From BIPV to Building Component

28th European Photovoltaic Solar Energy Conference and Exhibition

FROM BIPV TO BUILDING COMPONENT

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F. Frontini1, A. Scognamiglio2, G. Graditi2, C. Polo Lopez1, M. Pellegrino2 SUPSI, Institute for Applied Sustainability to the Built Environment (ISAAC), Lugano, Switzerland 2 ENEA, UTTP FOTO, Portici, Italy mail to: [email protected]; phone +41 052 666 6320, fax +41 052 666 6349

ABSTRACT: The present need to, dramatically, increase the renewable part of our energy supply is now pushing to maximize the Photovoltaics (PV) use on the building skins, making architectural and building integration a key issue. This will have an impact both in the building’s design by reducing the energy need by the building itself, and in the diffusion of renewable energies on site (near-by), which will produce the remaining part of energy if it is needed. PV will be gaining more and more relevance in the NZEBs design, thanks to its features and potentialities. “BIPV” is for technicians a well-known acronym to indicate PV module used in/on building when PV modules replace part of the traditional building elements of the envelope. Despite the discussion has been treated in several international projects and research programmes, settled up to find a common definition of BIPV and to help the PV manufactures to produce new innovative module suitable for their use in buildings, PV module are still not used on large scale in building and often are not considered at all by architect and designer as a further option in their projects. The paper tries to underline what are the main causes of this slowdown in the use of PV as building component. Possible solution are also presented especially in order to gives the main stakeholder affordable information of PV module as for a common building component. This paper will start from a review of current definitions used in the field of the use of PV in buildings, and will identify needs for further research. The starting point will be the experience of the authors in several international research project, in the International Energy Agency (SHC Task 41 Solar Energy and Architecture; SHC-ECBCS Task 40-Annex 52 Towards Net Zero Energy Solar Buildings) and, in particular, the participation in the EU 7th FP project “Construct PV”. Keywords: BIPV, building integration, multifunctional component, architecture

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The scope of this paper is to bring a preliminary analysis of the general issues of the use of PV as a building component, to better understand what are the main research needs that should be answered.

INTRODUCTION

Photovoltaic modules, available as flat or flexible surfaces, realized with cells or laminates, can be integrated normally into any surface of the building envelope and due to their features (size, flexibility, shape and appearance), are particularly suitable for being “designed”. In fact, these photovoltaic elements can be used together with materials that are common in architecture, such as glass or metal, in opaque as well as in semitransparent surfaces. Manufacturers can today provide the building sector with different interesting products, ready to be used by architects and planners. Nevertheless, PV is still looked with suspicion in the building sector. The reasons for this condition are complex, nevertheless an easy preliminary explanation for this is that, on one hand, its potentialities are still not well known by designers, and, on the other hand, its affordability is not sufficiently demonstrated. In a few words, PV is still a material difficult to use for designers, in the absence of a precise catalogue of design possibilities, in the absence of a technical datasheet comparable with the ones proper of the building materials, and last, but not least, in the absence of a dedicated regulation in terms of standards, technical and legislation requirements. It is therefore necessary to improve the effectiveness and affordability of PV as a building material component; this implies the need to specify new features to develop PV products that increase competitiveness of PV with respect to other conventional building materials, and to fill the gap causes also by the lack of harmonized regulation and standardization that penalizes its affordability.

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APPROACH

As it is well known, the use of PV in buildings is mainly associated in the “PV World” with the acronym BIPV, that stands for Building Integrated Photovoltaics. Several definitions of BIPV have been given in the last twenty years, and the discussion is still ongoing. Here one aspect the authors would like to underline is that, despite so much research carried on, and the many attempts to merge different technical fields visions, the use of the word “integrated”, still reflects a certain vision of PV, according to which PV components are somehow different from building components. In particular, PV modules are understood as electrical elements, heterogeneous with respect to traditional building elements, with the consequence that they have to be “integrated” into the building envelope (with all the possible consequences in terms of requirements and standards). So, there is still a gap to be filled between the building sector and the PV sector to change the vision of PV from technical elements to building components. The urgency to fill this gap is increased by the need to reply to the EBPDirective on Zero Energy Buildings [1], that somehow fosters to the use of PV in the building envelope. What might be the drivers for this desirable change of perspectives? The (expansive) cost of PV has been evaluated for years as the main barriers to the diffusion of the use of PV in buildings,

