Integration of Photovoltaic Technology in Architectural Envelopes. Design Guide by Javier Manjon

Integration of PV Technology in Architectural Envelopes. Design Guide

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MSc in European Construction Engineering 2012-2013 Integration of Photovoltaic Technology in Architectural Envelopes. Design Guide Author Javier Manj贸n

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Research University VIA University College Horsens, Denmark

Supervisor

Moderator

Malene Munch

Marina di Marco

Integration of PV Technology in Architectural Envelopes. Design Guide

I. ABSTRACT If due to the different available technologies, nowadays most of the energy needs of the buildings can be reach by solar energy, why this technology is still unexploited? The answer seems to be that, despite its proven efficiency, low cost and short payback period, these systems are perceived as architecturally unattractive option. A common criticism is that efforts to integrate solar technology into buildings fail because architects rarely support the design of roofs or facades with solar components. Perhaps it is because, despite there is a fully developed technology, this has been released from a more technical point of view. Therefore, this dissertation will seek to explore its aesthetic and design possibilities.

II. RESEARCH STATEMENT Since this research requires a thorough analysis of the potential of photovoltaic technology, in order to extract its possibilities from the point of view of design, a direct contact with the PV industry and its leaders has been required. So most of the effort to know the existing technology has been focused on getting it through these channels of information, leaving in the background the study based on library, papery catalogues, and, ultimately, all the kind of information that may not have been updated. In the context of this research, it had no kind of sense to work with obsolete or outdated data. Photovoltaic technology is constantly evolving and if we wanted to squeeze the full potential of it, it was necessary to work with the most up-todate information as possible. Whereupon, this Thesis has been developed on the basis of data from several sources: solar companies product brochures, magazines such as Detail (mainly in its Green edition) and scientific websites (ISI Web of knowledge). So, we could say that the study requires two types of visions: a first one, product of a team work, that uses those professionals with more experience and knowledge in the area of solar technology, and a second one, much more individually and which, helped by my experience as an architect, sifts through the information collected in order to determine which factors and features are the most interesting to add value to a project by means of the photovoltaic technology.

Integration of PV Technology in Architectural Envelopes. Design Guide

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III. ACKNOWLEDGEMENTS I am extremely thankful to those people who make possible this research: Miguel Angel Gonzalez Gomez (2G Arquitectos, Spain), all the team of RUM arkitekter a/s, Peter Baadsmand, Jake Baerentsen & Phil Witcomb (Horsens CrossFit), MarĂa Alberdi Pagola & Victor Marcos Meson (Master in European Construction Engineering). In the one case, their technical support and advices based on their experience and, in the other, their motivational help as well as their tips as researchers and friends, have been so very helpful to me. I would also like to thank Bo Riisbjerg Thomsen (Building & Construction Design Consultant), for assisting me to direct an initial and confusing proposal into a project with a great interest.

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Integration of PV Technology in Architectural Envelopes. Design Guide

IV. CONTENTS I. ABSTRACT ................................................... II. RESEARCH STATEMENT ........................................ IV. CONTENTS .................................................. V. LIST OF FIGURES ............................................ VI. LIST OF TABLES ............................................ VII. LIST OF ABBREVIATIONS/SYMBOLS ............................

3 3 5 7 8 8

1. INTRODUCTION ............................................... 9 1.1. Background ............................................. 9 1.2. Aims and objectives ................................... 12 1.3. Research methodology .................................. 13 1.4. Limitations and Scope ................................. 14 1.5. Dissertation Report Outline ........................... 15 2. PHOTOVOLTAIC SYSTEMS ...................................... 2.1. PV System components .................................. 2.2. PV System performance ................................. 2.3. Current technologies .................................. 2.3.1. Concentrating PV modules .......................... 2.3.2. Crystalline silicon modules ....................... 2.3.3. Thin film modules ................................. A. Amorphous silicon modules. .......................... B. Copper-indium selenide modules. ..................... C. Cadmium telluride modules ........................... 2.3.4. Organic Solar Cells ...............................

16 16 18 20 21 22 23 24 25 26 27

3. APPEARANCE ................................................ 3.1. Structure ............................................. 3.2. Proportions ........................................... 3.3. Shape ................................................. 3.3.1. Cell shape ........................................ 3.3.2. Module shape ...................................... 3.3.3. Flexibility ....................................... 3.4. Transparency .......................................... 3.5. Colour ................................................ 3.5.1. Cell colour ....................................... 3.5.2. Back cover film colour ............................ 3.6. Mounting Systems ...................................... 3.7. Thermal insulation .................................... 3.8. Frame .................................................

28 29 31 32 32 33 35 36 38 38 39 40 41 42

4. ARCHITECTURAL INTEGRATION ................................. 4.1. Integration on roofs .................................. 4.1.1. Pitched roofs ..................................... 4.1.2. Photovoltaic tiles ................................ 4.1.3. Flat roofs ........................................ 4.1.4. Integration in glazed roofs ....................... 4.2. Integration in facades ................................ 4.2.1. Integration in curtain walls ...................... 4.2.2. Integration in ventilated facades ................. 4.2.3. Integration in windows ............................ 4.2.4. Integration in sunshades ..........................

43 44 44 46 48 49 51 51 52 53 54

Integration of PV Technology in Architectural Envelopes. Design Guide

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4.3. Integration in other structures ....................... 4.3.1. Urban furniture ................................... 4.3.2. Noise barriers .................................... 4.3.3. Lighting .......................................... 4.3.4. Awnings and canopies .............................. 4.4. Essence of the architectural integration of PV modules

55 56 56 57 57 58

5. GUIDELINES FOR THE DESIGN AND OPERATION ................... 5.1. Solar radiation received. ............................. 5.2. Factors affecting the productivity .................... 5.2.1. Shading losses .................................... 5.2.2. Temperature losses ................................ 5.2.3. Dust losses ....................................... 5.2.4. Losses caused by wiring ........................... 5.2.5. Losses caused by decoupling ....................... 5.3. Maintenance ...........................................

60 61 63 63 68 70 71 72 73

6. CONCLUSIONS ............................................... 74 7. BIBLIOGRAPHY AND REFERENCES ............................... 76

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Integration of PV Technology in Architectural Envelopes. Design Guide

V. LIST OF FIGURES FIGURE 1: SAVINGS AS A RESULT OF THE INTEGRATION OF PV GENERATORS IN BUILDINGS COMPARED TO ABOVE-GROUND INSTALLATIONS .................. 10 FIGURE 2: THE TWO MAIN PHASES OF THE RESEARCH ....................... 13 FIGURE 3: PV SYSTEM COMPONENTS ................................... 16 FIGURE 4: 2010 CELL PRODUCTION BY TECHNOLOGY (SOURCE: PHOTON INTERNATIONAL, 2011) .................................................... 20 FIGURE 5: CONCENTRATING PV MODULE, (JAISUN SOLAR, 2013) ............ 21 FIGURE 6: CRYSTALLINE SILICON MODULE STRUCTURE ...................... 22 FIGURE 7: THIN FILM MODULE STRUCTURE ............................... 23 FIGURE 8: AMORPHOUS SILICON MODULE (GETIT, 201?) ................... 24 FIGURE 9: COPPER -INDIUM SELENIDE MODULE. RIGID AND FLEXIBLE OPTIONS (SOLOPOWER, 2010) .......................................... 25 FIGURE 10: CADMIUM TELLURIDE MODULE (FIRST SOLAR, 2011) ............. 26 FIGURE 11: PROTOTYPE OF AN ORGANIC SOLAR CELL (FRAUNHOFER ISE, 2013; HOFMANN, W. 200?,) ......................................... 27 FIGURE 12: CHANCES FOR PV GLASS SHEETS ............................ 29 FIGURE 13: PV ELEMENTS CAPABLE OF BEING REPLACED .................... 30 FIGURE 14: HOTEL AT GRAND CANAL SQUARE, DUBLIN, BY AIRES MATEUS (STRUCTURAE, 2013) ......................................... 31 FIGURE 15: USUAL CRYSTALLINE-SILICON CELLS SHAPE .................... 32 FIGURE 16: EXAMPLES OF MODULES WITH TRIANGULAR, HEXAGONAL AND CIRCULAR SHAPE (ZOKA ZOLA 201?) ........................................... 33 FIGURE 17: CITE DU DESIGN BY LIN (RICHTERS, C., 2010) .............. 34 FIGURE 18: JAPAN PAVILION AT THE WORLD EXPO 2010 IN SHANGHAI BY HIKOSAKA (DESIGNBOOM, 2009) ......................................... 35 FIGURE 19: SCHOTT HEADQUARTERS IN MAINZ BY JSK ARCHITECTS (SCHOTT/A. STEPHAN, 2010) ............................................ 37 FIGURE 20: PERFORMANCE OF A MULTI-SI SILICON MODULE ACCORDING TO THE COLOUR OF ITS CELLS (VALUES PROVIDED BY SUNAWAYS .EU) ................... 38 FIGURE 21: POLYSOLAR A-SI PV MODULE -20% TRANSPARENCY- (POLYSOLAR, 2011) ......................................................... 39 FIGURE 22: KALYPSO SP BY ARCELOR MITTAL (ARCELOR MITTAL, 2012) ....... 40 FIGURE 23: SEMI-TRANSPARENT DOUBLE AND TRIPLE GLAZED INSULATING PV GLASS UNITS ..................................................... 41 FIGURE 24: AMORPHOUS SILICON THIN FILM FRAMELESS PV PANEL (KUPITER, 201?) ......................................................... 42 FIGURE 25: TRUE PV INTEGRATION ................................... 43 FIGURE 26: SYDESL HEADQUARTERS BY NICOLAS ......................... 44 FIGURE 27: THE NEW BOUWKUNDE BY ADAM WOJTALIK (WOJTALIK, A., 2009) ... 45 FIGURE 28: SOLAR TILES TIPOLOGIES ................................. 46 FIGURE 29: SOLAR SLATE ROOFS (DUER, 2012; SOLARSLATE -LTD, 2013) ..... 47 FIGURE 30: BARNES FOUNDATION BY TOD WILLIAMS + BILLIE TSIEN (CRANE, T.,2013) ................................................. 48 FIGURE 31: TYPICAL GLASS-GLASS LAMINATE PV CONFIGURATION .............. 49 FIGURE 32: SAN ANTON MARKET SKYLIGHT BY QVE-ARQUITECTOS (QVE, 2010) .. 50 FIGURE 33: GREENPIX MEDIA WALL BY SGPA (SGPA, 2008) ............... 51 FIGURE 34: GENYO LABORATORIES BY PLANHO (GONZÁLEZ, A., 2008) ........ 52 FIGURE 35: TRANSMISSION OF THE LIGHT INTO THE BUILDING THROUGH THE PV GLASS ......................................................... 53 FIGURE 36: PRATT INSTITUTE BY WASA / STUDIO A (SEVERIN, A., 2010) ... 54 FIGURE 37: A22 HIGHWAY AT BRENNERO IN ITALY (WORLD HIGHWAYS, 2012); GREEN BUBBLE BY BREAD STUDIO (BREAD STUDIO, 2012) .................. 56 Integration of PV Technology in Architectural Envelopes. Design Guide

