MW Wind farm 1– 740 MW Hydroelectric power plant 5 kW – 130 MW Pumped-storage hydroelectricity 500 kW – 18 GW Solar thermal power plant 10 kW – 80 MW Biomass, biogas power plant 100 kW – 90 MW Geothermal power plant 2 – 10 MW Volcanic regions 20 – 700 MW Fossil-fuel + nuclear power stations 50 MW – 8 GW Vehicles 90 bhp car Electric car

66 kW 9 – 80 kW

1 GW = 1000 MW = 1 000 000 kW 1 kW = 1000 W = 1 000 000 mW

40 Grid-connected PV installation attached to a noise barrier adjacent to the A13 motorway near Domat/Ems (CH), with an output of 100 kWp 41 Installation concepts for grid-connected PV installations. The right choice depends on the size and the local circumstances. a Central inverter concept b String inverter concept c Module inverter concept

26

Electricity supplies are poised on the brink of a fundamental reform. Traditional, centralised systems are based on a few large, fossil-fuel and nuclear power stations. They supply a huge number of users distributed over a huge area by way of a hierarchical grid with different voltage levels. With a growing number of co-generation plants, biomass plants, wind turbines and PV installations feeding into the grid, the suitability of this system for modern, sustainable energy supplies is limited. Just like the information flows in the Internet, the electricity grid will in future have to distribute electricity in more than one direction; instead, it will have to gather supplies from small, decentralised electricity generators close to users and distribute these according to demand. When the new small power plants are located directly where the energy is required, there are no longer any significant line losses caused by long transport distances across the grid. For the user, the risk of a failure in the electricity supply, e.g. due to an accident, is reduced [3]. This decentralisation calls for greater networking in the medium-term, but also complex load management in the low-voltage grid and more flexibility in power station capacity. Only in this way can the fluctuating availability of renewable energy systems remain fully usable without risking the quality of the grid and the reliability of supplies, or having to maintain large reserves of capacity. Important components will be storage units that buffer temporary excess capacity (e.g. in flywheels made from high-strength materials, or compressed-air systems, but also in batteries for hybrid and electric vehicles) and stabilise the grid. Experts

are working both on the idea of converting solar electricity into hydrogen to create a transportable and storable energy medium and on innovative transport systems. The latter could take the form of a high-voltage DC network stretching from the deserts of North Africa to northern Europe. Although PV power plants in the output range of many megawatts to gigawatts – corresponding to several conventional 600 MW power plants – in uninhabited desert regions are still a vision, they are feasible, at least technically (Tab. T2). System technology Grid-connected PV installations require a series of technical components in order to feed solar electricity safely into the electricity grid with minimal losses and at the same time guarantee reliable operation. Those components can vary from system to system. Every installation design is individually adapted according to size and boundary conditions and optimised for a high annual yield. Systems for buildings frequently make use of different module types mounted on different surfaces with different inclinations and orientations. It is then sensible to split the generator into smaller units, homogeneous in themselves, or even to use separate, individual systems with their own inverters. Inverters Besides the generator, the inverter forms the second key component in a PV installation. In contrast to the modules, the inverter is a complex electronic component with the associated wear phenomena and more frequent breakdowns. It functions as an energy and system manager with the following tasks: • Conversion of DC electricity into AC electricity • MPP (maximum power point) tracking • Protection of electricity grid and PV generator

Generating and using solar electricity System technology

PV generator

PV generator

PV modules with integral inverters

=

~

=

~

=

~

=

~

=

~

Generator junction box Inverter

=

~

41 a Public grid

• Operations monitoring and communications interface In the first place, the inverter converts the direct current (DC) produced by the generator into alternating current (AC) with the voltage and frequency of the electricity grid (230 V, 50 Hz). Its power electronics break up the direct current and output impulses in alternating directions in order to emulate the sine-wave form of the grid voltage as accurately as possible. In the past all solar inverters were fitted with a transformer, but these days more and more devices adapt the voltage electronically. Inverters without transformers are smaller, quieter and lighter, and are characterised by a high degree of efficiency. However, the omission of a transformer increases the electromagnetic influence and calls for additional safety measures. Some thin-film modules, and also back-contact and ribbon silicone cells, can suffer irreversible cell damage when operated with transformerless inverters and may only be combined with approved equipment. In order to feed the maximum output into the electricity grid at all times, even with constantly fluctuating irradiation and temperature conditions, a so-called MPP tracker continuously compares the inverter voltage with the current MPP voltage of the generator. In addition, an automatic grid monitoring system switches off the solar electricity system automatically in the case of grid failure. The inverter monitors the PV installation for insulation faults. The efficiency of an inverter depends on its degree of utilisation and hence on the current solar irradiation. Inverters operating at small outputs achieve only a poor degree of efficiency – the maximum is at about 50 % of the rated output. Where modules do not have an optimum orientation and therefore do not achieve high irradiation figures (especially in the case of PV facades), it is therefore advisable to

Inverter

=

~

=

~

=

~

b Public grid/building subdistribution

select an inverter output that is much lower than that of the PV generator, an approach that increases the efficiency and reduces the cost of the inverters. Interesting for the system operation is the dynamically weighted Euro efficiency, which corresponds to an average annual degree of efficiency for a Central European climate. Good inverters achieve Euro efficiencies of between 92 % and 96 %. If control losses plus voltage and temperature effects are included in the equation, inverters lead to a 5 –10 % loss in yield over the year, in unfavourable circumstances up to 15 %. Installation concepts Besides the size of the installation, the choice of inverter concept is determined by the geometry and arrangement of the PV modules on the one hand and the local options for routing the cables and installing the inverter equipment on the other. For large installations exceeding about 30 kW, a centralised concept is usually the best option (Fig. 41a). A larger number of parallel PV strings is combined via generator junction boxes and connected via a main DC cable to a powerful central inverter. The more complex wiring and protection components required on the DC side must be balanced against the price advantage of the large inverter and, often, its higher degree of efficiency. In so-called masterslave operation, such an inverter will switch individual power units on as required and therefore achieve a high degree of efficiency even with a low solar irradiation level. However, this concept is only advisable for installations free from shadows and with a consistent orientation and temperature rise, which is not always the situation with building-mounted PV systems, where decentralised concepts with string inverters, which are connected directly to just one or two parallel strings, are more suitable (Fig. 41b). The DC wiring is amazingly simple and is reduced to plug-in module

c Public grid/building subdistribution

cables plus string cables at the start and end of each string. In the case of larger installations, several inverters are connected with the grid in parallel, which makes later expansion very easy. Shadows no longer have an effect on the entire PV generator, but only on the individually regulated strings. The module inverter concept goes one step further and integrates a separate inverter into every module (Fig. 41c). These independent mini-systems then feed directly into the grid. Owing to the high costs and the increased maintenance and monitoring requirements, this concept has not yet asserted itself in the market. However, research is being carried out into practical solutions because with standardised AC technology the planning and installation work is reduced and the applications for building-integrated PV look promising. Choosing a location for the inverter Inverters warm up and hum when in operation. The best locations are therefore cool, dry, dust-free roof spaces, basements or plant rooms, provided they are accessible for maintenance and replacement. Central inverters are mostly housed in switching cabinets in plant rooms (Fig. 42). String inverters require somewhat more space for the same output in order to avoid mutual heating effects (Fig. 43). They can be wall-mounted at an appropriate spacing, e.g. approx. 500 mm, or can be located separately in the vicinity of the PV string concerned, e.g. on a flat roof in the shade of roof-mounted modules (Figs. 47 and 49). When mounted outdoors, the inverters must be protected against direct sunlight. Statistically, string inverters must be replaced once during the lifetime of the installation. On the other hand, centralised inverters are designed for a service life of 20 years. Nevertheless, several 27

Generating and using solar electricity System technology

42 Central inverter of 100 kW output power 43 Wall-mounted string inverters and DC disconnectors in a basement plant room. A unit with about 5 kW output measures, for example, approx. 400 ≈ 600 ≈ 200 mm (W ≈ H ≈ D). 44 A prototype module inverter: integrating an efficient module inverter into the junction box < 35 mm deep 45 Module interconnection with string inverters a Inverter located outdoors (e.g. flat roof installation): building envelope penetrated by AC cable(s) b Inverter located indoors (e.g. pitched roof installation): building envelope penetrated by DC cable(s) 46 Module interconnection with central inverter

a Generator junction box located outdoors (e.g. flat roof installation): building envelope penetrated by main AC cable(s) b Generator junction box located indoors (e.g. roof and facade installations): building envelope penetrated by string cables 47 String inverters and small central inverters with IP 54 class of protection (dust and splashing water) or higher can be mounted on the roof adjacent to the PV strings. 48 PV installation display unit, showing the most important data and operating figures. 49 Inverters mounted outdoors protected from the weather by the PV modules themselves in the form of a roof.

repairs may be necessary. Well-ventilated locations reduce the failure rate, prolong the service life and also ensure efficient operation.

string cables can be routed together (Figs. 45 and 46). In doing so, it is important to observe the fire protection and sound insulation requirements and to avoid thermal bridges. Lightning arresters are required, especially with large arrays, in order to prevent nearby lightning strikes from being conducted via the installation cables into the building’s electrical systems or the inverter and causing damage. The individual cables are relatively thin and flexible. However, in larger installations they can aggregate to form a considerable package. Within the building, existing service shafts and ducts should be used wherever possible, otherwise new cable trunking will have to be laid. When working with an existing building, in some circumstances it may be possible to utilise chimneys or ventilation shafts that are no longer in use.

Cables and connections Direct current (DC) brings with it the risk of arcs between positive and negative in the event of insulation faults in the cabling or loose connections, which can lead to injuries and fires. The cables on the DC side must therefore be routed to prevent earthing faults and short-circuits. That normally means separate positive and negative cables with double insulation. Special solar cables are the best choice. They are UV- and ozone-resistant and approved for high temperatures (max. 125 °C). Cable ties, fasteners, conduits or trunking fix them firmly to the supporting construction and protect against mechanical damage caused by scuffing or rodents. On roofs and facades, the structural members generally offer sufficient space for the cables. When the cables are laid indoors or in conduits, less costly standard cables can be used. The same cable types normally used for electrical installations in buildings can be used for the AC lines from the inverter to the connection to the public electricity grid. But outside, such cables also require protective conduits because of their low UV resistance. The cable insulation should be free from PVC and halogens. The majority of solar modules are factoryfitted with plug-in connectors, which are simply plugged together by the roofing or facade contractor’s personnel. The main and connecting cables can also be supplied prefitted with plugs.

42

43

If the inverter is located outside the insulated building envelope, fewer cable penetrations are required – just one inverter AC connecting cable per inverter. Otherwise, the main DC cable or the bundled

44

28

Safety features and connection to grid Solar modules are permanently “live” during the hours of daylight and cannot be switched off. A DC disconnector (isolator) is therefore obligatory close to the inverter on the upstream side or integrated into the inverter. This is used to isolate the generator from the rest of the system in the event of a fault or during maintenance work. In centralised concepts, the disconnector is mounted together with other DC side protective elements in the generator junction box. Furthermore, the network operator must be able to isolate the PV installation at any time when work on the grid itself is necessary. The generation meter is normally rented from the network operator and installed in the existing building distribution board alongside the consumer meter. In very extensive building complexes, where several buildings may share a connection, the distance from the inverter to the connection point can be considerable. In order to avoid disproportionately long cables, it is possible,

Generating and using solar electricity Yields and economics

outside

inside

outside

inside

=

=

~

~

a

a outside

inside

outside

=

inside

=

~

45 b

following a special agreement, to make the connection at a more favourable point. Small and medium-sized installations are connected to the grid with 230 or 400 V, whereas large solar farms usually feed in at the 5 – 50 kV medium-voltage level. A direct 600 V feed into a DC network, e.g. for trams, may also be possible. Monitoring and communication Permanent operation indicators ensure that the PV installation reliably achieves the calculated yields and that faults are detected quickly. As inverters record the main operating data of the solar electricity installation for their control tasks anyway, the measurements can also be used for monitoring the system and for displays. Modern equipment shows the most important data in a display and in the event of a fault sends alarm signals via fax, e-mail, SMS or Internet. With the help of appropriate accessories and software for the inverter or an independent monitoring system, the client can read out the data, evaluate this on a computer or appoint a company to control the operation of the system. Increasingly, Internet portals prepare the results graphically in a way that is also understandable for non-specialists. Large displays outdoors or in reception foyers can attract the public’s attention to a PV installation and illustrate the yields or carbon dioxide savings (Fig. 48). Yields and economics The energy yield of a grid-connected PV installation is the solar electricity measured by the meter. In order to achieve a better comparison of different sizes of installations, it is customary to relate the annual quantity of kilowatt-hours fed into the grid to the system’s rated power output and express the specific yield in kWh/kWpa. The yield of a solar electricity system depends on:

~

46 b

• Weather and shadow conditions at the location • Orientation and inclination of the modules • Mounting situation (ventilation and temperature gradient) • Manufacturing tolerances, the partial load and temperature behaviour of the modules • Quality of the system technology, including planning and installation Experience has shown that PV installations in Germany produce – per kWp of rated output per year – between 750 and 47 1000 kWh of electricity with roof-mounted systems, between 850 and 1100 kWh with ground-mounted arrays (with tracking systems up to 1550 kWh) and between 500 and 800 kWh with facade-mounted systems. It is possible to make an estimate using the reference values in Fig. 51 for optimally oriented, well-ventilated and essentially shadow-free roof-mounted systems. Large installations with optimised technology on the roofs of commercial premises, for example, can certainly achieve higher yields. The yield per unit area depends on the conversion efficiency of the module and, depending on cell type and number of cells per 48 unit area, fluctuates between 45 and 190 kWh/m2. Where surfaces face in non-optimum directions, the potential yield can be estimated with the help of the corresponding conversion factors given in Fig. 5 (p. 12). There is a tendency for east-facing systems to achieve slightly higher yields than those facing west because the modules are warmer in the afternoons when west-facing surfaces receive their maximum solar radiation. Installations with thin-film modules sometimes achieve yields up to 5 % higher. But the natural vagaries of the weather will lead to different solar electricity yields from year to year. 49 29

Generating and using solar electricity Yields and economics

T3: Temperature increase and reduction in solar electricity yield of crystalline modules for various types of installation Type of installation

50 Energy flow diagram and performance ratio for a PV installation: average losses (in %) up to grid feeding 51 Procedure and sample calculation for step-by-step yield estimate for PV installations. The reference to the rated output or the generator surface area supplies the specific system yield in kWh/kWpa as the normal comparative value or the yield per unit area. The regional rules of thumb apply to an unshaded roof-mounted installation with an optimum south orientation and approx. 30° module inclination.

30

Temperature increase over ambient

Reduction in annual energy yield

Warm (single-leaf) facade

55 K

10.5 %

Warm roof

43 K

7.5 %

Cold (double-leaf) facade, poor ventilation

39 K

7.0 %

Cold (double-leaf) facade, good ventilation

35 K

6.0 %

Cold roof, poor ventilation

32 K

5.0 %

Cold roof, good ventilation

29 K

4.0 %

Roof-mounted, large clearance

28 K

3.5 %

Ground-mounted array

22 K

2.0 %

Performance ratio and system efficiency The influence of the system technology is reflected in the performance ratio (PR). This is an evaluation criterion for the balancing of the system components and the quality of the system as a whole. As the PR is based on the irradiation level and the conversion efficiency of the PV modules, it enables installations with different technologies, locations and orientations to be compared with one another. The PR is defined as the ratio of the actual yield to the theoretical potential yield of a PV installation when the generator can operate under STC at all times and the downstream system technology does not exhibit any losses. In practice, however, the energy incident on the module surface is not converted perfectly. Energy is lost at many points in the system: the additional reflection losses at the glass of the module when the angle of incidence is not 90°, soiling of the module and a temperature rise beyond 25 °C, conversion losses and mismatching at the inverter. The chain of losses within the photovoltaic system accumulates to about 15 – 30 %, taken as an annual average, which corresponds to a PR of 70 – 85 %. The examples (specified as percentages) given in Fig. 50 for the individual loss mechanisms should be understood as average values. Welldesigned, well-constructed roof-mounted installations should achieve a PR of at least 75 %, whereas in facade systems the PR often remains below 70 %. The reasons for this are that neither modules nor inverters function ideally in the case of low irradiation levels on vertical surfaces, and also the fact that shadows have a negative effect on the PR. The performance ratio should not be confused with the overall efficiency of a PV installation, which also takes into account the conversion efficiency of the module and lies in the range of 4 –13 %.

Yield predictions The performance ratio can also be used to provide a rough estimate of the energy yield in advance (Fig. 51). If we take the solar irradiation on a horizontal surface for a certain location and adjust it for the inclination, orientation and area of the generator and multiply this by the module conversion efficiency and the PR, we obtain the annual yield of the PV installation in kWh/a, and finally the specific yield in kWh/kWpa. A plausible PR value requires individual estimates of the shadow and temperature losses (in %). Non-ventilated or, indeed, thermally insulated elements supply up to 10 % less electricity than PV modules mounted in an uninterrupted airflow. Tab. T3 lists the temperature rises of modules mounted in different ways compared to the ambient temperature for an irradiation value of 1000 W/m2 and the resulting reduction in the annual yield for German weather conditions. Thin-film modules react less severely to high temperatures and therefore represent an interesting alternative for facades from the energy viewpoint, too. With variable irradiation and temperature conditions, the interplay of the various module/inverter combinations and their interconnections is complex. Professional yield forecasts are therefore produced with simulation programs, which normally simulate an average climate year in hourly steps and add up the ensuing electricity production. To do this, they employ the weather data records of various locations and product databases that contain the necessary technical data of solar modules and inverters. The option of being able to include shadows and calculate their effects on the energy yield is particularly useful. At the same time, the simulation results enable the electrical and geometrical design of the installation to be optimised. An accurate yield calculation

Example: CIS warm (single-leaf) facade 29 % losses Example: roof-mounted installation 24 % losses

50

forms the basis for a sound feasibility study, which helps to minimise the investment risk of the client. Some suppliers of prefabricated PV installations offer warranties for the complete system and also guarantee a certain annual yield. Moreover, special solar insurance policies will also cover diminished yields as well as claims for repairs or damage. Financial yields: the feed-in tariffs The revised Renewable Energies Act (EEG) came into force at the start of 2009 and now prescribes the remuneration for solar electricity for the next four to five years (Tab. T4). The tariffs, which remain constant over 20 complete calendar years plus the year in which the system first came on line, are organised in such a way that profits in line with market standards can be realised with photovoltaic systems.

Global irradiation horizontal [kWh/m2a]

Irradiation on generator surface [%]

First year of Groundoperation mounted array

Building or noise barrier installations < 30 kW

≤ 30 kW

≤ 100 kW

≤ 1000 kW

2009

31.94

43.01

40.91

39.58

33.00

2010

28.75

39.57

37.64

35.62

29.70

2011

26.16

36.01

34.25

32.42

27.03

2012

23.81

32.77

31.17

29.50

24.59

2013

21.66

29.82

28.36

26.84

22.38

1

1.5 %

Line losses, meters

Grid feeding 70–85 % performance ratio (installation quality)

1.5 %

Inverter losses 10.0 % 7.0 %

Shadows

Module tolerance and mismatching 2.0 %

0.0 % 2.0 %

2.0 %

Module temperature 6.0 % 3.5 %

Deviations from 1000 W/m2 and AM 1.5

Module soiling, snow 1.0 %

Reflection losses

T4: Feed-in tariff for solar electricity according to German Renewable Energies Act (EEG) cent/kWh1

2.5 %

3.5 %

5.0 % 3.0 %

2.5 %

100 % incident radiation

Generating and using solar electricity Yields and economics

From 2010 onwards, the degression increases or decreases by 1 % if the market growth of the previous year lies outside the corridor allowed for.

Feed-in tariff calculation using the example of a roof-mounted installation with 150 kW output, first operated in 2010: 30 kW x 39.57 ct/kWh + 70 kW x 37.64 ct/kWh + 50 kW x 35.62 ct/kWh

For instance, the fact that large installations result in specifically lower costs is taken into account. The tariffs decrease by 8 –10 % each year for new installations in order to force manufacturers into genuine price reductions. Besides the year of installation, the tariff also depends on the location and size of the system. Installations mounted on buildings or noise barriers attract the maximum tariff up to an output of 30 kW per installation. In addition, a bonus scheme is intended to encourage the use of the solar energy in the building itself instead of feeding it into the grid. This requires a third meter to register consumption. The remuneration decreases progressively for larger installations > 30 kW. The lowest tariff applies to ground-mounted arrays, which by 2013 will have dropped to below 22 cent/kWh. So in the normal case a PV installation

Module efficiency [%]

Module area [m2]

anywhere in Germany will have paid for itself within 20 years. However, at locations in the north of the country with only moderate solar irradiation, the economic limits are quickly reached when less favourable orientations or shadows curtail the yields or, for example, elaborate, costly roof constructions entail additional investment. Photovoltaic facades are generally linked with higher design and construction costs but significantly lower yields. As a result, they are usually only economical when they replace conventional facade components and the ensuing cost-savings can be offset as a credit. This approach enables even east- or west-facing facades to achieve a positive costs/benefits ratio, provided they allow the use of standard module sizes or the costs are comparable with a high-quality facade for a prestigious building.

Performance ratio (PR) [%]

Annual yield [kWh/a]

Yield per unit area [kWh/m2a]

Specific yield [kWh/kWpa]

regional rules of thumb, south/flat roof:

b

a

= 37.35 ct/kWh

150 kW

kWh

c p. 12, Fig. 4

p.12, Fig. 5

900 –1200 kWh/m2a

North: 35 – 100 % East/West: 65 – 116 % South: 80 – 116 %

Regional average values: a) 975 kWh/m2a b)1025 kWh/m2a c)1100 kWh/m2a

p. 22, Tab. 1

a) 850 b) 900 c) 950

mono, poly a) 9 5 – 170 b) 1 0 0 – 180 c) 10 5 – 190

p. 22, Tab. 1

Fig. 50

mono, poly 11.5 – 2 0 % a-Si, μc-Si 5–9% CIS, CdTe 6 – 11 %

< 70 % Warm (single-leaf) facade in shadow

a-Si, μc-Si a) 45 – 75 b) 47.5 – 80 c) 5 0 – 85

≤ 85 % with optimum orientation, ventilation, planning, installation & maintenance

CIS, CdTe a) 5 0 – 95 b) 52.5 – 100 c) 5 5 – 105

Examples: 10 kWp flat roof-mounted installation in Würzburg (southern Germany) with polycrystalline modules (14.5 % conversion efficiency), mounted in south-facing rows with 30° inclination. 69 m2 module area, area of roof required = approx. 3 x 69 m2  210 m2, mutual shading approx. 2 %, estimated PR = 76 % 1090 kWh/m2a

x

114 %

x

69 m2

x

14.5 %

x

76 %

100 m2 warm (single-leaf) facade in Berlin with CIS modules (10.5% conversion efficiency), south-west orientation, no shadows, 95m2 module area, PV output = 95 m2 x 10.5% = 10 kWp, estimated PR = 71% 78 % 98 m2 10.5 % 71 % x x x x 51 1011 kWh/m2a

= 9448 kWh/a = 945 kWh

= 5585 kWh/a = 558 kWh

= 137 kWh/m2a

=

56 kWh/m2a

31

Generating and using solar electricity Ecology

52

53

Ecology Photovoltaic systems are extremely environmentally friendly electricity producers. They convert solar radiation, a primary energy source, directly into final energy without the need for any fuel. In doing so, they produce neither emissions nor toxic waste nor noise. Malfunctions are not dangerous for people or the environment. The relatively large surface area required is only critical in certain circumstances because with PV systems on buildings in particular, the systems utilise existing surfaces and infrastructures. However, if we consider the environmental effects over the total life cycle, from obtaining the raw materials to final disposal, the following principal questions arise: • Energy requirements during production • Availability of resources • Use of pollutants • Recyclability at end of useful life The life cycle assessment (LCA) of a PV installation essentially depends on the modules used. But the other components such as inverters, cables, fixings and supporting constructions also involve the conversion of materials and energy media. Recycling We expect to see the return of solar modules of all technologies some 20 –30 years after market growth. As almost all manufacturers reuse production waste internally or dispose of it, significant quantities of defective and scrap photovoltaic modules

54

are not expected before 2015. The glass and silicon components are particular significant for recycling. Glass accounts for the largest proportion (by weight) in a PV module and is fairly easy to recycle (Tab. T5). Reuse and recycling reduce the requirements regarding energy and primary raw materials such as quartz sand or lime in the production of new glass products. Crystalline solar cells and aluminium frames are relevant for energy reasons. The recycling of the silicon cells, which consume great amounts of energy during production, leads to a drastic reduction in the energy payback time and justifies the high cost of dismantling the composite elements into their individual parts. Industrial methods for crystalline modules are already well advanced and are being employed in the first recycling plant, where the embedding film and the backing film are incinerated in a special furnace at 500 °C (Fig. 53) to leave behind glass, metal, intact cells and cell fragments. The module frames can be sold for scrap or reused. The cell fragments can be melted down and processed to form new wafers. The intact cells are treated chemically to remove the front contacts, the anti-reflection coating and the n-doped coating. The resulting recycled wafers are used for the production of new solar cells (Fig. 54). Thanks to new production technologies, these can achieve conversion efficiencies higher than the original solar cells ready for fitting into new modules.

T5: Configuration of PV modules by weight [6] Weighted standard crystalline silicon module (glass/plastic laminate) Glass

Frame

EVA

Cells

Backing sheet

Junction box

Weight/output

62.7 %

22.0 %

7.5 %

4.0 %

2.5 %

1.2 %

103.6 kg/kWp

Thin-film modules (glass/glass laminate) Glass

Frame

EVA

Chemical elements

Backing sheet

Junction box

Weight/output

74.53 %

20.4 %

3.5 %

0.1 %

0.0 %

1.1 %

285.2 kg/kWp

32

A pilot project in 2005 enabled the first German PV power plant, which generated solar electricity from 1983 to 1989 on the North Sea island of Pellworm (Fig. 52), to start a new life as a photovoltaic facade with a full warranty for all the modules! Thin-film modules can also be recycled, but the separation is more complex. The best results so far have been achieved with amorphous silicon modules. Placed in an acid bath, the silicon and TCO layers become detached from the glass. Both can be used to produce new solar cells with the same efficiency. One alternative without any pretreatment is the direct use of the coated glasses as an ingredient for glass melts; the quality is adequate for reuse in insulating materials for the building industry or as a raw material for glass bottles [4]. The largest manufacturer of cadmium telluride modules operates a collection and recycling system for scrap modules from his own production. The laminated glasses are first broken down mechanically so that the layer of semiconductor can be removed with an alkaline solution. All the glass is passed on for recycling. However, the amount of semiconductor mass recovered is currently so small that it is being stored for later use in new solar modules or other products.

52 22-year-old PV generator on the North Sea island of Pellworm 53 Furnace for the thermal separation of scrap crystalline modules (incineration of embedding material) 54 Recycled wafers: the conversion efficiency of the cells is similar to cells produced from new wafers. 55 Energy payback times for PV installations with various cell technologies based on the state of production technology in 2004/05 (crystalline) and 2006 (thin-film) for corresponding module conversion efficiencies in % [5].

Generating and using solar electricity Ecology

Monocrystalline 14.0 %

C. Europe Southern Europe Central Europe

Polycrystalline 132 %

Southern Europe Central Europe

Cells made from ribbon of silicon 12.5 % CIS 11.5 %

Southern Europe Central Europe Southern Europe Central Europe

CdTe 9.0 %

Raw silicon Wafers Cells Laminate

Southern Europe

Frame Central Europe

Amorphous silicon 5.5 %

Southern Europe 0

55

1

2

System technology Overall

3 4 Energy payback time [years]

Energy balance Whether the use of photovoltaics leads to a saving in non-renewable primary energy, despite the high energy consumption during the production of the modules, is shown by the energy payback time. In other words: the operating time in which an energy system can supply as much usable energy as was necessary for the production of its components. The energy payback time depends very heavily on the cell technology and the electricity supplies to the production plants, but also on the installation yields and the electricity mix in the grid which the solar electricity replaces. If building-integrated PV modules replace other components, the energy that would have been required to produce those components can be included in the equation as a credit. The yield from facadeintegrated PV modules is lower than that obtained with irradiation-optimised roofmounted systems, but in the form of multifunctional components, such facades are able to achieve numerous energy-savings. For example, in the form of sunshades, they can reduce the cooling requirement. Owing to the high energy requirements in the production of silicon and the high temperatures during wafer production, crystalline cells have the highest energy input. But also relevant here is whether the silicon was obtained from, for example, Norway, where a high proportion of electricity is generated by hydroelectric power, and whether scrap or solar-grade silicon, with a reduced production input, was used. Despite their lower energy output, thin-film modules have a better balance because such cells require much less energy during production and often require no frame. Many studies over many years have investigated the energy payback times of photovoltaic systems. With today’s production technology, systems with crystalline modules installed in Central

Europe achieve an energy payback time of between two-and-a-half and just over three years; in the case of thin-film modules it is about two years (Fig. 55). At southern European sites with their higher solar irradiation, these times are cut to about 12 months for thin-film technology and 18 months for (poly)crystalline modules. During their 30-year service life, today’s PV installations produce about 10 – 30 times as much energy as they consume. Over the next four to five years, improved production methods and increases in conversion efficiency will result in even shorter energy payback times. The times for thin-film modules will then come down to less than a year, whereas nano solar cells promise a payback time of less than a month. Resources and hazardous substances Silicon, the basic material for the majority of solar cells, is non-toxic and available in virtually unlimited amounts. Contrasting with this, the deposits of elements for alternative cell materials, e.g. indium tellurium, are finite. A further reduction in material consumption is therefore an important field of research for thin-film cells as well. Many steps in the production of solar cells use chemicals. In the production of crystalline silicon cells, ecologically harmful substances remain in closed processes [6]. In the finished solar module, only the soldered connections contain constituents that are detrimental to the environment because the majority of manufacturers still use lead solder. Various toxic substances are used in thinfilm modules with CdTe and CIS solar cells. In its gas state, the heavy metal cadmium presents potential environmental and health risks. But this is only the case during production in completely enclosed reduction plants. Just small amounts of CdTe can contaminate drinking water. However, even in the event of fire this

does not normally represent a hazard for people or the environment because the glass melts at a much earlier stage and bonds the heavy metal. There is currently no evidence of hazardous substances leaching out of dumped or broken modules [7]. Fires with high temperatures > 1000 °C are, however, critical. Cadmium is a waste product of zinc mining. Its use in solar modules is seen as ecologically advantageous provided environmentally compatible disposal is guaranteed. And it should be remembered that 1 m2 of a CdTe module contains less cadmium than a NiCd size C (baby) battery! CIS modules contain much less cadmium in the thin buffer layer of CdS. Alternative materials are currently the subject of research. Another problematic substance in CIS modules, selenium, is replaced by sulphur in technologies based on copper-indium disulphide. The levels of selenium and cadmium in CIS modules are so low that, like CdTe modules, they could be disposed of in normal domestic waste sites. However, to prevent this, the photovoltaics industry is obliged to set up a reliable collection and recycling system which prevents environmental problems caused by contamination and returns valuable raw materials to the materials and energy life cycles.

References: [1] Haselhuhn et al., 2008, pp. 4 – 8 [2] Häberlin, 2007, p. 95 [3] Aulich, 2007, p. 40 [4] Hagemann, 2002, p. 175 [5] de Wild-Scholten, 2008; Alsema et al., 2006, p. 2304f [6] Haselhuhn et al., 2008, pp. 10 – 28 [7] Fthenakis, 2004, p. 322

33

Designing with photovoltaics

Photovoltaics (PV) and space technology are linked by their “artificial appearance” as well as their parallel histories. The special look of applications in space results from their extremely functional, constructionoriented design concept. Low weight, small transport dimensions plus forms and materials optimised for use outside the earth’s atmosphere determine their appearance. Synthetic, hybrid and metallic materials predominate. Where neither gravitation nor aerodynamics play a role and there are no neighbours to be considered, the forms that evolve are simply the summation of various functional components which nevertheless – or perhaps for that very reason – appear as one consistent, harmonious entity. One particularly conspicuous feature of satellites and space stations is their PV technology. Like the leaves of a plant, the large solar panels open out in space and turn automatically to face the sun (p. 36, Figs. 1, 2). But back on earth, the conditions are totally different to those of space. Besides the local climate conditions and the availability of raw materials, it has been economic and cultural influences that, in the main, have led to the development of typical building materials, building methods and building forms. PV technology that has been only marginally adapted to terrestrial needs often results in unsatisfactory architectural solutions when it is used in forms of construction characterised by generations of tradition. It is the aesthetic aspects that are partly to blame for the reticence frequently encountered, which means that despite the obvious advantages and substantial financial aid, applications for solar electricity technology still lag far behind their potential.