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so as a cost decrease might be understood as a possible driver. Nevertheless, investigations show that the recent dramatic cost decrease of PV is not the main barrier for the diffusion of photovoltaic anymore [2]. Does this new (favorable) condition of PV have an effect on its use in the building sector? Apparently not, despite now PV modules can be considered as cheap as many other building materials (about 100€/m2). An international survey has been carried out in the framework of the IEA Task 41 “Solar Energy and Architecture” to understand what are needs, barriers and strategies for the integration of solar technologies. The focus group of the survey consisted mainly of architects and other building practitioners [3]. One result of the survey attests that cost is one of the main problem for the diffusion of PV for architecture ( PV modules for architecture are still more expensive than conventional ones [4]). Meanwhile the survey also shows that price reduction of BiPV modules is more a strategy for spreading this technology then the main bottleneck (Figure 1).

To better understand how affordability and performance can affect the possible use of PV in buildings, in this paper the authors compare conventional PV module characteristics and the ones of BIPV modules under the perspective of their use in buildings and the way they have to comply with standards, regulations and building processes. The aim is to provide knowledge background for further discussion. In particular the key research question is: how to “morph” a PV module into a building component?

Figure 3: Considering BiPV as multifunctional building component means to reflect on the real role of the module in the building concept (picture source: IEA Tak 41) 3

CONVENTIONAL PV MODULES VS BUILDING COMPONENTS KEY ISSUES: INTEGRABILITY AND NORMATIVE FRAMEWORK.

Conventional PV modules (having fixed number of cells, sizes and shapes), are often not suited for substituting building elements. As they are obviously conceived for being energy generation devices, they cannot meet many requirements requested by the building sector. For instance, the mechanical resistance that the module can provide, through the use of the external glass, aims to protect the solar cells, but could not fulfill the requirements needed for any structural element of a roof or of a façade. Moreover, using a conventional PV module into a building envelope is possible only when using a special fixing system, suited to match the technological features of the traditional parts of the building’s envelope. This is the reason why the industry has been providing many so called “BIPV components” that should be able to fulfill all the requirements requested for their use in buildings. Nevertheless, in the absence of a clear regulatory and standard framework, it is very difficult to assess the affordability of PV when used as a building component, even when referring to BIPV components. A practical consequence of this is that very often choosing if using PV and, in the case yes, selecting the appropriate component is quite a difficult task for a designer. In the absence of clear and affordable data sheet (that provide useful information) of the PV component it is up to the designer understanding what is the performance that the PV component has to ensure, and what are the technical requirements that this implies. Only at this stage it would be possible to select the appropriated PV component available on the market. In particular, the process for selecting a PV component should be [5]: • selecting the technological unit in which it has to be used; • listing the features of such a technological unit, and designing/selecting the appropriate technological system (sandwich composed of different layers); • individuating which is the layer that the PV modules replaces, and describing the performance it has to ensure;

Figure 1: The International Energy Agency (IEA) Solar Heating and Cooling (SHC) Task 41 “Solar Energy and Architecture” has conducted an international survey concerning the integration of solar energy systems, the diagram shows the barriers and the strategies for the diffusion of PV in architecture [3]. This result is not easy to analyze. In fact, if one considers that the building sector normally uses expensive technologies and noble materials (such as marble facades or triple glaze windows), it is surprising that cost becomes a key element for the use of PV. The way designers approach and envision the use of PV in buildings seams to suggest that PV is not perceived as belonging to the range of conventional building materials, and, as a consequence, it is understood in a different way. As Figure 2 shows designers ask for more information useful to compare the PV module with conventional building components.

Figure 2: The qualification of BiPV products' offer is still fair [3]. Architects require more information in order to compare PV module with conventional building component. Why does it happen? What is missing? One immediate possible answer is that it is not a matter of cost but more a matter of affordability and performance.

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• once analyzed the performance, listing the requirements the PV component has to meet (e. g. thermal resistance, mechanical resistance, etc.), and selecting for the most appropriate available product. • checking that the use of PV complies with all the regulations requirements. In the following, in order to understand how to ease this process, conventional PV modules versus building components are compared, to understand what are the key issues. To do this, we will focus on two aspects: integrability and rules (normative frameworks). 3.1 Categories for the integrability of photovoltaic systems in buildings, and specific requirements Within the EU project Construct PV [6], the authors collect the technical and functional requirement of a building component, with a particular attention to the opaque part of the building (both façade and roof). The list of requirement is very long a reflect the long history of architecture that tries over the century to optimize the building to meet the user needs and the architect requirements. In the following Table 1 these points are summarized in a list of categories for the integrability of PV components in buildings, with a description for each category, and the associated specific requirements that PV components should ensure.