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FIGURE 38: EXAMPLE OF SOLAR CANOPY FOR PARKING LOTS; PURE TENSION BY SYNTHESIS DESIGN + ARCHITECTURE (SDA/VOLVO, 2013) .............. 57 FIGURE 39: INSERO HORSENS PROPOSAL, PART 1 ......................... 58 FIGURE 40: INSERO HORSENS PROPOSAL, PART 2 ......................... 59 FIGURE 41: ENDESA PAVILLION BY THE INSTITUTE FOR ADVANCED ARCHITECTURE OF CATALONIA (GOULA, A., 2012) ................................. 61 FIGURE 42: DESIGN TIPS REGARDING THE SOLAR RADIATION RECEIVED ......... 62 FIGURE 43: HORIZON LINE FOR HORSENS, DENMARK (POLAR GRAPH) ........... 64 FIGURE 44: HORIZON LINE FOR HORSENS, DENMARK (CARTESIAN GRAPH) ........ 65 FIGURE 45: FRACTION OF IRRADIATION NOT RECEIVED BY THE PV GENERATOR ..... 65 FIGURE 46: PV MODULES DISTANCE CALCULATION ......................... 66 FIGURE 47: DESIGN TIPS REGARDING THE SOLAR RADIATION RECEIVED ......... 67 FIGURE 48: SUN-ROOT BY GREEN ROOF TECHNOLOGY (GREEN ROOF TECHNOLOGY, 2012) ......................................................... 69 FIGURE 49: DESIGN TIPS REGARDING THE TEMPERATURE LOSSES .............. 69 FIGURE 50: PROBLEMS AND FORESIGHTS RELATED TO DUST LOSSES ............. 70 FIGURE 51: DESIGN TIPS REGARDING THE WIRING ......................... 71 FIGURE 52: DESIGN TIPS REGARDING THE DECOUPLING LOSSES ............... 72

VI. LIST OF TABLES TABLE 1: ACHIEVABLE LEVELS OF SOLAR ENERGY PRODUCTION FROM PV ROOFS AND FACADES IN SOME OF THE EU COUNTRIES. ........................... 11 TABLE 2: ELECTRICAL ENERGY STORAGE SYSTEMS (SOURCE: FRAUNHOFER ISE) .... 17 TABLE 3: CURRENT TECHNOLOGIES PERFORMANCE MEASURED UNDER STANDARD TEST CONDITIONS (STC) ........................................... 18 TABLE 4: TOP 10 WORLD'S MOST EFFICIENT SOLAR PV MONO-CRYSTALLINE CELLS ON THE MARKET TODAY (SOURCE: SOLARPLAZA, 2012) .................... 19 TABLE 5: FREQUENT APPLICATIONS OF PHOTOVOLTAIC INTEGRATION INTO URBAN ELEMENTS, AND APPROXIMATE SIZE OF THE PHOTOVOLTAIC MODULES. ......... 55 TABLE 6: REDUCTIONS IN PERFORMANCE COEFFICIENTS DUE TO THE TEMPERATURE INCREASE FOR COMMERCIAL MODULES OF DIFFERENT TECHNOLOGIES. .......... 68

VII. LIST OF ABBREVIATIONS/SYMBOLS a-Si AC BIPV c-Si CdTe CI(G)S CIS DC IEA IEC PV STC µc-Si

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AMORPHOUS SILICON ALTERNATING CURRENT BUILDING INTEGRATED PHOTOVOLTAIC CRYSTALINE SILICON CADMIUM TELLUDIRE CIS SEMICONDUCTORS ALLOYED WITH GALLIUM (G) COPPER-INDIUM-DISELENIDE AND COPPER-INDIUM-DISULPHIDE DIRECT CURRENT INTERNATIONAL ENERGY AGENCY INTERNATIONAL ELECTROTECHNICAL COMMISSION PHOTOVOLTAIC STANDARD TEST CONDITIONS MICROCRYSTALLINE SILICON

Integration of PV Technology in Architectural Envelopes. Design Guide

1. INTRODUCTION 1.1.

Background

According to the Key World Energy Statistics from the IEA, the International Energy Agency, the building industry, with all processes that are associated with it, represented in 2012 almost half of global energy consumption of our planet. This fact should make us reflect and certainly, we must act from different areas. Along with the design and construction strategies aimed at improving the energy efficiency of buildings, it is important to turn to the use of renewable energy sources. Those buildings that consume fossil fuels are destined to become obsolete in the course of their life. Integration technologies such as photovoltaic or solar thermal in building are already a reality, and it is expected that these technologies have increasing development. In particular, photovoltaics will play a leading role in replacing conventional energy sources because, by their nature, it is the renewable energies that best blends into the buildings. It is a mature technology constantly evolving, and there is already considerable experience in systems, both isolated and connected to the electric grid. However, this growth has not yet reached photovoltaic systems integrated into the building. It is true that the current regulatory framework promotes a certain extent this application. In addition, architects and developers are increasingly convinced about the good that integrated photovoltaics in new buildings can reach. Even with all, further measures are needed to encourage, support and promote larger-scale use of photovoltaics in the urban context.

Integration of PV Technology in Architectural Envelopes. Design Guide

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As show in figure 1, the integration of solar photovoltaic energy in buildings presents great advantages when compared to above-ground installations:

Figure 1: Savings as a result of the integration of PV generators in buildings compared to above-ground installations

In standalone applications, we can adapt the system power to the local needs of consumption. Even in grid-connected systems where it is interesting to reduce peak electrical demand at certain times, the generating system can be sized for this purpose. A typical case is the power consumption in office buildings, which reaches its maximum at the middle of the day, largely by the use of air conditioning. Experience shows that good examples of integration of photovoltaics in buildings have very good social acceptance, helping to promote this type of energy. This integration helps to preserve the natural landscape, by not using additional land for installation and causing little visual impact, which may even be positive. Also, the PV can participate in the energy efficient design of buildings, to provide them with a clean and elegant way of producing electricity.

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Integration of PV Technology in Architectural Envelopes. Design Guide

Potential of photovoltaics in buildings The European Union, in the framework of ALTENER programme (Lysen, 2003), predicted in 1996 a promising future for PV integration, which was then emerging. A few years later, in 2002, the IEA, in a specific task dedicated to the integration of PV in buildings, presented estimates also very positive about this potential in different countries. Table 1 shows an update for these estimates. The method proposed by the IEA estimates the potential of photovoltaics in buildings from the area available for the installation of PV modules, corrected for solar and architectural constraints. The estimate is based on the valid areas of roof and facade for integrating PV: 1. Architectural restrictions contemplate corrections due to space limitations: different objects of the building, such as air conditioners, chimneys, elevators, terraces, and so on. Also, it takes into account the shadows cast by these or other objects (or others outside the building), or spaces reserved for other uses. Other constraints in historic buildings or protected were taken into account as well. 2. Solar-type restrictions are based on the calculation of radiation on building surfaces, depending on their orientation and inclination. Country

Denmark UK Germany Italy Netherlands Spain (*) Denmark:

BIPV Area potential (km2)

Potencial production of solar energy (TWh/year)

Roofs Facades 87,98 32,99 914,67 343,00 1295,92 485,97 763,53 286,32 259,36 97,26 448,82 168,31 2006 electricity

Roofs Facades 8710 2155 83235 22160 128296 31745 103077 23827 25677 6210 70689 15789 consumption

2008 electricity consumption (TWh/year)

36,39 (*) 400,39 617,13 359,16 123,49 303,17

Ratio solar productionelectricity consumption

23% 26% 26% 35% 26% 29%

Table 1: Achievable levels of solar energy production from PV roofs and facades in some of the EU countries. Just surfaces with 80% of the maximum local annual solar irradiation have been considered. (Sources: International Energy Agency, 2002 & 2008, and Organisation for Economic Co-operation and Development, 2008) Integration of PV Technology in Architectural Envelopes. Design Guide

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1.2.

Aims and objectives

As explained in the abstract, the idea of the present dissertation is very simple: to make solar technology more attractive to architects. But it must be taken into account that also the architectural constraints may affect the final performance of the photovoltaic system (the orientation and inclination of the modules in buildings could be not optimal, there is always a greater likelihood of shading, and ventilation of the modules on its posterior surface might not be properly solved). This is precisely the challenge that should unite engineers and architects: to make the integration of photovoltaic systems reconciles adequately power generation and architectural function of PV modules, so that the advantages outweigh the disadvantages. So, as the architectural integration of photovoltaic systems is the result of the effort for architects, engineers and manufacturers, who must work in coordination between them, the challenge and the objective of this research will precisely be to give a joint response to the needs of power generation and architectural requirements.

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Integration of PV Technology in Architectural Envelopes. Design Guide

1.3.

Research methodology

The present research methodology is developed in are two clearly divided phases (Figure 2): Regarding the integration of solar technology in building envelopes, several strategies can be distinguished. These range from the hide of technical components and their camouflage, to solutions that allow to dominate the aesthetics of the building as well as technical and structural elements. To do that, however, we really need that the first phase, more theoretical, is based on the investigation and study of the existing photovoltaic technology. Thus, it is possible to identify all the factors that can influence, in one way or another, in the building final aesthetics. Once this phase is concluded, it is time to start "playing" with all these factors and see the degree of flexibility offered by each of them, in order to adapt them to the design that architects have in mind. The second phase therefore is more practical and less technical: building on the results of the research carried out during the first phase, it examines the possibilities of the existing current technology from a design point of view. Nevertheless, it should be mentioned that this selection of factors and customization options must be performed with strict criteria: keeping in mind that any decision taken on the aesthetics and location of the modules has implications on their final performance.

Figure 2: the two main phases of the research

Integration of PV Technology in Architectural Envelopes. Design Guide

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1.4.

Limitations and Scope

Regarding the scope of research, the areas covered are basically based on photovoltaic systems. Solar electricity technology is a subject sufficiently complex to justify to focus all the efforts on it. â&#x20AC;˘ â&#x20AC;˘ â&#x20AC;˘

Appearance Applications Guidelines for photovoltaic design and operation

Although in the beginning, this research pretended to cover fully solar technology, however, and due to the limited time available for the research, thermal collectors were excluded from the dissertation. Thereby, this could lead to further investigation in photovoltaic systems, a technology that, to this day, offers more possibilities from the point of view of design, if compared with solar hot water heating systems. Consequently, no one aspect related to the photovoltaic technology has been ignored or worked in less depth.!

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Integration of PV Technology in Architectural Envelopes. Design Guide

! 1.5.

Dissertation Report Outline

Once we have established the context, objectives and methodology for this dissertation, it is important to note how to structure the development of it. First, we will do a compilation about the existing photovoltaic technologies, with an emphasis on the knowledge of the various components both within the PV system and the PV generator itself. In other words, this is to meet the raw material with which we will be able to work in order to achieve a both elegant and effective integration into the project in which we work. Second, we will analyse all the factors that influence the appearance of the generator since these are, ultimately, the most interesting parameters to handle once we project a building or any other element that integrates photovoltaic modules. Knowing the possibilities but also the limitations of the technology, we will be able to control the design and therefore, the final result. Then, we will study all the possibilities of integration of photovoltaic modules in facades and roofs (in addition to other innovative opportunities), analysing their pros and cons, and using examples in which integration of solar technology has proved a success. Finally, I understand that this dissertation would be incomplete if we ignore all those factors that affect productivity, and which are directly related to the design. For this reason, a series of guidelines is being raised. In a very concise way, it can help the designer to obtain an effective photovoltaic envelope, and visually interesting at the same time.

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Integration of PV Technology in Architectural Envelopes. Design Guide

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! 2. PHOTOVOLTAIC SYSTEMS 2.1.

PV System components

A photovoltaic system integrated into a building consists mainly of a photovoltaic generator and system for conditioning the power generated (Figure 3). •

Generator: The generator is composed of an association of photovoltaic modules, which gets values of power, voltage and current suitable to the needs of each installation.