Features of crystalline photovoltaics Crystalline cell technology, with a market share of about 85 %, dominates not only the market but also the public’s general perception of solar electricity generation. A multitude of negative examples has strengthened public opinion and the limited number of positive examples are too little known in order to function as role models. The reasons behind the architectural problems can be attributed to conflicts at various levels of scale (p. 42, Fig. 21). Especially important aspects here are the relationship between the PV technology and other components or, indeed, the building itself and also the relationship between the building, with its PV installation, and its urban or rural surroundings. A solar panel is a composite product comprising various basic components and coatings. As several of these elements are visible simultaneously, it is difficult to speak of a material aesthetic. Conventional solar technology is more of a product aesthetic that has evolved over the past 50 years. It is primarily the solar cells themselves and the anti-reflection coatings that determine the appearance of the PV surfaces: dark blue-violet to anthraciteblack colour schemes prevail. However, the basic colour is not uniform because with polycrystalline technology especially, individual, angular, jagged zones can be seen, the colour of which alters abruptly, like a flip image, as the lighting conditions change (p. 36, Fig. 3). However, there are no light and shade effects as such because the crystalline cells are ultra thin and absolutely flat in comparison to the wavelengths of visible light. In addition, the perfectly regular, normally shiny and silvery,

35

Designing with photovoltaics Features of crystalline photovoltaics

1

3

2

grid of front contacts overlays the texture of the crystalline cells. The production methods customarily result in four-fold symmetric or circular forms, i.e. a very regular appearance (see “Generating and using solar electricity”, pp. 14 –18). The individual cells are arranged in a regular layout on square or rectangular panels, densely packed as close as possible, to create one interconnected group. To protect the sensitive cells from mechanical damage, the panel is given a cover – usually of glass – and a peripheral frame to

6. Nanotechnology generation

5. Hybrids & composites networking, alloying laminating

4. Synthesising condensing, polymerising carbonising

3. Chemical-physical, transformation crushing, melting firing, casting

2. Shaping treatments cutting, dressing, pressing 1. Raw materials of ancient shelters

guard the edges. The arrangement of the panels on the roof now follows the same principle: as close together as possible, regular, extensive and in one plane at an exposed position in order to exploit the space available and the solar irradiation to best effect. Monotony is the danger here. PV installations are characterised by a distinct modularity at all levels of scale and a grid-like segmentation of the surfaces on which they are mounted. Their components behave similarly on the micro, meso and macro levels – not

Lam. glasses, PV modules RC, fibre-reinforced conc. Stainless steels, alloys Resin mortars

Silicones

Clay bricks, ceramics, glass Mineral fibres Lime, cement, asbestos Iron, non-ferrous metals

Special bricks, dressed stones

Wooden laminates Fibreboards Resin laminates

Cellulose synthetic mat. Rubber

Particleboard Paper Natural rubber

Sawn timber, fibres

Hybrid textiles

Casein-based plastics

Low-molecular, multi-functional, miscellar reaction products

Thermosetting plastics, thermoplastics Elastomers Carbon fibres

Shellac

Wool, leather

Loam, rubble stones

Tree trunks, foliage, resins

Horns, milk, pelts

Stones & earths

Vegetable raw materials

Animal raw materials

Organic

Materials

36

Differences between traditional and PV materials and products The aforementioned features of a typical solar electricity installation differ in many ways fundamentally from those of traditional building materials, building products and forms of construction. This fact complicates the harmonious integration of a PV system into a building and, in turn, the building into its urban or rural environment.

Nano solar cells

Inorganic

6

unlike the artistic figures of fractal mathematics.

Tar

Coal, gas, petroleum

Designing with photovoltaics Differences between traditional and PV materials and products

4

5

The influence of the materials and their processing The history of building materials can be roughly divided into a number of development phases (Fig. 6). Following on from ancient shelters, built from the natural raw materials found in the immediate vicinity, a multitude of more complex mechanical and chemical treatment methods gradually evolved. Traditional building materials can be roughly distinguished from modern materials by way of the “chemical-physical transformation” and “synthesising”. Glass – also in conjunction with transparent intermediate layers – plays a special role in this portrayal because it fits into several groups. Thanks to their familiar tactile virtues and their well-known aesthetic qualities, traditional materials generally enjoy a special esteem. PV products, on the other hand, are hightech items requiring ideal factory conditions for their manufacture. They certainly fit best of all into the fifth stage of the graphic presentation in Fig. 6. As the degree of prefabrication of a product increases, so its subsequent processing options decrease. This means that modifications on site are ruled out in most instances – the PV installation is simply erected and connected, nothing else. The active solar level remains concealed behind its protective cover and is imperceptible to the observer. If we could touch that level, it would be like touching an extremely thin, smooth, metal-like surface. Colours Colours comprising different components combine to form various colour models. However, all are based on the fundamental attribute of the shade or hue. The colours of traditional materials and paints used in the construction industry are characterised by the yellow-red region of the colour wheel. We speak of “warm” colours because of

their psychological effect. The prevailing colours exhibit a relatively low saturation, they appear natural. The tendency is for brighter colours to dominate opaque parts of the facade in particular. Dark areas generally occur – with the exception of glazing in the facade – on pitched roofs covered with black-grey clay tiles or slates as neutral grey or warm colours. The very dark and “cold” colouring of PV components therefore form a colour as well as a lightdark contrast in conjunction with the majority of backgrounds. The building envelope and its PV installation must be very carefully coordinated in order to achieve a harmonious colour scheme. Textures Traditional materials normally exhibit an irregular texture because their natural origins are reflected in their surfaces. PV modules, on the other hand, are characterised by a geometrical, regular pattern. PV panels and windows Glass is normally used as the covering material and therefore PV modules exhibit a reflection behaviour that comes closest to that of windows, whereas traditional facades have a high proportion of opaque surfaces that produce diffuse reflections. In addition to the shine, PV modules and windows are also similar in terms of their size and brightness. From the outside, closed windows viewed from a distance during daylight appear to be the zones with the lowest luminance, i.e. with apparently the darkest surfaces. This analogy draws a certain attention to the PV installation, which, however, offers the observer much less information – in contrast to windows, the solar panels are “dummies”. Architects usually feature openings in the facade because these are the most important reference points for the building’s users, linking them with the outside

world. Windows divide up the facade not just in two dimensions, but in three: in fenestrate facades they are not only set back, but also allow a partial view of the interior. That architectural device “subtraction” normally entails more design input than “addition”, but this is frequently offset by the aesthetic gains. PV modules, on the other hand, are often simply added to the building envelope as the outermost layer. And the panels are mostly fitted so close to one another that shadows in the joints are negligible and a sense of depth absent. Mounting PV modules on the facade or the roof has an effect on the subjectively perceivable proportion of glazing, as well as colouring and brightness. A building with a dense covering of solar panels looks like a glasshouse!

1

PV technology in space travel: like the leaves of a plant, the solar panels fan out to face the sun. International Space Station (ISS) in June 2008. 2 The technology of space travel owes its appearance to a functional, additive form of construction. New, high-tech materials prevail. Space walk outside the ISS in September 2006. 3 Abrupt changes of colour of silicon crystals in a polycrystalline wafer with minimal changes of the lighting situation. 4, 5 Only when viewed from inside does the arrangement of the cells in this partially transparent PV roof become apparent. Fire Station, Houten (NL), 2000, Samyn & Partners 6 The materials “genealogical tree” according to Auer, 1995

37

Designing with photovoltaics Differences between traditional and PV materials and products

7

Ageing behaviour Looked after carefully, the cover glass to a PV module could retain its perfect surface and last for centuries because of its hardness and chemical resistance. Synthetic materials – like the encapsulation materials in the composite panel – do normally retain their transparency during their service lives but a delamination process can begin at any exposed or damaged edges. Outdoors, this usually leads to ugly discolouration, mould and even algae growth. Long-term experience with the comparatively new solar electricity technology is limited to installations dating from the late 1970s. As the service life of a PV module is about 25 years, the performance warranties of the manufacturers frequently tend to cling to this figure. Where new PV components replace old ones, a difference between these and their neighbours is evident due to the ageing of the materials. In contrast to PV modules, natural materials usually take on a certain expression and aesthetic quality over time; irregularities in texture and relief become emphasized and the thickness of a solid component perceptible. Functional differences: the PV as generator Once we move away from the materials side, we discover further differences, on the level of meaning. Traditionally, the building envelope performs two functions: firstly, separation between interior and exterior, and, secondly, representation. Both functions were somewhat stretched by the Modern Movement. Separation now often means connection because large expanses of glazing allow the visual blending of interior and exterior. And the building envelope now no longer primarily serves to demonstrate the social and economic position of its owner or user, but increasingly the internal uses and the construction of the building. 38

PV installations, on the other hand, are ends in themselves. Their original function is purely the production of electricity. Whereas it is normal for the engine of a technical device or the heart of an animal to be located well inside a protective enclosure, in photovoltaics the generator is a thin, fragile and virtually unprotected covering around the building. This deployment is in stark contrast to traditional forms of construction. One way of improving the acceptance of buildingmounted photovoltaics would seem to be allocating further functions to the solar

8

electricity components, additional to just the generation of electricity. Only when PV technology becomes an intrinsic part of the building envelope, and is accepted as such, will it be able to unfold its full potential.

7, 8 Exemplary design using traditional and new building materials: the partially transparent solar modules integrate harmoniously into the engineered, large-scale timber loadbearing structure. Interior views of facade and roof, Mont-Cenis Training Academy, Herne (D), 1999, Jourda Architectes, Hegger Hegger Schleiff Architekten

Designing with photovoltaics Photovoltaics and its relationship with the building, photovoltaics in the urban and rural landscape

Adaptation requirement Photovoltaics

Adaptation capability Building type New-build

Building stock Heritage asset

9

Photovoltaics and its relationship with the building The typical applications for building-mounted PV can be classified according to the constructional task on the one hand and their location on the building on the other. Constructional task In terms of the constructional task, we can distinguish measures according to: • New-build project • Building stock • Heritage asset The design freedoms are numerous when designing a new building. The PV installation and the associated building can be coordinated with each other and therefore take on the appearance of a unified entity. But when adding an installation to an existing building, e.g. within the scope of an energy efficiency upgrade, the integration work is certainly more difficult because there is a limit to the architectural and constructional adjustments the building and the PV system can undergo. However, in the countries of the industrialised world, which are generally heavily built up anyway, this type of application is becoming increasingly significant. In the threesome mentioned above, the heritage asset represents the most demanding task because here the PV installation must accommodate the existing construction (Fig. 9). Nonetheless, it is historic buildings in particular that frequently offer good conditions for a PV system, despite the design challenges, because such structures are often large-scale solitary objects in exposed positions that can provide large sloping roof surfaces free from shadows. Churches, for example, generally have a nave that runs east-west, which means they mostly have ideal, south-facing surfaces. Various research projects are specifically investigating the integration of PV technology into heritage assets, also with the aim of using the products and

9 Schematic presentation of how buildings and PV technology react to one another depending on the building task. 10 Distinct light-dark and colour contrasts clearly demarcate the various parts of the facade. The almost black PV sliding shutters animate the external cladding of this building in a playful way. Residential blocks in Hard (A), 2003, Hermann Kaufmann, Werner Wertaschnigg 11 Photovoltaics on a historic building protected by a conservation order. Evangelical Academy, Meissen (D), 2003, Pfau Architekten

design procedures developed for this demanding line of work for the other constructional tasks as well. Location on the building The following three sections of the building envelope are suitable as locations for setting up building-mounted PV installations: • Roof • Facade, including spandrel panels • Sunshades Up until now, roofs have been the favourite location, but the use of facades and sunshades as the supporting constructions for PV systems will become more important in the future (see “Construction and integration”, pp. 62– 69). Photovoltaics in the urban and rural landscape A building-mounted PV system has a relationship not only with the building on which it is mounted. Its relationship with its surroundings – the urban or rural landscape – is also relevant. At this level, the important thing for the design is whether the PV installation is visible and in what way. Whereas even steeply sloping roof surfaces are often hidden from view at street level, they frequently dominate the appearance of a structure when seen 10 from afar. In particular, the different reflection behaviour compared to traditional roof coverings is very significant here. Apart from that, reflections in buildings can compromise traffic safety in certain circumstances. Facade surfaces form urban spaces and therefore have to relate especially to the perspective of passers-by, i.e. a relatively close viewing distance. In the case of related building elements, the capacity of PV systems to link the elements to form a uniform ensemble is a crucial design criterion (p. 40, Fig. 13). Solitary structures naturally enjoy greater design freedoms.

11

39

Designing with photovoltaics Design strategies

Energy

Architecture

Construction

12

Facade-integrated PV on dominant urban structures, e.g. high-rise buildings, must, however, be checked with respect to the view of the building from afar in particular (Fig. 14). In addition, the design must consider building regulations stipulations, which prescribe the permissible types, sizes and orientations of structures, and roof pitches. Although design byelaws enacted by local authorities frequently limit the range of materials and colours that may be used, they often permit exceptions for solar installations. 13

12 The building design as a symbiosis of architecture-, construction- and energy-related requirements 13 Overall ensemble effect: the new building with PV modules integrates well into the historical urban setting. Residential and commercial development, Unterseen (CH), 2000, Mario Campi 14 Imposing view from afar: this cereals silo is the world’s tallest facade-integrated PV installation. Schapfen Mill, Ulm (D), 2004, Seidel Architekten 15 PV and the rural landscape: the facade design of this industrial facility uses colours and forms to achieve a formal approximation of the surrounding landscape. Hot-rolled strip slitting plant, Duisburg (D), 1962/2002, Cerny & Gunia 16 Fundamental design concepts for PV in construction 17 Like a dark concave mirror, the dark grey PV modules characterise the facade of this research laboratory. Ferdinand Braun Institute for UHF Technology, Berlin (D), 2007, msp Architekten 18 A solar system integrated successfully – in terms of both architecture and construction – into the roof of an existing building dating from the 1960s. The PV panels have a transmittance of 10 %. Private house in Tiefenbronn near Pforzheim (D), 2007, Architekturbüro Jost 19 A continuous row of window shutters determines the appearance of this student project. As the red-brownish amorphous thin-film cells attached to the individual lamella resemble the colour of the surrounding wood, they are not apparent at first glance. Solar house for the “Solar Decathlon” competition of the US Department of Energy in Washington D.C. (USA), 2007, Darmstadt University of Technology

14

15

40

Design strategies The photovoltaics industry faces a fundamental conflict. On the one hand, the market demands cost-savings from PV systems (related to their output) – not least because the feed-in tariffs regulated by the German Renewable Energies Act drop every year. This is achieved by increasing efficiency in production and erection, also ever better conversion efficiencies. It is precisely the economics of sustainable energy provision and the energy payback times of the associated production plants that provide the critical sales arguments and form the basis for acceptance and use in society. Apart from that, the alternative energies are competing with conventional methods of generating electricity, the prices of which do not include the external costs they cause. On the other hand, the photovoltaics industry must develop new applications, which, however, calls for the intensive and costly development of new methods and special solutions. The following design strategies for building-mounted PV technology are evident. It must be remembered that constructional and architectural integration are two fundamentally different things, which in the ideal case complement the energy concept to create a positive overall outcome (Fig. 12). Subjugation The term “subjugation” applies to those installations that are placed on or in front of a building without any architectural goals and whose sole task is to produce electricity. They may have been retrofitted to an existing building or their constructional and financial aspects even taken into account during the design phase. They use the building merely as a supporting medium and can be removed again relatively easily. If they are visible from

Designing with photovoltaics Design strategies

Design concepts for PV in construction

Subjugation

Domination

Integration

Subordination

Imitation

16

public spaces, they frequently impair the appearance of the building. In such cases it is often the financial gains, sometimes an ecological consciousness, but certainly not the aesthetic effects that dominate the planning. Domination When the solar technology has a decisive effect on the design of a new building, i.e. its orientation with respect to the sun, its volume and the configuration of the building envelope, then we speak of a “dominant” design. In many cases the PV installation contrasts markedly with the rest of the building envelope. These are frequently solutions with a certain degree of constructional integration, where the solar modules also provide some of the functions of the building envelope. Even retrofitted systems can be well integrated but nevertheless have a dominating effect if the PV installation has a distinctive effect on the appearance of the structure because of its colour, shape, size or arrangement. Integration An integrated PV installation is in harmony with its building; the solar technology and the structure are equal partners in a symbiotic system. The solar panels frequently supply not only the electricity required for running the building, but also satisfy architectural and other functions of the building envelope, e.g. protection from the weather, sunshading. It is precisely these additional tasks that fuse the PV installation and the building into a virtually inseparable unit. Both aspects are so well tuned to each other that the whole is more than the sum of its parts. In the ideal situation, the PV installation not only merges harmoniously with the building, it also enriches the locality, the immediate urban or rural environment.

Subordination If the solar electricity system is hardly apparent because of its shape and size, its position with respect to the observer and public spaces, or its colour, it plays a subordinate role, and the building itself dominates. In this design approach the solutions can be very demanding aesthetically, especially the details, and their elegance is not evident at first glance (Fig. 19). Such solutions are ideal for use in the heritage assets sector because they do not change the underlying character of the existing building, but rather demarcate old and new. 17 Imitation The imitating PV system tries to copy traditional forms of construction, replace their functions and at the same time add an active solar layer. Such approaches are frequently less than convincing, as is the case with solar roof tiles, for instance, because the imitation is seldom so good that the difference between copy and original is invisible. In addition, imitation obscures origin and purpose. Design options The aim of an attractive architectural design with photovoltaics is to integrate 18 the latter harmoniously into the building and its surroundings. In order to minimise the obvious differences between photovoltaics components and traditional building materials, the architect will attempt to give the PV installation a more consistent appearance, reduce the glossiness of its surfaces, resolve the modularity, create a wider range of colours and match the scale of the building, especially with opaque PV applications. Unfortunately, deviations from the standard products with their optimised yields normally result in diminished energy yields plus markedly higher production costs and reduced financial rewards. In future, however, high-tech, computer-controlled 19 41

Designing with photovoltaics Design strategies

20 Level

Influencing factors and boundary conditions

Feature

Crystalline

Cross-section

Thin-film Cover glass Encapsulation Anti-reflection coating Solar cells Encapsulation Backing material

Colour of material Shine Structure Visible depth of layer

Thin-film

Appearance of building-mounted PV technology

Component

Crystalline

Cell

Texture Light transmittance

Size

Form

Transparency

Curvature

Plasticity

Frame/fixings

Dummy modules

Building Surroundings

42

Separating cuts

Types of integration

Ensemble capability Effect from a distance Dominating effect

Ensemble 21

Transparency

Surface colour and material combinations Scale Proportions Modularity Rhythm Volume Plasticity Applications

Urban and rural landscape

Contacts

Form Degree of prefabrication Combination options Ageing behaviour Product colouring Size & density

Generator

Type

Form

Dummy cells

Module

Substrate Solar cells Encapsulation Backing or cover

Urban & rural landscape

Dominant, solitary

Designing with photovoltaics Design strategies

Minimising reflection losses

Reducing the degree of reflection

22

Light trap effect

AR coating Glass

Glass

Solar cell

Solar cell

manufacturing facilities will enable individual, cost-effective production. In the case of solutions integrated into the construction, the costs of components that are replaced by the PV elements can be included as credits in the costing. This aspect is particularly useful for those technologies, e.g. thin-film technology, that have a relatively low conversion efficiency but also a low price per unit area. They therefore represent a reasonable economical alternative to the more efficient but much more expensive cells, especially in building integration applications. Yield and architecture must be weighed up carefully against each other in every individual situation. Many different factors determine the appearance of a PV installation. The various influencing factors are described below in line with the scheme given in Fig. 21. Cross-section level: the influence of the material layers A solar module consists of various layers. The following breakdown examines the layers starting with the outer, sunlit side. Cover glass The covering on the sunlit side of the crystalline PV cells is normally glass with a low absorptance so that the maximum amount of solar radiation passes through the glass and reaches the solar cells. The production of this so-called extra-clear or low-iron glass requires a glass melt with a low iron oxide content, which considerably reduces the green tint so typical of standard float glass (Fig. 24). The higher cost of this glass and, in turn, the price of the panels is offset by the improved efficiency. Body-tinted glass is not generally used with the very expensive crystalline cells because of its negative influence on the conversion efficiency. When using thin-film

23 a

b

technology, tinting or printing the glass is, in principle, the only way of varying the impression of the colour of a panel marginally because the colour of the very dark cell material cannot be changed. In this case, the thin-film cells are attached to a substrate and covered with a body-tinted or silk screen-printed cover glass (see “Introduction”, p. 9, Fig. 8). This technique was developed in a number of research projects but the products are currently only available to special order. Part of the incident solar radiation is reflected directly at the boundary surface 24 between air and cover glass. This reflected component amounts to about 4 % in the case of standard float glass and an angle of incidence of 90°. The reflections are normally regular (or specular) reflections because the surface of the glass is smooth compared to the wavelengths of light (Fig. 23a). There are, in principle, two options available for influencing the reflection from the boundary surface (Fig. 22). Firstly, the amount of reflected light can be modified by applying an anti-reflection coating. However, the solar gains must be weighed up against the cost of this optical coating and its vulnerability to damage, which is why this solution is 25 only used with very efficient, expensive cells. Secondly, the quality of the reflection can be controlled via the roughness of the glass surface. Patterned glass spe- 20 cially developed for PV applications contains a macroscopic surface structure 21 that functions as a “light trap” according 22 to the principle of multiple reflections. 23 The transmittance is up to 91.5 %, which compares to about 90 % for a non-textured low-iron glass of the same thick24 ness. Textured glasses of this kind produce unfocused reflections but do not appear matt. If diffuse reflections (p. 43, Fig. 23b), which results in a matt appear25 ance, are required for architectural rea-

Balcony balustrade with PV modules. Private house in Passail (A), 2007, Architekturbüro Kaltenegger The features affecting the appearance of photovoltaics; influencing factors and boundary conditions The principles of the options for minimising reflection losses. Schematic presentation of types of reflection depending on surface properties a Regular (or specular) reflection b Diffuse reflection Owing to its iron oxide content, standard float glass (left) has a greenish tint. Extra-clear, lowiron glass (right) is mainly used in PV technology in order to increase the conversion efficiency of the module. Patterned glasses with surface texture optimised for PV applications.

43

Designing with photovoltaics Design strategies

26

sons, this can be achieved, in principle, using “subtractive” methods on the glass, e.g. sand-blasting, acid-etching. However, as the results do not increase the conversion efficiency of a module and, in addition, impair the self-cleaning effect of the glass, matt glass is hardly ever used. Modifying the rear face of the cover glass is unnecessary because this is where the glass is bonded to the encapsulating material. This material has a similar refractive index to that of glass and therefore any reflections at this boundary are minimal.

Encapsulation The encapsulation material, EVA or PVB, should, like the cover glass, exhibit a high transmittance, which makes it neutral in terms of its transparency. Modifying this layer for architectural reasons is unusual. If colour effects between the cells are required, it is better to modify the backing material. Anti-reflection coating An anti-reflection coating is generally applied to monocrystalline or polycrystalline solar cells in order to minimise the reflection losses on the upper side of the cells. The coating is in the form of a thin, transparent layer of silicon nitrite. It is this coating, with its optimised thickness, that gives the solar cells their characteristic dark blue-violet colouring. So by varying the thickness it is possible to vary the colour, an effect that can be exploited in order to produce coloured solar panels (Fig. 27). However, deviations from the ideal coating thickness reduce the conversion efficiency of the solar cell. In principle we can say that the lighter the colour of a solar cell, the lower is its conversion efficiency. Therefore, it may not be possible to achieve an inconspicuous integration of a PV system into a light-coloured facade area.

Solar cell type Monocrystalline cells without an anti-reflection coating appear grey and homogeneous. The addition of the coating leads to a seemingly dark-blue to black colouring. The characteristic feature of polycrystalline cells, on the other hand, is their frost-like structure, the appearance of which varies according to manufacturer. Without an anti-reflection coating, these cells have a silvery grey colouring (Fig. 26), but with the coating appear dark blue to violet. Thin-film technology results in an extremely uniform structure and a dark grey-black, red-brown or blueviolet colouring, depending on type.

27

44

28

Backing material The backing material becomes visible between the cells and around the edges of the module, and if the underside is visible. In the case of opaque crystalline panels, the standard backing is a white plastic sheet. In order to achieve a more uniform appearance for the module, sheet colours that match the colour of the cells are chosen. However, darker backing materials generally increase the temperature of the module because of their higher light absorption, which in turn reduces the conversion efficiency. The colour selected for the backing material can also blend with the solar cells visually to create the desired colouring when viewed from a distance, e.g. rooftop installations. In addition, inhomogeneous textures can be created with printing. In the case of partially transparent PV applications, glass is normally employed as the backing material in order to guarantee light permeability between the cells and also to protect the rear of the module against mechanical damage (see pp. 46 – 47).

Designing with photovoltaics Design strategies

29

Cell level Cell form and size The crystalline wafers are multiple-symmetry forms with a side length of approx. 100 –150 mm or diameter of approx. 125 –150 mm. These blanks can be subdivided and arranged in various patterns (Fig. 28). However, the cost of attaching the cell contacts is higher for smaller cells. Circular cells result in fewer cells per unit area, but they are especially advantageous in partially transparent applications. The decisive architectural advantage of thin-film technology over crystalline technology is that the individual cells – applied to a substrate as continuous coatings – create a very flat, homogeneous impression. Only the cell contacts are visible as very fine lines – forming a pattern like a pin-striped fabric which merges with the cells when viewed from a distance of a few metres or more (Fig. 30b). These lines are between 0.05 and 0.5 mm wide. (As a comparison, the width of the lines representing the borders of the modules in Fig. 28 is 0.08 mm.)

Back contacts The area covered by the back contacts can be greater than that of the front contacts because the sun does not generally shine on the rear of the modules. And where the rear surface remains concealed, any particular arrangement of the back contacts is unnecessary. But where they are visible, they can be included in the design because the light permeability does not play a role. The rear faces of crystalline cells are medium grey and matt, those of thin-film cells silvery and shiny (Fig. 30c).

Front contacts Standard on the sunlight side of the crystalline cells are the shiny, silvery front

30 a

26 Without an anti-reflection coating, crystalline solar cells have a neutral grey appearance. Centre for Environmental, Bio & Energy Technology, Berlin (D) 1998, Eisele + Fritz, Bott, Hilka, Begemann 27 The thickness of the anti-reflection coating determines the colour effect of the crystalline solar cells. 28 Cells can be arranged in numerous – albeit mostly very regular – patterns (selection). 29 partially transparent PV façade; Tobias Grau company building, Rellingen (D), 2001, BRT Architekten 30 Samples of various solar modules. To be able to compare the colour and reflection effects, all photographs were taken with the same settings and the panels reflecting the same matt white sphere. a Cell background and frame can emphasize the cells (left) or disguise them (right). b Typical appearance of front of crystalline cells (left) and thin-film cells (right). c Appearance of rear of crystalline cells (left) and thin-film cells (right).

contacts, which are mostly parallel, fine lines forming a pattern. These can vary depending on the manufacturer and may also be designed to create a certain effect. However, such non-standard front contacts are generally associated with yields lower than those obtained with an optimised arrangement. The colour of the busbars can be matched to that of the cells by using self-adhesive film in order to standardise the appearance. In addition, it is possible to position the busbars on the back of the cells, but this represents a bespoke design.

b

c

45

Designing with photovoltaics Transparency

32

31

Module level Module size The assembly of solar cells to form panels and then PV modules has a considerable influence on the appearance of photovoltaics. Whereas individual solar cells are hardly discernible from a distance, the modules, measuring typically 0.80 ≈ 1.60 m or thereabouts, dominate when viewed from any distance, near or far. Various manufacturers offer solar modules that integrate well with the scale of their location. For instance, there are panels available whose overall dimensions are similar to those of roof tiles, which can then be integrated well into the architecture. Module frames are usually made from silver anodised aluminium sections and this emphasizes the modularity owing to the contrast between the light frame and the dark cells. Here again, it is possible to reduce the conspicuousness of the modularity and different materials by matching the colour of the backing mate-

31 The degree of transparency of a module with crystalline cells can be adjusted in different ways. A coarse grid is produced by the spaces between the individual cells, a finer grid by openings within the cells themselves (left). Lasers can produce an even finer network on partially transparent thinfilm cells, which is especially recommended for modules seen close-up (right). 32 Interior view of a semi-transparent facade with crystalline cells. The relatively coarse pattern is produced by the layout of the cells over the area. Office and production building in Kassel (D), 2002, Hegger Hegger Schleiff 33 Interior view of a facade with partially transparent thin-film cells. Even when viewed from just a few metres, the fine pattern of dots has already become a grey veil. The shadows in the interior are hardly noticeable. 34 partially transparent, curved modules functioning as sunshade and electricity generator simultaneously for this motor launch in Hamburg. Electric catamaran Alstersonne, 2000, Kopf Solardesign 35 The sloping solar facade collects sunlight and rainwater for use in the building. Optic Centre, St. Asaph (GB), 2004, Percy Thomas Partnership 36 Building and generator are linked via the same additive architectural language. iT House in Pioneertown, California (USA), 2007, Taalman Koch

46

33

rial and frame to that of the cells (p. 45, Fig. 30a). If the frame is omitted completely, however, the vulnerable glass edges are left exposed and that involves risks for the composite make-up of the panel. In addition, fixings are then necessary, which means clamp fasteners at the edges or even fasteners drilled into or through the panels. Research and industry are currently investigating adhesive solutions so that the back of the solar panel can be glued to a substrate, thus avoiding all visible fixings. Module form The form of the module depends on several factors. Firstly, the economic production and utilisation of the panels, i.e. the arrangement and interconnection of the cells, also the customary forms of supply of components such as glass, frames and fixings. Secondly, the manageability of the modules during transport and erection, and the efficient layout of the modules within the area available. This is why the rectangular form has become standard. Custom shapes are possible, but certain panel geometries can lead to complicated interconnection requirements and hence increase the cost of a module. It may therefore be more economical to leave certain cells unconnected. Nevertheless, for reasons of appearance, these socalled dummy cells can still be included or printed onto the substrate as a substitute. Bending and flexibility The maximum curvature of crystalline cells is quite limited, but hot- or cold-formed modules with some curvature can be produced. At smaller bending radii or for use on flexible structures, the recommendation is to use thin-film technology in a composite configuration with other flexible materials (see “Generating and using solar electricity”, p. 22 Figs. 31 and 32).

Transparency The similarities between windows and PV modules with respect to size, form, brightness, locations and choice of materials have already been mentioned above. A successful symbiosis, in terms of both architecture and construction, is often possible where daylight is required, but at the same time sunshading must be provided. In such cases, an integral PV layer can filter the sunlight, create shade and generate electricity simultaneously. Partial light permeability is achieved with crystalline PV technology by modifying the spacing of the cells and/or cutouts in the cells themselves (Fig. 31). This leads to a relatively coarse grid (Fig. 32) and hence, in the interior, sometimes to light and shade effects rich in contrast. A translucent intermediate layer can soften this effect when a clear view through to the outside is not necessary. A finer grid is possible with thin-film cells. A laser can remove small areas of the solar layer, in the form of circles, diamonds or strips, thus changing the degree of transparency of the panel (Fig. 31). In partially transparent applications, the conversion efficiency of the PV installation – with respect to the total area of the module – drops in proportion to the degree of transparency. Design potential The PV products currently available for use in building-mounted applications are normally based on prefabricated modules in the form of composite products involving various materials. There are two fundamental approaches to the use of this technology. On the one hand, the conscious exploitation of the modularity. The whole spectrum of design options for the modules with respect to form, colour, light permeability and arrangement of the cells can be used on the building envelope to

Designing with photovoltaics Transparency

34

35

form expansive, large-scale, appealing patterns. This means that shimmering PV energy-producing surfaces enclose the entire building. A wider range of colours that are predictable and can be reliably reproduced is desirable for such concepts. On the other hand, some building tasks call for small-scale elements with a homogeneous texture and inconspicuous colouring. This requirement is best met with thin-film technology, which, however, is very much tied to standard sizes – which in turn emphasizes the modularity.