Figure 4: Left picture shows a fritted glass unit by Dupont. Right picture presents what is possible to make with common glass-glass PV module to increase the color possibility (source: Intersolar Munich. Ertex Stand).

Specific requirements

Table 1: Integrability categories for a building component Technological integrability

Morphological integrability Passive energy performance

Constructive compatibility

Color variation

Caption and control of the solar radiation

Static compatibility

Grain variation

Ability to re-use or to dissipate the heat coming from the PV conversion.

Materials compatibility

Texture variation

Figure 5: Patterns promote performance study: emerging parametric photovoltaic patterns - cultural, social and technical symbiosis. (Source R. Baum [7]) In this sense what will be really the future development of the technology and BIPV market? Is it towards new products that camouflage solar cells despite a small amount- of electrical performance like some research developments seem to suggest? Or it will better address the issue of keeping together energy performance and good morphological qualities, while exploiting the intrinsic features of the (best) PV technologies?

3.1.1 Technological integrability It takes into account the constructive compatibility between new and traditional building components. Related also to the compliances of the standard (static compatibility) and safety issues (safety of people and electrical safety) the technological integrability refers also to the compatibility between one element (i.e. the PV module) and the other building component in particular how they are connected together and if they are compatible. In fact we speak also about material compatibility in order to identify special constraints between different material (either technological and aesthetical). 3.1.2 Morphological integrability (color, grain and texture) It takes into account the modification of the material qualities of the technological sub-systems involved in the process of using PV. It deals with the visual perception of the surfaces of the building. One of BIPV’s core advantages is that it might better address the aesthetic interests of many stakeholders which sometime are willing to pay something more for “BiPV nice installation” [8]. But it is very difficult to predict how aesthetics can drive the large deployment of PV in architecture. Anyhow, “adapted” conventional PV components, suited for a good morphological integration, can be drivers for this penetration.

Figure 6: Sport palace TüArena, Tübingen (D). Allmann Sattler Wappner Architects: SunTechnics, Solarfabrik AG PV modules. 3.1.3 Energy performance It takes into account the possible effects that the use of PV components replacing traditional building elements can have in terms of improvement of the energy performance of the envelope, considering only their passive contribute as envelope materials and components and the contribute they can give the net zero energy balance of the building. As discussed previously the new European requests (Nearly Zero Energy Buildings Directive) suggest that a step further should be taken. In particular, when PV modules

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replace traditional building elements, in a high performance building, as well as in a NZEB, it is very important a real knowledge of its performance, in terms of multi-functionality, and in terms of energy performance, too. In the new perspectives where buildings are NZEBs, a designer (a project manager as well as an architect) needs to know perfectly which performance he can expect from a certain envelope component. From this perspective a new challenge for BIPV is being for the designer an affordable component that is: offering (by means of appropriate certifications and testing procedures) the same performances of a traditional building component, so as to be seen as a building material component. New construction protocols and good standards for new buildings and refurbishment (LEED, ITACA, BREEAM, Minergie, CASACLIMA, PASSIVE HOUSE, …) are not always mandatory in the different countries but offer a quality mark. For some of this quality building standards PV systems becomes an alternative and a tangible option towards nZEB (Minergie-A category for example [9]) to implement solutions for energy improvement in building sector. A good PV component for façade installation purposes should take into account thermal and insulation properties, factors as transparency (Figure 7) to allow solar gains if possible or a good solar control if necessary, aspects that are linked and high dependence on climate conditions that they will be installed. That’s mean also customization for each single situation. Unfortunately, many aspects regarding this subjects are not yet well known (as also evidenced by the lack of standardization). The variability on electrical performance depending of solar radiation different angles of incident (AOI measurement) is still an open question. In the same way only a few BIPV manufacturers provide accurate information about thermal and visual properties of PV modules (Heat transmission coefficient, U-value; solar factor, g-value; lighting transmission value for example).