•

Inverter: In turn, the inverter is a power electronic device that converts the direct current (DC) from the generator into alternating current (AC) power. This energy can be injected into the public electricity network or consumed directly in the building, option towards which we will move in the future.

•

The system has two energy meters: o o

Electricity meter for injection to the public power grid. Electricity meter for consumption, for the transfer of the PV produced.

Figure 3: PV System components 16

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Integration of PV Technology in Architectural Envelopes. Design Guide

â&#x20AC;˘

Batteries: In a grid-connected PV system is not necessary the use of batteries. Usually, the energy generated is injected in its entirety to the local power grid, after being transformed into AC power by an inverter. However, there are also examples of integrated autonomous systems. In those, it is necessary a device for accumulating the electricity produced. Battery systems can nearly double the proportion of PV electricity that can be used for own consumption in a home. So far, in domestic applications, lead acid batteries have been common, and although they are cheap, they only have a performance ratio of 85%. Lithium ion batteries are more expensive but also more efficient and durable (Table 2).

Type of storage Electrochemical batteries Lead acid battery Nickel cadmium NiCd Nickel metal NiMh hydride Lithium ion Li-ion Sodium sulfur NaS Mechanical storage Pumped hydro PHS Compressed air CAES Flywheel FES

Energy Efficiency

Lifetime (years)

75-90 60-80 65-75

3-15 5-20 5-10

85-98 70-85

5-15 10-15

70-80 41-75 80-90

>50 >25 15-20

Table 2: Electrical energy storage systems (Source: Fraunhofer ISE, 2011)

Integration of PV Technology in Architectural Envelopes. Design Guide

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2.2.

PV System performance

The behaviour of a PV system is described mainly by its performance ratio: PR. This performance gives an idea of how well a photovoltaic system is designed, installed and maintained. To it contributes, first, losses factors of the photovoltaic generator and, secondly, the factors of the rest of the system, mainly those associated with the inverter, which should be selected according to the actual system operation. In the integration of photovoltaic systems in buildings, generator losses tend to be higher than in other systems, because of the conditions in which modules work. The maximum value of the power module under standard test conditions is called nominal power and is frequently indicated by adding a subscript "p" to the symbol of the watt, being renamed Watt-peak. The standard test conditions (STC) are 1000 W/m2 of solar irradiance, 25째C PV module temperature and 1.5 of Air Mass (AM). The performance of a photovoltaic module is the maximum power that can be generated per unit area and unit of irradiance received. Is calculated by dividing the value of its peak power in W for its area in square meters and 1000 W/m2. Normally, the performance values are shown in percentage, for which the value calculated must be multiplied by 100 (Table 3). Cell technology

Performance (%) under STC

Area needed for 1 kWp

16-22,5% (Backside solar cells) 12-16% (Standard cells) 11,5-15%

5-6,5 m2

7-14% 9-11% 5-8% 2-3%

9-13 m2 9,5-11,5 m2 15-21 m2 30-40 m2

Crystalline c-Si Monocrystalline Polycristalline Thin Film CIS CdTe a-Si Organic PV Cells

6,5-9 m2 7-9 m2

Table 3: Current technologies performance measured under standard test conditions (STC)

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Integration of PV Technology in Architectural Envelopes. Design Guide

As an example, for properly oriented Central Europe PV installations, well ventilated and without shadows, an average of 860-980 kWh of electricity is produced per kWp and year (550650 kWh in vertical south-facing facades). Thus, in the case of crystalline modules with a performance ratio of 13-14%, this translates to 110-140 kWh per kWp per year (70-85 kWh in facades). Table 4 shows that higher performance modules are those whose cells, with moon crystalline structure, have all contacts on the top (backside solar cells). Recently, SunPower has developed a cell type called Maxeon Cell Technology, which reaches 22.5% efficiency (SunPower Corporation, 2011). Manufacturer Sunpower Sanyo Electric JA Solar Suntech Suniva Shinsung Solar Energy E-Ton Motech Neo Solar Power Solartech Energy

Cell Efficiency 22.5% 20.2% 20.0% 19.7% 19.4% 19.4% 19.3% 19.2% 19.2% 19.1%

Cell Type Maxeon Cell Technology HIT Solar Cell Structure JAC M6SL Secium Pluto Cell ARTisun Select SH-1940S3 Mono Cell 3BB XS156B3-200R X-Cells Perfect 19 SR-156-3

Table 4: Top 10 World's Most Efficient Solar PV Mono-Crystalline Cells on the market today (Source: Solarplaza, 2012)

Integration of PV Technology in Architectural Envelopes. Design Guide

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2.3.

Current technologies

At present the majority of photovoltaic modules are manufactured using cells of silicon (Si). Depending on its structure, this semiconductor material can be monocrystalline (mono c-Si), multicrystalline (multi c-Si), microcrystalline (Âľc-Si) and amorphous (a-Si). There are other semiconductor materials with properties suitable for the manufacture of photovoltaic cells and modules, such as gallium arsenide (gaAs), used in solar cells for terrestrial concentration systems, cadmium telluride (CdTe) and copper indium selenide (CIS), polycrystalline materials that are used for manufacturing thin film modules alternative to the amorphous silicon ones. Currently, the dominant technology in photovoltaic systems is the multicrystalline silicon. Multicrystalline cell production reached the 52,9 percent of global cell production in 2010 followed by the monocrystalline with the 33,2%(Figure 4). Therefore, crystalline silicon modules together represent more than 86% of the total. The predominant use of this material for the manufacture of commercial modules is mainly due to the abundance of silicon, the good knowledge of the technology, and the performance achieved in commercial modules.

! Figure 4: 2010 Cell production by technology (Source: Photon International, 2011)

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Integration of PV Technology in Architectural Envelopes. Design Guide

2.3.1.

Concentrating PV modules

! Module efficiency: up to 28 % Concentrating systems are suitable mainly for autonomous installations. In this case, generally, motorized panels track the sun and the solar radiation is concentrated by mirrors or lenses on special concentrating solar cells, highly efficient (and expensive). Within these cells, several layers of different semiconductors are stacked one above the other, each using a wavelength of sunlight different. In the concentrating module (Figure 5), approximately 10 cm above the solar cell of just 3 mm2, a Fresnel lens is placed, concentrating the light between 400 and 500 times. These modules achieve a performance ratio of 28%, almost the double than the silicon modules available on the market. Another advantage is that most of the surface of the module is not occupied by expensive semiconductors but by a relatively inexpensive lenses. Consequently, experts expect the cost of the concentrating modules decrease in a short period of time. Today, its application in buildings is limited and of experimental character (University of Lleida, 2009). For this reason we wonÂ´t develop this typology more in depth. However it is interesting to take it into account as it opens an interesting field of research.

! ! ! ! ! ! ! ! ! ! Figure 5: Concentrating PV Module, (JAISUN Solar, 2013) Integration of PV Technology in Architectural Envelopes. Design Guide

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2.3.2.

Crystalline silicon modules Module efficiency: 13 % - 20 %

A typical crystalline silicon module is constituted by a set of photovoltaic cells (Figure 15) connected in series, electrically and mechanically protected, and also from the effects of the weather. They are encapsulated in a transparent polymeric material, and thermoplastic insulator, which commonly is the Ethylene vinyl acetate (also known as EVA), and protected by means of a front glass cover and a back sheet which typically includes layers of polyvinyl fluoride, whose name best known is Tedlar (DuPont, 2013). The back cover is partly visible from the front of the glass, between the gaps left by the cells (Figure 6). The glass used in the front cover is tempered to withstand thermal efforts, and has a high light transmittance, which is achieved by reducing the iron content. The set rolled through the simultaneous application of heat, vacuum and pressure. The edges of the laminate obtained are protected by a silicone gasket and metal frame, which is usually aluminium. Finally, the junction box is fixed to the back of the module, which take including relevant bypass diodes. The standard module is complete, and its properties are guaranteed by testing electrical, mechanical and environmental that the applicable regulations demand.

Figure 6: Crystalline silicon module structure 22

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Integration of PV Technology in Architectural Envelopes. Design Guide

2.3.3.

Thin film modules Module efficiency: 9 % - 15 %

Thin film technologies arise with the main aim of reducing manufacturing costs of the photovoltaic modules. Alternative materials to the silicon are looked for, with high absorption coefficients, so as to be effective in thin layers and also can be deposited with non very complex processes on cheap large-area substrates. Although the manufacturing of thin film modules differs much from the ones of silicon wafers-based, its final structure is usually similar, being fully equivalent laminates (Figure 7). The thin film material most widely used until now is the amorphous silicon and its alloys with hydrogen. Other materials such as polycrystalline silicon thin film, cadmium telluride, and the semiconductor materials from family of chalcopyrite, globally called CIS - or CI(G)S if also carry gallium in its composition-, are proving to be viable alternatives for the manufacture of photovoltaic modules. Deposition techniques for these materials are varied, and include from vacuum methods to simple procedures by means of chemical bath deposition.

Figure 7: Thin film module structure Integration of PV Technology in Architectural Envelopes. Design Guide

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Amorphous silicon modules.

Amorphous silicon modules (Figure 8) were the first thin film ones marketed and, consequently, have now a more mature technology. Amorphous silicon absorbs light up to forty times more efficiently than crystalline silicon, so that a film of a micron can absorb 90% of the total available energy. This is one of the main advantages of this material, which means a reduction in manufacturing costs. Another important advantage is that it can be deposited at lower temperatures and on highly diverse substrates. However, it has a major drawback, and this is its poor performance compared to crystalline silicon technologies (about half). In order to increase its performance, amorphous silicon modules are designed by triple-junction structure, in which each cell consists of three semiconductor junctions, mounted one above the other: the lower one is sensitive to red light, the centre one to the green and the yellow, and above one to the blue light. The final yield can reach up to 7%, representing an increase of more than one percentage point, if compared with the modules with single-junction cells. By means of the amorphous, best examples of flexible PV modules have been reached, as shows the Japan Pavilion at the World Expo 2010 in Shanghai by the architectural firm Hikosaka (Figure 18).

Figure 8: Amorphous silicon module (GetIt, 201?) 24

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Integration of PV Technology in Architectural Envelopes. Design Guide

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Copper-indium selenide modules.

For several decades it is known that copper-indium selenide (CIS) is an efficient material for photovoltaic conversion. However, the production of CIS photovoltaic modules on an industrial scale has recently started. The reason for this slow development is the complexity of manufacturing technologies. Most of the techniques used are new and not directly compatible with most known industrial processes. One of the most complicated issues is to make the layers with sufficient homogeneity and quality However, the highest yields in thin film commercial modules have been obtained with CIS modules, which have exceeded 11%. There are interesting examples of integration of photovoltaic in buildings with such modules, in both standard designs as with special modules, semi transparent and anagrams, and different colours. Also flexible modules can be manufactured with this material (Figure 9). In terms of uniformity and appearance, these modules are probably the best PV option.

! ! Figure 9: Copper indium selenide module. Rigid and flexible options (SoloPower, 2010) Integration of PV Technology in Architectural Envelopes. Design Guide

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Cadmium telluride modules

Cadmium telluride modules are experiencing a remarkable growth in the last years (Figure 10). Its main advantage is that they have the lowest per-unit power price in the current market of photovoltaic modules. They achieve efficiencies up to 11%, and the problems related to cadmium toxicity seem to have been solved with the guarantee of recycling of the modules by manufacturers. First Solar, the leading producer of this type of modules, offers this warranty for recycling (FirstSolar, 2012). The typical structure of a cadmium telluride cell comprises a glass substrate coated with a layer of tin oxide, on which a layer of cadmium sulfide is deposited. On the latter a CdTe absorber layer is made grown, and finally the back metal contact is deposited, which is usually a film of copper or nickel. The final aspect of the modules is a dark and homogeneous surface. For now, its application is limited to photovoltaic plants, with little installation in buildings.