Perhaps in future we shall be able to employ other solutions apart from the solar panel as a constructional unit. That would enable the PV layer to achieve an independent quality no longer influenced by the surface of the cover glass. Organic cells already exist in the laboratory and in future it might be possible to apply these – in the form of paints, varnishes or inks – to various (also rough) substrates in order to expand the design options and the applications for building-mounted photovoltaics.

36

47

Construction and integration

In principle, it is possible to use photovoltaics (PV) in any area of the building envelope that is exposed to direct sunlight. Roofs, facades and sunshades are currently used. On the construction level, we basically distinguish between three different concepts for the integration of solar energy systems (Fig. 1): • Addition • Substitution • Integration All three concepts must take into account the construction-, energy- and architecturerelated aspects to the same extent and harmonise these with the building design as a whole. Besides the generation of electricity from sunlight, PV installations can be designed to perform other building functions such as protection from the weather, thermal insulation, sunshading, protection from glare and screening for privacy. PV installations are frequently simply added to an existing building envelope – often in the form of a roof-mounted system, i.e. solar panels are retrofitted to an existing roof construction. As in this arrangement the modules do not provide any protection from the weather, a fully functioning, separate roof covering is

necessary. It is especially important to ensure that the installation does not disrupt the architecture when using the “addition” principle. The solutions we see implemented in practice are, however, often unsatisfactory with regard to their construction and especially their architecture (see “Designing with photovoltaics”, p. 35). The “substitution” principle is where the solar modules replace certain elements of the building envelope and take on their functions, at least partially. For example, a PV installation can function as weatherproof cladding when positioned in front of an external wall, thus creating a cold (double-leaf) facade. Maximum integration in terms of construction and architecture should be the aim. In a total building integration, the PV module forms complete facade or roof elements and performs all their functions such as weather protection, thermal insulation, sunshading and sound insulation. The PV module becomes the building envelope, e.g. in the form of an insulating glass unit. However, as the degree of integration of the PV element in a warm (single-leaf) facade increases, so the module temperature increases, too, which reduces the conversion efficiency of the cells employed.

Constructional integration

Addition

1

Various options for integrating photovoltaics into the construction of a building

Substitution

Integration

1

49

Construction and integration Designing with photovoltaics

Designing with photovoltaics Glass is the principal component in conventional PV modules and also the material that governs the design and construction. It is for this reason that the deployment of PV systems is much influenced by the rules and ideas controlling the use of glass in building. The one exception is flexible PV cells, which are always embedded in synthetic materials. The use of glass in PV applications presumes good knowledge of the particular properties of this material. Glass is a very brittle material that reacts very sensitively to local stress peaks. If the microstructure of the glass is intact and its surface undamaged, glass has a very high mechanical strength. But damage such as scratches, notches or chipped edges can occur during the production, transport and erection of PV modules, and these reduce the strength considerably compared to the theoretical values. And as glass does not have any reserves of plasticity, failure, when it happens, is sudden. There is also the additional risk of sharp fragments. In order to reduce the risk of brittle failure, materials with an identical or higher hardness should not

come into contact with glass. Elastic and soft plastics, casting resin and adhesives are very good as bearing materials. Furthermore, the thermal loads caused by the absorption of solar radiation by the PV modules place a higher load on the glass. No significant temperature differences should be allowed to occur within a pane of glass. The thickness is calculated according to the tensile bending strength of the type of glass used; the compressive strength of glass is much higher and mostly not fully exploited.

differences between flat roofs and pitched roofs to be observed. PV installations mounted above an existing roof are known as stand-off systems. But if the PV modules replace the roof covering and provide a rainproof layer, we speak of an integral system. On the facade, the systems currently in use are distinguished according to the thermal properties, i.e. cold and warm facades (single- and double-leaf respectively). A warm facade implies full integration; the PV elements are incorporated into insulating glass units and can then fulfil all facade functions. In cold facades the PV installation is either additional to or a substitute for the weatherproofing. Sunshading elements represent another suitable area of application for photovoltaics. In the form of fixed sunshades, they protect the building and users against overheating and at the same time generate electricity. Movable sunshades adapt to the solar altitude angle and thus also optimise their energy yield.

Typical applications have evolved within the domain of building photovoltaics (Fig. 2). The descriptive terms now commonly used were derived from the essential constructional features. In Germany the use of a regulated type of construction according to the technical construction regulations can simplify the approval procedure considerably. Where a design deviates significantly from the stipulations in these regulations, special approval and authorisation procedures are necessary (see “Technical rules and building legislation”, p. 73). When planning a PV installation on the roof, there are fundamental

2

The principal installation options for photovoltaics: roofs, facades and sunshades

Position of installation

Facade

Roof

Flat roof

Stand-off 2

50

Sunshade

Fixed systems

Pitched roof

Integral

Stand-off

Integral

Cold facade

Warm facade

Glass roof

Fixed louvres

Movable systems

Sliding shutters

Movable louvres

Construction and integration Designing with photovoltaics

3

f

d

e

e

a

a

c

a

d

b

b

b

b

b

a

a

a

a

a

4

When designing with photovoltaics it is also necessary to ensure that the choice of constructional integration is directly tied to the architecture. On a facade in particular, PV installations are much more obvious. The facade to the sports hall in Burgweinting (Fig. 8, see also “Photovoltaics case studies”, pp. 92 – 93) shows how the constructional solution supports the architectural concept of the facade and achieves a clear design language. The design of the glazing bars for fixing the PV modules has led to a horizontal segmentation of the facade. Building integration has been successful here, in terms of both construction and architecture. [1] Module configurations The design process begins with the selection of a suitable module configuration. This depends on the type and location of the installation and the cell technology being used. Different building legislation conditions apply depending on the type of application and these have a decisive influence on the design and construction. In principle, all cell technologies permit the production of solar modules with or without a frame. Frameless PV modules

5

6

have advantages for full building integration because they are connected directly to the supporting construction without the need for any further ancillary items. Both rolled and float glass, also in the form of either heat-strengthened or toughened safety glass, may be used for the modules depending on the production facilities. Owing to their better strength, toughened safety glass panes are advantageous in the case of high loads on the glass and an unfavourable heat build-up in the module. One exception is PV modules employing thin-film technology. Due to the high temperatures of the manufacturing process, the PV coating is generally applied to float glass, which means that the backing pane at least should not made from a toughened glass product. Where no thermal insulation requirements have been specified, the following module configurations can be used: • Glass/plastic laminates (Fig. 3) • Glass/glass laminates (Fig. 4) • Glass/glass/casting resin technology • Embedment in acrylic sheet • Solar modules on sheet metal embedded in plastic film According to building legislation, a glass/ glass laminate is not classed as laminated

7

safety glass, but simply as laminated glass. Thermal insulation requirements can be satisfied by using insulating glass units incorporating PV elements (Fig. 6). To do this, a second backing glass is added to the existing module. The thermal break ensures that the inner pane of the insulating glass unit is not loaded excessively and that laminated safety glass made from non-toughened float glass, which is more sensitive to thermal loads, may be used (Fig. 7). For overhead applications in particular, the German Technical Rules for the Use of Glazing on Linear Supports (TRLV) specifies laminated safety glass made from float glass (see “Technical rules and building legislation”, p. 77).

3 4 5

8

Glass /plastic laminate Glass /glass laminate Glass /glass laminate with lam. safety glass backing 6 Glass /glass laminate in the form of insulating glass 7 Glass /glass laminate in the form of insulating glass with lam. safety glass backing Legend for Figs. 3 – 7 a Toughened safety glass b PV layer with encapsulation c Backing sheet d Laminated safety glass e Cavity f Float glass 8 Facade with building-integrated, partially transparent PV modules. The crystalline silicon cells function as shading elements and ensure glare-free illumination of the interior with daylight. The multipane insulating glass unit with an inner pane of laminated safety glass can resist ball impacts and functions as thermal insulation. Sports hall in Burgweinting (D), 2004, Regensburg Building Department, Tobias Ruf

51

Construction and integration Fixing

9a

b

c

Fixing Once the configuration of the module has been established, a suitable method of fixing the module to the supporting or facade construction must be chosen. Stability, corrosion protection and easy erection are important factors here. Module types are divided into frameless and framed versions. When frameless modules are specified, the well-known forms of support and fixing used for regulated forms of glass construction can be used (Fig. 9). These include: • Linear supports according to the Technical Rules for the Use of Glazing on Linear Supports (TRLV) • Point supports according to the Technical Rules for the Design and Construction of Point-Supported Glazing (TRPV) • Facade fixings according to DIN 18516 Back-ventilated, non-loadbearing, external enclosures of buildings, made from tempered safety glass panels Framed modules belong to the linear support category of the TRLV and it is a relatively straightforward matter to screw, bolt or clamp these to the supporting construction (Fig. 9a). This method is frequently preferred for stand-off installations or curtain wall-type facade systems. Besides the aforementioned regulated forms of construction, there are other popular solutions for fixing PV modules: • Point fixings drilled through the panes (Fig. 9e) • Fixing with adhesive (Fig. 9d) When using these methods in an installation with building legislation relevance, an individual approval (ZiE), a National Technical Approval (AbZ) or a European Technical Approval (ETA) is required (see “Technical rules and building legislation”, p. 73). In less significant areas of the building the installation can be carried out according to the acknowledged technical construction regulations. [2] 52

d

e

Linear supports A TRLV-compliant linear support for a PV module presumes that certain boundary conditions are met: the glass must be supported on at least two opposite sides and must remain effective for all loading cases, which means that an adequate glass edge cover at the support must be ensured. Support on three or four sides is also permissible. The maximum deflection of the supporting members may not exceed 1/200 of the length of pane to be supported, but in no case 15 mm. No hard materials are permitted to touch the glass under the effect of loads (including thermal loads) and suitable measures must be taken to prevent the panes slipping out of their fixings. The simplest and most common form of linear support for a PV module is to fix it into an aluminium, occasionally steel, frame (Fig. 12). The composite module is inserted into the groove of the frame and also glued in place. Self-adhesive tape or a silicon adhesive are used to seal the joint and secure the module. Connecting the framed module to the supporting construction is then relatively easy to achieve by way of individual or continuous clamp fixings, a clip-in arrangement, or bolts/ screws (Fig. 12). Linear supports for frameless PV modules are usually in the form of glazing bars or beads attached directly to the supporting construction. The capping bars designed to exert pressure on the glass are normally of aluminium, steel, wood or plastic. An elastic sealing strip is placed between the glass and the supporting construction, and also between the glass and the glazing bar/ bead. Modules installed vertically require setting blocks to carry the self-weight of each PV module in addition to the clamp fixings (Figs. 13 and 14). A typical supporting construction for vertical PV modules is a post-and-rail facade. A disad-

Construction and integration Fixing

a

a

d b

b c

10

vantage of the peripheral, continuous frame is the overhanging edge, which can lead to undesirable shading effects. In addition, it encourages the accumulation of dust and dirt and tends to prevent snow from sliding off easily – all factors that in the end reduce the energy yield. The shallower the angle of the installed modules, the more pronounced is this effect. On the roof, the self-cleaning effect can be improved by omitting the frame from the bottom edge of each PV module (see p. 54). Another linear support option is to glue the module to the supporting construction along its entire perimeter. As the supporting construction remains concealed behind the PV modules, this fixing solution results in a very homogeneous and smooth appearance (Fig. 11). Other advantages are the improved thermal and sound insulation. However, the use of glued glass designs in the facade requires an individual approval (ZiE) or National Technical Approval (AbZ). The production and testing of the adhesive joint is regulated by the European Technical Approval Guideline for bonded glass constructions ETAG 002. In Germany the self-weight of the glazing must be carried on setting blocks and may not be carried by the adhesive, which is only designed to transfer the wind loads to the supporting construction. In addition, mechanical retention of the panes of glass is necessary at installation heights of 8 m or more to prevent the PV modules from becoming detached from the supporting construction (Fig. 10). Peripheral bars, additional point fixings, hooks in ground recesses or undercut anchors are suitable forms of retention. The omission of this mechanical retention is customary and permitted in many European countries. Silicones have a long history of successful use as adhesives for such appli-

11

cations. The use of other adhesives or deviations from approved building systems require the approval of the appropriate building authority. a b

c d

12

a e g d 9 The principles of the fixing options for framed and frameless PV modules a Frame screwed in place b Continuous clamping c Individual clamping d Adhesive e Drilled holes 10 Fixing of glued PV facades according to ETAG 002. The self-weight is carried on a mechanical support. The figure on the right shows additional mechanical retention to withstand wind suction. a Adhesive b Setting block c Mechanical support for self-weight d Mechanical retention 11 Flat facade appearance thanks to structural sealant glazing (SSG); Solar Centre, Freiburg (D), 1993, Hölken + Berghoff 12 Fixing a PV module by screwing through its frame 13 Continuously clamped support for a glass/glass laminate in the form of a glazing bar 14 Vertical section through a post-and-rail facade with PV modules in the form of insulating glass units Legend for Figs. 12 –14 a PV module b Frame clip c Module frame d Loadbearing section e Seal f Glazing bar capping strip g Setting block

f

13

a d e f

g

14

53

Construction and integration Fixing

Point supports PV modules can also be fixed at individual points as an alternative to continuous linear supports. Point fixings permit the use of frameless solar modules and that avoids the need for edge members. This means that this form of support has certain advantages: the individual fasteners cast only minimal shadows and present little chance for dust and dirt to accumulate. Glass /glass and glass /plastic laminates in standard or custom designs are suitable for this type of fixing (see p. 51). The following point fixing systems are used for solar modules: • Clamp fixings in the joints • Clamp fixing systems at the corners • Clip fixings in the joints • Conventional point fixings, with countersunk or raised head, in holes drilled through the glass • Undercut anchors

15

Module clamp fixings represent a simple solution for point support and are in widespread use (Figs. 15 and 16). They grip the edges of the PV modules and include UV-resistant ethylene-propylene-diene rubber (EPDM) bearing pads. Standard clamp fixings can accommodate different module thicknesses and are fitted in the joints between the modules. The end modules in an array are fixed with matching end clamps. Additional anti-slip retainers are required for vertical installations. Their simple design means that module clamp fixings help to achieve quick and easy erection. Standard module clamp fixings are ideal for fixing ground-mounted arrays and stand-off roof modules, but are not always suitable for PV panels in facades. As the TRPV stipulates laminated safety glass for point-supported panes of glass, standard PV modules fall outside this regulation. And if the system to be used does not comply with the requirements of DIN 18516 either, an

16

17

54

additional approval or authorisation procedure will be necessary. However, the manufacturers of such systems generally assist in such procedures and simplify the work required when standard products are involved. But in principle, those planning PV installations are recommended to comply with the design and construction recommendations of the aforementioned technical rules. All the panes of vertical and overhead glazing must be held in place by interlocking mechanical point fixings. The fixings may be in the form of discs held in place by a screw or bolt that passes through a cylindrical hole drilled through the glass, or edge clamp fixings, i.e. U-shaped clamps that grip the edge of the glass. The glass edge cover for edge clamp fixings must be at least 25 mm and the clamping area per fixing must be at least 1000 mm2. Glazing that functions as a safety barrier or is required to carry temporary or constant foot traffic or other forms of point support are not considered in the TRPV. An undercut anchor is a concealed form of mechanical fixing for PV modules (Fig. 17). A cylindrical-conical hole drilled in the back of the pane of glass means that it is not necessary to penetrate the glass completely. However, the geometry of the drilled hole results in a smaller bearing area, which leads to higher stresses in the glass and calls for the use of toughened safety or heat-strengthened glass. The system consists of conical bolt, expanding sleeve, plastic cap, washer and retaining nut, and all metal parts are manufactured from stainless steel.

Construction and integration Roof installations

18

Roof installations Roof areas are preferred locations for PV systems. In Central Europe a south-facing module surface mounted at an angle of 30° achieves the maximum energy yield when considered over a 12-month period. Small deviations from this orientation result in only very minor losses and changing the angle does not have a very significant effect on the yields attainable either. Even a horizontal rooftop installation leads to only a 10 % drop in the yield compared to the ideal orientation and angle. (see “Generating and using solar electricity”, p. 12, Fig. 5). Preferred rooftop installations for PV applications are (Fig. 20): • Flat roofs • Pitched roofs • Sawtooth roofs • Canopies • Atrium roofs We distinguish roofs according to the pitch of their surfaces (Fig. 19). Flat roofs are generally built with a pitch of 5 –10°, and according to the guidelines of the German roofing trade a minimum pitch of 2 % should be maintained. Three basic forms of flat roof are possible: cold roof (with air space below roof covering), warm roof (no air space) and inverted (or upside-down) roof (thermal insulation above waterproofing). At angles > 10° we generally speak of a shallow pitched roof and at angles > 22° a steep pitched roof. In the following, roofs between 10° and 80° are grouped under the heading of pitched roofs. The subdivision at 22° is based on the minimum pitch of the very common small-format roof covering materials (clay or concrete tiles, slates) and represents the minimum for ensuring a rainproof design. Opaque metal roof coverings or transparent glass elements tend to be used for shallow pitched roofs. Glazing or glass PV modules inclined at an angle > 10° to

the vertical are classed as overhead glazing (see p. 61). Constructions between 80° and 90° to the horizontal are classed as facades. PV modules in this range fall into the vertical glazing category. This division into vertical and overhead glazing is based on the different loads and risks associated with the angle of the installation.

90° 80° g

f

d e c

22°

b

Rooftop PV installations are broken down into stand-off and integral systems depending on the nature of the constructional integration. In a stand-off system the PV modules are supported clear of the roof on separate loadbearing supports. Contrasting with this, in an integral system PV elements replace the conventional roof covering. Complying with stability requirements is critical; the individual parts of PV installations as well as the installation as a whole must be stable. DIN 1055-1 defines the actions to be considered. With existing roofs in particular, the roof structure must be able to carry the additional loads and transfer them to other parts of the structure.

15 Point supports for a glass /glass laminate in the form of individual clamp fixings 16 Close-up view of an individual clamp fixing 17 Undercut anchor with cylindrical-conical drilled hole 18 Photovoltaics on the roof; Munich Airport (D), 2002, Koch + Partner 19 Classification of roof areas and allocation according to building legislation a Flat roof b Shallow pitched roof c Steep pitched roof d Facade e Pitched roof f Overhead glazing g Vertical glazing 20 Preferred roof areas for PV applications a Pitched roof b Flat roof, stand-off mounting c Flat roof, as roof waterproofing d Canopy e Atrium roof f Sawtooth roof

a 19

20

a

b

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e

f

10° 0°

55

Construction and integration Roof installations

21

23 a

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c

56

22

Flat roofs Flat roofs potentially offer ample space and have a number of advantages in terms of planning. As a rule, there is a certain freedom of choice regarding the exact inclination and orientation of the essentially south-facing PV modules. The roof waterproofing is generally at the water run-off level and in the form of bituminous or synthetic sheeting. However, such forms of waterproofing are vulnerable to damage and great care must be taken because even minor damage can lead to leaks and moisture problems. A PV installation mounted on a flat roof does curtail accessibility for roof maintenance and repairs. For this reason, prior to installing a PV system it should be ensured that the roof will remain functional over the service life of the installation. Roof-mounted PV modules (stand-off and integral systems) with mechanical fixings which do not fulfil any further constructional or safety/security functions are in Germany classed as “other” building products. They are not relevant to safety and therefore do not require verification of applicability (see “Technical rules and building legislation”, p. 73). However, the requirements of the respective federal state building regulations must be satisfied with respect to the materials used, specifically stability and fire protection. The PV installation must be designed and constructed according to the technical construction regulations. In particular, larger pieces of glass should be prevented from falling out of their fixings. Stand-off systems The stand-off installation represents a low-cost approach and is among the forms of installation encountered most frequently. The solar modules are mounted on a metal framework above the roof

waterproofing. Numerous standardised mounting systems are available on the market which essentially can be divided into free-standing and fixed anchorage systems. The free-standing system is worthwhile when the roof structure has enough loadbearing reserves or the PV installation has already been taken into account in the structural analysis. In this approach the construction supporting the PV installation is held in place by additional ballast in the form of concrete paving slabs, concrete sleepers or loose gravel fill, an arrangement that avoids having to penetrate the waterproofing materials. If there is already gravel on the roof to protect the waterproofing, this can be used as ballast. Gravel-filled trapezoidal profile sheeting or trough systems can serve as a counterweight to prevent wind uplift (Figs. 21 and 23a). Where the roof construction has a higher loadbearing capacity along certain axes, concrete plinths represent a better solution (Fig. 23b). On flat roofs where point loads can be better accommodated, concrete paving slabs are to be preferred (Fig. 23c). Whatever the form of support, protective sheeting must be laid underneath to protect the waterproofing materials against damage by the framework supporting the PV installation. If the free-standing method is unsuitable for structural reasons, a fixed anchorage system is the best choice. In such systems each row of modules is generally supported on a grid of members (often a type of grillage) erected in situ. These in turn rest on a row of individual supports which penetrate the roof covering and are permanently connected to the structure below (Fig. 22). Critical here is matching the grid of the PV installation with convenient support points in the roof structure. Beams must provide a structural and con-

Construction and integration Roof installations

Module spacing

Max. elevation of sun on 21 Dec, 12 noon

d

γ

Mo

wid

b Height h

th

ule

Module mounting angle β Module spacing =

h , h = sin β x b tan γ (21 Dec, 12 noon)

24

structional connection between the two defined grid systems. If the specification for the PV installation results in an unreasonable supporting framework, the arrangement of the solar modules must be adjusted to ensure a viable anchorage system. Attention should be given to the design of the various layers of loadbearing members to ensure proper paths for the forces, also the force transfer points; a minimum number of penetrations should be allowed for in the design and special waterproofing measures considered for these points. Closed sections (square, rectangular and circular hollow sections) are generally much better than open rolled sections (I-sections, channels). Circular hollow sections are ideal because they can be fitted with a prefabricated sealing collar to ensure a good, permanent seal at the penetration point. [3] The PV modules are arranged in rows for both the free-standing and anchorage methods. Sufficient clearance between the rows is essential in order to avoid one row of modules casting a shadow on another row. The spacing of the rows depends on the width of the modules, the mounting angle and the lowest elevation of the sun at which shadows are undesirable. For planning purposes, the angle of the sun at 12 noon on 21 December has proved useful as the so-called shading angle; this angle varies between 12° and 19° in Germany depending on latitude, but an average value of 15° can be assumed for simplicity. So with an ideal mounting angle of 30° the rule of thumb is a module spacing of three times the module width (Fig. 24), which means that the area of the roof must be greater than the total area of the modules that are to be installed. [4]

21 Integral systems An integral system can be used to achieve a PV installation that forms part of the flat 22 roof construction itself. Yields are lower 23 because of the shallow mounting angle, higher module temperatures and poor self-cleaning. However, these negative 24 aspects are compensated for by the lower weight and the reduced erection work. There are essentially two technolo25 gies for integral systems on flat roofs: synthetic sheeting with flexible solar cells, and PV modules in the form of an inverted 26 roof (Figs. 25 and 26). PV synthetic sheeting is a viable solution for both new-build and refurbishment projects. These multi-functional laminates create a weatherproof finish on roofs with a shallow pitch and replace the conventional waterproofing. The sheeting consists of thin-film solar modules made from amorphous silicon (a-Si) which are bonded to flexible synthetic sheeting. Their extremely low weight also makes them ideal for roofs with minimal loadbearing reserves. The solar cells used are 25 optimised for a shallow angle of incidence and also exhibit good thermal behaviour, which means they can be used on a cold or warm roof construction. The flexible cells also adapt well to various roof forms, e.g. barrel vaults with a generous radius.

Free-standing system with loose gravel fill on trapezoidal profile sheeting. This method avoids having to penetrate the roof finishes. Penetrating the roof finishes with a favourable tubular section. Schematic presentation of the different freestanding methods a Gravel-filled trapezoidal profile sheeting b Concrete plinths c Concrete paving slabs Calculating the module spacing for rows of PV modules on a flat roof. The module spacing based on the shading angle minimises shadows cast by other rows of modules. Roof sheeting with flexible PV modules for implementing integral systems on flat roofs. The flexible sheeting replaces the conventional waterproofing materials. PV roof sheeting in use

Roof-integrated systems in the form of an inverted roof combine PV technology with thermal insulation. Tongue and groove joints plus heavy sheet metal edges prevent wind uplift, and large module dimensions improve stability. However, additional fixings are necessary at installation heights exceeding 20 m. Furthermore, the layer of thermal insulation prevents any ventilation beneath the modules.

26

57

Construction and integration Roof installations

28

29

Pitched roofs In contrast to a flat roof, the angle and orientation of PV modules on a pitched roof are determined by the roof surface itself. The south-facing surfaces of pitched roofs represent those surfaces of the building envelope with the highest energy yields for PV systems. This fact has led to the appearance of a multitude of different fixing systems for new and existing buildings. Roof surfaces facing south-east or southwest, although not optimal, are still suitable (see “Generating and using solar electricity”, p. 12, Fig. 5). Dormer windows or structures that penetrate and rise above the roof covering diminish the yield if they cast shadows on the PV installation. Traditional roof structures generally have enough loadbearing reserves to enable the addition of a PV installation to an existing roof. A structural engineer should be consulted in cases of doubt and where roofs are possibly on the limit of their loadbearing capacity. As with flat roofs, PV installations can be erected on pitched roofs according to two principles: the stand-off system and the integral system. Stand-off systems The stand-off installation requires a metal supporting construction above the existing roof covering. In this case a fully functioning, separate roof covering is necessary. Systems consisting of aluminium or stainless steel rails enable quick erection and render the PV installation independent of the grid of the roof structure. The minimal erection work involved with stand-off systems makes them the least expensive variant for a retrofitted PV system on an existing roof. Ventilation below the PV modules is generally good, which boosts their conversion efficiency. The actual mounting system for a stand-off construction consists of three main components: the roof fixings, the mounting rails and 27 58

30

the module fixings. The mounting rails are connected to the roof construction using one of the following methods: • Hooks (Figs. 28 and 29) • Special mounting tiles • Clips for sheet metal roofing (Fig. 30) • Fixing brackets (Fig. 31) • Screw anchors (Fig. 32) The choice of fixing depends on the roof structure and roof covering. Rafter-based and non-rafter-based systems are available on the market. Hooks can be used with small-format roof coverings such as clay or concrete tiles or slates (Figs. 28 and 29). The hooks are firmly screwed to the roof structure and provide a connection point for the mounting rails. The fixings can often compensate for the unavoidable differences in tolerances

between the precisely prefabricated PV modules and the roof construction. Many manufacturers of roof tiles now offer special plastic or metal tiles designed for PV installation fixings – similar to those for access steps or snowguards. When using these tiles it is possible to attach the PV installation independently of the rafters, but the tiles must still be fitted into the roof tile layout. The use of such tiles avoids the need to cut standard roof tiles and the rainproofing characteristics are not impaired in any way. The disadvantage, however, is the that these fixings are not as strong as fixings attached directly to the rafters. Where a metal roof covering (either manually laid or industrially prefabricated) on a steep or shallow pitched roof is capable of accommodating the loads of a PV

Construction and integration Roof installations

31

32

installation, special clamps or clips can be used to fix the mounting rails, possibly attached to the welted joints (Fig. 30). There are also special clips available for trapezoidal profile metal sheeting, which are fixed with the help of self-drilling screws and then serve as the anchorage points for the PV system mountings (Fig. 31). Another option is screw anchors, which are particularly useful for trapezoidal profile or corrugated roof coverings, although this does mean penetrating the roof covering (Fig. 32). An integral sealing washer is pressed into the hole during tightening to seal the opening. Counternuts permit the distance between mounting rail and roof to be varied, which allows the mounting angle of the modules to be optimised and changed from that of the given roof pitch, thus improving the yield and the self-cleaning effect. Screw anchors for fixing PV installations are normally 300 mm long. The next main component in the stand-off system is the mounting rail. In the standard arrangement the PV modules are positioned between horizontal mounting rails and clamped or screwed at four points (Fig. 33a). Two mounting rails are required per row of modules. Their positions depend on the spacing of the tiling battens and the permissible spacing of the PV module fixings. The modules can be mounted horizontally as an alternative, in which case the mounting rails are fixed vertically (Fig. 33b). This arrangement can reduce the losses due to shadows in certain situations. When the lower rows of modules are temporarily in the shade, a smaller area of the total installation is nonproductive – assuming appropriate electrical connections between the modules. If the roof structure support points are not ideal or the roof surface is uneven, mounting rails in both directions is an option, i.e. a second, lower layer of rails

at 90° to the main rails (Fig. 33c). This arrangement consumes more materials, of course. However, generously sized members in the second layer can reduce the number of fixing points. In some circumstances such a grid of members in both directions may be necessary if the permissible spacings have been exceeded. Furthermore, a double layer of rails is necessary for PV modules that are clipped in along two edges only because the length of the module must coincide exactly with the spacing of the mounting rails. As with the standard arrangement, modules can also be positioned horizontally.

33 a

All the methods of fixing the modules described on pp. 52– 54 can be used for stand-off systems. Individual clamp fixings are popular with framed modules. Linear clamping systems or interlocking or clip-in modules are also widely used.

b

27 PV modules on a pitched roof. With a favourable orientation, pitched roofs present ideal conditions for the use of photovoltaics. 28 Hook for pantiles 29 Hook for bullnose tiles 30 Clip for standing seam 31 Fixing for trapezoidal profile sheeting with selfdrilling screws 32 Screw anchor 33 Stand-off mounting system variations a Standard mounting b Standard mounting with horizontal modules c Grid of mounting rails

c

59

Construction and integration Roof installations

Integral systems In the integral approach, the PV modules replace the roof covering and therefore also provide other roof functions. According to the guidelines of the German roofing trade, a roof-integrated PV system has to guarantee a rainproof roof covering. It is generally the responsibility of the manufacturer to verify this by means of tests. A rainproof design can be achieved in various ways: modules overlapping like shingles or placed in plastic housings with special cover strips over the joints. When the system-specific minimum roof pitch of about 22° is maintained, a rainproof roof covering is easy to ensure provided that the junctions with the standard roof covering or at the edges of the roof are properly designed and constructed. In this context it should be mentioned that even if the rainproofing function is reliably maintained, an additional layer of roofing felt, better still a complete covering of sheeting, is still necessary. This sheeting creates a second water run-off layer that allows rain and snow driven by the wind between the PV modules – also condensation – to be drained away from the underside of the modules. According to current building legislation, roof-integrated PV systems are covered by the provisions of existing standards and technical regulations, which means that neither a National Technical Approval (AbZ) nor an individual approval (ZiE) are required. Fire protection represents an exception, however. Depending on the requirements of the respective federal state building regulations, a classification as a “hard roofing material” may be necessary. The manufacturer must verify this, e.g. by way of a National Test Certificate (AbP).