Architects need PV modules suitable for adapting itself, as building component, to many different design possibilities, variability of sizes and forms, increasing their attractiveness. That’s implies custom made solutions, but standard regulations only checks the reliability performance of commercial standard solutions, by extending the approval certification for the other multiple customized solutions. Moreover, this compromise that too simplify approval procedures in order to benefit the diffusion of this BIPV solutions may, in the long term, not favor the BIPV industry if this systems fails or not performs as expected due to a personalized manufacturing process. Furthermore new BIPV products are put in the market continuously, offering innovative solutions for building components but its reliability and durability characteristics are not yet proved as occurs with other building materials. Mayor guarantees are need and it is a key point to more in deep discussion. As already discussed in [13] and [14] when dealing with Photovoltaic in building we have to comply with a series of international and national construction directive and regulation. The construction Product Directive (in force until July 2013) and now the Construction Product Regulation CPR [15] together with all relevant standards for façade, roof, balcony, etc. represents the legal framework under which a Building Component (or BiPV) has to lies. This first difference makes the legal framework for a “Multifunctional” Building component more complex. A solar tile (active roof tiles) have to compete with common tile such as a Clay roof tile (Marselleis) or a Canadian tile (tegola canadese) and a semitransparent PV module must “race” with an insulated triple glaze unit for example. In all cases (some of them are reported in Figure 8) the PV component has an “added” value, respect to the common building component: the electricity production when exposed to sunlight.

Figure 8: Different part of a building skin can be “transformed” in renewable energy producer. Each component has to be treated indipendently with its contraints and freedom.

Figure 7: Semi transparent curtain wall façade. The Multifuctional elements provide both solar control and electricity production (source: Living Tomorrow, Brussels, SAPA solar).

What it is still unclear are not the relevant standard but how to comply with them and if they are compatible with PV technology (electrical system). Different international community [16], [17] and European projects [18], [6] worked and are working on this issue trying to harmonize the present situation where each Country or Region has its own rule and procedures. However, navigating codes and standards issues may continue to be more complex for BIPV.

3.2 Normative frameworks: electrical safety vs Building requirement PV modules and PV installation are ends in themselves [10], the original function is purely the transformation of solar energy in electricity. PV manufactures in order to be competitive in the PV sector have to comply with electrical safety standard and IEC regulation (such as IEC 61730 [11] or IEC 61215 for crystalline modules [12]). This make clear to all PV costumers what are the quality control to be done in order to evaluate a PV module and compare it with its competitors.

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DISCUSSION and PRELIMINARY CONCLUSION What previously discussed underlines that even if the use of PV in buildings is investigated since long time (especially in

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terms of so called BIPV and BAPV) and the technology is mature, some information and research are needed for a massive diffusion and utilization on large scale. Policy already fosters the use of PV and renewable in general by introducing first special feed-in tariff of “integrated solution” and also by promoting high efficient building standard like for example the Minergie-A [9] standard, which numerous researches have shown to be achievable only by the integration of Photovoltaic in the building envelop. The PV technology in buildings seems to miss some integrability concepts that are intrinsic for a building component. Without a clear understand of this features PV module cannot be easily compared to conventional building materials that are used by architects or planners since long time and are part of their design language.

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[8] Figure 9: Different building systems and materials for façade solutions: i.e. Heavy weigth stone curtain wall (Venistone product); Ceramic solar control system and phono absorver materials (Terreal); Green wall, pollutant absorver façade (Perlite); Media façade. Some solutions materials for building products in façade: timber cladding systems; metal cladding; metal wire mesh; plastic, hpl claddigs; ceramic and composite materials.

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The authors in this paper present the complexity of the utilization of PV modules as building component. The discussion started from the experience of different International project that treats the integration of Photovoltaic technologies in the constructed environment and presents some preliminary discussion within the EU project Construct PV. The paper tries to reverse the perspective how to treat PV in building identify different Integrability criteria for building component that BiPV module should foresee. The lack of helpful information, translated into an affordable data-sheet for architects and planner, seems to be the main bottleneck for the diffusion of this technology that is completely appropriate to be used as building element (roof or façade for example). The publication of an exhaustive and harmonized standard (which covers both electrical safety and buildings issues) has also to be foresee in order to provide clear information and a coordinated way to present the technical properties of a PV modules such as the constructive properties, the morphological freedom (i.e. dimensions possibilities or color palette) and energy retention (i.e. g-value, U-value and solar absorptivity) characteristics. Although the deployment of BIPV is relatively small, opportunities remain promising. Increasing consumer interest in solar energy together with the reduction of module costs, with always the support of policy schemes to promote distributed renewable energy production systems have the potential to boost the BIPV market. The commercialization of solar products that have the full functionality of building materials has been very limited, despite this seems to be a very powerful driver for the issues discussed in the paper.

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