Figure 10: Cadmium telluride module (First Solar, 2011)

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Integration of PV Technology in Architectural Envelopes. Design Guide

2.3.4.

Organic Solar Cells Module efficiency: 4 % - 10 %

The organic solar cells (or Dye Sensitized solar cells, DSC) are often described as the third generation of solar cells (after the crystalline and thin film ones). They are based on tinted molecules, have just a few hundred nanometres thick, and can be manufactured using economically efficient dyeing processes. Also, they offer greater design freedom. There is a relatively large range of colours and degrees of transparency of the cells (Figure 11). However, so far organic solar cells have a performance ratio of about 4% and an useful life of only a few years. However, they are attracting attention for their use in building: in early 2011 the Fraunhofer-Instituts f端r Solare Energiesysteme in Freiburg (Germany) presented the first tinted solar module of 60x100 cm (W端rfel, 2012). During the coming years it will be developed for series production. The aim is to increase the performance from 3 to 10% by means of improvements in printing technologies.

Figure 11: Prototype of an organic solar cell (Hofmann, W. 200?, Fraunhofe ISE, 2013) Integration of PV Technology in Architectural Envelopes. Design Guide

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3. APPEARANCE Regarding to the integration of solar technologies in buildings, the main focus is on photovoltaic panels. However, their ecological, economic and design potential of solar technology is often neglected. Basic solar systems are fully developed in regard to manufacture and economic efficiency. And as multifunctional components, offer a wide variety of opportunities for construction and design. Two types of demands influence the PV module design for photovoltaic architectural integration: on one hand photovoltaic generation criteria, looking for maximum power production, and on the other, the architectural criteria that define its constructive role. Both can be coupled in many cases, being able to get very good results, both energy, functional and aesthetic. The type of application and the characteristics of each technology open up a wide range of possibilities, as discussed below.

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Integration of PV Technology in Architectural Envelopes. Design Guide

3.1.

Structure

The typical construction of PV laminate structure described in the previous chapter can be modified in order to adapt the module design to architectural requirements. Materials commonly used in the manufacture of conventional modules can be replaced with others that provide better performance or appearance (Figure 13). Nowadays, it for PV glass depending on degree, peak later.

is possible to work with the infinite possibilities that exist in the market (Figure 12). Of course, the pattern, colour, texture or semi-transparency power module may decrease, as will be discussed

One example is the replacement of the back sheet, which usually is of polyvinyl fluoride, is substitutable for a glass. This photovoltaic laminate configuration as double glass structure is the most used for integration in buildings, because of its greater mechanical strength. The outer glass is tempered to withstand the thermal loads and has a high transparency. Its thickness is usually about 3 to 4 millimetres, and can be textured or not for an anti-slid finishing. Furthermore, an antireflective layer can be added, a process that slightly alters the refractive index of the surface and extends its transmittance by 5%. The glass thickness of the back cover face is determined by the mechanical strength requirements in each case. The total thickness of this laminate, formed by two glasses and cells embedded in the encapsulant, oscillates between 10 and 12 mm.

Figure 12: Chances for PV glass sheets Integration of PV Technology in Architectural Envelopes. Design Guide

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Also the encapsulant, typically is EVA, may be replaced by other materials such as the polyvinyl butyral (or PVB), used for over two decades to laminate safety glass. This option is very common in the manufacturing of modules with double glass structure for its integration into facades and glass roofs. The structure of the modules can find the similarity with other elements of the building such as the roof, the tiles or awnings. In these cases, the elements of the front and back covers of the laminate can be replaced by other more suitable for each application. The support materials of the laminate may be of ceramic for the manufacture of photovoltaic tiles, or flexible, both metallic or plastic type fabric for light tiles, awnings and canopies. These flexible structures can be achieved thanks to the versatility constitutive of the amorphous silicon modules. The front side is usually a tough transparent polymer, and the back side a similar material or a thin film of stainless steel or aluminium. The result is lightweight and flexible modules, able for manufacturing roof-waterproofing systems (by means of sandwich panels).

Figure 13: PV elements capable of being replaced 30

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Integration of PV Technology in Architectural Envelopes. Design Guide

3.2.

Proportions

Bruno Taut spoke once of architecture as the art of proportion (1919). In this theory of the architecture, he made an interpretation of the proportions and relationships in buildings that are beyond the faรงade design. However, his thoughts about the proportions also play an important role in the choice of dimensions of the components and solar elements. In the case of PV facades, the fact of splitting the surface in many small format modules is sometimes criticized because it not only increases the cost of wiring but also generates a compartmentalized structure of the solar energy system. However, such an argument does not convince much in view of the different functional and structural requirements required to facades. In these in particular is important that solar energy systems can be adapted to the design of the building and its structure in the most personalized way. In any case, the big facades and roofs, which are power generators, need to be designed so that the proportions and the internal structure of the modules become important, especially in the case of thin-film PV technology, with its two-dimensional appearance. This is evident in architectonic envelopes such as the one of the Hotel at Grand Canal Square by Aires Mateus, which is likely to integrate PV modules, offering an attractive result.

Figure 14: Hotel at Grand Canal Square, Dublin, by Aires Mateus (Structurae, 2013) Integration of PV Technology in Architectural Envelopes. Design Guide

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3.3.

Shape

3.3.1.

Cell shape

The cell shape varies depending on photovoltaic technology (Figure 15). Thin-film cells are the result of printing on a glass plane in different thin layers, creating the final modules. No cutting is needed and therefore, we cannot talk about shape in this technology. The monocrystalline silicon cells are made of wafers from a cylindrical ingot, so that they can maintain a circular shape. However, they are usually cut with a form to facilitate their "placement" on the modules. The result is cell side about 10 centimeters with rounded corners. These corners are left rounded in order not to lose too much material, after obtaining a square section from a cylindrical element. However recently, monocrystalline silicon modules with larger cells and completely square appeared on the market, looking to increase the performance of this type of module. Multicrystalline silicon cells have the same shape, which come from the cut of square section blocks, with side lengths ranging between 10 and 15 cm. Figure 15: Usual crystalline-silicon cells shape Anyway, the crystalline cells may be rectangular and of varying lengths, as with the manufacture of wafers using the EFG method patented by SCHOTT (Von Keller, 2013). It consists in stretching from silicon fluid foil octagonal tubes, whose sides corresponding to the side of a wafer. After cooling, the tubes are cut into individual wafers using lasers instead of wire saw.

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Integration of PV Technology in Architectural Envelopes. Design Guide

3.3.2.

Module shape

Modules typically have a rigid structure, with rectangular or square shape, of between 0.5 to 1.5 square meters. However, they may have other sizes, since new rollings allow manufacturing larger surface modules. There are also modules with triangular, hexagonal or circular shape (Figure 16), and can be curved, either rigid or flexible. A good example of the use of circular solar panels is shown in figure 16: the Solar Tower, by the architectural firm Zoka Zola, that will be explained more in detail on chapter 5.

Figure 16: Examples of modules with triangular, hexagonal and circular shape (Zoka Zola, 201?) Integration of PV Technology in Architectural Envelopes. Design Guide

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In Saint-Etienne, France, the architectural firm LIN (Finn Geipel + Giulia Andi) designed the Cite du Design in 2009. Its architectural envelope is characterized by a design in the form of triangular mesh in which 14000 panels with 10 different layers structure have been integrated (Figure 17).

Figure 17: Cite du Design by LIN (Richters, C., 2010)

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Integration of PV Technology in Architectural Envelopes. Design Guide

! 3.3.3.

Flexibility

Amorphous silicon versatility allows manufacture easily lightweight flexible modules by depositing the material on different types of substrates. However, it is important to note that through CIGS technology, flexible integration photovoltaic panels have been achieved that provide 12.6% efficiency, making these modules are among the highest percentages of the flexible ones. This was the material used by Hikosaka for the flexible PV modules placed in the Japan Pavilion at the World Expo 2010 in Shanghai (Figure 18). The architectural firm Hikosaka incorporates amorphous silicon PV modules inside the doublelayer ETFE membrane, able to filter sunshine. PowerFLEX BIVP, developed by Global Solar Energy, is a photovoltaic panel modular and flexible, designed primarily for industrial buildings with low carrying capacity roofs. These panels can be applied directly to a surface without mounting hardware or holes in it, so that they do not generate additional wind loads. The biggest modules (575x50 cm) have 108 CIGS cells each, and reach to provide a capacity of 300 W (50% higher than the average of flexible amorphous silicon panels) Also, prototypes of flexible monocrystalline silicon modules have been developed recently, achieving a 13,8% efficiency, but with an aesthetic somewhat "rigid".

Figure 18: Japan Pavilion at the World Expo 2010 in Shanghai by Hikosaka (Designboom, 2009) Integration of PV Technology in Architectural Envelopes. Design Guide

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3.4.

Transparency

Before developing this point more in detail, it is important to emphasize that, in general, more transparency means less yield. Choosing a transparent back cover can achieve a certain level of transparency in the module, which will be more or less broken by technology. The possibility that the PV modules can transmit some light into the buildings opens up many possibilities for architectural integration. In any case, this partial light transmission modifies the energy performance of the building, a fact that should be taken into account in the design phase. If you opt for conventional crystalline technology, in principle the cells that compose the module will be fully opaque, iridescent, blue if they are made with multicrystalline silicon and homogeneous and darker if it is monocrystalline silicon. There is, however, a manufacturer of monocrystalline silicon cells (Sunways) that converts opaque cells into semitransparent cells through small perforations in the material. Can be played using the colour and transparency of the front cover film and varying the spacing between cells, achieving the same or similar colours of cells, higher or lower light transmissivity. If higher degrees of transparency are desired, it may be preferable to combine modules with a reasonable number of cells with double glass transparent laminates.

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Integration of PV Technology in Architectural Envelopes. Design Guide

If using thin film modules, transparent surfaces with almost homogeneous appearance can be achieved by increasing the distance between adjacent cells. Take, for example, the southern faรงade of the SCHOTT Headquarters in Mainz by JSK Architects (Figure 19). Although amorphous silicon modules with up to a transparency of 50% have been manufactured, it should be noted that the electrical performance decreases as the transmittance increases, and it will be necessary to find an optimal balance between the degree of transparency and power per unit area. In general, amorphous silicon modules are recommended whose transparency does not exceed 15%-20% (Figure 24) Also CIS modules have been manufactured in which the active material is alternated with dots or transparent strips. The result is modules with a certain level of transparency that allow vision sifted through them.

Figure 19: SCHOTT Headquarters in Mainz by JSK Architects (SCHOTT/A. Stephan, 2010) Integration of PV Technology in Architectural Envelopes. Design Guide

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3.5.

Colour

3.5.1.

Cell colour

The bluish colour present in crystalline silicon cells can be modified by varying the thickness of the antireflective layer. Small variations in the thickness of this layer can cause significant changes in the performance of the photovoltaic cell, since wavelengths useful for photovoltaic conversion are reflected. Therefore it is appropriate to ascertain the performance of the modules of colours before making a decision and consider, or not, these modules for specific applications as appropriate. Figure 20 shows the performance of commercial multicrystalline silicon modules made with cells differing only in colour. Note that the change in performance can be significant for some colours. After the standard blue, green is the most efficient semi-transparent colour for producing electricity, but reddish colours (magenta, brown, gold) work well equally.