34

35

A constantly growing number of special modules and systems is available for integral systems (Fig. 35), ranging from small-

36

60

format “solar roof tiles” to grouped PV roof elements and large-format modules. They can be used in conjunction with virtually all types of roof covering – bullnose tiles, pantiles, slates, etc. Although the small modules involve considerably more erection and cabling work, their advantage is that experienced roofing contractors are able to cover complicated roof surfaces with PV systems. Furthermore, solar roof tiles can be easily combined with conventional roof covering materials and their functional properties are identical. The extra wiring work required has led to the development of PV roofing elements that replace several tiles with one panel (Fig. 34). The edges of these elements are identical with those of standard tiles and therefore they can be readily integrated into a tiled roof. These elements also maintain all the rainproofing properties of conventional roof coverings. Integral systems with frameless or framed standard modules are also in widespread use. These installations are much less costly than those using special solar roofing elements. Systems of framing sections with glazing bars or capping strips in the direction of fall ensure a rainproof covering. Drainage is by way of the scalelike overlapping of the elements and/or drainage channels in the framing sections themselves. Besides having to comply with the overlap rules of the roofing and metalworking trades, additional sealing strips may be necessary in certain systems. Large roof areas require adequate ventilation underneath. The roof tiles industry recommends an uninterrupted space at least 20 mm deep and a minimum ventilation cross-section of 200 cm2/m, figures that are based on DIN 4108-3. Larger ventilation cavities are advisable in order to minimise the module temperature and increase the yield. Metal roof coverings represent another

Construction and integration Roof installations

roof

37

option for integrating a PV installation into a pitched roof (Fig. 36). Here, flexible solar cells made from amorphous silicon are fully encapsulated in plastic and laminated to profiled metal sheets. Owing to the low additional weight, the normal fixings for such roof coverings are adequate. Overhead glazing Overhead glazing is often involved when a PV installation is fitted into a roof, and this represents a special situation in terms of building legislation. In this situation the design must comply with the stipulations of the TRLV, otherwise a special approval and authorisation procedure will be necessary (see “Technical rules and building legislation”, p. 77). According to the TRLV, laminated safety glass with a lower pane of non-toughened float glass must be used for overhead glazing, or other suitable measures must be taken to prevent large fragments of glass from falling onto the floor below. The technical construction regulations state that only laminated safety glass with an interlayer of polyvinyl butyral (PVB) is classed as a regulated building product. Standard modules do not satisfy this stipulation and require special constructional measures when used overhead. PV applications employ mainly toughened safety glass and an interlayer of ethylene vinyl acetate (EVA) (see “Generating and using solar electricity”, p. 20). Laminated safety glass made from toughened safety glass is not permitted owing to its fracture pattern, which results in an inadequate residual loadbearing capacity (Fig. 37). The practical solution is often to use laminated safety glass made from heat-strengthened glass, which represents a compromise between the high strength of toughened safety glass and the advantageous fracture pattern of float glass (Fig. 37). This is cur-

38

39

rently still a non-regulated form of construction, which means that special approval and authorisation procedures are necessary. In the case of insulating glazing, another pane of glass can be laminated to the rear of the inner pane in order to satisfy the requirement that nontoughened float glass should be used in laminated safety glass. Atria and sawtooth roofs Roofs to atria and internal courtyards frequently employ overhead glazing (Fig. 38). The inclusion of PV modules enables the solar cells to be used as sunshading elements as well – additional sunshades outside may well prove unnecessary. The amount of incoming light can be varied via the transmittance. These modules are visible from inside the building and characterise the atmosphere of the interior, especially by way of the shadows they cast. A sawtooth roof provides a good solution to this constructional task in both new and existing buildings. The principle of the sawtooth roof is the addition of rows of pitched roof-type structures. The vertical or inclined north-facing glass surfaces admit diffuse daylight, the sloping south-facing surfaces are used for generating electricity with a PV system. In fully glazed roofs there is a gradual transition to the sunshading, and controlling the transparency is more important (see “Designing with photovoltaics”, p. 46). Partially transparent modules can guarantee non-glare illumination with daylight. Canopies In the form of canopies, solar modules can provide protection from both the rain and the sun. In legal terms, glass canopies are also classed as overhead glazing. Where the panes have an area of max. 1.6 m2, linear support on all sides and are not installed at a great height, then an exemption from the overhead

glazing stipulations is possible. However, this should be agreed with the building authority responsible beforehand. Numerous approved systems are available for installations with larger dimensions. Attachment is by way of point fixings or continuous clamp fixings. Wind loads need careful consideration when designing a canopy. Pressure and suction forces generate opposing stresses and depend on the region, topography, height of installation and aerodynamic coefficient of the structure. PV applications are also suitable for roofing over entrance zones, open areas or access routes. In such instances the combination of PV modules with membranes and cable nets represent interesting architectural possibilities.

34 PV roof elements as replacements for groups of roof tiles. Solar roof tiles have only a small share of the market because of the considerable cabling work required. 35 Roof-integrated PV modules. Currently, a number of manufacturers have several different integral systems on offer. 36 PV metal roof. Flexible PV modules can supplement conventional profiled metal decking. 37 Comparison of the fracture patterns of non-toughened float glass (left) and toughened safety glass (right). Untreated float glass breaks into larger fragments than toughened safety glass, which has a positive effect on the residual loadbearing capacity. 38 Example of a roof over an internal courtyard with overhead glazing; local government offices, Ludesch (A), 2006, Hermann Kaufmann 39 PV canopy providing protection against sun and rain

61

Construction and integration Facade installations

40

to the PV modules to form functional glass assemblies, thermal insulation and safety/security requirements can be satisfied as well. In principle, double-leaf or prefabricated facades also offer opportunities for integrating photovoltaics. Diverse options are conceivable depending on the architectural concept. The use of photovoltaics on a facade often requires the fabrication of custom modules, which always involves higher production costs and can compromise the economic viability of the entire installa-

Facade installations In the past, facade constructions were essentially passive components from the energy viewpoint. Maximum thermal insulation was intended to minimise the energy flows between interior and exterior. Maximising the solar gains in winter through transparent components also represented a passive use of solar energy. But thanks to photovoltaics we are now able to shift from a passive to an active approach and exploit the substantial energy potential of facade surfaces. Although vertical surfaces are not ideal in terms of their orientation and are associated with lower yields, when PV elements also provide other facade functions, these deficits can be offset. The following forms of construction can be used for an extensive use of PV elements on part of the facade and open up numerous applications: • Cladding plus ventilation cavity • Post-and-rail facades • Double-leaf facades • Prefabricated facades South-facing cold facades, i.e. with a ventilation cavity, are preferred for PV applications. In these designs the PV modules replace the exterior cladding and provide the weather protection. The remaining elements such as thermal insulation, loadbearing structure and anchorages are the same as for a conventional design (Fig. 40). The ventilation cavity in the facade reduces the temperature of the modules, which has a positive effect on the conversion efficiency. In traditional post-and-rail designs, it is mainly the opaque areas, e.g. spandrel panels and parapets, that are suitable for integrating PV elements. Where the design includes high-level windows, partially transparent modules can provide shading and light-scattering functions. And if further panes of glass are added 62

41

tion. Planners must therefore consider PV integration at an early stage where photovoltaics are included in the design brief and coordinate this with the layout of the building or facade. Moreover, the visual quality of the PV modules is crucial on the facade. Modules employing thin-film technology have a much more homogeneous appearance, which is seen as an advantage. The manufacturers can now produce coloured modules as well, a development that expands the design options (see “Introduction”, p. 9).

Construction and integration Facade installations

42

43

Cladding plus ventilation cavity This involves a multi-layer external wall construction in which the weather protection layer is separated from the thermal insulation by an air cavity. Planned in conjunction with the retrofitting of additional thermal insulation, such a facade can achieve a high energy-saving potential, and also realise the activation of the building envelope for energy purposes in both new and existing buildings. DIN 18516 regulates the design and construction of these facades. The design and verification principles are specified in part 1 of this standard, irrespective of the planned design of the building envelope. Part 1 together with part 4 cover external wall cladding made from heat-soaked toughened safety glass attached in front of a ventilation cavity.

As with conventional cladding materials, e.g. tiles or panels of fibre cement, ceramics, clay or metal, they are attached to the supporting construction with various types of metal fixings. Each glass facade element must be fixed separately; clamped linear (on two, three or more sides) or point supports are possible. According to the stipulations of DIN 18516-4, all glazing must be made from heat-soaked toughened safety glass. PV modules may therefore fall outside the area covered by the standard, which means that their use must first be clarified with the regional building authorities (see “Technical rules and building legislation”, p. 75). Point fixings in drilled holes according to the Model List of Technical Construction Regulations (MLTB) are not covered by this standard either.

According to DIN 18516-1, the construction comprises the following elements: • Cladding • Supporting construction • Anchorage elements • Layer of insulating material • Supplementary parts of the cladding The cladding, the outer leaf of the construction, provides protection from the weather and determines the architectural effect. The loadbearing external wall behind this provides the structural functions and is thermally insulated if necessary. Between these two leaves there is a layer of air that can dissipate any condensation and water vapour that collects here. It is precisely this ventilated air space that makes this type of construction ideal for supporting PV elements, which can extend over the entire area of the facade or just the spandrel panels. As the PV modules conceal the thermal insulation behind, opaque glass /plastic or glass /glass laminates can be used. The majority of these panels have junction boxes fitted to the rear, which therefore can remain concealed.

Actions according to DIN 1055 due to self-weight, dead loads, wind, snow, ice and exceptional loads must normally be considered when designing the facade elements. Additional requirements are specified in DIN 18516-1, section 5. For example, external cladding with a certain wind permeability (due to open joints) can reduce the wind suction loads at the edges and corners of a facade. It must also be remembered that components can change their shape with the temperature, structures can deform and the subsoil can settle. The nominal thickness of the glazing may not be less than 6 mm and all sharp arrises must be removed. A visual inspection to rule out damaged edges must be carried out before assembly. Any damage discovered may not extend deeper than 15 % of the pane thickness into the body of the glass. The installation of point-supported toughened safety glass ≥ 8 m above ground level must be supervised by an institute accredited by the building authorities. Several PV facade systems complying

40 Example of a PV facade with framed thin-film modules 41 Active energy facade; fire station, Heidelberg (D), 2007, Peter Kulka 42 Individual clamp fixings for glass/glass laminates 43 Detail of a point support with associated supporting construction

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Construction and integration Facade installations

right

wrong

a ≥1

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a b c d e f

45

44 Glazing supported and positioned by setting and location blocks a Setting block positioned correctly b Bridge packer positioned correctly c Setting block positioned incorrectly d Setting block positioned incorrectly in profiled rebate 45 Example of photovoltaics on cladding in front of a ventilation cavity; cladding secured by concealed hook fixings a Cover glass b PV thin-film cells c Backing glass d Mounting plate e T-section f Thermal insulation

64

with DIN 18516 are available on the market. These systems are generally approved forms of construction or acknowledged as regulated forms of construction according to DIN 18516. The system suppliers cooperate with the PV element manufacturers and together they market complete systems. Standard calculations are usually available, meaning that separate structural analyses are unnecessary. Most of these facade systems are approved for use on facades up to a height of 100 m. The supporting constructions are either lightly modified standard systems or solutions specifically devised for PV applications. The systems can therefore be readily combined with other facade elements and those parts of the facade unsuitable for electricity generation can be clad with dummy panels. Fixings are usually in the form of continuous or separate clamping fasteners. Concealed fixings (hooks) on the rear of each panel are also possible, which means that the glass edge cover required with conventional PV facades disappears altogether (Fig. 45). Post-and-rail facades A post-and-rail construction essentially consists of the vertical posts, the horizontal rails and (usually) glazed infill elements. In contrast to a solution with cladding plus a ventilation cavity, a post-andrail facade fulfils all the functions of the building envelope, including thermal insulation, in one layer. The posts are the main loadbearing members; the rails function as horizontal lateral supports, transfer loads to the posts and drain any condensation. Steel, aluminium or timber are the structural materials most frequently encountered. Infill elements, e.g. glazing or cladding panels, are fixed in rebates without restraint. It is these conventional infill elements that can be replaced by PV modules. Capping strips

b

c ≥1mm

d

screwed in place fix them in a similar way to glazing. Installation of the glazing without restraint must be ensured during design and construction. The glass edge cover for panes with linear support on all sides should be at least 10 mm and for panes with linear support on two or three sides at least 15 mm or the thickness of the glass plus 1/500 of the span. The PV elements must be supported by setting blocks made from plastic or hardwood (Fig. 44). Setting blocks are about 80 –100 mm long and should be about 2 mm wider than the thickness of the PV module to be supported so that direct contact between module and supporting construction is avoided. A special form of construction within the post-and-rail category is the structural sealant glazing facade (SSG, see p. 53). In contrast to the clamped design, the panes of glass or PV modules are not held in place by glazing bars, but instead by a loadbearing silicone adhesive. The modules are glued – without any visible form of connection – to adapter frames which are then fitted into the post-and-rail construction on the building site. Prefabrication reduces the risk of damaging the modules during erection and also helps to ensure the durability of the adhesive bond. Anodised or powder-coated aluminium or stainless steel surfaces are suitable for the supporting construction. The glass can have an inorganic coating or be left uncoated. As post-and-rail designs are warm (i.e. single-leaf) facades, a thermal break between sections and glazing with a low U-value are necessary. Accordingly, PV modules must form part of an insulating glass concept (see p. 51). Design and construction is carried out according to the TRLV. When analysing the loadbearing capacity, climate loads must be considered in addition to the normal actions according

Construction and integration Facade installations

46

47

to DIN 1055. Climate loads are caused by the change in volume of the infill gas due to temperature and air pressure differences between the cavity and the surrounding atmosphere. The hermetically sealed cavity between the panes of glass in an insulating glass unit also gives rise to a “coupling effect” for loads perpendicular to the plane of the glass. The load transfer via the enclosed volume of gas leads to both individual panes of the insulating glass unit contributing to withstanding the load depending on their elasticity. Consequently, the inner pane not directly impinged upon by the load carries part of the externally applied load (e.g. wind load). Besides this coupling effect, additional panes of laminated safety glass laminated onto the insulating glass unit should be taken into account in the theoretical analysis of the shear bond. The two extreme cases – full bond and no bond – must be examined in the calculations. Despite correct design and construction, driving rain and condensation can infiltrate the post-and-rail system. The water must be able to drain away to the outside via a vapour pressure equalisation and drainage system, with openings at the

48

lowest points of the rebates or capping strips. The openings should measure 5 ≈ 15 mm or  8 mm at least in order that the water can drain away unhindered. Apart from that, the aforementioned setting blocks for the PV modules should not interfere with the drainage. The use of hollow sections for the post and rails simplifies the routing of the PV cables, which are laid either directly in the sections themselves or behind additional cladding elements. The connections to the insulating glass units are via the cables exiting from the sides of the units, which means that all wires and cables can be concealed. Double-leaf and prefabricated facades Further forms of construction are suitable for integrating PV elements in addition to those described in detail above. However, there are only a few individual examples and no tried-and-tested construction systems for these applications. In principle, the aforementioned fixing methods and module configurations can be used for the constructional integration according to the technical rules for vertical glazing. In the case of double-leaf facades, the outer leaf to the unheated

thermal buffer space is ideal for PV systems because of the lower module temperatures. Prefabricated facades are produced in factories and are normally erected on the building site as storey-high elements. This form of construction enables the integration of complex building services in the facade. PV installations can be combined with, for example, ventilation units to form multi-functional facades. The special design of the GreenPix – Zero Energy Media Wall combines PV elements with modern media technology (Figs. 46 and 47). The 35 m high and 60 m wide display consists of RGB LEDs and polycrystalline cells. During the day the facade produces the quantity of electricity needed for the LED lighting effects at night.

46, 47 This curtain wall glass facade combines 2292 RGB LEDs and polycrystalline PV cells arranged in different numbers per unit area. GreenPix – Zero Energy Media Wall, Peking (CN), 2008, Simone Giostra 48 Example of a structural sealant glazing facade with PV modules in the form of insulating glass units; Tobias Grau company building, Rellingen (D), 2001, BRT Architekten

65

Construction and integration Sunshade installations

Depth t Max. elevation of sun on 21 Jun, 12 noon

Module spacing

γ

hb

idt

w ule

d

Mo

Module mounting angle β

Module spacing =

49

66

t , t = cos β x b tan γ (21 Jun, 12 noon)

Sunshade installations Photovoltaics and sunshading elements are ideal partners. An external sunshading system positioned to protect against direct sunlight provides maximum efficiency against overheating and glare. At the same time, this means an optimum orientation for PV elements and hence improved shading in conjunction with maximum energy yields. The good ventilation below the modules also helps to maximise the amount of solar electricity generated. As the transparency of PV modules can be individually adjusted by way of the cell spacing or cell strips, PV elements can be used to replace the shading glass or metal panels in sunshading systems. Crystalline silicon cells in standard sizes of 125 ≈ 125 mm or 156 ≈ 156 mm attached with a spacing of 2 – 5 mm exhibit a light transmittance of 10 %. That is sufficient to illuminate ancillary areas that do not require full daylighting. In thinfilm technology, light-permeable striped, chequered or perforation patterns can interrupt the coating of cells to achieve a much more consistent lighting effect. This enables diverse variations to be realised and used for architectural purposes (Fig. 52, see “Designing with photovoltaics”, p. 46). Sunshade installations are divided into fixed and movable systems. Tracking systems optimise the energy yields and the sunshading function, but are associated with very much higher production and maintenance costs. The combination of fixed PV modules and movable shading elements represents an alternative. Fig. 50 shows pairs of sliding shutters made of expanded metal behind fixed vertical PV elements. On the east and north elevations the PV modules are replaced by panes of glass with silkscreen printing.

Fixed systems One very simple and effective form of sunshade is the rigid awning. In terms of its design it is similar to a PV canopy arrangement (see p. 61). Brackets for awnings above window openings would therefore seem to be a good solution. On the south side of a building and with an optimum inclination they ensure selective shading over the year and primarily protect against the summer sun high in the sky. During winter, however, it may be necessary to provide additional screening to protect against the glare of the sun low on the horizon. Fixed sunshades above east- and west-facing openings are not sufficient because of the unfavourable angle of incidence. Vertical sunshading elements should not be positioned too close to other awnings in order to reduce the shadows cast by the elements themselves – similar to the stand-off installation on a flat roof. In contrast to the horizontal arrangement, the critical shading angle for a vertical arrangement occurs on 21 June (Fig. 49). On this date the angle of the sun in Germany is 63° on average. This results in a spacing of about 1.7 times the width of the module for a mounting angle of 30°. The modules should not be attached directly to the facade because the ensuing build-up of heat has a negative effect on the conversion efficiency of the PV elements. A clearance between the sunshade/PV system and the facade prevents this undesirable effect. Where glazing elements projecting from the facade extend over circulation zones, the requirements for overhead glazing must be met (see p. 61). [4] Fixed louvres represent another option for integrating a PV system into a sunshade. In this design, several PV elements are arranged parallel to one another at a close spacing. The louvres can be in the form of a horizontal cantilever or be positioned horizontally or vertically in the

Construction and integration Sunshade installations

51

50

facade itself. Horizontal louvres in front of window openings are the most common arrangement. In order to guarantee maximum sunshading but at the same time minimise the shadows cast by the elements themselves, PV elements are attached only to those parts of the individual louvres that are never in shadow. As a rule, bespoke glass /glass laminates are used here, but glass /plastic variants are also possible. Several manufacturers already offer standardised mounting systems for accommodating solar modules. However, the relatively small areas result in a high cabling requirement. Furthermore, fixed louvres do not allow for any

52

adaptation to suit the changing position of the sun. Movable systems In contrast to fixed components, tracking sunshading systems enable infinite adjustment to ensure glare-free shading throughout the day and at the same time optimum daylighting plus better solar electricity yields. Sliding shutters represent a simple form of movable system. Although these are not genuine tracking systems, they are able to regulate and vary the amount of daylight in the interior. The angle of movable louvres can be adapted to the elevation of the sun. In

49 Calculating the module spacing for a vertical installation. In contrast to a horizontal arrangement, the shading angle is based on the maximum elevation of the sun on 21 June, 12 noon. 50 Combination of fixed PV modules and movable sunshades; Q-Cells company headquarters, Bitterfeld-Wolfen (D), 2007, bhss Architekten 51 Louvre-type sunshades fitted with PV cells; GoodsTesting Institute, Eindhoven (NL), 2003, Vera Yanovshtchinsky Architecten 52 Combination of coloured louvres and PV elements; school in Pic Saint-Loup (F), 2003, Pierre Tourre

67

Construction and integration Sunshade installations

d

a

b

c

53

such systems elements are usually grouped together and fixed to a suitable framework so that several parallel louvres can be moved via connecting rods to track the sun. Point fixings help achieve an elegant and transparent appearance. Tracking systems for the PV elements are mostly based on computer-controlled electric motors and solar-powered thermohydraulic drives. Computer-controlled systems align the louvres with the sun’s trajectory according to date, time and location, whereas solar-powered thermohydraulic drives regulate themselves without the need for any auxiliary power input. These latter systems require no further electrical connections but react only very slowly. The HCC Hannover project is an excellent example of a movable thermohydraulic PV system (Fig. 54). Two opposing solar collectors are linked to a hydraulic ram via a thermohydraulic fluid. The collectors receive different amounts of solar radiation depending on the position of the sun. This causes different pressure conditions that then align the system optimally with the sun via a connecting rod. In this example the PV installation at the same time forms a canopy on the south side of a glazed foyer. At a height of 9 m above ground level, seven steel beams cantilever approx. 2.6 m out of the building to support six groups of louvres each with seven PV louvres parallel to the facade. There are three rows of cells on the front louvre in each group, two rows on all the other louvres behind in order to minimise the shadow effects caused by the louvres themselves. The design was granted an individual approval (ZiE) for overhead glazing by Lower Saxony’s senior building authority. Another example can be found at the EWE Arena in Oldenburg, which has been fitted with a movable and controlla-

54

55

68

ble sunshading system. The special feature here is that a complete PV glass curtain wall facade tracks the position of the sun. The tracking mechanism is silent and traces the curvature of the building as the sun moves around it during the day. The 40 m long construction is more than 6 m high and consists of 18 segments each comprising 72 PV modules and 72 silk screen-printed glass elements. The PV modules are interconnected to form nine large groups, so-called strings. Every 30 minutes, the construction moves along a stainless steel rail fitted around the southern half of the building. The construction is suspended from a lightweight concrete ring at the top. The primary task of the lower ring is to provide lateral support. Wind loads are resisted by the guide rail. All the PV modules are held in place by individual clamp fixings. This is a very imposing example of how the sunshading function is combined with the transformation of sunlight into electricity on a building.

References: [1] Haselhuhn et al., 2008 [2] Baden-Württemberg Ministry of the Economy, 2005 [3] ERFURTH + PARTNER GmbH, 2001 [4] Hagemann, 2002

Construction and integration Sunshade installations

53 Drawing showing the principle of a thermohydraulically controlled sunshading system a PV element b Connecting rod c Hydraulic cylinder d Solar collector 54 Example of a thermohydraulically controlled sunshading system; Congress Centre, Hannover (D), 2002, ASP Schweger Assoziierte 55 Detail of corner of hinged shutters with movable louvres with PV cells along their lower edges. Solar house for the “Solar Decathlon” competition of the US Department of Energy in Washington D.C. (USA), 2007, Darmstadt University of Technology 56 Section through movable facade, scale 1:50; EWE Arena, Oldenburg (D), 2005, ‘asp’ architekten Arat – Siegel – Schust a

a Photovoltaic outer leaf, glass/plastic laminate consisting of 8 mm low-iron heat-soaked tough. safety glass + Tedlar backing sheet with monocrystalline PV in between encapsulated in EVA hot-melt film b Upper roller bearing c Annulus with plates for welding d Frame of aluminium hollow sections: 200 ≈ 50 ≈ 4 mm vertical, 200 ≈ 50 ≈ 8 mm and 100 ≈ 50 ≈ 4 mm horizontal e Profiled glass facade f Silk screen-printed lam. safety glass: 6 mm tough. safety glass + PVB interlayer + 6 mm tough. safety glass g Lower roller bearing with height adjustment 57 EWE Arena, Oldenburg (D), 2005, ‘asp’ architekten Arat – Siegel – Schust

b

c

a

d

e

f

f g

56

57

69

Technical rules and building legislation

an

d na m e

TVG

Z-70.4-123

1 1

2

2

NU

ER

.

MPA NRW

FA C TU

R

The performance is measured under artificial lighting conditions with a defined homogeneity and reference spectrum. The modules must pass all tests without a significant drop in performance or visible damage such as delamination, broken cells or glass, and while maintaining their full electrical insulation. The tests simulate an external application over 20 –25 years. Every change to the design, materials, components or manufacture of the typetested PV elements will require a complete or partial requalification. Manufacturers therefore tend not to certify custom modules.

Electrical installation and safety The EU’s Low-Voltage Directive (2006/95/ EC) prescribes the CE marking for PV modules and inverters. Manufacturers use the CE marking to indicate that their products comply with the corresponding EU directives where applicable. Without the CE marking, products with a relevance for safety may not even be marketed in the European Union (Fig. 1). To start with, all modules must comply with the harmonised standard DIN EN 61730 “Photovoltaic (PV) module safety qualification”. This standard allocates modules to one of three classes, A, B and C. The majority of modules are certified to class A and assigned to protection class II, which means they may be used in buildings without restricting access. The tests go beyond those of IEC 61215 and 61646 and include, for instance, a surge voltage test and a module breakage test with a test sack weighing 45.5 kg (p. 72, Fig. 4). Fire tests are also specified, but these have not yet been included in the European standard. The CE marking for inverters also includes electromagnetic compatibility (EMC) tests according to the European EMC Directive, which requires that the products themselves do not cause any unacceptable disturbances and their function is not impaired by other equipment.

MA

Type approval of PV modules The test certificate to IEC 61215 “Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval” or IEC 61646 “Thin-film terrestrial photovoltaic (PV) modules – Design qualification and type approval” has become established as a sign of quality for PV modules worldwide. The International IEC standards, and in Germany

their equivalents in the form of DIN EN standards, describe the qualifying tests on the basis of accelerated ageing due to radiation, thermal and mechanical effects. The modules have to pass the following tests: • Visual inspection for damage • Electrical performance at standard test conditions (STC) (p. 72, Fig. 3); pre-exposure to light in the case of thin-film PV • Measurement of operating temperature and temperature coefficients • Electrical insulation test, also in wet conditions • Long-term outdoor exposure • Hotspot endurance test • UV preconditioning • Thermal cycling test: 50 or 200 cycles from -40 to +85 °C under electrical loading • Humidity freeze test: 10 cycles from -40 to +85 °C at 85 % relative humidity • Damp heat test: 1000 h at 85 °C and 85 % relative humidity • Robustness of electrical terminations • Mechanical load test with a uniformly distributed load of 2.4 kN/m2 (optional: 5.4 kN/m2 for higher snow loads) • Hail test with ice balls 25 mm in diameter • Bypass diode thermal test

Br

Photovoltaic (PV) systems are electrical installations and therefore in Germany they must comply with the standards and regulations of the VDE, the Association for Electrical, Electronic & Information Technologies. The intention of the DIN-VDE standards is to regulate the safety, functionality, performance and reliability of PV components and systems. PV installations are, however, also constructional installations in the meaning of building legislation. As the degree of integration within the building envelope increases, so the technical regulations governing the building industry become more and more relevant for PV systems; however, these contain no provisions regarding photovoltaics as such. To redress this imbalance, the draft electrical standard DIN VDE 0126-21 tries to bridge the gap between the electrical engineering and the construction engineering disciplines, providing a multidisciplinary reference work for the relevant provisions. In most cases the primary material of PV modules is glass and therefore they fall within the remit of the regulations covering the use of glass in building. But the standard solar modules most frequently encountered these days often do not satisfy these regulations. Considering the multiplicity of designs and the still inadequate level of regulation (even in the case of glazing without solar cells), PV modules are sometimes in a grey area of building legislation.

The CE marking indicates that a product complies with the relevant EU directives; fundamental safety requirements are deemed to be satisfied. Regulated glass products are marked on the edge with a stamp to indicate compliance with the appropriate standard or National Technical Approval, in this example heat-strengthened glass (TVG) tested by the materials-testing body (MPA) of the state of North Rhine-Westphalia (NRW).

71

Technical rules and building legislation Electrical installation and safety, an overview of building legislation

3

4

Measuring the performance of a PV module according to IEC or DIN EN 61215 with a sunshine simulator consisting of xenon lamps. The artificial light source must reproduce the reference solar spectrum with adequate accuracy and homogeneity. Module failure test: pendulum impact test on the front of a module with a test sack weighing 45.5 kg according to IEC or DIN EN 61730. Any fragments must measure less than 6.5 cm2 in area. The results of the test cannot be used for the purposes of building legislation because the test setup does not correspond to the building authority standards. 3

The design and installation of electrical systems must take into account the relevant VDE regulations, especially VDE 0100 (low-voltage installations for buildings). Part 712 of this standard deals specifically with PV systems. Grid operators specify the technical connection conditions (TAB) for those systems connected to the public electricity grid. As a rule, they also take into account the regulations of the German Energy & Water Management Association (BDEW) for the parallel operation of private generation systems and low- or mediumvoltage networks. The idea behind this is to prevent PV installations from having a negative influence on the quality of the public grid, endangering operators’ maintenance personnel or affecting electricity supplies to other customers. As these requirements concern the inverters, manufacturers must declare their full compliance. The most important aim of protection concerning solar modules and inverters is that they should not represent any danger for persons, e.g. due to electric shock. It is precisely in the situation of building-integrated PV installations that the modules are often readily accessible. The level of safety must be such that it is possible to touch even the broken glass pane of a module without suffering any unpleasant consequences. The simplest safety precaution is to adhere to the safety extra-low voltage (SELV) recommendations, which limit DC voltages to a harmless 120 V. In order to minimise the cabling requirements, however, many modules are normally connected in series with higher voltages up to 1000 V. One common precaution against electric shock in the event of a fault is then to provide protective insulation, which is only possible with protection class II equipment. The installation of all components on the DC side such that earthing faults and short-circuits are prevented separates the positive, negative and earth 72

4

potentials safely from one another and prevents dangerous electric arcs. Electrical installation Following appropriate instruction by an electrician, even other trades, e.g. roofing contractors or facade erectors, may connect together PV modules fitted with plug connectors. However, the electrical installation on the AC side of the inverter and the connection between the PV system and the grid must always be carried out by a suitably qualified electrician who, incidentally, is responsible for the electrical work on the entire PV installation and who guarantees – with his signature in the commissioning documentation – that the acknowledged rules and regulations have been complied with. Such work presumes good cooperation between the erection and electrical teams. Lightning protection Where a building is fitted with a lightning protection system, then the PV installation must be integrated into this and additional air terminals may be necessary. But retrofitting a lightning protection system to a previously unprotected building is only necessary where the additional height of the PV components, e.g. a stand-off system mounted on a flat roof at an exposed location, presents an increased risk. An overview of building legislation In the course of the European harmonisation of technical regulations covering practicable building products, the German Construction Products Act (Bauproduktengesetz, BauPG) represents the implementation of the EU’s Construction Products Directive (CPD). The federal law of Germany stipulates that building regulations are the responsibility of the individual federal states. The building regulations of the federal states (LBO) are essentially identical to the Model Building Code (MBO), a document agreed upon by the ministers

responsible for building and public works. The MBO calls for buildings and structures to be designed, erected, modified and maintained in such a way that public safety and order, in particular life, health and the natural resources essential to life, are not endangered [1]. In accordance with this principle, the various LBOs specify which building products and which forms of construction may be used in which situations. They also regulate the responsibilities of the authorities and the approvals required for construction projects. According to the LBOs, the installation of PV modules in and on roof and facade surfaces, and also very small groundmounted arrays with heights up to 3 m and total lengths up to 9 m, does not normally require approval. Of course, approval for the building envelope itself will still have to be obtained. In certain federal states PV systems for heritage buildings or sites protected by conservation orders will, however, require approval. But even if no official procedure is involved, the installations themselves must of course comply with all the relevant statutory instruments. Therefore, a whole series of requirements that the LBOs specify with regard to stability, fire protection, clearance to adjacent structures, building products and forms of construction must be taken into account. Furthermore, PV installations can touch on laws covering planning requirements, landscape and heritage conservation, and occupational health and safety. If the installation of a PV system has an effect on the continued existence or the appearance of a heritage asset, permission from the appropriate authorities will be required. The PV installation must not contravene any stipulations of the relevant local development plan. Particularly important here is the maximum height of roof-mounted stand-off systems, but also design regulations and building lines.