Figure 20: Performance of a multiSi silicon module according to the colour of its cells (values provided by sunaways .eu) 38

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Integration of PV Technology in Architectural Envelopes. Design Guide

3.5.2.

Back cover film colour

Less impact on module performance involves changing the colour of the back cover layer. Similar or different colours to the one of the cells can be searched and, simultaneously, vary the degree of transparency. Although the standard finish is white, it may have other tinges or be transparent. In this case, interior blinds of different colours can be used, managing to change the colour appearance of the building. The amorphous silicon modules may have different tones, and if they are semi-transparent, and coloured glass are used in its back layer or in double glazing glasses, the possibilities are many and with very showy results (Figure 21), both from without and from within the building. In the CIS modules, different coloured primer can be included in their surface, forming various types of drawings.

Figure 21: Polysolar aSi PV Module -20% transparency(Polysolar, 2011)

Integration of PV Technology in Architectural Envelopes. Design Guide

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3.6.

Mounting Systems

Innovative trends in building design have allowed not just to mount photovoltaic panels on existing roofs or faรงades, but to be integrated as substitutional elements in these structures. Support systems include from almost standard fasteners for ventilated facades or a curtain walls, until specific to photovoltaic tiles. There is a huge variety of support and fixing structures for flat roofs. Most are made of aluminium, although there are also steel and plastic materials. Some allow the reorientation of the module within a range of tilt and azimuth angle. Some manufacturers offer almost universal mounting systems, valid for most modules, and applications. It is desirable that the cleats from module structures are easy and quick to assemble. The photovoltaic cladding structures should ensure consistent behaviour according to the application that play, and meet the demands of the construction. Every PV mounting system should be designed to reduce the visual impact that involves the placement of these facilities on the decks. Systems such as Kalypso SP (Figure 22), offer a solution in the same plane, modular and flexible, in addition to minimize the sail-effect of these facilities, avoiding the strains produced by wind resulting in vibrations that ultimately cause slack in the screws and roof leaks. Non-static mounting systems are a good idea for increasing energy production (See Chapter 5).

Figure 22: Kalypso SP by Arcelor Mittal (Arcelor Mittal, 2012) 40

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Integration of PV Technology in Architectural Envelopes. Design Guide

3.7.

Thermal insulation

Insulation materials play a crucial role in the module yield and may not be given the proper attention during the moduleâ&#x20AC;&#x2122;s design stage. PV systems manufacturers should understand the insulation materials that are placed between module layers. If the PV module is part of the building envelope it may be interesting it to have a low heat transfer, as this helps to reduce the energy consumption of the building. In these cases, in order to improve the insulation capacity of the module, modules can be made following the configuration of doubleglazing structures with air camera, with a thickness optimized to minimize heat transfer. Also a coloured glass can be used in the back cover film, to reduce or refine the transmittance of light through the gaps between cells. The elements of a double-glazing semi-transparent PV glass can be incorporated into the project for better thermal insulation. They normally consist on an outer laminated PV glass of 6, 8, 10, 12 or 19 mm thick, an air chamber of 16 mm in thickness to optimize the thermal insulation and a conventional glass sheet inside 6 mm thick. To achieve even greater isolation, the semi-transparent PV glass with triple glazing could be considered as one of the most interesting solutions (Figure 23). Typically an additional glass 6mm thick is incorporated to double-glazing element.

Figure 23: Semitransparent double and triple glazed insulating PV glass units Integration of PV Technology in Architectural Envelopes. Design Guide

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3.8.

Frame

Modules are usually included into an aluminium frame. It provides them the necessary structural strength and resistance to corrosion. The choice of the proper fame of a PV module is not just a matter of the pursuit of a smart appearance. As we will discuss in the fifth chapter, it should prevent the module frame from casting shadows over the cells. Moreover, in cases of low inclination is important that the module has no frame capable of retaining dirt on its lower edge. However, frameless PV modules have been reached using one layer of glass substrate laminated with another layer of the same material for encapsulation and mechanical strength. Modules such as DUO Glass and SEE Thru (Figure 24), developed by Kupiter, dispense with frame by means of this technique and the amorphous silicon.

Figure 24: Amorphous Silicon Thin Film frameless PV Panel (Kupiter, 201?) 42

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Integration of PV Technology in Architectural Envelopes. Design Guide

4. ARCHITECTURAL INTEGRATION The architectural applications of PV modules integration are very diverse. The different surfaces of the building envelope can be used, if well designed, to accommodate different applications, highlighting, among others, the roofs, walls, overhangs, skylights, atriums and pergolas. Nowadays, overlaying on existing materials is the most common way of application. Nevertheless, this is not the aim of this Thesis. True integration is to replace the conventional elements of the roofs for photovoltaic modules (Figure 25). No doubt this is what should be done when projecting a building with a photovoltaic surfaces. The modules can have various types of structures, from simple laminate, to sandwich cladding panels, or shape and characteristics of traditional elements, such as tiles, carpentries and so on. Because of this, we will focus in considering the PV modules not as an addendum, but as an element of the building.

Figure 25: True PV integration Integration of PV Technology in Architectural Envelopes. Design Guide

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4.1.

Integration on roofs

The decks offer the greatest potential for PV integration in buildings in urban environments, in terms of energy production, being the surfaces best placed and most extensive, free of obstacles and constraints. Depending on the type of building, the integration can be performed on pitched roofs or in flat roofs, whether or not walkable. 4.1.1.

Pitched roofs

As a general rule, in already built pitched roofs, it is appropriate that the modules are placed rather parallel to any of the sides of the roof. However, there are low-height clamping structures that enable slightly reorienting modules on deck surface. In industrial-type buildings may find interesting using amorphous silicon modules, because of its low weight and ease of assembly. An interesting solution is the saw-tooth roof, alternating inclined surfaces facing south (in the northern hemisphere) in which PV modules are integrated, with north-facing surfaces that diffuse the light inside. Thus, to the photovoltaic power generation, the benefits of day lighting indirect and reduction of the thermal load of the building are added, which means a significant reduction of this electric power consumption, both for illumination as cooling.

Figure 26: SYDESL Headquarters by Nicolas Favet Architects (NFA, 2009)

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Integration of PV Technology in Architectural Envelopes. Design Guide

A good example of this roof typology is the SYDESL headquarter, by the French architectural firm NFA (Figure 26). The architectural design of the building, which is identified with the industrial architecture of the area, uses a saw-tooth roof for getting the maximum natural light as possible on the north side, and for the installation of 350 m2 of photovoltaic panels on its south side. However, more and more often there are new proposals that seek new ways of integration of photovoltaic technology in pitched roofs. Take for instance the conceptual idea for the Delft University of Technology's, called The New Bouwkunde (Figure 27). The design proposes a curved roof, almost half of which would be covered with photovoltaic modules. It uses the existing flexible PV technology and the inclination of the roof for producing 4000kWh (Turner, 2009) per day by means of its 1500m2 of PV cells.

Figure 27: The New Bouwkunde by Adam Wojtalik (Wojtalik, A., 2009) Integration of PV Technology in Architectural Envelopes. Design Guide

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4.1.2.

Photovoltaic tiles

The modules with structure and appearance of tiles, suitable for its integration in roofs, are called photovoltaic tiles. The purpose of these elements is to substitute conventional shingles, maintaining its aesthetic and constructive function, and simultaneously producing electricity. Various technologies for photovoltaic tiles have been developed, encapsulated in a very different ways. Some are self-sustained, that is, they do not need specific base structure for each module, and others that require a mounting bracket, which may be of ceramic material, in which the modules are attached. Tiles of this second group are often easier to replace if necessary, as they simply need to replace the module, but not the constructive structure. It happens that the results are more convincing the more simple the tile is. More complex structures, which store a small module inside, are not practical, since the final useful surface of the tile is small relative to the total space occupied and with the price of the set (Figure 28). It is also advisable to avoid tiles with transparent covers away from the module, as they reduce light uptake by solar cells, increasing significantly the losses by reflection. Lately, it tends to seek solutions with tiles made of laminated module and some small fasteners to anchor to the deck. It is desirable that there is an air chamber under the tile to ensure ventilation in the back face, especially in crystalline silicon modules.

Figure 28: Solar Tiles Tipologies 46

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Integration of PV Technology in Architectural Envelopes. Design Guide

The slate roofs are very common in Europe due to the tradition, and also because of their waterproofing and resistance to the low temperatures. In this respect, some variations have been styled to emulate the colour and shape of conventional slates, matching perfectly to the rest of the traditional slates of the roof. Significant results have been obtained with products such as Duer or Solar Slate (Figure 29). The first system replaces the habitual frame of the photovoltaic modules by other made of slate and uses the aesthetic uniformity that the monocrystalline silicon technology has. Solar Slate, however, goes further and generates DC through the PV cells embedded in the element.

Figure 29: Solar slate roofs (Duer, 2012; Solarslate ltd, 2013) Integration of PV Technology in Architectural Envelopes. Design Guide

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4.1.3.

Flat roofs

In the flat roofs, module Installation requires support structures, usually low-rise, which place the modules with optimal inclination and orientation. Fixing to the deck depends on the type of materials of the roof, and must always maintain water tightness. In general, there are two types of mounting systems for flat roofs: perforation of the roof material and using weights, if the wind loads on structures allow it. Cables should be protected in gutters or holes, and some space should be left between rows, both for maintenance and for avoiding possible shading of rows over others, as applicable. There are also interesting applications like canopies or pergolas, which may be associated with some element of a roof or the facade. The projection of shadows of these elements on the building reduces the thermal load and therefore it helps to improve their energy efficiency. In some cases, modules not seen from the street may be wanted, like in the case of the Barnes Foundation (Figure 30). For solving it, there are low-height modular structures of different materials (iron, concrete, plastic materials, etc.) that solve both the protection and the wiring of the modules. In this type of solution it is necessary to predict the possible existence of snow or leaves of trees accumulated in the soil, and their effect on partial shading of the modules in the case that the structures are too low. To avoid these problems it is best to raise the structures, or just distance the modules from each other sufficiently.

Figure 30: Barnes Foundation by Tod Williams + Billie Tsien (Crane, T.,2013)

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Integration of PV Technology in Architectural Envelopes. Design Guide

4.1.4.

Integration in glazed roofs

Glazed ceilings are very attractive to integrate PV modules: the more or less transparent roofs made of glass and metal sections covering large areas of buildings, such as patios, greenhouses and walkways. It is easy to replace glasses, commonly by photovoltaic modules (Figure 31), maintaining the same clamping profiles, although slightly adapted to accommodate wiring. Semitransparent photovoltaic modules, or even the opaque ones combined with glass, when capturing some of the light, reduce the thermal load of the building and at the same time they act as efficient power producers. In any case, too small inclination of the modules must be avoided, because this would involve a high accumulation of dirt on the surface, or even snow, leaves, and so on, reducing photovoltaic production. Furthermore, in localities with average or high latitudes, the inclination of the modules promotes the uptake of sunlight, if these are well oriented. Also the skylights can accommodate semitransparent photovoltaic modules. These openings made on the roofs to allow passage of light can be of very different shapes. While the modules can be integrated into horizontal skylights, it is interesting to have some inclination for the same reasons described above (to avoid the accumulation of dirt and improving the capture of solar radiation).

Figure 31: Typical glass-glass laminate PV configuration

Integration of PV Technology in Architectural Envelopes. Design Guide

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The fact that traditional tile roofs can be converted into energy generating surfaces is shown in the San Anton market in Madrid by QVE-arquitectos (Figure 32). The project's aim is to ensure that the building has a fully regenerative power supply, with a glass roof over its patio as a central element in which are integrated solar technology systems. The architects achieved a harmonious result that demonstrates the potential of solar technology in changing traditional typologies.

Figure 32: San Anton market skylight by QVEarquitectos (QVE, 2011)

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Integration of PV Technology in Architectural Envelopes. Design Guide

4.2.

Integration in facades

The facades of the buildings also have various possibilities of integration, highlighting ventilated facades and curtain wall structures (both modular and mounted on site). In all them, PV modules replace the usual elements of the facades. 4.2.1.

Integration in curtain walls

In the curtain walls, the PV modules can be substituted for either transparent glass or opaque elements, with single glazing structure or with double structure (Figure 31). In viewing zones may be attractive to use semitransparent a-Si modules or other thin film technologies, since with they, uniform light transmittances are achieved inside the building. But there are many possibilities for using semitransparent crystalline silicon modules in rooms that do not require a homogeneous distribution of natural light, such as corridors or building entrances. Two important issues to be solved, in each case, are the location of the connections of the modules and wiring routing along the facade structure. Wiring can be output in each module whether the profiles are conventional, or ensure that the cables go inside the structure and make connections within it. In each case best solution must be find, depending on the space and the need for accessibility. It is possible to play with the density of the cells, allowing the entry of natural light when required inside and creating interesting effects outside. The New York based architectural firm Simone Giostra & Partners has used this strategy for its Greenpix Media Wall in Beijing (Figure 33), by means of multi crystalline PV cells that are laminated within the glass of the curtain wall and are placed with changing density on the whole envelope.

Figure 33: Greenpix Media Wall by SGPA (SGPA, 2008) Integration of PV Technology in Architectural Envelopes. Design Guide

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4.2.2.

Integration in ventilated facades

Ventilated faรงades show many facilities for the PV modules integration. The exterior layer of a ventilated facade such as glass panels, stone, wood, aluminium or ceramic, tile, and so on can be replaced without problems by photovoltaic modules. An advantage of these structures is that they are kept aired modules by its rear face, which allows reducing the operating temperatures, and thus improves the electrical performance. Modules can have standard structures, double glass, or be made on different types of supports, as appropriate in each case. GENyO Laboratories by Planho Arquitectos (Figure 34) uses the thin film technology for its photovoltaic second skin. From an architectural standpoint, the final facade convince thanks to its uniform aesthetic and variable transparency. The current market allows great flexibility in the design of ventilated facades. The modules are available in various formats and, in some cases, with large sizes. Systems such as Prosol TF allow ventilated or non-ventilated facades, or facades with windows and blinds. They even can be placed on existing faรงades to improve building energy efficiency.

Figure 34: GENyO Laboratories by Planho (Gonzรกlez, A., 2008) 52

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Integration of PV Technology in Architectural Envelopes. Design Guide

4.2.3.

Integration in windows

Photovoltaic modules can also be integrated in windows, replacing any of the exterior glass sheets. Usually, they are integrated into the fixed part, although moving parts can also accommodate photovoltaic cells. In these cases it is preferable to perform the integration in windows that move in parallel, rather than in hinged window, because in these if the opening is made during the day, the blade position significantly change the energy generated by the photovoltaic module. In sliding windows, the module should always go in the outer sheet. In photovoltaic windows, designers can also play with the transparency of the module and try to get more or less uniformity, as desired. Thin film technologies achieved results more homogeneous, while crystalline silicon ones transmit light into the building in a discontinuous manner, and therefore they are not recommended for viewing areas (Figure 35).

Figure 35: Transmission of the light into the building through the PV glass Integration of PV Technology in Architectural Envelopes. Design Guide

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4.2.4.

Integration in sunshades

In Mediterranean countries the application that best combines architectural photovoltaic production with building energy saving is undoubtedly the shadow elements. With the same position that sunshades control the action of the sun, the PV modules capture solar energy to produce electricity. A clear example is the fixed sunshades over the windows, where modules can be integrated. Moreover, another advantage presented by these structures is that they are very well ventilated in their rear face, reducing its working temperature and increase its performance. The modules can be opaque or allow some light transmission. In this case are generally made with doubleglazing structures. The south facade of the Pratt Institute by WASA/Studio A is a glass curtain wall protected by PV sunshades (Figure The architecture firm was looking for a slats system that give sun protection, increasing the thermal insulation of building, but which in turn allowed him to take advantage tons of natural daylighting that its south-facing facade receives each day.

36). would the of the

Something to be considered in the design of PV sunshades is the possible projection of shadows on other elements. It is important to avoid these shadows happen during the middle of the day, since under conditions of high insolation, shading effects are more harmful, both from an electrical point of view (greater losses) and in relation to the heating and deterioration of shaded modules.

Figure 36: Pratt Institute by WASA / Studio A (Severin, A., 2010) 54

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Integration of PV Technology in Architectural Envelopes. Design Guide

4.3.

Integration in other structures

PV modules can also be integrated in many urban elements beyond buildings. In fact, the potential for this type of application is very high, as it includes a variety of possibility, such as bus/train shelters, street lights, parking aisles, noise barriers, informative panels, fences, telephone booths or kiosks. As occurs in building integration, it is desirable that, when designing the structure element in question is taken into account the integration of photovoltaic modules and in some cases, accommodation of batteries (in autonomous systems accumulation). Key issues to address in designing these PV urban structures are, apart from the shading and correct orientation, inclination and ventilation, on the one hand the risk of vandalism and, on the other, access for repairing. There are good examples of urban photovoltaic structures that solve these problems, and also reach aesthetic and functional results. Different types of non-integrated applications in buildings can be grouped according to Table 5, which also indicates the approximate size of the modules needed, if the application is autonomous. Most Common Applications Urban furniture

Noise barriers and fences Awnings and pergolas

Lighting

Information boards, ticket machines, parking meters… Parking lots, train stations, bus shelters… Lampposts for lighting streets, lighting panels, traffic signals, beacons…

Usual size of the module. (Autonomous PV system) 0,15 m2 - 0,8 m2 > 1 m2 > 0,5 m2 0,1 m2 – 10 m2

Table 5: Frequent applications of photovoltaic integration into urban elements, and approximate size of the photovoltaic modules.

Integration of PV Technology in Architectural Envelopes. Design Guide

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4.3.1.

Urban furniture

There are also possibilities for integration of photovoltaic modules on urban furniture, such as information boards, banks, ticket machines or parking meters. In all of them is necessary that the PV modules are not too accessible and that this protected against vandalism, breakage or theft. There are specific designs for these applications modules that solve these problems and adapt well to the design of the elements in which they are integrated. 4.3.2.

Noise barriers

This group of applications include noise barriers, for their potential in roads and highways. The first PV noise barrier was built in 1989 in Switzerland and had a total capacity of 100 kWp (Remmer, et al., 2005). Since then it has been designed and built various types of noise barriers, ranging from simple vertical structure, or inclined surface awning-type, to the one of inclined slats or zigzag structure. The latter allows easily combine photovoltaic generation function (upward-facing surfaces) with sound absorption (downward-facing surfaces) As for the formalization of these noise barriers, depends exclusively on the limitations of the project and the creativity of architects. Thus, we find more or less conventional designs like the one for the A22 at Brennero (Figure 37 left); and more innovative proposals such as the one by studio BREAD (Figure 37 right), which proposes a steel structural grid, which will be filled either by vegetation, glass skylight or PV modules.

Figure 37: A22 highway at Brennero in Italy (World Highways, 2012); Green Bubble by BREAD Studio (BREAD Studio, 2012) 56

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Integration of PV Technology in Architectural Envelopes. Design Guide

4.3.3.

Lighting

In the case of lighting must distinguish between lampposts for lighting streets and parks, which may well be considered elements of urban furniture and lighting panels, traffic signal or beacons, which are usually located outside urban centres. The PV lampposts generally are autonomous and hold an internal battery that stores the energy power generated by the module during sunshine hours. They also tend to carry a device which controls the on and off of the lamp according to the ambient light level. 4.3.4.

Awnings and canopies

There are many roofing applications for open spaces of different use, such as parking lots (Figure 38 left), train stations, bus shelters, etc. With all of them you get the dual function of power generation and roofing, to protect you from solar radiation and / or rain. Canopies are structures easy to perform and also have the advantage that, by means of the optimal positioning for shading, also good guidance for photovoltaic conversion is achieved. The same happens with the sunshades on the facades of buildings. Furthermore, this type of structure allows the total ventilation of the modules, which reduces its working temperature and increases electrical efficiency. Developed by Los Angeles-based firm Synthesis Design + Architecture, the "Pure Tension" system (Figure 38 right) is basically a huge solar canopy that can recharge the batteries of Volvo hybrid cars in around half a day.

Figure 38: Example of solar canopy for parking lots; Pure Tension by Synthesis Design + Architecture (SDA/Volvo, 2013) Integration of PV Technology in Architectural Envelopes. Design Guide

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4.4. Essence of the architectural integration of PV modules As we have seen, possibilities for PV integration are endless. The essence of is dissertation can be summed up in the two following images (Figures 38 and 39).

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Figure 39: Insero Horsens proposal, part 1 58

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Integration of PV Technology in Architectural Envelopes. Design Guide

Such presentation belongs to an ongoing proposal for the area of Horsens, Denmark, that arises from this research.

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Figure 40: Insero Horsens proposal, part 2

Integration of PV Technology in Architectural Envelopes. Design Guide

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5. GUIDELINES FOR THE DESIGN AND OPERATION First, we will analyse the importance of positioning of the modules in electricity generation, since this determines the solar radiation received. Then, we will review the main factors affecting the productivity of a photovoltaic generator integrated in a building. As this dissertation is planned as a design guide, we will develop these guidelines with respect to static mounting systems. Nevertheless, in order to increase energy production, it could be interesting to have non-static mounting systems. Zoka Zola Architects have proposed a sustainable tower of solar energy in Chicago (Figure 16), which incorporates an active array of solar panels mounted on the building's facade. The building uses its large surface area with circular mounting units, attaching to them tracking solar arms which can increase the power output by up to 40 percent.

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Integration of PV Technology in Architectural Envelopes. Design Guide

5.1.

Solar radiation received.

The electric power generated by a module is proportional to the received light energy and, therefore, where the module is located in the building is the most critical point. ENDESA Pavilion (Figure 41), designed by IAAC (Instituto de Arquitectura Avanzada de Catalu単a) uses its structure, made of laminated timber with triangular section, to create a photovoltaic roof can produce up to 100 kWh, the energy equivalent of 12 homes needs. Each one of these modules facade features a specific geometry and arrangement especially designed to capture solar energy. Furthermore, higher overhangs allow higher energy capture and at the same time, increase the protection against radiation indoors. The IAAC used mathematical algorithms to modify the geometry of the envelope, based on the inclination and solar orientation. Each module, at each point, responds mathematically to the needs of its orientation and position.