Technical rules and building legislation Building products and forms of construction

T1: Classification of building products according to the Model Building Code (MBO) National Regulated

Construction Products List A part 1

Other

According to harmonised European standards or with ETA4

General

No significant requirements Of minor importance for building legislation or acknowledged test methods

–

Construction Products List A part 2

Construction Products List C

Acknowledged codes of Construction Products List B practice

AbP 3

No verification of applicability

No verification of applicability

National technical rules ZiE1 or AbZ 2

Attestation of conformity Ü mark 1

European

Non-regulated

No attestation of conformity No Ü mark

European technical rules and restricted applicability at national level Proof of conformity CE marking

ZiE: Individual approval; 2 AbZ: National Technical Approval; 3 AbP: National Test Certificate; 4 ETA: European Technical Approval

Building products and forms of construction As PV modules in the building envelope take on more and more functions, so the requirements they have to fulfil in terms of building products and forms of construction become more numerous and more stringent. If a building-integrated PV installation can be implemented in accordance with the technical rules specified by the building authorities, time and money can be saved, because it is not necessary to obtain approval. However, for other designs and types of module, the National Test Certificate (AbP), National Technical Approval (AbZ), European Technical Approval (ETA) or individual approval (ZiE) options are available (pp. 76 –77). Moreover, the building authorities possess a certain leeway with respect to their decisions in individual cases. Building products The MBO describes building products as “building materials, building components and constructions that are produced for permanent use in buildings and structures”. This term also encompasses “prefabricated constructions made from building materials and building components”, e.g. curtain walls or factory-prefabricated glass safety barriers. The German Institute of Building Technology (DIBt), together with the senior building authorities of the federal states, is responsible for the Construction Products List (BRL) and publishes the current status in its annual DIBt bulletins. The MBO divides building products into four BRL categories (Tab. T1): • Regulated building products that do not deviate or do not deviate significantly from the product standards of BRL A part 1. Their manufacturers label these with the Ü mark. • CE-marked building products may be marketed and traded according to Euro-

pean regulations and are listed in BRL B. In Germany building products with the CE marking alone are not yet classed as regulated, but only in conjunction with national application standards or regulations. Examples of this are heatstrengthened glass, which requires a National Technical Approval (AbZ) as well for most applications, synthetic roof sheeting materials and curtain walls. • Other building products that play only a subsidiary role in terms of technical safety provisions are not specified in BRL A even though there are acknowledged codes of practice for these products. They may not be labelled with the Ü mark. • Non-regulated building products deviate significantly from the Technical Construction Regulations or are not covered by any acknowledged codes of practice. They require verification of applicability unless they are of only minor importance in terms of building regulations and are listed in BRL C. PV modules are not explicitly mentioned in the Construction Products Lists. Their CE marking is not based on the CPD and therefore has no relevance for building legislation. Instead, they can be classified depending on configuration and application (Tab. T2). PV modules of “conventional construction with mechanically retained panes of glass” which fulfil no further constructional functions are classed as other building products according to the decision of 20/21 June 2001 of the Building Technology Special Commission. This informal “approval” is essentially based on the widely used stand-off roof installations with framed solar modules. The acknowledged codes of practice here are DIN EN 61215 or 61646 and DIN EN 61730. Of course, such installations must still comply with stability and fire protection requirements. “Solar roof tiles” up to 5 kg in weight and 0.4 m2 in area are classed

as small-format roofing elements; they are non-regulated building products according to BRL C and therefore do not require verification of applicability either. This also applies to metal roof coverings with integral PV modules up to a mounting height of 1 m. Synthetic roof sheeting with integral thin-film modules are classed as European regulated building products when their CE marking also applies to the PV elements. When integrating PV systems into glass roofs, facades, sunshading elements or structural sealant glazing, the first aspect to be considered is whether the types of glass used are regulated building products. This is because the addition of solar cells may count as an insignificant deviation from the valid construction provisions provided the loadbearing capacity and durability of the assembly is not negatively affected and there are no dangers for circulation zones [2]. But the interpretation is not always unequivocal. For instance, some building authorities treat glass/plastic laminates with toughened safety glass as equivalent to regulated toughened safety glass products. And glass/glass laminates in the form of laminated glass according to DIN EN 14449 turn out to be regulated glass products. Nevertheless, they are not approved for every application because restrictions apply to some forms of construction, e.g. overhead glazing. In this case they are treated as non-regulated building products. The difficulties arise because of the holes drilled for the electrical connections in the backing glass and also the non-regulated intermediate layers. Forms of construction In the case of forms of construction, defined in the MBO as “the assembly of building products to form buildings or structures or parts thereof”, we only distinguish between regulated and non-regulated forms. The 73

Technical rules and building legislation Building products and forms of construction

T2: Status of regulations for photovoltaic elements Location

Examples

Status of regulations

Explanations

Roof, stand-off

Raised above surface of flat or pitched roof

Panes with mechanical retention: other building product; verification of applicability not required; acknowledged codes of practice: DIN EN 61215 or 61646, DIN EN 61730.

Preferably framed glass/glass or glass/plastic laminates (linear retention of glass according to TRLV); glued fixings are non-regulated. Modules projecting beyond the edge of the roof are classed as overhead glazing (see glass roof).

Roof, integral

Synthetic roof sheeting with solar cells bonded to it Exception: laying in 2 layers

Building product with CE marking according to harmonised standard DIN EN 13956. Form of hard roof covering requires verification of applicability.

Design according to the national design and application standards DIN 18531-2 and DIN V 20000-201 (pre-standard). The CE marking must include the PV laminate. Verification of applicability normally in the form of an AbP3 or classification as BROOF (t1) if the LBO requires a hard roof covering.

Substitute for roof covering on pitched roofs

Panes with mechanical retention: depending on design, possibly classed as other building product that does not require verification of applicability; acknowledged codes of practice: DIN EN 61215 or 61646, DIN EN 61730. Form of hard roof covering requires verification of applicability.

Glass/glass or glass/plastic laminates with linear retention of glass according to TRLV represent a regulated form of construction if the roof design prevents larger pieces of glass falling onto circulation zones below. Glued fixings are non-regulated. Verification of applicability normally in the form of an AbP3 if the LBO requires a hard roof covering.

Small-format “solar roof tiles” up to 0.4 m2 in area and 5 kg in weight, roofing elements with solar cells bonded to them and on framework with max. 1 m mounting height

Non-regulated building product according to Construction Products List C: verification of applicability not required. Form of hard roof covering requires verification of applicability.

Verification of applicability normally in the form of an AbP3 if the LBO requires a hard roof covering. Metal roof covering products/materials are to be laid on a complete sheathing of timber or wood-based products with separating layer.

Metal roofing (and facade) elements with solar cells bonded to them and > 1 m clearance to roof, or as sandwich elements

Building products with AbZ2 or CE marking according to harmonised standard DIN EN 14782 (or DIN EN 14509 for sandwich elements) and additional Ü mark labelling obligation (or application approval for sandwich elements). Form of hard roof covering requires verification of applicability.

Verification of hard roof covering within the scope of the CE marking or the AbZ2 or AbP3. Verification of structural safety according to AbZ2 or DIN 4113, DIN 18800, DIN 18807, DASt directive 016. Metal roof covering products/materials are to be laid on a complete sheathing of timber or wood-based products with separating layer.

Glass roof, canopy (0 – 80° inclination to the horizontal)

Atria, railway platform canopies, separate and continuous rooflights

Overhead glazing; linear support regulated by TRLV; possibly relaxation of regulations in the federal state-specific annexes to the LTB for overhead glazing in residential buildings and for canopies. Where vertical glazing gradually changes to overhead glazing, the individual areas must either be treated according to their angles or the whole as a homogeneous construction according to the more unfavourable case. Point supports for PV modules are not regulated because the TRPV covers only laminated safety glass.

Regulated designs are glass/glass laminates in single or insulating glazing units made from • float, wired, patterned, wired patterned, toughened safety or heat-soaked tough. safety glass, all to Construct. Products List A part 1; • heat-strengthened glass according to AbZ2; • laminated or laminated safety glass made from these types of glass. The back of the module, or rather the lower pane of insulating glazing, must be made from wired or laminated safety glass (made from float or heat-strengthened glass according to AbZ2) unless constructional measures (e.g. safety nets) prevent any larger pieces of glass from falling onto circulation zones below. Drilled holes are not permitted. ZiE1 or AbZ2 required for glass/plastic laminates, glued fixings, point supports, glass for occasional/constant foot traffic or glass elements acting as bracing.

Vertical glazing (up to 10° deviation from the vertical)

Facades, glazed walls, rooflights, balcony balustrades

Linear support regulated by TRLV; safety barrier applications and point supports for PV modules are non-regulated because the TRAV and TRPV cover only laminated safety glass.

Regulated designs are glass/glass laminates in single or insulating glazing units made from • float, wired, patterned, wired patterned, toughened safety or heat-soaked tough. safety glass, all to Construct. Products List A part 1; • heat-strengthened glass according to AbZ2; • laminated or laminated safety glass made from these types of glass. At installation heights ≥ 4 m, monolithic toughened safety glass must be replaced by heat-soaked toughened safety glass. Single glazing must have linear supports on all sides. Framed modules made from the aforementioned types of glass whose glass edge cover complies with the TRLV satisfy this requirement. Drilled holes are only permitted in toughened safety, heat-soaked toughened safety and heat-strengthened glass. Glued fixings, point supports, glass for occasional and constant foot traffic plus glass elements designed to function as bracing require a ZiE1 or AbZ2.

• Cladding plus ventilation cavity

PV modules made from heat-soaked toughened safety glass used as external wall cladding

Regulated by DIN 18516-4

Only monolithic heat-soaked toughened safety glass with min. 6 mm pane thickness, linear or point supports and no holes drilled through the glass are classed as regulated designs. Use of glass/plastic and glass/glass laminates made from heat-soaked toughened safety glass with or without frames is only permitted at the discretion of the building authority or in accordance with a ZiE1. Designs with individual mechanical retainers at installation heights > 8 m require supervision by an external institute during erection.

• Curtain wall

Post-and-rail construction, prefabricated facade, double-leaf facade

Building product with CE marking according to harmonised standard DIN EN 13830

The CE marking must include the PV module. Verification of the structural safety of the supporting construction, the facade elements and mechanical connections according to technical construction regulations: TRLV, TRAV, design standards for steel, aluminium or timber structures.

Glued glass design

Structural sealant glazing system

Non-regulated

ETA4 or AbZ2 for the facade system, which includes the PV module, or ZiE1 necessary, testing according to ETAG 002

Horizontal sunshading louvres or awnings

Movable or fixed PV panels

Glazing that projects into a circulation zone, e.g. glass roof or canopy (overhead glazing).

As for glass roof

Vertical sunshading shutters or louvres

Movable or fixed PV panels

As for vertical glazing

As for vertical glazing

1

ZiE: Individual approval; 2 AbZ: National Technical Approval; 3 AbP: National Test Certificate; 4 ETA: European Technical Approval

74

Technical rules and building legislation Building products and forms of construction

T3: Application standards and regulations introduced by the building authorities for building-integrated PV according to the MLTB, Feb 2008 edition

List of Technical Construction Regulations (LTB) specifies the regulated forms of construction. It contains application standards and rules for planning, design and construction in addition to the product standards of the Construction Products Lists. Each federal state issues its own LTB, which in turn is based on the Model List of Technical Construction Regulations (MLTB) published several times a year by the DIBt. Despite considerable common ground, the status of regulations varies across the federal states because their LTBs come into force at different times and do not necessarily include all regulations, or might even add further provisions. The current edition of the MLTB contains five design and construction rules for forms of construction using glass (Tab. T3). The Technical Rules for the Use of Glazing on Linear Supports (TRLV) and the Technical Rules for the Design and Construction of Point-Supported Glazing (TRPV) make a distinction between vertical and overhead glazing. Glazing forms intended for temporary or constant foot traffic are regulated by the TRLV only in the form of glazing on linear supports and must satisfy more stringent requirements. Glazing on linear supports that is intended to prevent persons falling to a lower level is covered by its own set of regulations, the Technical Rules for Glass in Safety Barriers (TRAV). Adhesive fixings, curved overhead glazing and glass elements that serve as bracing members are all non-regulated forms. The construction details, e.g. glass edge cover, area of clamp fitting or restraint, that result from this and are relevant for the installation of PV modules are described in the chapter “Construction and integration” (pp. 52–54, 56). In future a new series of standards, DIN 18008 “Glass in building”, will replace the TRLV, TRAV and TRPV and at the same time cover a large number of other forms of construction with glass that are currently classed as non-regulated. However, the

Title

Edition

DIN 18516-4: Back-ventilated, non-loadbearing, external enclosures of buildings, made from tempered safety glass panels; requirements and testing

February 1990

Technical Rules for the Use of Glazing on Linear Supports (TRLV)

August 2006

Technical Rules for Glass in Safety Barriers (TRAV)

January 2003

Technical Rules for the Design and Construction of Point-Supported Glazing (TRPV)

August 2006

DIN V 11535-1: Greenhouses – Part 1: Basic principles for design and construction (pre-standard)

February 1998

DIN V 20000-201: Adaptation standard for flexible sheets for waterproofing according to European standards for the use as waterproofing of roofs (pre-standard)

November 2006

date on which this series of standards will come into force has not yet been fixed. Vertical glazing Basically, the TRLV is valid for glazing with continuous linear supports on at least two opposite sides. Vertical glazing, i.e. facades and windows, may be assembled from regulated glass products, or from laminated glasses made from regulated basic glass products and other interlayers. This means that glass/glass laminates with integral solar cells encapsulated in EVA, PVB or casting resin are also permitted. The TRLV refers to DIN 18545-1 and 18516-4 for the glass edge cover. Vertical glazing whose top edge is no more than 4 m above a circulation zone, e.g. display windows, are exempt from the TRLV provisions but must be made from toughened or laminated safety glass for applications in public areas, e.g. workplaces, places of assembly, nurseries, schools. Stricter requirements apply to point-supported systems because the TRPV stipulates exclusively laminated safety glasses, and such glasses must include an interlayer of polyvinyl butyral (PVB) with certain properties. This means that PV modules – even those with a PVB interlayer – do not comply with the requirements of the Construction Products Lists and either require a backing pane of laminated safety glass or a National Technical Approval or individual approval. And a PV module with a backing of laminated safety glass is a heavier, three-pane construction with corresponding consequences for the loadbearing construction. Facades with a ventilation cavity must also comply with DIN 18516-4 “Back-ventilated, non-loadbearing, external enclosures of buildings, made from tempered safety glass panels; requirements and testing”. This standard regulates the use of heatsoaked toughened safety glass. The heatsoak test prior to sale eliminates panes

with nickel sulphide inclusions, which tend to break spontaneously. The standard permits linear supports on two, three and four sides, and also point supports in the form of edge clamps (see “Photovoltaics case studies”, pp. 90 – 91). The use of monolithic PV modules (glass/plastic) or glass/glass laminates using heat-soaked toughened safety glass is not directly addressed in the standard but is up to the discretion of the building authority responsible. Other module configurations complying with the TRLV may be possible. Curtain wall-type facades, e.g. post-andrail or prefabricated designs, in the form of modular products are covered by the product standard DIN EN 13830 and require a CE marking. The system supplier can test the PV components as part of a facade and include them in his proof of conformity. Part II of the MLTB prescribes the national application regulations as the basis for verifying the structural safety. Overhead glazing The TRLV includes more stringent requirements to deal with the higher safety risks of sloping or horizontal glazing above areas used by persons. Only wired glass or laminated safety glass made from float or heat-strengthened glass with a National Technical Approval may be used for single glazing or as the lower pane of insulating glazing. Such glazing provides adequate residual loadbearing capacity and is able to bond fragments together and prevent them falling onto persons below. Laminated safety glass made from toughened safety glass is not permitted because of its inferior residual loadbearing capacity. Accordingly, PV modules require at least a three-pane configuration with a backing of laminated safety glass. Other module configurations made from regulated glass products are possible when, for example, nets (max. mesh size 40 mm) are spanned below the 75

Technical rules and building legislation Non-regulated building products and forms of construction

5

6

glass to prevent whole panes or dangerous fragments from falling onto circulation zones below. PV overhead glazing is not usually a problem in conjunction with multipane insulating glass either because the lower pane can almost always be made from laminated safety glass (Fig. 6). However, no holes whatsoever may be drilled in this and so it is best for the connecting cables to exit the modules at the side. Pointsupported overhead glazing requires an individual approval, National Technical Approval or European Technical Approval because the TRPV is restricted to laminated safety glass. Overhead glazing accessible for cleaning, maintenance and repair purposes only (Fig. 7) located above an area that cannot be cordoned off for the duration of the work will require an individual approval in which tests are carried out to establish the load-carrying capacity of the glazing. Glazing for foot traffic Glazing accessible to building users, possibly even the public, as part of a circulation zone will be subjected to much higher loads than glazing only accessible for cleaning, maintenance and repairs. The TRLV mentions only stair treads or stair landings and then only to a very limited extent, which means that virtually all conceivable PV applications will require a National Technical Approval or individual approval. The minimum configuration is three panes, the uppermost of which is a sacrificial wearing course. In addition, the client or the relevant employers’ liability insurance association may require a non-slip surface finish, e.g. in the form of printing on the topmost pane (Fig. 8). Since the effect of printing, foot traffic and the additional pane of glass will reduce the efficiency considerably, integrating solar cells into glazing for traffic areas can only be an option in exceptional circumstances. 76

Glazing in safety barriers Where accessible areas are more than 1 m higher than adjacent areas, vertical glazing must in certain circumstances prevent persons falling to the lower area. This is frequently the case with the storey-high glazing of modern office blocks, but can also apply to the spandrel panels in postand-rail designs or glazed walls and balcony balustrades. A person colliding with the glazing should not suffer any injuries and on no account should be able to fall through the glass. If the glass is broken, the fragments should be blunt and should not be able to fall onto the lower area. The requirements that go beyond those of the TRLV are contained in the TRAV. As the rules permit the use of a regulated product only when laminated safety glass is used, PV modules will require a National Technical Approval or individual approval. Both involve testing, e.g. pendulum impact tests, to assess the performance of the modules. Non-regulated building products and forms of construction The technical rules introduced by the building authorities reflect empirical values obtained with proven forms of construction and therefore guarantee an adequate level of safety. Non-regulated building products – with the exception of those in BRL C – and non-regulated forms of construction must be tested individually to ensure their suitability for the intended application. The so-called verification of applicability for building products or forms of construction can be effected in various ways (Tab. T4): • National Test Certificate (AbP) • National Technical Approval (AbZ) • Individual approval (ZiE) • European Technical Approval (ETA) in conjunction with national restrictions National Test Certificate (AbP) A National Test Certificate involves the

least work but does require the use of building products according to BRL A part 2 or forms of construction according to part 3 with minimal safety requirements for which acknowledged testing methods exist (Tab. T4). The certificates are generally valid for five years and are issued by testing institutes approved by the building authorities. Roof-integrated PV modules can be certified as “hard roof coverings” in this way (see p. 79). National Technical Approval (AbZ) When a building product or form of construction is used frequently in an identical way but a National Test Certificate is not possible, then a National Technical Approval may be the answer. In order to obtain a National Technical Approval, the manufacturer must submit an application to the German Institute of Building Technology (DIBt). National Technical Approvals are often available for glass products such as laminated safety glass made from heat-strengthened glass or laminated safety glass with special interlayers whose properties differ from those of PVB. Owing to the relatively expensive and time-consuming procedure, approvals for PV modules have so far been few and far between. The programme of verification consists of tests on components, assessments of stability and reports by experts. The DIBt, and, if applicable, the expert committees consulted, together with representatives from building authorities, research, testing centres and industry decide on the requirements for the respective building product or form of construction depending on the proposed use or application. Typical forms of construction with National Technical Approvals are canopies or sunshading systems in all manner of variations. Manufacturers can include the integration of solar cells in the approval as an option in order to avoid the need for individual verification

Technical rules and building legislation Experimental testing

5

6

7

8

7

8

for each project. National Technical Approvals are generally valid for five years, are restricted to the application(s) specified in the approval and stipulate dimensions, design and construction. The approval applies only to the system of the applicant and not to identical copies by other manufacturers. European Technical Approval (ETA) Supplementing the technical approval at national level is an alternative at European level, the European Technical Approval. In Germany the DIBt is responsible for ETAs as well as National Technical Approvals. Guidelines are available for some building products or forms of construction (European Technical Approval Guideline, ETAG), and these simplify the approval procedure. For example, ETAG 002 specifies the requirements for structural sealant glazing (SSG). The guideline is restricted to adhesive joints that are produced in controlled factory conditions to connect the glass to a metal loadbearing frame so that the resulting facade element can be fixed to a traditional post-and-rail construction. In contrast to a National Technical Approval, the content of the ETA is, however, restricted to the specification of the product. Stipulations regarding usage and dimensions are not included and are the responsibility of the respective EU member state in which the project is being realised. In Germany the MLTB permits only certain forms of construction, which are also dependent on the height of the installation above ground level (see “Construction and integration”, pp. 52–54). In addition, the silicone adhesive used itself requires a national technical approval if it is to be used in this form of construction. An ETA is generally valid for a period of five years. However, glued glass assemblies can continue to be built based on the stipulations of a National Technical Approval or individual approval.

Individual approval (ZiE) If no approvals are available and a National Test Certificate is not an option, non-regulated building products and forms of construction require an individual approval. This is the most common variant in the case of building-integrated PV installations. The client must submit his application to the senior building authority of the federal state in which the project is located. An individual approval is valid for one specific construction project only and cannot be transferred to other projects, even if these are similar or even practically identical. However, it may be possible to use the documentation used for obtaining the initial individual approval to apply for further individual approvals, thus simplifying the whole procedure. Where building products and forms of construction do not differ significantly from the technical rules, the senior building authority may even waive the individual approval requirement in certain cases. Following several test cases, some federal states now issue an individual approval – which has been applied for merely because a PV element, a non-regulated building product, is being used in place of conventional glazing – relatively quickly and without excessive bureaucracy. However, an individual approval is not a substitute for approval for the building as a whole. In principle, planners must contact the senior building authority responsible at an early stage in order to agree on the procedure, the institutes and specialists that should be involved and the scope of the analyses, certification and component testing. In doing so, it is also possible to clarify whether any changes to the design are possible that might render certain tests superfluous. The costs and duration of the procedure differ considerably from state to state. Besides experimental investigations and reports, the authority may also demand supervision of the work on site.

Vertical glazing with PV modules in 36 mm thick multi-pane insulating glass units. Post-and-rail curtain wall. Fashion store, Cologne (D), 2002, Georg Feinhals architectural practice Overhead glazing (insulating glass) as a regulated type of construction according to the TRLV: 6 mm heat-strength. glass, 3 mm float glass w. part. transparent amorphous silicon coat., cavity, 8 mm lam. safety glass. Primary school, Munich (D), 2003, Krug & Partner Architekten Partially transparent glass/glass laminate made from heat-strength. glass which as overhead glazing designed for occasional foot traffic requires a ZiE with verification of residual loadbearing capacity. Berliner Hauptbahnhof, Berlin (D), 2006, von Gerkan, Marg & Partner Glazing for foot traffic with non-slip printing: 6 mm low-iron tough. safety glass, PVB, 12 mm low-iron heat-strength. glass, PVB, polycrystalline solar cells, PVB, 12 mm heat-strength. glass with printing on underside (light blue). “Monument to the Sun” in Zadar (HR), 2007, Nikola Bašić

Experimental testing Approval or authorisation procedures for non-regulated building products or forms of construction frequently require experimental tests to be carried out. The application-related requirements specified by the senior building authority vary from state to state and depending on the authority’s approach to photovoltaics. Many building-integrated PV designs, however, involve the same obligatory standard tests as for conventional glazing. Such tests must always be carried out on specimens that are identical to the original components with respect to module configuration, support conditions and other factors. Overhead glazing Designs outside the scope of the TRLV must be tested to verify the residual loadbearing capacity of overhead glazing that has been damaged. This is to ensure that the PV elements, once broken, remain securely in their fixings until the area below has been completely cleared and cordoned off. To test this, the glazing, already subjected to a uniformly distributed load, is struck in such a way that the most unfavourable cracks are caused in both panes of the laminated safety glass. Afterwards, the damaged glazing must carry the load for at least 24 hours, depending on the potential risks, without failing completely and without any broken fragments falling to the floor below. The load per unit area is applied by way of sacks of sand, for example, which are intended to simulate the load of snow or dust and dirt on the glazing. The actual weight of the sacks therefore depends on the intended location of the glazing. Whereas PVB and EVA films in PV modules guarantee a good residual loadbearing capacity, in modules with casting resin the “weave” effect of the interconnected solar cells can have a positive influence on the less favourable material behaviour of the resin (p. 79, Fig. 12). 77

Technical rules and building legislation Experimental testing

9 Testing the bending strength of a glass substrate with thin-film solar cells; coaxial double ring test to DIN EN 1288-5 10 Four-point bending test for determining the deformation behaviour and shear bonding of thin-film PV modules 11 Pendulum impact test for verifying the impact strength of a glazed safety barrier according to the TRAV; the example shown here is a glass infill panel to a balcony balustrade. The testing centre also assesses the suitability of the glass retention. 9

Glazing for occasional foot traffic The component testing regime includes tests to establish whether a glass component designed for foot traffic is able to carry the intended loads after the topmost layer of glazing has been damaged by an impact. In a worst-case scenario, a person carrying a plastic bucket containing 10 l of water/ cleaning agent drops a hard tool and then falls onto the glass himself. This test generally adheres to the principles for testing and certifying glass for constant or occasional foot traffic (GS-BAU-18). In this test a 100 kg weight, intended to simulate a person, is twice applied to an area measuring 200 x 200 mm on the damaged topmost pane of glass, each time for 15 minutes. In between, an impact body is dropped onto the pane from a height of at least 1.2 m to represent a falling person. The impact body in this case is a linen sack filled with glass beads weighing 50 kg. During the test, the glazing may neither slip out of its fixings nor be penetrated by the impact body, and no fragments of glass are allowed to fall out and endanger a circulation zone below. Glazing for constant foot traffic In this case proof of adequate impact resistance is tested with a hard impact simulated by a steel body weighing 40 kg, the top part of which is cylindrical, the bottom conical. This is allowed to fall from a height of 800 mm onto the pane of glass

10

already subjected to half the intended imposed load in such a way that it causes maximum damage to the glass and its fixings. The imposed load represents the weight of several persons (each 100 kg applied to an area measuring 200 x 200 mm) in the most unfavourable loading arrangement. After passing the test successfully, the totally damaged glazing is tested for its residual loadbearing capacity: the glass must remain in place for at least 30 minutes and no fragments are permitted to fall out. Glazed safety barriers Pendulum impact tests provide experimental proof of the impact resistance of glazed safety barriers. The pendulum itself is in the form of a pair of tyres weighing 50 kg, which, depending on the form of the safety barrier construction, are swung against the glass from a height of 450, 700 or 900 mm to simulate the impact of a person on the glass (Fig. 11). In doing so, the pendulum may neither penetrate the glass nor dislodge it from its fixings. The laminated safety glass may break but should not exhibit any cracks with apertures exceeding 76 mm, and no fragments of glass are permitted to fall out. Special aspects of photovoltaics Although the mechanical behaviour of solar modules constitutes a inherent part of the electrical certification, such tests do not usually help when assessing

whether facades or glazing comply with building legislation requirements. As the manufacturers of PV elements use different intermediate layers which are not customary in the building industry, there is little experience so far regarding the loadbearing and composite behaviour at the relevant service temperatures. Added to this is the possible influence of the solar cells themselves. In particular, the glass substrates are damaged by the cell coatings and texturing used in thin-film applications and this alters the bending strength and bonding characteristics. Using standard tests for glass in building as a starting point, such fundamental material properties can be investigated successfully using small-scale specimens in tests with specific temperature and duration conditions. For example, a coaxial double ring test can be used to check the bending strength, or shearing, tensile and peeling tests the bonding strength under various loading conditions (Fig. 9). Research projects are currently investigating further properties using full-size modules and adapted methods of testing, e.g. the residual loadbearing behaviour by means of ball drop tests or the composite action of various module configurations by means of the four-point bending test (Fig. 10). The results could contribute to the qualification of PV elements within future building legislation.

T4: Verification of applicability for non-regulated building products and forms of construction National Test Certificate according to Model Building Code (MBO) cl. 19

National Technical Approval according to Model Building Code (MBO) cl. 18

Individual approval according to Model Building Code (MBO) cl. 20

European Technical Approval

Authority responsible

Testing institute approved by the building authority according to MBO cl. 25

German Institute of Building Technology (DIBt)

The senior building authority of the respective federal state

Germany: German Institute of Building Technology (DIBt)

Object of application

Non-regulated building products and forms of construction that are not required to satisfy significant safety requirements or can be assessed according to acknowledged methods of testing.

Non-regulated building products and forms of construction

Non-regulated building products and forms of construction

Non-regulated building products and forms of construction; use and design according to national application standards and regulations

Period of validity

Normally 5 years

Normally 5 years

Once only for building product/ form of construction described in application

Normally 5 years

78

Technical rules and building legislation Fire protection

11

12

Fire protection Fire protection measures are intended to prevent the outbreak of fires and the spread of smoke and flames (propagation of fire) and, in the event of a fire occurring, to enable people and animals to escape and effective fire-fighting and rescue operations to be carried out. In accordance with these protective aims, the MBO specifies requirements for the reaction to fire of building materials and the fire resistance of building components. Building materials are classed as follows: • incombustible • not readily flammable • flammable Building components are divided into the following three groups: • fire-retardant • highly fire-retardant • fire-resistant For example, depending on the particular application, the height of the building and the distance to neighbouring structures, it may be that only not readily flammable materials are permitted in a facade. BRL A part 1 allocates the building authority designations to the various national and European classes for testing and classification standards: DIN 4102 “Fire behaviour of building materials and building components” and DIN EN 13501 “Fire classification of construction products and building elements”. As the manufacturers of PV

13

modules do not normally classify their products, their reaction to fire in practical situations remains uncertain. A classification without a fire test is not possible for PV elements due to the lack of practical testing experience, but at best we are dealing with not readily flammable building materials because of the synthetic substances they contain, which may affect the fire load. Their use is therefore projectrelated and must be agreed with a fire safety specialist if the modules have to comply with specific fire protection legislation. For example, the MBO permits only incombustible building materials in certain buildings such as hospitals, places of assembly, retail premises or high-rise offices. An individual approval may be necessary. Special attention must be given to the routing of cables in order to minimise the fire load. Penetrations and cables passing through several fire compartments represent a problem in terms of fire protection. Protected routes for the cables, e.g. within the sections of the facade framework or in cable ducts, plus junction boxes as small as possible ease the granting of approvals. The MBO generally calls for a “hard roof covering” for the outermost layer of the roof – and hence for any PV elements integrated into the roof surface. Exceptions are possible in the case of, for example,

small unheated buildings or habitable rooms or if certain minimum clearances to the plot boundary and neighbouring structures can be maintained. A hard roof covering is one that demonstrates a qualified resistance to sparks and radiant heat. Such a roof covering prevents the propagation of fire across the roof and the spread of flames to the interior of the building. The hard roof coverings listed in DIN 4102-4 include, for example, clay tiles and min. 0.5 mm thick sheet metal, but not PV elements. Roof-integrated PV systems therefore require verification of applicability. The majority of manufacturers usually opt for the simple National Test Certificate. BRL A part 3 recognises fire tests to DIN 4102-7 or test method 1 to pre-standard DIN V ENV 1187 “Test methods for external fire exposure to roofs” as proof of compliance (Tab. T5). The identical tests evaluate the reaction to fire of roof coverings with the seat of the fire outside the building and involve a wire cage filled with wood wool being set alight on a representative specimen of the roof (Fig. 13). The fire may spread to a limited extent only and no burning or glowing material may fall down. References: [1] Model Building Code, MBO, Nov 2002 edition (all quotes are taken from this edition). [2] Baden-Württemberg Trade & Industry Ministry, 2005, p. 38.

T5: Extract from Construction Products List A part 3, edition 2008/1, or amendments, edition 2008/2 (non-regulated forms of construction that can be assessed according to acknowledged testing methods) No.

Form of construction

Verification of appli cability

Acknowledged testing method according to…

Attestation of conformity

1

2

3

4

5

2.8

Forms of construction for constructing roof coverings that must comply with requirements regarding resistance to sparks and radiant heat. Sentence 2 from No. 2.1 is also valid.

P1

DIN 4102-7:1998-07 or DIN V ENV 1187:2006-10 test method 1 in conjunction with DIN EN 13501-5:2006-03, DIN EN 13501-5 /corrigendum 1:2007-02 and annex 0.1.3 of Construction Products List A part 1

User’s attestation of conformity

1

P: National Test Certificate

12 Experimental verification of the residual loadbearing capacity of a PV overhead glazing unit for the summertime case with the solar cells heated to a temperature of 60 °C. Configuration: 6 mm heat-strength. glass, 2 mm casting resin with polycrystalline cells, 8 mm heat-strength. glass 13 Testing a roof covering’s resistance to sparks and radiant heat (hard roof covering) to DIN 4102-7 and DIN V ENV 1187 (pre-standard) by means of a fire on a sloping specimen of the roof with horizontal and vertical joints.

79

Photovoltaics case studies

82

Federal Environment Agency offices in Dessau Sauerbruch Hutton, Berlin

84

Institute premises in Beijing Mario Cucinella Architects, Bologna

87

Local government offices in Ludesch Hermann Kaufmann, Schwarzach

90

Paul Horn Arena in Tübingen Allmann Sattler Wappner, Munich

92

Sports hall in Burgweinting Regensburg Building Department, Tobias Ruf

94

Mixed commercial and residential building in Munich a+p Architekten, Munich

97

Additional residential storeys and new office building in Darmstadt opus Architekten, Darmstadt

100

Private house in Hegenlohe Tina Volz, Stuttgart Michael Resch, Langenargen

Reference: [1] Klobasa, 2005

81

Federal Environment Agency offices in Dessau

Architects:

Sauerbruch Hutton, Berlin Matthias Sauerbruch, Louisa Hutton Project team: Juan Lucas Young, Jens Ludloff Project managers: Andrew Kiel, René Lotz Structural engineers: Krebs & Kiefer, Berlin Energy concept: Zibell Willner & Partner, Cologne/Berlin Energy consultant: IEMB, Berlin PV consultant: Ingenieurbüro Lehr, Dessau Completed: 2005

A model project for innovative building, the 460 m long Federal Environment Agency (UBA) building wends its way demonstrably, dynamically and colourfully across the site of the former Wörlitzer railway station not far from the centre of Dessau. The winding form is a response to the particular and varied constraints of the urban surroundings and hence leads to differentiated spatial qualities both internally and externally. A semi-circular forum with a glass facade forms the entrance; there is space for public events and exhibitions here. Beyond this stretches the long, gardenlike atrium, covered by a fully glazed roof structure with integral sunshades. In terms of its materials and colouring, the external facade emphasizes the concept of the long building: 33 shades from seven basic colours divide up the building in chromatic gradations. Continuous, prefabricated spandrel panel elements clad with larch boards alternate with set-back windows and flush glass panels with coloured printing. Night-time ventilation of the offices is achieved via motorised vents behind opaque glass. Besides channelling daylight into the inner row of offices, both atrium and forum help to optimise the energy and climate balance: the entire building is ventilated via the roof of the central folded-plate structure, the internal courtyard functions as a thermal buffer zone. Thanks to highly insulated external walls, a solar thermal system and a large ground coupling, this office building almost achieves the energy standard of a passive house! The photovoltaic installation is integrated into the south-facing surfaces of the forum roof. The PV modules, in the form of glass /glass laminates, are fitted to the top half of each roof surface in order to remain clear of any shadows cast by the adjacent roof section.

Section Plan of ground floor Scale 1:2000 Axonometric view A 1 2 3 4 5

aa

6 7 8

a

8

3

? 1

8

4 7

8 7 2 8

6

a

82

Forum Lecture theatre Exhibition New library wing Former Wörlitzer railway station (library) Cafeteria Atrium Meeting zone

5

Photovoltaics case studies Federal Environment Agency offices in Dessau

Vertical section through roof Scale 1:20 9 Laminated safety glass, 16 mm, mounted on post-and-rail structure of steel hollow sections 10 Fabric sunshade, fire protection class B1, 0.43 mm 11 PV element, laminated glass made from 6 mm heat-strengthened glass + 8 mm heat-strengthened glass, with solar cells between the two panes embedded in 2 mm casting resin 12 Top and bottom chords of roof structure, Ø 219 mm steel circular hollow sections 13 Glass louvres, frameless, with electric drive, 12 mm laminated safety glass 14 Steel circular hollow section, Ø 140 mm 15 Steel tie, Ø 42 mm

12 11

13

14 9

10

15

12

A

Technical specification of PV installation: Size of installation

387 m2

(Rated) power output

32 kWp

Orientation, angle

south-east, 30°

Yield

approx. 25 000 kWh/a

CO2 saving1

approx. 14 600 kg/a

Location on building

roof-integrated (sawtooth roof), overhead glazing

Modules number dimensions configuration manufacturer

bespoke production 140 2040 ≈ 1340 mm glass/glass laminate Saint-Gobain Glass Solar, Aachen

Cells manufacturer

polycrystalline, blue ersol Solar Energy, Erfurt

Special features

28 % partial transparency due to low number of cells per unit area, individual approval

1

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of about 0.584 kg CO2 per kWh in Germany. [1]

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Institute premises in Beijing

Architects: Project team: Project management:

Mario Cucinella Architects, Bologna Elizabeth Francis, David Hirsch, Giulio Altieri Favero & Milan Ingegneria, Mirano/Beijing

Structural engineers:

Favero & Milan Ingegneria, Mirano/Beijing China Architecture Design & Research Group, Beijing Energy concept: Federico Butera, Milan Polytechnic PV consultants: Milan Polytechnic Favero & Milan Ingegneria, Venice Completed: 2006

The “Sino-Italian Ecological and EnergyEfficient Building” (SIEEB) on the campus of Tsinghua University in Beijing is the outcome of a joint Italian/Chinese project. The intention behind the project is to demonstrate the possibilities of energyefficient construction in China and at the same time establish a platform for longterm, international cooperation in the areas of energy and environment. On the north side the 40 m high institute building appears compact, presenting an essentially closed face to the cold winds of the Beijing winter; on the south side, however, facing the sun, it is much more open, with two wings – partly advancing, partly retreating – framing a courtyard. This arrangement maximises the amount of light and energy despite the presence of a neighbouring 10-storey tower. Breaking up the form of this expressive building even further are the cantilevering steel structures that support the fixed photovoltaic panels. The panels provide shade for the terraces and office facades below and supply 20 kWp from 190 solar modules each with an output power of 105 W. Feeding electrical energy into the public grid is not yet permitted in China and so the electricity generated is used in the building itself. The other facades are double-leaf designs. Printed glass curtain walls form the east and west elevations, with horizontal sunshades in the cavity and roller blinds on the inside. On the facades facing the courtyard there are horizontal, in some cases pivoting, glass louvres for controlling the solar gains and incoming daylight. Cooled or heated fresh air circulates at floor level and regulates the climate within the building. Gas-fired generators produce most of the additional electricity required; the waste heat is used for hot water and space heating.

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1 Reception 2 Student information 3 Foyer 4 Auditorium 5 Open passageway 6 Low-level courtyard with planting 7 Pond 8 Exhibition 9 Laboratory 10 Office 11 Terrace

Photovoltaics case studies Institute premises in Beijing

Technical specification of PV installation: Size of installation

150 m2

(Rated) power output

19.95 kWp

Orientation, angle

south, 35°

Yield

approx. 25 000 kWh/a

CO2 saving1

approx. 36 900 kg/a

Location on building

free-standing PV elements on terraces, sunshades

Modules Number, dimensions configuration manufacturer

bespoke production 190, 1900 ≈ 790 mm no details available EniTecnologie, San Donato Milanese

Cells manufacturer

polycrystalline EniTecnologie, San Donato Milanese

1

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of CO2. [1]

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Photovoltaics case studies Institute premises in Beijing

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1 Roof construction: 30 mm stone paving slabs 55 mm mortar bed concrete laid to falls 2 layers of bitumen sheeting 50 mm foam insulation vapour barrier 120 mm lightweight precast concrete elements 2 Partially transparent photovoltaic panel, frame of aluminium hollow sections, 38 ≈ 38 ≈ 4 mm 3 Steel hollow section, 150 ≈ 100 ≈ 8 mm 4 Steel channel, 300 ≈ 100 ≈ 15 mm 5 Steel flat stiffeners, 10 mm 6 Aluminium panel, 3 mm ventilation cavity 150 mm rock wool insulation 7 Laminated safety glass, 13 mm, printed with matt horizontal stripes 8 Insulating glass, 8 mm + 16 cavity + 10 mm 9 Floor panel of raised access floor tiled finish, 600 ≈ 600 ≈ 60 mm 10 Suspended ceiling: 4 mm aluminium 95 mm thermal insulation 11 Safety barrier, 17 mm laminated safety glass

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Local government offices in Ludesch

Architect: Project team:

Hermann Kaufmann, Schwarzach Roland Wehinger, Martin Längle, Norbert Kaufmann

Structural engineers:

Mader & Flatz, Bregenz merz kley partner, Dornbirn Energy concept: Synergy, Dornbirn PV consultant: Ertex Solar, Amstetten Completed: 2006

Three new buildings positioned to create a covered outdoor area; that was the idea behind this design, as a result of which the very heterogeneous structure of this little community, which has no old or mature centre, now has a true focal point for the first time. The loose relationship between the existing local public buildings, such as church, school and a hall, has now been given more substance. Amenities such as the local government offices, post office, café, shops, local societies’ headquarters and businesses plus a nursery and a small hall surround the new covered “village square”. Lively daily life beneath the shade of the roof, covered with partially transparent photovoltaic elements, is therefore guaranteed. The photovoltaic elements not only provide protection from the rain and shade from the sun, they also produce approx. 16 000 kWh of electricity every year. A total of 120 modules arranged like a sawtooth roof facing south-west make up the roof. The modules in glass/glass laminate form, each with an area of almost 2.5 m2, comply with the rules for overhead glazing and are designed to carry the heavy snowfalls usual in this region. In order to achieve both a maximum annual yield from the PV system and also a uniform appearance for the sawtooth roof providing protection from the sun, the solar modules are divided into three different electrical zones. The four bottommost rows of cells are permanently in the shade and therefore are merely dummies, not connected to the electrical installation. The middle rows of cells, which are shaded in winter by the adjacent roof members and snow, are interconnected to form a separate electrical circuit so that the efficiency of the topmost rows of cells is not impaired. The facades of the timber buildings are characterised by the interplay between the timber cladding and the vertical rough-sawn timber louvres, the large expanse of the frameless glazing and the precisely positioned steel elements.

Section • Plans Scale 1:800 1 2 3 4

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Business unit Library Post office Infant welfare centre 9 Office 10 Local government offices

Covered “village square” Café Multi-purpose hall Children’s play centre

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Photovoltaics case studies Local government offices in Ludesch

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1 Roof construction: elastomer-base bitumen sheeting with slate granule finish, 2 layers, 10 mm 2 No. 120 mm mineral wool thermal insulation EPS insulation with integral falls, 70 mm on average bituminous vapour barrier 27 mm rough-sawn diagonal boarding, spruce 110 ≈ 280 mm roof beams 280 mm timber ceiling hangers 40 mm sheep’s wool insulation acoustic fleece 20 ≈ 40 mm acoustic ceiling, silver fir 2 Laminated safety glass made from 2 No. 8 mm heat-strengthened glass 3 Steel plate edge beam, 8 + 15 mm 4 Photovoltaic element: laminated glass made from 6 mm low-iron toughened safety glass + 8 mm float glass, partiallyy transparent solar cells embedded in PVB in between 5 Silver fir cladding, 120 ≈ 40 mm 6 Glued laminated timber, 100 ≈ 240 7 Insulating glass: 6 mm toughened safety glass + 16 mm cavity + 6 mm float glass + 16 mm cavity + 6 mm toughened safety glass 8 Rough-sawn silver fir cladding, 120 ≈ 40 mm 9 Column, steel circular hollow section, Ø 159 ≈ 10 mm 10 Wooden window with thermal break and triple glazing, 51 mm, UW = 0.6 W/m2K (complete window: UG = 0.8 W/m2K)

Photovoltaics case studies Local government offices in Ludesch

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278.51 m2

(Rated) power output

18.05 kWp

Orientation, angle

south-west, 16°

Yield

approx. 16 000 kWh/a

CO2 saving1

approx. 13 400 kg/a

Location on building

open sawtooth roof

Modules number dimensions configuration manufacturer

bespoke production 120 1060 ≈ 2260 mm2 glass/glass laminate Ertex Solar, Amstetten

Cells

monocrystalline Sunways transparent solar cells, square Sunways, Constance

manufacturer Special features

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18 % partial transparency, inactive cells over lower quarter (also shaded in summer), second quarter from below interconnected separately (only shaded in winter)

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of CO2.

89

Paul Horn Arena in Tübingen

Architects: Project team:

Allmann Sattler Wappner, Munich Dirk Bauer, Birgit Bader, Eva Hartl, Kai Homm, Christof Kilius, Thomas Meusburger, Martin Plock, Ulf Rössler, Steffen Schwarz Structural Werner Sobek Ingenieure, engineers: Stuttgart Energy concept: Transsolar Energietechnik, Stuttgart PV consultant: SunTechnics Fabrisolar, Küsnacht Completed: 2004

This multi-function facility is located in the immediate vicinity of the sports grounds in Tübingen and the spacious open-air swimming pool complex along the banks of the River Neckar. The hall has to serve a variety of sports and so it was necessary to exploit not only the full internal volume in the concept, but also the external walls as well! All four facades have additional functions as well as just providing protection from the weather, e.g. complete solar facade, outdoor climbing wall, half-pipe. Inside, the sports arena itself, one floor lower than the surrounding ground, is naturally the central focus of the building; the seating for spectators on all sides accommodates the change in level. The entrance level serves as a circulation and service zone, the changing rooms are located in the basement and special events can be held on the upper level. The roof to the sports hall is carried by steel girders which are supported on fair-face concrete external walls and three service cores. The minimum possible consumption of primary energy and the use of natural resources form the heart of the energy concept. White-framed solar modules with a shimmering green appearance occupy the entire surface of the south-west elevation. The modules, in four different sizes, were specially developed for this project and consist of a total of 20 000 solar cells. The shimmering green appearance of the facade specified in the design brief was achieved through precise adjustment of the thickness of the antireflection coating. An individual approval was granted without the need for testing because the point-fixing system in conjunction with the laminate configuration used here for the solar modules had already been proved in practice a number of times. All the electricity generated is fed into the public grid.

Section Plan of ground floor Scale 1:1000 Vertical section Scale 1:20

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Photovoltaics case studies Paul Horn Arena in Tübingen

1 2 3 4 5

Spectator concourse/ players’ entrance Gallery Playing area Halfpipe/streetball area Roof construction: extensive rooftop planting 50 mm substrate 50 mm drainage and filter sheet waterproofing, elastomer-base bitumen sheeting 140 mm thermal insulation, rock wool with bitumen coating vapour barrier, elastomer-base bitumen sheeting acoustic insulation in ribs, fleece facing 100 ≈ 275 ≈ 0.75 mm steel trapezoidal profile sheeting

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Wall construction, photovoltaic facade: glass/plastic laminate, 8 mm toughened safety glass with solar cells embedded in EVA, white backing sheet on support brackets, supporting framework wall mounting (sliding/fixed supports) 85 mm air cavity 100 mm mineral wall with fleece facing 300 or 360 mm reinforced concrete Wall construction, post-and-rail facade with fixed glazing: solar-control glass with internal glare screen, argon-filled cavity, 50 % silk-screen printing on outer pane

5

Technical specification of PV installation: Size of installation

525 m2

(Rated) power output

43.7 kWp

Orientation, angle

south-west, 90°

Yield

approx. 30 000 kWh/a

CO2 saving1

approx. 17 500 kg /a

Form of construction

individual fixings in open joints cladding in front of ventilation cavity

Modules number dimensions

bespoke production 970 4 different module sizes standard module 511 ≈ 1008 mm, 3 ≈ 7 cells frameless glass/plastic laminate GSS Gebäude Solar Systeme, Löbichau

configuration manufacturer Cells manufacturer

polycrystalline, green Sunways, Constance

Special features

solder tracks covered along the edges to achieve a uniform white edge to the laminate

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6

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of about 0.584 kg CO2 per kWh in Germany. [1]

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Sports hall in Burgweinting

Architects:

Regensburg Building Department, Tobias Ruf

Structural engineers: Ingenieurbüro Graf, Regensburg Energy concept: Regensburg Building Department Fraunhofer ISE, Freiburg PV design: Regensburg Building Department Fraunhofer ISE, Freiburg Grammer Solar, Amberg Completed: 2004

The position of the existing facility and urban planning stipulations resulted in a long south-facing facade to this new single sports hall in Regensburg. So right from the very start of the planning work the question was how to make best use of this facade, which, left unconsidered, would have an adverse effect on the interior climate. In conjunction with the Fraunhofer ISE (Institute for Solar Energy) in Freiburg and with financial support from the innovation programme of the German Environment Foundation and the Federal State of Bavaria, the design team developed multi-functional, partially transparent photovoltaic modules and integrated them into the insulating glass of the high-level glazing on the south side of the building. Computer simulations and tests in the lighting laboratory helped the team devise the optimum glazing configuration to suit the requirements. The polycrystalline silicon cells are embedded in casting resin between the two panes of safety glass at what was discovered to be the ideal spacing of 20 mm. The daylight that enters between the cells ensures optimum illumination of the interior. The inner pane of the insulating glass can resist ball impacts and the two matt PVB interlayers scatter the incoming light; a transparent low E coating on the inside of the outer pane reflects the heat in summer and reduces heat losses in winter. Lightscattering glazing on the east and west ends of the hall eliminate any direct glare from the sun. On the north elevation, transparent low E glazing completes the whole spectrum of different degrees of light permeability. To ensure ventilation and night-time cooling of the hall, internal and external heat sensors control the vacuum panel louvres concealed behind the wooden cladding on the lower part of the walls at the east and west ends.

Sections Plan of upper floor Scale 1:400 6

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Entrance Showers Changing room Sports hall Connecting corridor Existing building

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Photovoltaics case studies Sports hall in Burgweinting 8 Technical specification of PV installation: 7

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Size of installation

117 m2

(Rated) power output

10.07 kWp

Orientation, angle

south, 90°

Yield

approx. 6800 kWh/a

CO2 saving1

approx. 4000 kg /a

Form of construction

post-and-rail facade with aluminium clamping bars

Modules number dimensions configuration manufacturer

bespoke production 98 main module: 2115 ≈ 1096 mm, frameless insulating glass Saint-Gobain Glass Solar, Aachen

Cells manufacturer

polycrystalline, blue ersol, Erfurt

Special features

zero glare with uniform illumination of the interior; light-scattering PVB sheet light transmittance, direct radiation = 0.0 light transmittance, diffuse radiation = 0.3

12 11 1

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of about 0.584 kg CO2 per kWh in Germany. [1]

7 Roof construction: 100 mm gravel, 16/32 mm grading 1.5 mm waterproofing 100 –50 mm insulation with integral falls 100 mm thermal insulation 4 mm bituminous vapour barrier with aluminium inlay 30 mm timber sheathing 100 ≈ 200 mm secondary purlins 40 ≈ 60 mm battens with 40 mm acoustic insulation in between, fleece 24 ≈ 48 mm battens 8 Sheet aluminium finish, 3 mm 5 mm drainage sheet 20 mm vacuum insulation panel 6 mm sheet steel fixed with aluminium clamping bars 80 x 60 mm timber framework 9 Outer pane: lam. glass made from 4 mm heat-strength. glass, 2 mm PV cells embedded in casting resin, 6 mm heat-strength. glass, 10 mm cavity Inner pane: 8 mm lam. safety glass with 2 No. matt interlayers, ball impactresistant 10 Glulam rail, 80 ≈ 160 mm

13

11 Glulam post, 160 ≈ 300 mm 12 Trussed glulam roof beams 13 Stainless steel perimeter heating pipe, Ø 36 mm 14 Wall construction: 40 ≈ 55 mm larch battens insect screen 40 ≈ 48 mm battens, glaze finish, waterproofing 60 ≈ 120 mm posts and rails, with 120 mm thermal insulation in between 350 mm reinforced concrete 60 ≈ 120 mm posts and rails 60 ≈ 80 mm battens 19 ≈ 47 mm fir lining, glaze finish 15 Floor construction: 4 mm linoleum 2 No. 9 mm plywood 15 mm PUR rebound foam 35 mm underfloor heating 2 No. 0.6 mm metal heat diffusion plates 100 mm thermal insulation 0 –20 mm loose fill levelling layer waterproofing 200 mm reinforced concrete

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Mixed commercial and residential building, Munich

Architects: Assistant: Energy concept: PV consultant: Completed

a+p Architekten, Munich Claudia Heiß Kulle & Hofstetter, Munich Kulle & Hofstetter, Munich 2004

An inner court in Munich surrounded by fire walls with garages and a dilapidated two-storey commercial building – an obvious case for an infill development and a challenge for the architects. The existing building has made way for a new fourstorey structure that in no way has to hide itself. The ground and first floors contain offices, the two floors above form a maisonette, and on the roof there is a terrace that can be used by the office staff. In order to maintain the required clearances to the neighbouring buildings and also to improve the quality of the living conditions in the maisonette, the building steps back on the north and east sides. The north facade is a plain fire wall without openings, merely narrow window slits on the upper floors to illuminate the ancillary rooms on this side of the building. The strictly segmented west facade of the building, facing the inner court, consists of storey-high elements. Tall fixed lights paired with narrower full-height opening lights behind transparent spandrel panels as safety barriers alternate with panels of the same height each consisting of four thin-film photovoltaic modules. The frameless laminates, separated only by thin black silicon joints, appear to be single units; metal strips delineate the vertical edges. These photovoltaic panels form the cladding between the windows and feed the electricity they produce into the building’s electrical installation. As the glazing constitutes more than 50 % of the facade area, shading to prevent overheating of the rooms on hot, sunny days is necessary. This is provided in the form of sliding aluminium louvre shutters that are neatly parked behind the stationary photovoltaic panels when not in use and therefore protected against the weather.

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Photovoltaics case studies Mixed commercial and residential building, Munich

Technical specification of PV installation:

Location plan Scale 1:1250 Section Plans Scale 1:250 1 2 3 4 5 6 7 8

Entrance Secretariat Office Meeting room Server room Plant room Bedroom Room for guests

Size of installation

41 m2

(Rated) power output

3.9 kWp

Orientation, angle

south-west, 90°

Yield

approx. 2000 kWh/a

CO2 saving1

approx. 1200 kg /a

Location on building

facade-integrated, ventilation cavity

Modules number dimensions configuration manufacturer

standard 56 1200 mm ≈ 600 mm glass/glass laminate Würth Solar, Schwäbisch Hall

Cells manufacturer

CIS Würth Solar, Schwäbisch Hall

Special features

feeding into building network

1

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of about 0.584 kg CO2 per kWh in Germany. [1]

95

Photovoltaics case studies Mixed commercial and residential building, Munich

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Precast concrete element, 230 mm, 8 with thermal activation 120 mm thermal insulation 80 ≈ 80 mm steel angle frame 31 mm photovoltaic module in aluminium frame Wooden window with insulating 9 glass: 5 mm tough. safety glass + 16 mm cavity + ESG 5 mm tough. safety glass Spandrel panel, 12 mm lam. safety glass Photovoltaic element: 4 mm heat-strength. glass + 3 mm 10 float glass with CIS coating embedded in EVA, clamped in steel frame and sealed Aluminium sliding shutter, 35 mm Precast fair-face concrete element, 80 mm, water-repellent finish 200 mm reinforced concrete separating joint board, 20 mm glass wool

8 masonry (existing) Extensive rooftop planting 140 mm XPS thermal insulation root barrier waterproofing 40 –160 mm reinforced concrete with integral falls 12 mm wood-block flooring floating asphalt subfloor, 50 mm separating layer, PE sheet 35 mm impact sound insulation 280 mm reinforced concrete Ground floor construction: 25 mm stone tiles 25 mm mortar bed 75 mm floating screed separating layer 25 mm impact sound insulation 200 mm reinforced concrete separating layer 100 mm XPS thermal insulation 50 mm blinding

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Additional residential storeys and new office building in Darmstadt

Architects:

opus Architekten, Darmstadt Anke Mensing, Andreas Sedler

Structural engineers:

Ingenieurbüro Schlier & Partner, Darmstadt Energy concept: inPlan, Pfungstadt PV consultants: opus Architekten, Darmstadt BUSO, Berlin Completed: 2007

Location plan Scale 1:1500

An unsightly opening in a 100-year-old perimeter block development in a residential area of Darmstadt has now been filled in. The architects closed the gap with a fully glazed office building and also added two storeys to the (formerly two-storey) building alongside, which now contains two maisonettes. A shared staircase links old and new with their disparate storey heights. The front facade of the new office building consists of storey-height tripleglazed elements. Contrasting with this, the high plinth below ground floor level – aligned with the string courses of the existing buildings on either side – has a steel-

grey cladding concealing the garage behind. On the existing building containing the new maisonettes, only the continuous glazing below the eaves discloses the fact that alterations have taken place here. In fact the facade directly below the glass is also new, but has been built in the same style as the existing floors below. The east-west alignment of the building enabled solar technology to be incorporated over the whole of the pitched roof. Photovoltaic elements occupy the entire west half of the roof, whereas on the east side (the road side), half of the roof is in the form of solar collectors providing hot water for the

building and assisting the space heating. On this side there is minimal partial shading when the sun is in a certain position. This is not a problem for the solar thermal system, but led to the disconnection of one entire string of the PV modules. The grey colouring of the elements and their small-format appearance enables them to blend in well with the sheet metal and slate roof coverings of the neighbourhood.

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Photovoltaics case studies Additional residential storeys and new office building in Darmstadt

Technical specification of PV installation: Size of installation

72 m2

(Rated) power output

8.64 kWp

Section • Plans Scale 1:250

Orientation, angle

east-west, 32,5°

Yield

approx. 7500 kWh/a

1 2 3

CO2 saving1

approx. 4400 kg /a

Location on building

roof-integrated, ventilation cavity

Modules number, dimensions configuration manufacturer

bespoke production 72, 1000 ≈ 1000 mm frameless glass/plastic laminate Solea, Plattling

Cells manufacturer

monocrystalline, anthracite Sharp, Hamburg

Special features

solar roof system: PV installation and solar thermal system with identical appearance

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Staircase Office Corridor, kitchenette, WC Bedroom/bathroom Child’s room Playroom Kitchen Living/dining room Rooftop terrace

1

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of about 0.584 kg CO2 per kWh in Germany. [1]

11 Solar roof, 100 mm: phovovoltaic modules, ventilation cavity solar thermal system, thermally insulated 60 ≈ 60 mm battens waterproofing 22 mm OSB 240 ≈ 80 mm timber purlins, on 4 No. steel frames, HEB 140 sections, notched 240 mm mineral wool thermal insulation vapour barrier 40 ≈ 60 mm counter battens with 60 mm mineral wool thermal insulation in between 2 No. 12.5 mm plasterboard, skim coat finish 12 Eaves fillet, 70 mm solid timber 13 Steel section, HEB 140 14 Aluminium window with triple glazing 15 Wall construction: 25 mm render 200 mm mineral wool thermal insulation 175 mm clay brickwork 15 mm plaster 16 Floor construction: 22 mm oak wood-block flooring 35 mm screed 10 mm impact sound insulation 200 mm hollow precast concrete planks laid in steel frame of HEB 140 sections 15 mm plaster

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Photovoltaics case studies Additional residential storeys and new office building in Darmstadt

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Private house in Hegenlohe

Architects: Structural engineer: Energy & PV consultant: Completed:

Tina Wolf, Stuttgart, Michael Resch, Langenargen Ingenieurbüro Dieter Heller, Ulm ee-plan Thomas Stark, Stuttgart 2003

This private house with a floor area of 290 m2 for the client and a separate 35 m2 apartment is located in an area set aside for new housing in the Mittlerer Schurwald nature conservation area. The stipulation in the local development plan called for a pitched roof with a slope of 20 – 35°. In order to realise the client’s requirement for energy exclusively from renewable sources, 66 photovoltaic modules arranged to match the layout of the building below were mounted above the roof. Concrete roof tiles in an anthracite colour proved to be the most economic option for waterproofing the roof and installing the PV system. The size of the solar panels was determined from calculations of the building’s electricity needs. In order to achieve the area of 120 m2 required, an asymmetric pitched roof was constructed. An exemption permitting the 18° pitch necessary for this roof design was approved. However, the electricity generated is not used directly in the building itself, but rather fed in its entirety into the public grid. The yield of approx. 11 000 kWh/a is adequate for the average household requirement of approx. 3500 kWh/a plus approx. 6500 kWh/a for operating the heat pump. Consequently, the client’s desire to construct a zerocarbon house has been satisfied. In order to optimise the efficiency of the heat pump, two ground couplings were installed in 99 m boreholes. Thanks to the highly insulated building envelope and the choice of a very compact design (A/V ratio 0.58), a specific heating energy requirement of approx. 40 kWh/m2a has been achieved. The mass of the concrete walls together with the floor built into the sloping ground, which also acts as a heat sink, curtail temperature peaks and contribute to a pleasant interior climate in the summer, too.

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Entrance Separate apartment Room Plant room Cellar Low-level yard/garage

Photovoltaics case studies Private house in Hegenlohe

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120 m2

(Rated) power output

12 kWp

Orientation, angle

south-west, 18°

Yield

approx. 11 000 kWh /a

CO2 saving1

approx. 6400 kg /a

Form of construction

rooftop stand-off system

Modules number dimensions

bespoke production 66 1700 ≈ 1000 mm and 1750 ≈ 1000 mm frameless glass/plastic laminateSunset Energietechnik, Adelsdorf

configuration manufacturer Cells manufacturer

polycrystalline, dark blue unknown

Special features

German Solar Prize 2005

1

Using solar electricity or feeding it into the public grid replaces conventional electricity and therefore avoids the emission of about 0.584 kg CO2 per kWh in Germany. [1]

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bb 7 Ridge purlin, HEA 180 steel section 8 Photovoltaic element: glass/plastic laminate, 4 mm tough. safety glass with solar cells embedded in EVA, backing sheet, anthracite, aluminium rafter anchors 9 Roof construction, U = 0.14 W/m2K: concrete roof tiles, anthracite 30 ≈ 50 mm battens 30 ≈ 50 mm counter battens 16 mm wood-based board product, vapour-permeable 50 mm mineral wool thermal insulation 80 ≈ 200 mm rafters with 200 mm mineral wool thermal insulation in between vapour barrier 2 No. 12.5 mm plasterboard 10 Intermediate purlin, HEA 200 steel section 11 Steel flats, 12 ≈ 100 mm, supporting larch louvres, 18 ≈ 100 mm 12 Wall construction, U = 0.21 W/m2K: 30 ≈ 35 mm mountain larch battens, 10° splay 30 ≈ 50 mm counter battens polyester fleece on 2 No. 80 mm mineral wool 200 mm reinforced concrete 13 Sheet titanium-zinc verge capping plastic-faced separating layer 30 ≈ 550 mm verge board 14 Reinforced concrete, 200 – 300 mm

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Appendix

Glossary Absorption Designation for the retention of incident electromagnetic waves in a material. The opposite of ∫ transmission. AC ∫ alternating current Air Mass (AM) The measure of the relative length of the path of sunlight through the atmosphere as a multiple of the shortest path when the sun is perpendicular to the earth’s surface, i.e. directly overhead. The mass of the atmosphere reduces the intensity of the radiation as the AM factor increases. AM 1.5 represents the average spectral composition of the sunlight in Central Europe. Albedo Measure of the “whiteness”, i.e. the reflecting power of a surface, expressed as a percentage. Light-coloured surfaces reflect a high proportion of the incident sunlight in the form of ∫ diffuse radiation and therefore have a high albedo value. Alternating current (AC) An electric ∫ current with an alternating direction of flow, e.g. in sine-wave form in public grids with a frequency of 50 Hertz [Hz]. Amorphous silicon (a-Si) Non-crystalline ∫ silicon with a random atomic structure used for producing thin-film solar cells. Angle of inclination Mounting angle of ∫ PV modules relative to the horizontal. Anti-reflection coating A thin, transparent coating applied to crystalline solar cells or the coloured glasses of modules to reduce the amount of ∫ reflection. The coating minimises reflection losses and therefore increases the ∫ conversion efficiency of a ∫ solar cell or ∫ PV module. Azimuth angle 1. Angle between module surface and due south (orientation). 2. Angle between sun and due south. Backing material The laminating material and/or the backing layer visible between the ∫ solar cells and around the edges of a crystalline ∫ PV module. Both can be exploited for architectural purposes. Bi-facial solar cells ∫ Solar cells that absorb the incident light on both the front and rear sides and convert it into electricity. Bonding of fragments A necessary property of ∫ laminated safety glass. Upon breakage, the fragments of glass are held together by the ∫ PVB interlayer. Bowing and dishing effect An optical effect caused by the convex and concave deflections of the individual panes of ∫ multi-pane insulating glass. The cause is the relative change in the air pressure in the ∫ cavity compared to that of its surroundings. The bowing and dishing effect is particularly evident in ∫ reflections. Bypass diode Component for conducting electricity past shaded or faulty groups of cells in order to protect them against overheating (∫ hotspot) and to limit the output losses of other cells and modules connected in series. Cadmium telluride (CdTe) ∫ Semiconductor material for thin-film ∫ solar cells. Casting resin Clear intermediate material for ∫ laminated glass that is applied as a liquid between the two panes to be joined and subsequently cures through exposure to heat or ultraviolet radiation. Cavity 1. Hermetically sealed volume between two adjacent panes of a ∫ multi-pane insulating glass unit. 2. The space between the panes of a ∫ multi-pane insulating glass unit. CE marking In the building industry the obligatory proof of conformity for products that may only be marketed and traded in accordance with European regulations. Charge carrier An electrically charged particle. In semiconductor physics thermal or optical excitation creates pairs of positive and negative charge carriers. Liberated

∫ electrons have a negative charge, whereas the gaps at their original positions act as positive charge carriers. Clamp fixing Point- or linear-type U-shaped fastener that encloses the edge of the ∫ glass and hence supports the pane without penetrating it by way of a ∫ nonpositive and a ∫ positive connection. Coated glass ∫ Glass products with a coating of uniform thickness applied in order to change its physical properties. Glass /plastic laminates fall under this heading. Construction Products List (BRL) This is published by the German Institute of Building Technology (DIBt) and contains the technical rules for building products and forms of construction. The BRL is made up of three lists, A, B and C. BRL A part 1: regulated building products. BRL A parts 2 and 3: non-regulated building products (part 2) and forms of construction (part 3) that require only a ∫ National Test Certificate instead of a ∫ National Technical Approval. BRL B: building products that may only be marketed and traded according to European regulations. List C: non-regulated building products that do not require a ∫ verification of applicability. Consumer meter Calibrated electricity meter for measuring consumption for invoicing purposes. Conversion efficiency The efficiency of an energy conversion; in PV applications the ratio of electrical ∫ energy supplied, or the ∫ output power, to the incident ∫ solar radiation. We distinguish between cell, module and system efficiency depending on the reference output and area. The system efficiency also includes the losses due to the ∫ system technology. Copper-indium diselenide, copper-indium disulphide (CIS) ∫ Semiconductor material for thin-film ∫ solar cells, alloyed with gallium as an option. Crystalline silicon (c-Si) ∫ Silicon with a monocrystalline or polycrystalline atomic structure for producing ∫ wafers as blanks for ∫ solar cells. Current A flow, i.e. a directional movement of free electrical ∫ charge carriers. The physical variable is denoted by the letter I and the unit of measurement is the ampere [A]. DC ∫ direct current Diffuse radiation Non-directional radiation. In the case of ∫ PV installations this is the non-directional component of the ∫ global irradiance because it is scattered during its passage through the atmosphere. Direct current (DC) An electric ∫ current that flows in one direction only. Direct radiation The directional component of the ∫ global irradiance that reaches the earth’s surface in a straight line without being scattered in the atmosphere and therefore causes harsh shadows. Disc fixing A component for the ∫ point fixing of panes of glass. It consists of two metal plates connected by a bolt or screw in a cylindrical hole drilled through the ∫ glass. The force transfer is by way of a ∫ non-positive and a ∫ positive connection. Drawn sheet glass Flat, transparent, colourless or tinted ∫ sheet glass that is produced in a continuous, initially vertical, drawing process with fire-polished surfaces on both sides. Dye-sensitised solar cell ∫ Solar cell with a nano structure based on the ∫ semiconductor titanium dioxide plus an organic pigment. Edge cover The amount of ∫ glass within a linear, supporting frame, determined by the distance between the edge of the pane and the structurally effective element of the supporting member, e.g. a frame or a ∫ glazing bead.