Figure 41: ENDESA Pavillion by the Institute for Advanced Architecture of Catalonia (Goula, A., 2012) Integration of PV Technology in Architectural Envelopes. Design Guide

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Where possible we should look those enclosure surfaces that receive the greatest amount of annual solar irradiation, and reject those involving losses of more than 40% from optimal positioning. Both orientation and inclination of the module are important, although for low inclinations orientation is not as critical. The optimal situation is achieved with orientation towards Ecuador and an inclination about ten degrees below of latitude value (Figure 42). For example, if the latitude Horsens, Denmark, is 55° 52' 18" N, the optimal inclination for a PV generator in this city would be 44 degrees. It is possible to calculate the radiation value for any surface. The Spanish Building Technical Code (Código Tecnico de la Edificación) includes a method for calculating the radiation factor of the different surfaces of the building envelope, from a diagram with latitude of 41 ˚. The correction for other latitudes is done by a formula that includes the latitude, the angle of inclination and azimuth of the surface.

Figure 42: Design tips regarding the solar radiation received 62

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Integration of PV Technology in Architectural Envelopes. Design Guide

5.2.

Factors affecting the productivity

5.2.1.

Shading losses

One important aspect to consider in the integration of photovoltaic modules in buildings is the study of possible shadings. If possible, placing modules should be avoided in areas where other nearby objects can cast shadows on surface at some time during the year. Coffers, chimneys, adjacent buildings or nearby trees are examples of items whose shadows should be avoided. The partial shading of the PV generator has, first, a negative effect on electric power generated, both because of the reduction of the amount of radiation received by the module, and electrical association between cells and between modules. Take the example of a shaded cell: its current reduction also limits the flowing through those cells to which it is connected in series. Similarly happens with a totally or partially shaded module and those with which it is associated. To reduce these losses most of the modules include a bypass diode associated in parallel to groups of cells (typically 18 units). If a cell is shaded, current flows through the diode and continues for the remaining unshaded cells. But also the shadow areas of a module can reach tens of degrees above the average temperature of the remaining unshaded cells, because these cells can be polarized in reverse and dissipate the energy that the rest of the module generates. These high temperatures can damage the encapsulating or the cell itself (hot spot effect) in an irreversible way. For that reason, if it is not possible to avoid shadows in full, it is necessary to make sure that they are temporary and to use modules with bypass diodes. We should also check that no part of the module, nor the fixing system, project shadow over the cells. The perimeter should leave a margin between cells and frame, with the necessary width to avoid this problem, or if need, to paint false cells in areas that will receive the shadows.

Integration of PV Technology in Architectural Envelopes. Design Guide

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For the calculation of the shadows projected on the PV generator, it is necessary to know the local evolution of daily solar paths for a full year, which are delimited by solar paths of winter and summer solstices. The figure 43 shows the daily solar path for a hypothetic PV generator placed in Horsens, Denmark. Thanks to online tools such us sunearthtools.com, we can check the evolution of daily solar paths for 2013, which are delimited by solar paths of winter solstice (21th of June) and summer solstice (21th of December).

Figure 43: Horizon line for Horsens, Denmark (Polar graph) 64

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Integration of PV Technology in Architectural Envelopes. Design Guide

It is possible to represent this daily solar path by means of a Cartesian graph (Figure 44).

Figure 44: Horizon line for Horsens, Denmark (Cartesian graph)

In this way, we can overlay the shadow casted by the studied building on the solar path seen from a PV generator. The intersection between the two regions -red coloured- represents the fraction of irradiation not received by the generator (Figure 45).!

Figure 45: Fraction of irradiation not received by the PV generator

Integration of PV Technology in Architectural Envelopes. Design Guide

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During the winter solstice the sun crosses the sky hemisphere with its lowest height, and therefore casts longest horizontal shadows. During the summer solstice the sun's path is the highest of the year, and this causes the biggest shadows on objects arranged vertically.

! Figure 46: PV modules distance calculation On flat roofs, ordinarily photovoltaic modules are placed oriented towards the equator, in rows spaced a minimum distance in order shading losses not to exceed a certain limit. For given dimensions of the rows, in each case the inclination of the modules and the distance between them must be analysed, and thus make the right decision (Figure 46). On one hand, the optimal inclination of a photovoltaic generator connected to network is about ten degrees below the value of the local latitude. Secondly, the lower the inclination of the modules, the smaller the casted shadows, so that the distance between rows may be reduced. This allows modules to add more rows in the same deck area and, therefore, to install more power. Keep in mind that reducing the inclination a few degrees reduces shading without affecting PV production too. The simplest criteria, regarding calculation of shadows on roofs, is to establish that, at noon on the winter solstice, rows donÂ´t cast shadows on the ones that are behind them. The optimal distance between the rows is the minimum distance that achieves this requirement. However, depending on the dimensions of the rows, shadows of varying sizes will be casted over the ones behind them at other times of day, during periods close to the winter solstice. 66

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Integration of PV Technology in Architectural Envelopes. Design Guide

The most conservative criteria would be to avoid shadows at 100% throughout the year. However, this cannot be an underuse of available roof space. A reasonable way to proceed is to avoid shadows up to a certain value of the angle of incidence. That is, it tries to ignore the effects of shading when the angle of incidence of radiation on the generator exceeds a certain value, considering that, from this value, the radiation received is low enough. Recently, the company Sch端co has released support structures for horizontal decks where the modules are placed in rows facing alternately east and west, with an inclination of 10 degrees. This position involves a loss of not-capturing the maximum irradiation below 10% in places like Madrid, but instead uses the surface area of the roof up to 75%. In these cases of low inclination is important that the module has no frame or structure to retain dirt on its lower edge. On sunshades located in vertical facades, shading study must be done at noon of the summer solstice, which is the time when the sun has a higher elevation and therefore is more likely photovoltaic sunshades to cast shadows on which are beneath them. In this case, being insolation so high, the negative consequences of partial shading described above are accentuated. The photovoltaic sunshade, in anticipation of this kind of situation, it is advisable to include a diode associated with the row of cells to be placed at the top of the element, which is the one that probably will be shaded.

Figure 47: Design tips regarding the solar radiation received Integration of PV Technology in Architectural Envelopes. Design Guide

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5.2.2.

Temperature losses

On the other hand, in a lower order of importance, we must take into account the influence of other parameters on the performance of the module, such as operating temperature, which increase decreases the power to a greater or lesser extent, depending on the technology used in the material of the cell (Table 6). Technology Mono c-Si Multi c-Si CIS CdTe a-Si

Temperature coefficient (%/째C) 0,43 0,43 0,38 0,23 0,21

Table 6: Reductions in performance coefficients due to the temperature increase for commercial modules of different technologies. On average, a crystalline silicon PV module loses 4% performance for every 10 degrees Celsius that its temperature increases. In the case of amorphous silicon or cadmium telluride, this factor is halved, ie 2%. In general, this behaviour with the temperature depends on the technology. The modules that are less affected by the temperature, provided in relative terms, are those of amorphous silicon. Recent studies (Agrawal, et al., 2009) show also that semitransparent photovoltaic modules have a better performance when compared with opaque photovoltaic modules in terms of temperature losses (although, as explained in section 3.5, their yield decreases). In any case, it is desirable to ensure good ventilation in the back of the modules, especially if they are of crystalline silicon or CIS. The fact of not being ventilated increases its temperature, so that it would undervalue its value, as it is designed for ventilated modules on both sides.

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Integration of PV Technology in Architectural Envelopes. Design Guide

The roofs of many buildings have extraordinary potential for PV energy production, but there is a factor against him: the high temperatures, that the paved surface can reach, decrease the efficiency of photovoltaic panels. It is also a known fact that when a roof is covered with mulch, while increasing the insulation of the building, causes the temperature at the surface decreases. In this way, there is a system that combines green roof + PV modules. It is known as Sun-Root and was developed by the company Green Roof Technology (Figure 48).

Figure 48: Sun-Root by Green Roof Technology (Green Roof Technology, 2012) Basically it's like using an installation of PV modules, but placing it on the roof of a house or a building, providing insulation to the architecture and also managing stormwater in order to create a cooler microclimate for solar panels. Sun-Root uses that rainwater for watering the plants, and cooling panels through evaporation.

Figure 49: Design tips regarding the temperature losses Integration of PV Technology in Architectural Envelopes. Design Guide

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5.2.3.

Dust losses

Surface dirt can play an important role in the generation losses of the photovoltaic module. The results of a study carried out by the Applied Physics Dept. of the University of Malaga (Zorrilla-Casanova, et al., 2011), show that the average daily loss during a year caused by the dust deposited on the surface of the photovoltaic module is about 4.4%. But in periods without rains, energy losses may be greater than 20%. It should be emphasized in the inconvenience of the horizontal position for PV modules, as this greatly increases the accumulation of surface dirt. Even in those places where rains are frequent, low inclination may prevent flushing of surfaces. A layer of dust on the front cover of a module reduces transmission of radiation inside at normal incidence, and at the same time, increases angular losses due to reflection. So, the presence of dirt alters the angular dependency of the irradiance, being different for the clean or the dirty PV module. For that reason, for a clean PV module, angular losses acquire their minimum value. And these will increase in function of the degree of dirt. Dust comes from various sources that evolve uncontrollably throughout the year. Should be noted two types of dust affecting systems: the uniform, leading to a decrease in radiation reaching the cells and increases the angular losses, and also a localized soiling which leads to increased losses by formation of hot spots (Figure 50).

Figure 50: Problems and foresights related to dust losses 70

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Integration of PV Technology in Architectural Envelopes. Design Guide

5.2.4.

Losses caused by wiring

As in any other wiring, the cable size in a PV system must be appropriate to the maximum current that will move trough them (Figure 51). Usually, the cable size for a PV system is selected by following empirical rules related to the voltage drop in cabling (smaller than 5% or 3% depending on the system voltage) and also, the cabling length. Nevertheless, a study carried 8 years ago by the British Columbia Institute of Technology (M.D. Ross, 2005), has demonstrated that the optimal cable size is independent of the cabling length. To reduce the losses that take place in the cabling, PV modules should be as close as possible to inverters, so that the distances travelled by the direct current are short. In a building, this can mean to enable a special room next to the PV generator for power conditioning equipment. If the modules are on the roof and this is passable, may be interested to build a small booth to house the equipment.

Figure 51: Design tips regarding the wiring Integration of PV Technology in Architectural Envelopes. Design Guide

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5.2.5.

Losses caused by decoupling

Decoupling losses are those caused by connecting together several modules with different electrical characteristics. By associating several modules in series, the final current intensity is equal to the lesser of those that each one provides individually. If they are associated in parallel, the parameter affected is the voltage delivered by the group. These losses are largely preventable and, as in any other photovoltaic system, it is necessary to meet their electric features before installing the modules in order to classify and group them. The parameter that is often considered is the current of each module in the maximum power point current (Im) Furthermore, the interpretation of buildings must take into account the specific conditions of operation that will have the modules (different inclination or orientation, shading or temperature). Dividing the system when necessary, and associating different inverters to each subsystem are two good measures (Figure 52).

Figure 52: Design tips regarding the decoupling losses 72

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Integration of PV Technology in Architectural Envelopes. Design Guide

5.3.

Maintenance

As in any other PV application, installations in buildings require to perform proper maintenance to ensure proper operation. In general, we must monitor modules, structures, junction boxes and the conversion and transformation systems. As the installation is in a building, everything that affects the security of the system and the people must be emphasized. The insulation resistance and the ground electrodes resistance should be checked periodically. The insulation resistance should be as large as possible and be within the recommendations (20 k!, 10 mA). The ground electrodes resistance must be as low as possible (the NTE -Norma Tecnol贸gica de la Edificaci贸nrecommends a maximum value of 37 ! for systems without lightning conductor). Periodic cleaning of the modules may be required if the building is in an area exposed to pollution and the rains are not very frequent. Because of this, accessibility to the panels should be provided. In the case of photovoltaic facades, conventional methods for cleaning and maintenance of glazed surfaces can be used.