Edge protection Constructional measure for protecting the edges of ∫ glass against mechanical damage, the aim of which is to reduce the risk of failure of the pane concerned. Edge seal Peripheral, sealing, linear-type connection between two panes in a ∫ multi-pane insulating glass unit. Electron A fundamental particle with a negative electric charge. Materials are electrically conductive when they contain free electrons. Encapsulation Protective embedment of the ∫ solar cells in transparent intermediate layers. Typical embedment materials are ∫ EVA, ∫ PVB and ∫ casting resin. Energy The capacity of a body to do work. Energy can be neither created nor consumed, only stored, transported or converted into another state, e.g. electrical or radiation energy. The useful value can decrease as a result of conversion and transport because energy conversion does not function in every direction. Besides the basic unit of the joule [J], in energy supplies the ∫ kilowatt-hour [kWh] is in common usage. Energy payback time The time period in which an energy-producing system supplies the amount of energy equivalent to that required for its original production. Once this time has expired, a system exhibits a positive energy balance. ETAG European Technical Approval Guideline (requirements for issuing a ∫ European Technical Approval). Ethylene tetrafluoroethylene (ETFE) A fluorinated copolymer with a low self-weight and high light and UV permeability that is used in photovoltaics as an encapsulation and insulating material for ∫ solar cells. In the building industry ETFE film is an innovative material employed for pneumatic and membrane structures. Ethylene vinyl acetate (EVA) A thermoplastic hot-melt film that is the most common intermediate layer for embedding the ∫ solar cells, thus forming the laminating material for standard ∫ PV modules. European Technical Approval (ETA) ∫ Verification of applicability for non-regulated building products or forms of construction issued on a European level. Extra-clear glass (low-iron glass) A type of ∫ glass with a very low iron oxide content that does not exhibit the typical greenish tinge of normal glass and has a higher ∫ transmission than that of conventional ∫ soda-lime-silica glass. It increases the ∫ conversion efficiency of a module. Feed-in tariff The remuneration that installation operators receive from network operators when they feed the electricity they generate into the public electricity grid. In Germany the ∫ Renewable Energies Act (EEG) specifies minimum tariffs. Final energy Energy in the form received by consumers, e.g. natural gas, heating oil, fuels, electricity or district heat. The final energy corresponds to the remaining component of the ∫ primary energy after deducting the conversion and transport losses, e.g. in power stations, refineries or distribution networks. Float glass Flat, transparent, colourless or tinted ∫ sheet glass with parallel and fire-polished surfaces produced by means of continuous casting on and flowing over a bath of molten metal. Generator The component in a power plant that converts other forms of energy into an electrical ∫ current. Generation meter Calibrated electricity meter for measuring the solar electricity fed into the public grid for invoicing purposes. Glass Inorganic non-metallic material that is obtained through the complete melting of a mixture of raw materials at high temperatures, which produces a

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homogenous fluid that is then cooled to a solid state, normally without crystallisation. Glazing General term for a unit consisting of panes of ∫ glass, glass fixings, seals and other ancillary items. Glazing bead Removable retaining member for the pane of ∫ glass which forms part of the ∫ glazing system. Glazing for constant foot traffic ∫ Horizontal glazing to which people (including the public) have permanent access and which is intended to form part of a circulation zone. A certain glass configuration is necessary. Glazing for occasional foot traffic ∫ Overhead glazing that must satisfy certain requirements because it is walked on for the purpose of cleaning, maintenance and/or repairs. Global irradiance The total ∫ solar radiation, which is made up of ∫ direct and ∫ diffuse radiation plus radiation reflected from the surroundings ( ∫ albedo), incident on a horizontal receiving plane at the surface of the earth. Grid-connected system A ∫ PV installation that is connected to the public electricity grid and can feed either all or part of the solar electricity generated into the grid. The opposite of a ∫ stand-alone system. Hard roof covering A roof covering material that – in contrast to a soft roof covering – can withstand sparks and radiant heat, e.g. clay and concrete roof tiles, sheet metal or slates. Heat soak test Hot storage of ∫ toughened safety glass in order to eliminate panes with nickel sulphide inclusions (which shatter). Heat-soaked toughened safety glass ∫ Toughened safety glass that has passed the ∫ heat soak test and therefore has a much lower risk of nickel sulphide failure. Heat-strengthened glass A type of ∫ glass with increased resistance to mechanical and thermal stresses, achieved by way of heat treatment, which, however, does not achieve the strength values of ∫ toughened safety glass and has a fracture pattern similar to that of ∫ float glass. Horizontal glazing General designation for ∫ overhead glazing at an angle < 10° to the horizontal. Hotspot Local, excessively severe and damaging rise in temperature in a shaded or faulty ∫ solar cell. Inclined glazing (sloping glazing) ∫ Overhead glazing at an angle > 10° to the horizontal. Individual approval (ZiE) In Germany a unique ∫ verification of applicability for a non-regulated building product or form of construction issued by the senior building authority of a federal state. International Electrotechnical Commission (IEC) International standardisation body for electrical engineering and electronics. Inverter Electrical apparatus whose main task is to convert the ∫ direct current generated by a PV ∫ generator into conventional ∫ alternating current. Irradiance The intensity of radiation incident on a surface with a certain orientation and angle. Unit of measurement: W/m2. The total irradiation over a period of time, e.g. one year, denotes the quantity of energy in kWh/m2a. Kilowatt-hour [kWh] The unit of measure for work and energy, 1 kWh = 3600 Ws = 3600 J. Laminate General: planar combination of material layers with a material bond. In PV applications: 1. Composite module consisting of front and back layers; 2. Designation for a frameless module. Laminated glass A product consisting of a pane of ∫ glass with one or more panes of glass and or plastic glazing materials that are joined together by one or more intermediate layers.

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Laminated safety glass ∫ Laminated glass in which, in the case of breakage, the intermediate layer retains the fragments of glass, limits the size of any openings that may ensue, offers a residual strength and reduces the risk of injuries. As the intermediate layer(s) may consist exclusively of ∫ PVB film, glass/glass ∫ laminates with PVB encapsulation are not classed as safety glass owing to the ∫ solar cells embedded within. “Light trap” effect In geometrical optics the designation for the reduction in ∫ reflections by means of a specific, rough surface structure. This effect is based on multiple and total reflection. In PV applications textured cell surfaces and cover glasses made from ∫ patterned glass exploit the light trap effect in order to increase the ∫ conversion efficiency. Linear-type support Continuous line bearing that can be on one, two, three or four sides. An alternative to ∫ point-type support. List of Technical Construction Regulations (LTB) The LTB contains the building authorities’ technical rules for planning, designing and constructing buildings and structures and parts thereof and is implemented in each German federal state on the basis of the Model List of Technical Construction Regulations (MLTB). Low-Voltage Directive (2006/95/EC) The EU directive for electrical equipment with an input voltage of 50 –1000 V ∫ AC or 75 –1500 V ∫ DC. It prescribes the ∫ CE marking for corresponding electrical products, which include solar modules and ∫ inverters. Material bond Irreversible jointing of parts that are held together by atomic and molecular forces consisting of adhesion and cohesion. Material bond jointing methods include welding, soldering and gluing. Maximum Power Point (MPP) A current/voltage combination at which a ∫ solar cell, a ∫ PV module or PV ∫ generator delivers its maximum ∫ output power in ∫ wattpeak [Wp] for the respective ∫ irradiance and temperature. Microcrystalline silicon (µc-Si) ∫ Silicon with a very fine crystal structure for thinfilm ∫ solar cells. Micromorphous silicon (a-Si/µc-Si) A combination of ∫ amorphous and ∫ microcrystalline silicon in thin-film ∫ solar cells. Model Building Code (MBO) A document agreed upon by the conference of building/public works ministers that each individual German state implements in the form of its Federal State Building Regulations (LBO). Monocrystalline silicon Homogeneous ∫ silicon consisting of a single high-quality crystal (in contrast to ∫ polycrystalline silicon) for producing ∫ wafers as blanks for ∫ solar cells. Monolithic glass ∫ Sheet glass that consists of only one structurally effective pane. The opposite of ∫ laminated glass. Multi-junction solar cell A thin-film ∫ solar cell comprising a stack of partial cells that respond to different ranges of the spectrum and hence exploit a greater part of the sunlight. ∫ Tandem and ∫ triple-junction solar cells are in use. Multi-pane insulating glass A ∫ glazing unit consisting of at least two panes of ∫ glass that are separated by at least one ∫ cavity filled with gas or air. At the edges the panes are connected by airtight/gastight and moisture-resistant elements ( ∫ edge seal). Nano solar cell A new type of ∫ solar cell based on ∫ semiconductors with a nano structure which can be produced quickly and inexpensively using a printing method that requires very little energy, e.g. ∫ dyesensitised, ∫ organic or CIS nano cells. National Technical Approval (AbZ) In Germany a ∫ verification of applicability for nonregulated building products or forms of construction issued by the German Institute of Building Technology (DIBt).

National Test Certificate (AbP) In Germany a ∫ verification of applicability that is used as an alternative to the ∫ National Technical Approval when the non-regulated building product or form of construction concerned can be assessed according to acknowledged test methods and its use is not connected with the fulfilment of significant building safety requirements. Verification as a ∫ hard roof covering for roof-integrated ∫ PV installations is one example. Network operator (distribution network operator) A company that maintains the electricity networks for supplying end customers in the low- and mediumvoltage segments. The supraregional high-voltage networks are, on the other hand, operated by just a few transmission network operators. Non-positive connection Method of jointing in which the application of a force guarantees that the connection remains intact. Clamped, screwed and bolted connections are among this type. Organic solar cell A ∫ nano solar cell based on synthetic, or rather polymer, materials with ∫ semiconductor properties. Output power The amount of ∫ energy converted per unit of time, i.e. the work done within a time span denoted by the letter P. Unit of measurement: watt [W]. The electrical output is the product of ∫ current and ∫ voltage. In PV applications the momentary output is mostly below the maximum possible ∫ rated output. Overhead glazing ∫ Glazing at an angle > 10° to the vertical. This installation situation calls for special safety measures. Parallel connection Electrical connection of terminals with the same polarity. In PV applications identical ∫ strings are connected in parallel in some module and installation concepts. In doing so, the individual string currents are added together to create a total ∫ current. The opposite of ∫ series connection. Partial transparency A property of building components that, on a macroscopic level, consist of opaque and light-permeable areas. Patent glazing bar A framing section mainly used for ∫ linear-type support which connects the pane of ∫ glass to the supporting construction by means of contact pressure. Patterned glass Flat, translucent, colourless or tinted ∫ sheet glass, manufactured by means of continuous casting and rolling. In PV applications special patterned glass is one of the products that can be used. Its surface affects the ∫ reflections in such a way that it acts as a ∫ light trap. Patterned glass for PV applications exhibits enhanced ∫ transmission. Performance Ratio (PR) Evaluation criterion for the quality of a PV-installation, essentially irrespective of location, orientation, module ∫ conversion efficiency and size of ∫ generator, in the form of a ratio between the actual and the theoretical ∫ yield under ∫ standard test conditions (STC). Photon According to quantum physics, a fundamental particle that transmits electromagnetic radiation at the speed of light. Every photon corresponds to a discrete packet of energy (light quantum) whose energy content is dependent on the ∫ wavelength in the ∫ spectrum of ∫ solar radiation. Photovoltaics (PV) The direct conversion of light into electrical ∫ energy by means of ∫ solar cells. p-n junction The functional heart of the ∫ solar cell at the boundary between the positive (p-doped) and negative (n-doped) ∫ semiconductor layers where the light absorption and the separation of the charge carriers takes place. Point fixing General term for individual glass fasteners that are either in the form of a U-shaped component enclos-

Appendix

ing the edge of the ∫ glass through a positive connection ( ∫ clamp fixing) or make use of drilled holes, e.g. ∫ disc fixing, ∫ undercut anchor. Point-type support Supporting the pane of ∫ glass at individual points either on the perimeter of the glass by way of clamping or within the area of the glass by way of fixings in drilled holes. An alternative to ∫ lineartype support. Polycrystalline silicon ∫ Silicon cast in blocks and in the form of many solidified individual crystals for the production of ∫ wafers as blanks for ∫ solar cells. Positive connection Method of jointing in which the force transfer is achieved by interlocking the components. Primary energy ∫ Energy in its naturally occurring, not yet technically processed form. Primary energy media include, for example, coal, petroleum, wind, uranium, ∫ solar radiation. Proof of conformity The ∫ CE marking of a product in order to confirm its compliance with the harmonised European standards. PVB (polyvinyl butyral) interlayer A viscoelastic film that is used as an intermediate layer when producing ∫ laminated safety glass. In PV applications PVB is used as a laminating layer in some thin-film and building-mounted crystalline modules. PV installation (PV system) The total assembly of components for converting ∫ solar radiation into electrical ∫ energy for use in situ or for feeding into the grid. PV module (PV panel) A prefabricated unit consisting of several interconnected ∫ solar cells that, depending on the type of construction, consists of cover glass, encapsulation, solar cells, backing sheet, frame and electrical connections. Rated power output The peak ∫ output power at the ∫ maximum power point under ∫ standard test conditions (STC) as declared by the manufacturer. Rechargeable battery Means of, in most cases, electrochemical storage for electrical ∫ energy. Reflection In optics reflection is the rebounding of the light at the boundary surfaces of two neighbouring media with dissimilar optical densities. The angle of incidence, the surface properties, the ∫ wavelength, polarisation and the material properties all affect the nature and magnitude of the reflection. Renewable Energies Act (EEG) Federal legislation that gives precedence to renewable sources of energy in the electricity sector. It regulates the connection to the grid, the purchase of electricity and remuneration. Residual loadbearing capacity The property of a ∫ glass element to be able to carry certain loads even after breakage. Residual stability The property of a ∫ glass element to remain in position and not fall after breakage. Ribbon silicon ∫ Polycrystalline silicon that is not cast in blocks but instead grown as a continuous strip in the same thickness as the ∫ wafers produced later. This method saves material and energy because there is no need to saw the blocks into slices. The Edge-defined Film-fed Growth (EFG) and the string-ribbon processes are the methods in use on an industrial scale. Roofing Roof covering or roof waterproofing as a component of the total roof construction. Safety barrier glazing ∫ Vertical glazing, loadbearing glass balustrades and spandrel panels and balustrade infill panels made from ∫ glass that prevent persons from falling sideways and /or to a lower level. Such glazing must comply with special regulations.

Safety/security glass ∫ Sheet glass that, for example, reduces the risk of injury in the case of breakage, acts as a safety barrier or provides protection against attacks. We distinguish between ∫ toughened safety glass and ∫ laminated safety glass depending on the configuration and the safety or security specification. Semiconductor An element or compound having higher resistivity than a conductor, but lower resistivity than an insulator. Series connection A connection between the positive terminal of one electrical component and the negative terminal of the next. In PV applications connection in series creates a ∫ string of cells or modules. Here, the same ∫ current flows through all the elements, whereas the individual ∫ voltages are added together. The opposite of ∫ parallel connection. Setting blocks Components, made from plastic or another suitable material, for positioning a pane of ∫ glass in a frame and transferring the forces to the supporting construction. We distinguish between setting and location blocks depending on the function. Shading angle Lowest elevation of the sun at which ∫ PV modules mounted in rows do not cast shadows on each other. In Germany the angle of the sun on 21 December is used for planning purposes, an average value of 15°. Sheet glass General term for all relatively thin, flat and bent panes of glass with essentially parallel surfaces. Silhouette The horizontal line in a sun path diagram that represents the outline of the surroundings (structures, vegetation and natural elevations) drawn from the point of view of the location of the PV ∫ generator. It is used to analyse shadows. Silica glass ∫ Glass in which silicon dioxide is the main constituent. This is by far the most common type of glass produced, and includes lead glass, borosilicate glass and ∫ soda-lime-silica glass. Silicon ∫ Semiconductor and the most important raw material for the production of ∫ solar cells. Single glazing ∫ Glazing that consists of only one pane of ∫ sheet glass (also a pane of ∫ laminated glass). Soda-lime-silica glass This is the type of ∫ glass used most often in the building industry, in photovoltaics mostly in the form of ∫ extra-clear glass. Solar altitude angle (elevation) The angle of the sun relative to the horizontal. Solar cell Smallest fully functional photovoltaic element. We distinguish between ∫ crystalline silicon, ∫ thinfilm technology and ∫ nano solar cell products. Solar constant The almost constant intensity of ∫ solar radiation incident perpendicular on the outer edge of the earth’s atmosphere with an average ∫ irradiance of 1367 W/m2 over the year. Solar glass Thermally ∫ toughened ∫ extra-clear glass used as the cover glass for ∫ PV modules. Solar module, solar installation ∫ PV module, ∫ PV installation Solar radiation The totality of electromagnetic waves emitted continuously by the sun. The ∫ spectrum extends from x-rays to radio waves. Spectrum Characteristic composition of radiation consisting of different ∫ wavelengths. Stand-alone system An autonomous electricity supply system that is not connected to the public electricity grid. The opposite of a ∫ grid-connected system. Standard test conditions (STC) International, standardised laboratory conditions to enable comparable measurements of the electrical parameters of solar cells and modules: ∫ irradiance

level 1000 W/m², reference ∫ air mass AM 1.5, cell/module temperature 25 °C. String ∫ Series connection of several ∫ solar cells in one ∫ PV module or several modules in one PV ∫ generator. Structural sealant glazing (SSG) A type of facade construction in which the panes of ∫ glass are connected to the supporting construction permanently by way of a loadbearing and sealing silicone adhesive to create a flush external surface without framing members. Substrate Backing material and base for coating in ∫ thinfilm technology and ∫ nano solar cells, e.g. panes of ∫ glass, less often metal foils or plastic films. System technology All the components of a ∫ PV installation with the exception of the ∫ PV modules. Tandem solar cell ∫ Multi-junction solar cell consisting of two ∫ p-n junctions, one above the other. Temperature coefficient The relative or absolute change in the ∫ current, ∫ voltage or ∫ output power of a ∫ solar cell or a ∫ PV module for a temperature rise of 1 °C. Thin-film technology The production of solar cells just a few micrometres thick from ∫ amorphous, ∫ microcrystalline or ∫ micromorphous silicon, also ∫ cadmium telluride or ∫ copper-indium diselenide/disulphide on panes of glass or flexible ∫ substrates (transparent or opaque sheets) by means of various coating methods. Toughened glass A ∫ glass product with artificially generated compression zones at the glass surfaces and a tension zone within the body of the glass. The prestress is achieved by quenching temperatures in the viscoelastic range (thermal toughening) or by ion exchange (chemical toughening) ( ∫ toughened safety glass, ∫ laminated safety glass). Toughened safety glass ∫ Sheet glass that has undergone heat treatment to provide it with a greater resistance to mechanical and thermal stresses and which shatters into a multitude of blunt pieces (dice) upon breakage. Transmission Designation for the permeability of a medium with respect to electromagnetic waves. The ratio between the incident and transmitted components is called the transmittance. In PV applications the transmittance of the cover glass for radiation in the wavelength ∫ spectrum between ultraviolet and near infrared is especially important. The opposite of ∫ absorption. Transparency The term transparency is used differently depending on context. In the building industry a transparent component is one that exhibits a very high transmittance for a non-diffuse radiation passage. The view through is clear and focused. Triple solar cell ∫ Multi-junction solar cell consisting of three ∫ p-n junctions, one above the other. Ü mark German designation for building products that do not deviate significantly from the technical rules of Construction Products List A part 1, a ∫ National Technical Approval, a ∫ National Test Certificate or an ∫ individual approval. Undercut anchor ∫ Point fixing that holds a pane of ∫ glass at a discrete point via a hole drilled in only one side of the pane. Unsupported edge General expression for a visible, unprotected edge of a pane of ∫ glass without any support. VDE German Association for Electrical, Electronic & Information Technologies, the standardisation body responsible for photovoltaics. Verification of applicability Required when using non-regulated building products or forms of construction. ∫ National Technical Approval, ∫ European Technical Approval, ∫

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Standards, directives, statutory instruments and recommendations (selection) National Test Certificate or ∫ individual approval documents are classed as suitable verification. Vertical glazing ∫ Glazing at an angle < 10° to the vertical. Visible light The ∫ spectrum of electromagnetic radiation between ∫ wavelengths of about 380 and 780 nm that is visible to the human eye. Voltage Electrical potential difference, the cause of the electric ∫ current. The physical variable is denoted by the letter U and the unit of measurement is the volt [V]. Wafer Slices of ∫ semiconductor material, mostly ∫ crystalline silicon, used for producing ∫ solar cells and electronic chips. Watt-peak [Wp] The unit of peak output at ∫ maximum power point, mostly determined under ∫ standard test conditions (STC). Wavelength The distance between two similar and successive points on a harmonic wave. Wired glass, patterned wired glass Flat, translucent, colourless or tinted ∫ sheet glass that is produced by continuous casting and rolling and into which a mesh of steel wires, welded at every intersection, is inserted during production. The surfaces may be smooth or textured. Yield The electrical energy provided by a ∫ PV installation system and used over a certain period of time. In ∫ grid-connected systems where all the electricity generated is fed into the grid, the yield corresponds to the value measured by the ∫ generation meter and is frequently specified as a specific annual yield related to the ∫ rated power output in kWh/kWp.

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Änderungen der Bauregellisten A und B und der Liste C. Feb 2008 ed. DIBt Mitteilungen No. 6, Ernst & Sohn, Berlin, 2008 Anforderungen an begehbare Verglasungen; Empfehlungen für das Zustimmungsverfahren, Mar 2000 ed. In: Mitteilungen DIBt 2/2001, pp. 60–62 Bauregelliste A, Bauregelliste B und Liste C. Jan 2008 ed. DIBt Mitteilungen, special issue No. 36, Ernst & Sohn, Berlin, 2008 Bundesverband der Energie und Wasserwirtschaft BDEW (ed.): Technische Richtlinie Erzeugungsanlagen am Niederspannungsnetz. Draft Jun 2008 DASt-Richtlinie 016 Bemessung und konstruktive Gestaltung von Tragwerken aus dünnwandigen kaltgeformten Bauteilen. German RC Committee (ed.). Düsseldorf,1992 DIN 1055 Actions on structures, parts 1, 4, 5 and 100 DIN 4102 Fire behaviour of building materials and building components, parts 1, 4, 7 and 13 DIN 4108 Thermal insulation and energy economy in buildings DIN 4426 Equipment for building maintenance – Safety requirements for workplaces and accesses – Design and execution. Sept 2001 DIN 18516-4 Back-ventilated, non-loadbearing, external enclosures of buildings, made from tempered safety glass panels; requirements and testing. Feb 1990 DIN 18531-2 Waterproofing of roofs – Sealings for non-utilized roofs – Part 2: Materials. Nov 2008 DIN 18545-1 Glazing with sealants; rebates; requirements. Feb 1992 DIN EN 410 Glass in building – Determination of luminous and solar characteristics of glazing. Dec 1998 DIN EN 572 Glass in building – Basic soda lime silicate glass products, parts 1 to 9 DIN EN 673 Glass in building – Determination of thermal transmittance (U-value) – Calculation method. Jun 2003 DIN EN 1096 Glass in building – Coated glass, parts 1 to 4 DIN EN 1279 Glass in building – Insulating glass units, parts 1 to 6 DIN EN 1363-1 Fire resistance tests – Part 1: General requirements. Oct 1999 DIN EN 1364-1 Fire resistance tests on non-loadbearing elements – Part 1: Walls. Oct 1999 DIN EN 1863 Glass in building – Heat strengthened soda-lime-silicate glass, parts 1 and 2 DIN EN 12150 Glass in building – Thermally toughened soda-lime-silicate safety glass, parts 1 and 2 DIN EN 12337 Glass in building – Chemically strengthened soda-lime-silicate glass, parts 1 and 2 DIN EN 13501 Fire classification of construction products and building elements, parts 1, 2 and 5 DIN EN 13830 Curtain walling – Product standard. Nov 2003 DIN EN 13956 Flexible sheets for waterproofing – Plastic and rubber sheets for roof waterproofing – Definitions and characteristics. Apr 2007 DIN EN 14178 Glass in building – Basic alkaline earth silicate glass products, parts 1 and 2 DIN EN 14449 Glass in building – Laminated glass and laminated safety glass – Evaluation of conformity/ Product standard. Jul 2005 DIN EN 14509 Self-supporting double skin metal faced insulating panels – Factory made products – Specifications. Feb 2007 DIN EN 14782 Self-supporting metal sheet for roofing, external cladding and internal lining – Product specification and requirements. Mar 2006 DIN EN 50380 Data sheet and name plate information for photovoltaic modules. Sept 2003 DIN EN 61173 Overvoltage protection for photovoltaic (PV) power generating systems – Guide. Oct 1996 DIN EN 61215 (VDE 0126-31) Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval. Feb 2006 DIN EN 61277 Terrestrial photovoltaic (PV) power generating systems – General and guide. Feb 1999 DIN EN 61646 (VDE 0126-32) Thin-film terrestrial photovoltaic (PV) modules – Design qualification and type approval. Mar 2009 DIN EN 61730 (VDE 0126-30) Photovoltaic (PV) module safety qualification, parts 1 and 2. Oct 2007 DIN EN 62305 (VDE 0185-305) Protection against lightning, parts 1 to 4

DIN V 11535-1 (pre-standard) Greenhouses, parts 1 and 2 DIN V 20000 (pre-standard) Use of building products in construction works – Part 201: Adaption standard for flexible sheets for waterproofing according to European standards for the use as waterproofing of roofs. Nov 2006 DIN V VDE V 0126-1-1 (VDE V 0126-1-1) (pre-standard) Automatic disconnection device between a generator and the public low-voltage grid. Feb 2006 DIN V ENV 1187 (pre-standard) Test methods for external fire exposure to roofs. Oct 2006 DIN VDE 0100 (VDE 0100) Erection of low voltage installations, all relevant parts, especially part 7-712: VDE 0100-712 Low-voltage installations – Part 7-712: Requirements for special installations or locations – Solar photovoltaic (PV) power supply systems E DIN 18008 (draft) Glass in building – Design and construction rules, parts 1 to 7 E DIN 18531-2 (draft) Waterproofing of roofs – Sealings for non-utilised roofs – Part 2: Materials. Apr 2009 E DIN EN 15725 (draft) Extended application reports on the fire performance of construction products and building elements. Nov 2007 E DIN EN 50524 (VDE 0126-13) (draft) Data sheet and name plate for photovoltaic inverters. Oct 2008 E DIN IEC 62446 (VDE 0126-23) (draft) Grid-connected photovoltaic systems – Minimum system documentation, commissioning tests and inspection requirements. Jul 2007 E DIN VDE 0126-21 (VDE 0126-21) Photovoltaics in building. Jul 2007 ETAG 002 Structural sealant glazing systems, parts 1 to 3 GS-BAU-18 Grundsätze für die Prüfung und Zertifizierung der bedingten Betretbarkeit oder Durchsturzsicherheit von Bauteilen bei Bau- oder Instandhaltungsarbeiten. Feb 2001 ed. GUV-SI 8027 Mehr Sicherheit bei Glasbruch. GUVInformationen Sicherheit bei Bau und Einrichtung. Published by Bundesverband der Unfallkassen, Munich, Sept 2001 Musterbauordnung (MBO). Nov 2002 ed., Informationssystem Bauministerkonferenz, Berlin, 2002 Muster-Liste der Technischen Baubestimmungen (MLTB), Feb 2008 ed., Informationssystem Bauministerkonferenz, Berlin, 2008. Technische Regeln für die Bemessung und Ausführung von punktförmig gelagerten Verglasungen (TRPV); Aug 2006 ed. Technische Regeln für die Verwendung von absturzsichernden Verglasungen (TRAV); Jan 2003 ed. Technische Regeln für die Verwendung von linienförmig gelagerten Verglasungen (TRLV); Aug 2006 ed. Technische Richtlinien des Glaserhandwerks, Nos. 1 – 20, 8th ed., Verlagsanstalt Handwerk GmbH, Düsseldorf, 2004 Überkopfverglasungen im Rahmen von Zustimmungen im Einzelfall. Memorandum of the Baden-Württemberg Building Technology Office. Apr 2008 VDI 6012 Blatt 2: Technical rule – Local energy systems in buildings – Photovoltaics. Apr 2002 Verband der Elektrizitätswirtschaft VDEW (ed.): Eigenerzeugungsanlagen am Niederspannungsnetz. VWEW Energieverlag, Frankfurt am Main, 2001 Verband der Netzbetreiber VDN (ed.): Technische Anschlussbedingungen TAB 2007 für den Anschluss an das Niederspannungsnetz. Jul 2007 Baden-Württemberg Trade & Industry Ministry (ed.): Bauen mit Glas. Informationen für Bauherren, Architekten und Ingenieure. Stuttgart, 2002