Integration of PV Technology in Architectural Envelopes. Design Guide

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6. CONCLUSIONS As was stated from the beginning, this dissertation is conceived as an guide for architects, and for this reason, research has focused on exploring the potential of photovoltaic technology from the point of view of design, without forgetting that this decision-making has consequences on productivity as this is, in the end, the ultimate goal of a photovoltaic system. Nowadays PV technology allows to modify the typical construction of a PV laminate structure in order to adapt the module design to architectural requirements. Also, it is possible to work with infinite combinations of photovoltaic glass (colour, design, degree of translucency, thickness and size). Of course, depending on the pattern, colour or degree of semi-transparency, PV module energy production may decrease. Each project has a different context, constraints and needs, and therefore, this dissertation cannot go beyond extracting and analysing the potential of each technology, as it is the design team who must analyse them to finally opt for one or the other one. Consequently, if we are interested in incorporating photovoltaic technology to our project, the first question we have to ask is â&#x20AC;&#x153;What do we want to achieve?â&#x20AC;?. And once answered this question, is when this dissertation comes into play. Will be able to raise the tools we can use to achieve the objectives.

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Integration of PV Technology in Architectural Envelopes. Design Guide

In strict terms of design, and focusing on the two most developed and efficient technologies, the conclusions could be reduced to the following table, with â&#x20AC;&#x153;first placeâ&#x20AC;? going to the thin film technology, winner in all key aspects. Of course, there are hundreds of nuances; it is therefore interesting to rely on the information provided in each of the previous chapters.

In conclusion, and contrary to what is commonly thought, photovoltaic technology offers more possibilities than limitations for its application on architectural envelopes. Therefore, and keeping always the logic based on integration and not on the overlapping, project success will depend on knowledge and handling of it.

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7. BIBLIOGRAPHY AND REFERENCES ! Agrawal1, S., Singh, G.K., Tiwari, G.N., 2009, Comparative analysis of photovoltaic modules: an experimental study. In: IGNOU (School of Engineering and Technology), 2nd International Conference on Sustainable Energy Storage, Trinity College Dublin, Ireland, June 19-21. IGNOU: New Delhi. Detail España, 2012. Fotovoltaica de la A a la Z, Detail Green, 2012 (7), pp. 678-681. DuPont, 2013. Tedlar® SP polyvinyl fluoride film [Online] USA: DuPont/DuPont Available at: http://www2.dupont.com/Tedlar_PVF_Film/en_US/assets/downloads /pdf/h51252.pdf/[Accessed 2 June 2013]. FirstSolar, 2012. Innovative cadmium telluride technology [Online] Available at: http://www.nhs.uk.hth.walking [Accessed 6 April 2013] Fraunhofer ISE, 2011, Electrical Energy Storage [Online] Available at: http://www.iec.ch/whitepaper/pdf/iecWPenergystorage-LR-en.pdf [Accessed 2 May 2013] Hering, G., 2011, Year of the tiger, Photon International (March 11), p. 208 International Electrotechnical Commission, 2011. Electrical Energy Storage, Geneva: IEC International Energy Agency / Organisation for Economic Cooperation and Development, 2008. IEA Statistics/Electricity and Heat by country [internet] Available at: http://www.iea.org/stats/prodresult.asp?PRODUCT=Electricity/H eat [Accessed 19 May 2013]. International Energy Agency, 2002. Potential for Building Integrated Photovoltaics, Paris: IEA International Energy Agency, 2012. Key World Energy Statiscs, Paris: IEA Krippner, R., 2012. Tecnología solar en envolventes arquitectónicas, Detail Green, 2012 (7), pp. 674-677. Lysen, E., 2003. Photovoltaics: an outlook for the 21st century. RenewableENERGYWorld, (January-February), p. 46. M.D. Ross, M., 2005. Optimal wire size for photovoltaic systems operating at maximum power point: A closed form approach. In: British Columbia Institute of Technology Burnaby, SESCI 2005 Conference, British Columbia, Canada, 20-24 August 2005. RER Renewable Energy Research : Montréal Munari, M.C., Roecker, C., 2010. Integración arquitectónica de sistemas solares térmicos, Detail Green, 2010 (7), pp. 77881. Remmer, D., Rocha, J., 2005. Photovoltaic noise barrier -Canada. In: British Columbia Institute of Technology Burnaby, SESCI 2005 Conference, British Columbia, Canada, 20-24 August 2005. University of Guelph, School of Engineering : Guelph Solarplaza, 2011. Top 10 World's Most Efficient Solar PV Modules (Mono-Crystalline) [Online] (Updated 30 July 2012) Available at: http://www.solarplaza.com/top10-crystalline-moduleefficiency/[Accessed 19 April 2013].

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Integration of PV Technology in Architectural Envelopes. Design Guide

Sunways, 2009. Sunways Solar Cells [Online] Konstanz.: Sunways/Sunways. Available at: http://www.sunways.eu/static/sites/default/downloads/en/produ cts/solarcells/coloured/Sunways_SC_ColouredMulti156_Datasheet_GB_0904.pdf [Accessed 1 August 2013] Taut, B., 1997. Escritos 1919-1920. 1st ed. Madrid: El Croquis Turner, B., 2009. The New Bouwkunde by Adam Wojtalik [Online] (Updated 20 Oct 2005) Available at: http://www.dezeen.com/2009/10/20/the-new-bouwkunde-by-adamwojtalik/[Accessed 25 July 2013]. University of Lleida, 2009, May. Concentration Solar Power Module Integrates Into Side And Roof Of Buildings. ScienceDaily [Online] May 2012. Available at: http://www.sciencedaily.com/releases/2009/05/090505202912.htm [Accessed 17 July 2013]. VMZinc, 2012?. Fotovoltaico de silicio monocristalino flexible [Online] Barcelona: VMZinc/Umicore. Available at: http://www.vmzinc.es/images/vmzinc/documentation/pdf/vmz%20fo tovoltaico%20de%20silicio%20monocristalino%20flexible.pdf [Accessed 11 June 2013] Von Keller, V., 2013. Del silicio al módulo. [Online] Available at: http://www.schott.com/magazine/spanish/sol108/sol108_03_silic on.html [Accessed 30 April 2013]. Würfel, U., 2012. Dye and Organic Solar Cells [Online] Available at: http://www.ise.fraunhofer.de/en/areas-of-business-andmarket-areas/alternative-photovoltaic-technologies/dye-andorganic-solar-cells [Accessed 13 August 2013] Zorrilla-Casanova, J., Piliougine1, M., Carretero1, J., Bernaola1, P., Carpena1, P., Mora-López L., Sidrach-deCardona1, M., 2011. Analysis of dust losses in photovoltaic modules. In: Universidad de Málaga, World Renewable Energy Congress, Linköping, Sweeden, 8-13 May 2011. Universidad de Malaga: Malaga.

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FIGURES REFERENCE LIST

Arcelor Mittal, 2012, GlobalRoof Kalypso, [digital image] Available at: http://www.arcelormittal.com/distributionsolutions/constructi on/spain/15923/15934/ BREAD Studio, 2012, Highway Noise Barrier, [digital image] Available at: http://www.breadstudio.com/project%20index/noiseB.html Crane, T., 2013, Barnes Foundation, [digital image] Available at: http://www.archdaily.com/238238/the-barnes-foundationbuilding-tod-williams-billie-tsien/ Designboom, 2009, Japanese pavilion at Shanghai Expo 2010 [digital image] Available at: http://www.designboom.com/architecture/japanese-pavilion-atshanghai-expo-2010/ Duer, 2012; Solar Slate – Duer, [digital image] Available at: http://www.fangxingroofing.com/solar.php Integration of PV Technology in Architectural Envelopes. Design Guide

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FirstSolar, 2011, Thin-film CdTe photovoltaic module,[digital image] Available at: http://www.directindustry.com/prod/first-solar/thin-filmcdte-photovoltaic-modules-54324-357879.html Fraunhofer ISE, 2013, Dye and Organic Solar Cells, [digital image] Available at: http://www.ise.fraunhofer.de/en/areasof-business-and-market-areas/alternative-photovoltaictechnologies/dye-and-organic-solar-cells GetIt, 201?, Amorphous silicon modules, [digital image] Available at:: http://www.getit.in/c/sungeninternationallimited1/product/393 5371/amorphous-silicon-modules/ GonzĂĄlez, A., 2008, GENyO Laboratories, [digital image] Available at: http://planho.com/portfolio/genyo/ Goula, A., 2012, ENDESA Pavillion [digital image] Available at: http://www.archdaily.com/274900/endesa-pavilion-iaac/ Green Roof Technology, 2012, Sun-Root [digital image] Available at: http://www.greenrooftechnology.com/green-roofblog/the_sun_root_living_roof_system_green_roofs_embrace_rene wable_solar_energy Hofmann, W. 200?, Various colors in a series-connected dye solar cell modules, [digital image] Available at http://www.solarisnano.com/ JAISUN Solar, 2013, Solar CPV Module, [digital image] Available at: http://www.jaisunsolar.com/solar-PV-modules.php Kupiter, 201?, DUO Glass; SEE Thru, [digital images] Available at: http://www.kupiter.com/solar-panels-2/thin-filmcystalline-pv-system/ NFA, 2009, Siege Social Zero Energie - Macon, [digital image] Available at: http://www.nfa.fr/ Polysolar, 2011, Polysolar a-Si PV Module,[digital image] Available at: http://www.polysolar.co.uk/product.php QVE, 2011, San Anton,[digital images] Available at: http://www.qve-arquitectos.com/san-anton.html Richters, C., 2010,The CitĂŠ du design, [digital image] Available at: http://www.lin-a.com/ SCHOTT/A. Stephan, 2010, SCHOTT SOLAR Sede en Main [digital image] Available at: http://www.schott.com/architecture/spanish/products/photovolt aics/asi-thru.html?so=iberica&lang=spanish SDA/Volvo, 2013, Pure Tension, [digital image] Available at: http://synthesis-dna.com/pure-tension-volvo-v60-pavilion/ Severin, A., 2010, Pratt, [digital image] Available at: http://www.wasallp.com/#/projects/all?p=56 SGPA, 2008, Greenpix - Zero Energy Media Wall, [digital image] Available at: http://www.sgp-a.com/#/single/xicuientertainment-center-and-media-wall/ Solarslate-ltd, 2013, Solar Slate, [digital image] Available at: http://www.solarslate-ltd.com/product-information/theinnovative-slate.aspx SoloPower, 2010, SoloPower solar cell fabricated with copper indium gallium di-selenide (CIGS), [digital image] Available at: http://solopower.com/

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Integration of PV Technology in Architectural Envelopes. Design Guide

Structurae, 2013, Grand Canal Square Hotel [digital image] Available at: http://en.structurae.de/structures/data/index.cfm?id=s0058540 Wojtalik, A., 2009, The New Bouwkunde, [digital image] Available at: http://www.dezeen.com/2009/10/20/the-new-bouwkunde-byadam-wojtalik/ World Highways, 2012, A photovoltaic noise barrier runs alongside the A22 autostrada at Brennero in Italy [digital image] Available at: http://www.worldhighways.com/sections/irf/features/photovolta ic-noise-barriers/ Zoka Zola, 201?, Solar Tower [digital image] Available at: http://www.zokazola.com/solar_tower.html

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Integration of PV Technology in Architectural Envelopes. Design Guide

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Integration of PV Technology in Architectural Envelopes. Design Guide