Appendix

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Haselhuhn, R., Hemmerle, C., Hartmann, U., Zehner, M.: Deutsche Gesellschaft für Sonnenenergie (ed.): Planning and Installing Photovoltaic Systems: A Guide for Installers, Architects and Engineers; 2nd ed., Earthscan, London, 2008 Hegger, M., Fuchs, M., Stark, T., Zeumer, M.: Energy Manual – Sustainable Architecture. Institut für internationale Architektur-Dokumentation, Munich, 2008 Hermannsdörfer, I., Rüb, C.: Solardesign. Photovoltaik für Altbau, Stadtraum, Landschaft. jovis Verlag, Berlin, 2005 Hullmann, H. (ed.): Photovoltaik in Gebäuden. Handbuch für Architekten und Ingenieure. Fraunhofer IRB Verlag, Stuttgart, 2000 Hullmann, Willkomm & Partner (hwp), Institut für Solare Energieversorgungstechnik (ISET) (ed.): Multifunktionale Photovoltaik. Photovoltaik in der Gebäudehülle. Hamburg/Kassel, 2006 Humm, O., Toggweiler, P.: Photovoltaics in Architecture: The Integration of Photovoltaic Cells in Building Envelopes. Birkhäuser, Basel, 1993 Kiesow, G.: Einführung in die Denkmalpflege; 2nd ed. Wissenschaftliche Buchgesellschaft, Darmstadt, 1989 Klobasa, M., Ragwitz, M.: Gutachten zur CO2-Minderung im Stromsektor durch den Einsatz erneuerbarer Energien. Report for the Working Group on Renewable Energies – Statistics (AGEE-Stat) on behalf of the Baden-Württemberg Centre for Solar Energy and Hydrogen Research (ZSW). Fraunhofer Institute for Systems & Innovation Research, Karlsruhe, 2005 Konrad, F.: Planung von Photovoltaik-Anlagen. Grundlagen und Projektierung; 2nd ed. Vieweg+Teubner, Wiesbaden 2008 Krippner, R.: The building skin as heat and power generator. In: Schittich, C. (ed.): In Detail Building Skins; 2nd revised ed. Institut für Internationale Architektur-Dokumentation, Munich, 2006, pp. 48 – 59 Leonhardt, F.: Zu den Grundfragen der Ästhetik bei Bauwerken. Springer-Verlag, Berlin/Heidelberg, 1984 Löffler, V., Kutzer, C.: Bauaufsichtliche Regelung bei der Verwendung /Anwendung von ungeregelten Bauprodukten bzw. Bauarten im Einzelfall nach Sächsischer Bauordnung. In: Weller, B. (ed.): glasbau2004; Proceedings, Building Design Institute, Dresden TU, Dresden, 2004, pp. 19 – 37 Lüling, C. (ed.): Architektur unter Strom. Photovoltaik gestalten. Institute for Urban Planning & Architecture, Berlin TU, Berlin, 2000 Luther, J.: Photovoltaik – Neue Horizonte. In: Stadermann, G. (ed.): Themen 2003. Photovoltaik – Neue Horizonte. Annual conference of the Renewable Energy Research Association in Berlin, Berlin, 2004, pp. 5 –10 North Rhine-Westphalia Ministry for Economic Affairs & Energy (ed.): Photovoltaik in der Gebäudegestaltung. Zukunftsenergien. Unterstützt von Land und Wirtschaft. Düsseldorf, 2005 Oswald, R.: Die Zuverlässigkeit von Kunststoffdachbahnen. In: db deutsche bauzeitung, No. 01/2008, pp. 82 – 87 Pahl, K.A., Weber, R. (ed.): Thema Material. TUDpress, Verlag der Wissenschaften GmbH, Dresden, 2008 Perlin, J.: From Space to Earth. The story of solar electricity. aatec publications, Michigan, 1999 Podleschny, R.: CE-Kennzeichnung von Bauelementen im Metallleichtbau. In: Stahlbau, No. 5/2008, pp. 228 – 335 Quaschning, V.: Regenerative Energiesysteme. Technologie – Berechnung – Simulation; 5th revised ed. Carl Hanser Verlag, Munich, 2007 Reidt, A.: Erläuterungen zur Leitlinie für die europäische technische Zulassung für geklebte Glaskonstruktionen. In: VDI (ed.): VDI Report 1527. Bauen mit Glas. VDI Verlag GmbH, Düsseldorf, 2000, pp. 19 – 37 Reidt, A.: Europäische Technische Zulassungen. In: Weller, B. (ed.): glasbau2005; Proceedings, Building Design Institute, Dresden TU, Dresden, 2005, pp. 5 – 22 Rexroth, S.: Gestaltungspotenzial von Solarpaneelen als neue Bauelemente – Sonderaufgabe Baudenkmal. Dissertation. Berlin University of the Arts, Berlin, 2005 Rexroth, S. (ed.): Gestalten mit Solarzellen. Photovoltaik in der Gebäudehülle. C. F. Müller Verlag, Heidelberg, 2001

Rodeck, B., Meerwein, G., Mahnke, F. H.: MenschFarbe-Raum. Grundlagen der Farbgestaltung in Architektur, Innenarchitektur, Design und Planung; 3rd ed. Verlagsanstalt Alexander Koch, Leinfelden Echterdingen, 2002 Scheurmann, I., Meier, H.R. (ed.): Zeitschichten der Denkmalpflege. Echt alt schön wahr. Deutscher Kunstverlag, Munich/Berlin, 2006 Schlenker, S.: The second life of a 300 kW PV generator manufactured with recycled wafers from the oldest German PV power plant. In: WIP-Renewable Energies (ed.): 21st European Photovoltaic Solar Energy Conference in Dresden. WIP-Renewable Energies, Munich, 2006, pp. 2477– 2480 Schittich, C. et al.: Glass Construction Manual; 2nd ed. Institut für Internationale Architektur-Dokumentation, Munich, 2006 Schittich, C.: Shell, skin, materials. In: Schittich, C. (ed.): In Detail Building Skins; 2nd revised ed. Institut für Internationale Architektur-Dokumentation, Munich, 2006, pp. 8 – 27 Schittich, C. (ed.): In Detail Solar Architecture. Institut für Internationale Architektur-Dokumentation, Munich, 2003 Schmidt, L.: Einführung in die Denkmalpflege. Wissenschaftliche Buchgesellschaft (WGB), Darmstadt, 2008 Schmidt, C., Nordmann, T. (ed.): Im Prinzip Sonne. Visionen zum Energiemarkt. Kontrast Verlag, Zurich, 2000 Schneider, A. (ed.): Solararchitektur für Europa. Birkhäuser, Basel, 1996 Sedlacek, G., Kasper, R.: Bauzulassungen Laminate. 4th Workshop on PV Module Technology. TÜV Rheinland; Cologne, 30 Nov 2007 Sollmann, D., Podewils, C.: How dangerous is cadmium telluride? In: Photon International, No. 03/2009, pp. 100 –109 Tänzler, D. (ed.): Die sicherheitspolitische Bedeutung erneuerbarer Energien. Research report. Adelphi Consult GmbH, Berlin, 2007 Weller, B., Härth, K., Tasche, S., Unnewehr, S.: Detail Practice Glass in Building. Principles, Applications, Examples. Institut für internationale ArchitekturDokumentation, Munich, 2009 Weller, B.: Hemmerle, C.; Jakubetz, S.: Fassaden für das 21. Jahrhundert: Architektur und Photovoltaik. In: VDI (ed.): VDI Report 2034. Fassaden – Blick in die Zukunft. Düsseldorf, 2008, pp. 27– 43. Weller, B., Nicklisch, F., Thieme, S., Weimar, T.: Glasbau-Praxis. Konstruktion und Bemessung. Bauwerk Verlag, Berlin, 2009 Weller, B., Rexroth, S., Geyer, D., Schäffler, R.: Development of thin film photovoltaic modules in CIS technology in an interdisciplinary approach and subject to architectural criteria. In: WIP Renewable Energies (ed.): 21st European Photovoltaic Solar Energy Conference in Dresden. WIP Renewable Energies, Munich, 2006, pp. 2124 – 2127 Weller, B., Rexroth, S.: Forschungsprojekt Adaption und Weiterentwicklung der Photovoltaik-Dünnschichttechnologie für Kompositpaneele mit teils farbigem Glas für den Einsatz in vorgehängten hinterlüfteten Fassaden: PV-VH-Fassaden. Final report. Building Design Institute, Dresden TU, Dresden, 2008 Weston, R.: Materials, Form and Architecture. Laurence King Publishing, London, 2003

107

Appendix

Manufacturers, companies and trade associations (selection) The manufacturers named in this publication and listed below represent a selection of possible suppliers. Inclusion in this book and/or the list is not to be understood as a recommendation but merely as an example and the authors make no claim as to the completeness of the information.

3S Swiss Solar Systems AG www.3-s.ch abakus solar AG www.abakus-solar.de Advent Solar Inc. www.adventsolar.com aleo solar AG www.aleo-solar.de ALTEC Solartechnik AG www.ribic-systems.de alwitra GmbH & Co. Klaus Göbel www.alwitra.de Applied Solar, LLC www.appliedsolar.com Arup Ltd. www.arup.com asola Advanced and Automative Solar Systems GmbH www.asola-power.com AVANCIS GmbH & Co. KG www.avancis.de/en AZUR Solar GmbH www.azur-solar.com BINE Information Service www.bine.info Bosch Solar Energy AG www.bosch-solarenergy.de/en BP Solar International Inc. www.bpsolar.com Calyxo GmbH www.calyxo.com CENTROSOLAR Group AG www.centrosolar.com Colt International Licensing Ltd. www.colt-info.co.uk Conergy AG www.conergy.com Dyesol Global www.dyesol.com European Photovoltaic Industry Association (EPIA) www.epia.org European Renewable Energy Council (EREC) www.erec.org ertex solar GmbH www.ertex-solar.at European Association for Renewable Energy www.eurosolar.de FATH Solar GmbH www.fath-solar.com Federal Ministry for the Environment, Nature Conservation & Nuclear Safety www.erneuerbare-energien.de

108

First Solar Inc. www.firstsolar.com

Scheuten Solar Holding B. V. www.scheutensolar.com

fischerwerke GmbH & Co. KG www.fischer.de

Schletter GmbH www.schletter.de

German Renewable Energy Agency www.unendlich-viel-energie.de

SCHOTT Solar AG www.schottsolar.com/global

Glaswerke Arnold GmbH + Co. KG www.voltarlux.de

Schüco International KG www.schueco.com

GOLDBECK Solar GmbH www.goldbeck.de/solar/en

Sharp Electronics www.sharp-world.com

Grammer Solar GmbH www.grammer-solar.com

Signet Solar GmbH www.signetsolar.com

GSS GebäudeSolarsysteme GmbH www.zre-ot.de

Solar Century Holdings Ltd www.solarcentury.com

Heindl Server GmbH (ed.) www.solarserver.de

Solar Fabrik AG www.solar-fabrik.com

heroal Johann Henkenjohann GmbH & Co. KG www.heroal.de

Solar Integrated Technologies GmbH www.solarintegrated.com

International Renewable Energy Agency (IRENA) http://www.irena.org

SolarNext AG www.solarnext.eu

International Solar Energy Society (ISES) www.ises.org

Solarion AG/Photovoltaik www.solarion.de

Inventux Technologies AG www.inventux.com/en

solarnova Produktions- & Vertriebsgesellschaft mbH www.solarnova.de

Isofoton S.A. www.isofoton.com

SOLARWATT AG www.solarwatt.de

Kalzip® GmbH www.kalzip.com/solar

SolarWorld AG www.solarworld.de

Konarka Technologies, Inc. www.konarka.com

SOLON SE www.solon.com

Masdar PV GmbH www.masdarpv.de

Sovello AG www.sovello.com

Nanosolar GmbH www.nanosolar.com

stromaufwärts Photovoltaik GmbH www.stromaufwaerts.at

National Renewable Energy Laboratory www.nrel.gov

SULFURCELL Solartechnik GmbH www.sulfurcell.de

Odersun AG www.odersun.de

Sunfilm AG www.sunfilm.com

PV Database – Urban Scale Photovoltaic Systems www.pvdatabase.org

SunPower GmbH www.sunpowercorp.com

PVflex Solar GmbH www.pvflex.com/eng

Suntech Power Holdings Co. Ltd. www.suntech-power.com

Q-Cells SE www.q-cells.com

Sunways AG Photovoltaic Technology www.sunways.eu/en

Renusol GmbH www.renusol.com

systaic AG www.systaic.de

RHEINZINK GmbH & Co. KG www.rheinzink.co.uk

System Photonics www.system-photonics.com

Roto Dach- & Solartechnologie GmbH www.roto-frank.com

VidurSolar, S.L. www.vidursolar.es

SAINT-GOBAIN Glass www.saint-gobain-glass.com

Würth Solar GmbH & Co. KG www.wuerth-solar.de

SANYO Component Europe GmbH www.sanyo-solar.eu

ZinCo GmbH www.zinco.de

Sapa Building System www.sapa-solar.com

Appendix

Index absorptance absorption ageing air mass albedo alternating current aluminium aluminium frame amorphous silicon annual yield anti-reflection coating atmosphere atrium atrium roof attestation of conformity awning azimuth angle

43 14 – 17, 23, 44, 50 38, 42, 71 11, 12, 22 12 25, 27 15, 20, 32, 52, 58, 64 20, 21, 32 16, 17, 21, 23, 57 13, 26, 30, 31 15, 20, 32, 35, 42 – 45 7, 8, 11, 12, 35, 61, 65 55, 61, 74 55 73, 79 66, 74 13

back contact backing material backing sheet balcony ball drop test bespoke production bi-facial solar cell building envelope

14 –19, 45 16 – 20, 42, 44, 46 19, 20, 32, 51, 69 43, 74, 76, 78 78 19 16 9, 18, 28, 37 – 39, 41, 49, 58, 63, 71 – 73 building integration 23, 43, 49, 51 building-integrated photovoltaics 9, 21 building-integrated PV 9, 27, 33, 72, 73, 75, 77 building-mounted 9, 27, 38, 39, 42, 46, 47 busbar 15, 45 bypass diode 19, 23, 24, 71 27 – 32, 79 28, 60, 61, 67, 72 14, 16, 17, 22, 23, 32, 33 14, 16, 17, 22, 23, 32 55, 61, 66, 68, 74, 77 53, 60, 64, 65 7, 29 19, 50, 75, 78, 79 20, 23, 33 71, 73 – 75 66 11, 19 14, 15 66, 73, 74 – 76, 78 21, 31, 33 39, 49, 62 – 65, 74, 87, 88, 91, 92, 94, 97 cladding plus ventilation cavity 62, 63, 74 clamp fixing 52, 54, 55, 59, 61, 63, 68 coaxial double ring test 78 codes of practice 73, 74 co-generation plant 24, 26 cold facade 50, 62 cold roof 30, 55 colouring 37, 42, 44, 47 Construction Products Act 72 Construction Products Directive 72 Construction Products List 73, 74, 75, 79 consumer meter 24, 25, 28 contamination 33 conversion efficiency 9, 14 – 17, 22, 29 – 33, 43 – 46, 49, 58, 62, 66 copper-indium diselenide 23 copper-indium disulphide 14, 17, 33 coupling effect 65 cover glass 9, 16 – 20, 38, 42 – 44, 47, 64 crystalline module 13, 19 – 24, 30, 31 – 33 crystalline silicon 14 –18, 22, 23, 32 curtain wall 52, 65, 68, 73 – 75, 77 custom module 19 –21, 23, 62, 71

cable cabling cadmium cadmium telluride canopies capping strip carbon dioxide casting resin CdTe modules CE marking cell spacing cell string charge carrier circulation zone CIS module cladding

degression delamination diffuse radiation direct current direct radiation disconnector distribution network operator double-leaf facade drilled hole dummy cell

8, 31 38, 71 12, 13 25, 27, 28 12, 13, 17 28 8 30, 49, 62, 65, 74 19, 53 – 55, 63, 74 42, 46

dummy element dummy panel dye-sensitised solar cell

24 64 14

earthing economy economics edge cover edge seal electrical installation electricity generation electricity grid electricity price electric shock electromagnetic compatibility electromagnetic radiation electron elevation angle encapsulation energy balance energy consumption energy efficiency upgrade energy mix energy payback time equipotential bonding ethylene ethylene vinyl acetate Euro efficiency European Technical Approval facade-integrated PV feed-in tariff final energy fire protection fixed anchorage system fixed sunshade flat roof float glass four-point bending test frame clip frameless PV module free-standing system front contact

20, 28, 72 8, 68 22, 29, 30, 31, 40 52, 54, 64, 74, 75 18 28, 71, 72 7, 8, 25, 35, 64 8, 9, 25 –27, 28, 72 8, 9 72 71 11 14 –17, 26, 27, 71 13 19, 38, 42, 44, 51 33 7, 8, 33 39 25 32, 33, 40 20 19, 54, 61 61 27 52, 53, 73, 74, 76 –78

33, 40 8, 9, 11, 30, 31, 40 8, 32 28, 56, 60, 72, 73, 79 56 50, 66 27– 31, 50, 55 – 58, 66, 72 20, 43, 51, 61, 77 78, 79 53 51, 52, 53 56, 57 14, 16 – 19, 32, 35, 45

generation meter generator

24, 25, 28 9, 11, 13, 16, 22, 24 – 28, 30 – 32, 38, 46

German Institute of Building Technology glare glass /glass laminate

73, 76, 78 49, 51, 61, 66, 67 51 – 55, 63, 73 – 75, 82, 83, 87, 89, 95 glass /plastic laminate 51, 54, 69, 73, 74 glazing bar 13, 51, 52, 53, 60, 64 glazing for constant foot traffic 78 glazing for foot traffic 76, 77 glazing for occasional foot traffic 78 global irradiation 7, 8, 12, 31 grid parity 8, 9 grid-connected installation 9 grid-connected system 25 ground-mounted array 8, 9, 30, 54 hail 19, 71 hard roof covering 74, 76, 79 hazardous substance 33 heat-soak test 63, 69, 74, 75 heat-soaked toughened safety glass 63, 74, 75 heat-strengthened glass 54, 61, 71, 74 – 76 heritage asset 39, 41, 72 high-efficiency cell 14, 16, 22, 23 horizontal glazing 75 hot-melt film 19, 69 hotspot 19, 23, 24, 71 hybrid HIT solar cell 15, 16 incident radiation individual approval insulating glass unit integral system integral systems inverted roof inverter irradiation junction box

11–13, 31 52, 60, 68, 73 – 79 49 – 51, 53, 65, 77 50, 55 – 58, 60, 61 55 – 57, 60, 61 57 24 – 32, 71, 72 12, 22, 23, 27, 30, 31, 33 19 – 21, 23, 27, 28, 32, 63, 79

22

kilowatt-peak

19, 20, 32, 33, 51, 57, 61, 73 – 78 laminated glass 51, 73, 75 laminated safety glass 51, 54, 61, 65, 74 – 78 laser 15, 16, 17, 18, 46 light permeability 44 – 46 light trap 16, 17, 43 lightning protection 13, 72 linear support 51–54, 61, 64, 74, 75 List of Technical Construction Regulations 63, 75 local development plan 72 louvre 19, 50, 66 – 69, 74 low E glazing 21, 92 low-iron glass 43 Low-Voltage Directive 71 luminance 22, 37 laminate

Maximum Power Point mechanical damage mechanical retainer mechanical retainers metal roof covering microcrystalline silicon micromorphous silicon mismatching Model Building Code Model List of Technical Construction Regulations modularity module spacing monocrystalline silicon monocrystalline solar cell mounting angle mounting rail movable sunshade MPP tracker multi-pane insulating glass multiple reflection

22, 26 19, 28, 36, 44 74 74 55, 58, 60, 73, 74 17 16, 17, 22 25, 30, 31 72, 73, 78, 79 63, 75 36, 41, 42, 46, 47 57, 66, 67 16 15 57, 59, 66 58, 59 13, 50, 67 27 77 16, 43

nano solar cell 14, 18, 22, 33, 36 nanotechnology 9, 14, 36 National Technical Approval 52, 53, 60, 71, 73 – 78 National Test Certificate 60, 73, 74, 76 – 79 network operator 8, 28 noise barrier 9, 26, 30, 31 non-regulated building product 73, 74, 76 – 78 non-regulated form of construction 61 12 – 15, 26 – 31, 40, 41, 55 – 59, 62, 66 8, 12, 19 – 24, 26 – 33, 40 20, 54, 55, 61, 66, 68, 73 – 77, 79

orientation output overhead glazing

patterned glass pendulum impact test performance ratio photon photovoltaic element photovoltaic module pitched roof p-n junction point fixing point support polycrystalline silicon polycrystalline solar cell polyurethane post-and-rail facade power plant prefabricated facade primary energy printing propagation of fire public grid PV element PV generator PV module polyvinyl butyral rafter anchors rated output

43 72, 76, 78 30, 31 14, 17 74 20, 25, 32 28, 50, 55, 58, 59, 61, 74 14 –17 52 – 54, 61, 63, 68 52, 54, 55, 63, 74, 75 14 15, 44, 77 21 52, 53, 62, 64 8 – 11, 18, 24 – 26, 32 62, 65, 74 7, 22, 32, 33 43, 44, 76, 77 79 24, 27, 72 51, 55, 62 – 64, 66, 69, 71, 77 – 79 9, 24 – 27, 32 13, 15, 23, 25, 27, 30 – 33, 36, 37, 46, 49 – 52, 59 – 63, 71– 73, 79 19, 61, 75 101 12, 22, 23, 27, 29, 31

109

Appendix

reaction to fire rechargeable batteries recycling reflection

79 24, 25 32, 33 15, 16, 20, 30 – 32, 35, 37, 39, 42 – 45 refurbishment 57 regulated building product 61, 73, 74, 76 –78 regulated design 74 regulated form of construction 52, 64, 75, 76, 79 remuneration 8, 25, 30 Renewable Energies Act 8, 25, 30, 31, 40 renewable energy source 7, 8 residual loadbearing capacity 61, 75, 77–79 ribbon silicon 14, 15, 27, 33 roof tile 21, 41, 46, 58, 60, 61, 73, 74 rooflight 74 safety barrier safety extra-low voltage sawtooth roof self-cleaning effect semiconductor series connection setting block shading angle shadow

73 – 78 72 55, 61, 83, 87, 89 24, 53, 59 8, 14 –18, 32 17, 25 52, 53, 64, 65 57, 66, 67 13, 23, 24, 27, 29 – 31, 46, 61, 66 – 68 short-circuit 28, 72 shutter 39, 40, 50, 66, 67, 69, 74 silhouette 13 silicon 14 –17, 22, 23, 32, 33, 44 silicone 27, 36, 53, 64, 77 silk-screen printing 66 single glazing 74, 75 snow 12, 13, 31, 53, 58, 60, 63, 71, 77 soiling 13, 24, 30, 31 solar altitude angle 11, 12, 50 solar cell 8, 9, 11–19, 21– 24, 32, 33, 35, 42 – 46, 57, 61, 71, 73 – 79 solar constant 11 solar electricity 9, 11 – 33, 35 – 38, 41, 46, 55, 58, 61, 66, 67 solar energy 11, 12, 22, 25, 30, 49, 62 solar glass 20, 22 solar module 12, 13, 15, 16, 20 – 25, 30, 32, 33, 46, 49, 51, 71– 73 solar radiation 11–13, 22, 23, 29, 50, 68 solar roof tile 41, 60, 61, 73, 74 solar thermal system 18 solar trajectories 13 solder 19, 20, 33 space travel 8, 17, 37 spandrel panel 39, 62, 63, 76 spectra 11, 12, 17, 22, 23 spectral composition 11, 23 spectral sensitivity 23 spectrum 9, 11, 14, 15, 17, 22, 23, 46, 71, 72 stability 8, 18, 52, 55 – 57, 72, 73, 76 stainless steel 17, 18, 36, 54, 58, 64, 68 stand-alone system 25 standard test conditions 22, 71 stand-off system 50, 55 – 59, 72 string 11, 15, 16, 19, 24, 26 – 28, 68, 73, 75 string-ribbon process 15 structural sealant glazing 53, 64, 65, 73, 74, 77 substrate 14 – 18, 20, 42 – 47, 78 sunbelt 12 sunlight 7, 9, 11 – 18, 23, 27, 45, 46, 49, 66, 68 sun path diagram 13 sunshades 9, 13, 33, 39, 49, 50, 61, 66, 67 sunshading 19, 41, 46, 49, 50, 61, 66 – 69, 73, 74, 77 system efficiency 30 system technology 26 – 30, 33 tandem solar cell technical connection conditions Technical Rules for Glass in Safety Barriers Technical Rules for the Design and Construction of Point-Supported Glazing

110

17 72 75 52, 75

Technical Rules for the Use of Glazing on Linear Supports 51, 52, 75 temperature behaviour 22, 23, 29 temperature coefficient 23, 71 texture 9, 15 – 17, 35 – 38, 42 – 44, 47 thermal insulation 49, 51, 55, 57, 62 – 64 thermohydraulic drive 68 thin-film module 15 – 17, 20 – 24, 27, 29 – 33, 63, 73 thin-film technology 9, 16, 17, 22, 33, 43 – 47, 51, 62, 66 tolerance 23, 24, 29, 31, 58 toughened glass 20, 51 toughened safety glass 20, 51, 61, 63, 73 –75 trajectory of the sun 9, 12, 13 transformer 27 transmission 8 transparency 18, 21, 38, 42, 44, 46, 47, 61, 66 trapezoidal profile sheeting 56, 57, 59 triple-junction solar cell 17 Ü mark undercut anchor

73, 74 53 – 55

ventilation ventilation cavity verification of applicability vertical glazing voltage

wafer warm facade warm roof warranty waterproofing watt-peak wavelength weather wind load wired glass wiring yield yield estimate yield prediction

30, 60, 62 – 64, 75 62 – 64, 74, 75 56, 73 – 79 55, 65, 74 – 77 14, 19, 20, 22, 25 – 27, 29, 71, 72 9, 14 –16, 32, 33, 37, 45 50 30, 55, 57 21, 30, 32, 38 55 – 57, 75 22 12, 17, 23, 35, 43 12, 19, 20, 28 – 30, 41, 49, 50, 57, 62, 63 53, 61, 65, 68 75 23, 24, 27, 60

12, 13, 23, 25 – 27, 29 – 31, 33, 43, 55, 58, 62, 66 31 30

Appendix

Picture credits The authors and publishers would like to express their sincere gratitude to all those who have assisted in the production of this book, be it through providing photos or artwork or granting permission to reproduce their documents or providing other information. All the drawings in this book were specially commissioned. Photographs not specifically credited were supplied from the archives of the architects or the magazine DETAIL. Despite intensive endeavours we were unable to establish copyright ownership in just a few cases; however, copyright is assured. Please notify us accordingly in such instances.

page 26: TNC Consulting, CH – Erlenbach

page 54 top: IBC SOLAR AG, Bad Staffelstein

page 28 top: Kaco New Energy GmbH, Neckarsulm

page 54 centre: Schletter GmbH, Kirchdorf/Haag

page 28 centre, 46 left, 61 left: Sunways AG, Constance

page 55: BP Solar Deutschland GmbH, Hamburg

page 28 bottom: ISET e.V., Kassel

page 56 left: Kolb & Schmelcher Elektro, Mannheim

page 29 top, 56 right: SunStrom GmbH, Dresden

page 57 top: alwitra Flachdach-Systeme, Trier

page 29 centre, 51, 92, 93: Peter Ferstl, Regensburg

page 57 bottom: Solar Integrated Technologies GmbH

page 29 bottom: SMA Solar Technology AG, Niestetal

page 58 bottom: Soltech GmbH, Bielefeld

page 8 centre: Smithsonian, National Air & Space Museum, US – Chantilly, Virginia

page 32: SolarWorld AG, Bonn

page 60 top: asola – Advanced & Automotive Solar Systems GmbH, Isseroda

page 8 right, 76 left: Architekturbüro Georg Feinhals, Aachen

page 34: Uwe Schumann

page 9 left: FBH/Petra Immerz

page 36 left, centre: Deutsches Zentrum für Luft- & Raumfahrt e.V., Cologne

page 60 bottom: Kalzip, Koblenz

page 9 right: Dieter Geyer, Zentrum für Sonnenenergie & Wasserstoff-Forschung, Stuttgart

page 37: Samyn & Partners, Brussels

page 61 right: Schüco International KG, Bielefeld

page 10: Aitor Diago, ARTEUNO WELT S.L.

page 38 top: Christian Richters, Münster

page 62 top: GOLDBECK Solar GmbH, Hirschberg

page 13: Markus Metz, Berlin

page 38 bottom: Photo Archive of the City of Herne

page 63 right: ‘asp’ Architekten, Stuttgart

page 14 right: Konarka Technologies, Inc., US – Lowell

page 40 top: NET Nowak Energie & Technologie AG, CH – St. Ursen

page 65 top: Simone Giostra & Partners, Inc., USA – New York

Cover centre, page 70: Christian Schittich, Munich page 6: Dr Alzheimer’s Photo Blog, www.gallery.dralzheimer.stylesyndication.de

page 15 left: Sovello AG, BitterfeldWolfen page 15 centre, 20 bottom centre: SCHOTT Solar, Alzenau page 15 right: SANYO Component Europe GmbH, Munich page 16: Helmholtz-Zentrum Berlin für Materialien & Energie page 18 top right: FZ-Jülich page 18 centre: Odersun AG, Frankfurt page 18 bottom: Nanosolar GmbH, Luckenwalde page 21 top: Scheuten Solar, Venlo

page 40 centre: Würth Solar GmbH & Co. KG, Schwäbisch Hall page 40 bottom: Astrid Schneider, Berlin page 41 top: msp Architekten, Dresden page 41 centre, 46 right, 63 left, 76 right: Glaswerke Arnold GmbH + Co. KG, Merkendorf page 41 bottom: Leon Schmidt page 42, 77 right: ertex-solar GmbH, A – Amstetten page 44 top: WISTA-MG, www.adlershof.de, Berlin

page 60 centre: systaic AG, Düsseldorf

page 67 top, 68 top, 69: Colt International GmbH page 67 bottom: Pierre Tousse, Montpellier page 72: TÜV Rheinland Group page 77 left, 83: Bitter Bredt Fotografie, Berlin page 78 centre: Jan Wünsch, Dresden page 78 right, 79 left: Jan Ebert, Dresden page 79 centre: Friedrich May, Berlin

page 45 top, 65 bottom: Tobias Grau GmbH, Rellingen

page 79 right: Materials Testing Institute, University of Stuttgart – MPA Stuttgart

page 46 centre: Constantin Meyer, Cologne

page 80, 84: MCA /Daniele Domenicali

page 22 top: Prof. Dr. Jan Cremers, SolarNext AG/Hightex Group, Rimsting

page 47 top left: Kopf Solarschiff GmbH, SulzKastell

page 82: Ralf-Peter Busse, Leipzig

page 22 centre: Corus Bausysteme GmbH, Munich

page 47 top right: Karl Blockwell, Capita Symonds, UK – Cardiff

page 85: MCA/Alessandro Digaetano

page 24 top: SOLON SE für Solartechnik, Berlin

page 47 bottom: Art Gray, USA – Santa Monica

page 87, 88, 89: Bruno Klomfar, Vienna

page 24 bottom: Wilhelm Hofbauer, Vienna

page 48, 62 bottom: Lukas Roth, Cologne

page 90, 91: Jens Passoth, Berlin

page 25: Solarc Innovative Solarprodukte GmbH, Berlin

page 53: Planerwerkstatt Hölken-Berghoff, Vörstetten

page 95: Michael Voit, Munich

page 21 bottom: SOLARWATT AG, Dresden

111

Product credits

Full-page plates

The authors and publishers would like to thank the following companies for providing samples and /or for their permission to take photographs of products in situ.

page 10: 1 MW solar power plant with dual-axis-tracking SOLON-Mover units in Cabanillas (E)

page 97, 98 bottom, 99: Eibe Sönnecken, Darmstadt

Photos: Stefan Unnewehr, Dresden

page 100, 101: Andreas Keller, Altdorf

page 14 bottom (1st): ersol Solar Energy AG, Erfurt

page 34: Q-Cells company headquarters in Bitterfeld-Wolfen (D), 2007, bhss Architekten

page 102: Stefan Unnewehr, Dresden

page 14 bottom (2nd, 3rd), page 45 centre & right (4 No.), page 15 top right (a & b): ertex-solar GmbH, A – Amstetten

page 96: Melanie Weber, Munich

page 14 bottom (4th): Solar Integrated Technologies GmbH page 14 bottom (5th), page 20 bottom right: Würth Solar GmbH & Co. KG, Schwäbisch Hall page 19, page 20 top, bottom left, page 44 bottom, page 45 bottom left (2 No.), page 46 top left (l): SOLARWATT AG, Dresden page 22 bottom: Odersun AG, Frankfurt page 36 right (4 No.): Advent Solar Inc., US – Albuquerque Editor: page 43 top: Thiele Glas, Falkenhain (l) Hunsrücker Glasveredelung Wagener GmbH & Co. KG, Kirchberg (r) page 43 bottom: SAINT-GOBAIN Glass Deutschland GmbH, Aachen Editor: page 46 top left (r): Glaswerke Arnold GmbH + Co. KG, Merkendorf page 54 bottom: solarnova Produktions-& Vertriebsgesellschaft mbH fischerwerke GmbH & Co. KG, Wedel page 58f. top: Schletter GmbH, Kirchdorf/Haag

112

page 48: Fire station, Heidelberg (D), 2007, Peter Kulka page 70: Lehrter railway station in Berlin (D), 2006, von Gerkan, Marg & Partner page 80: Institute premises in Peking (CN), 2006, Mario Cucinella Architects page 102: Close-up image of a polycrystalline silicon wafer