Considering Photovoltaic Technology as a part of the building material

Transcription

1 Considering Photovoltaic Technology as a part of the building material H. Sozer College of Architecture, Illinois Institute of Technology, Chicago, USA. Abstract The use of PV technology in buildings is growing very fast throughout the world. In the U.S., Building Integrated Photovoltaics (BIPV) have been integrated into some limited, small-scale projects. However, BIPV S are now being considered on larger scale building projects, as replacements for typical high-performance envelope materials, This is a result of improved economics, including higher module efficiency and lower cost of the PV cell product, The higher efficiency makes BIPV modules more attractive for non-solar normal orientations, and the lower costs and financing subsidies makes B[PV more equivalent in cost to high quality materials such as stone or metal panel. BIPV applications are still not quite well known in the building construction industry, even though the quality of the materials is going up and cost of the system is going down. When it is compared with common building materials, BIPV materials are still more expensive and don t quite fit with the architectural design and construction process, Regular quality schemes for building materials such as constructability, structural properties, life expectancy, performance and aesthetic features have not been clearly defined for photovoltaic yet. This paper will attempt to answer the question of what do the architect and engineer need to know about the use of Photovoltaic modules as a building material and how can PV manufacturers implement solutions to these barriers, 1 Introduction PV panel systems typically consist of cell units, glass layers and inverters to form a part of the exterior wall or roof as a roof whole system it should work together in

2 the most efficient way. If PV is used on the exterior of a building it should also match with the codes and standards that apply to all envelope materials. Another important consideration is the installation of the system and cabling. A lack of understanding of how these components will interact, as places of the envelope system will have an impact on system cost. These undefined parts are important barriers on application of Photovoltaic system in the building industry. Comparison between Photovoltaic modules and other building materials such as glass, steel, stone wall materials will be made to show the differences between these building materials according to cost, constructability, performance and aesthetics. 2 Comparison between PV and traditional building materials In the design of building integrated photovoltaic systems, the PV modules are typically the most important of the building components. Cost, quality, dimensions, life expectancy, structural properties and constructibility of the system have to be compatible with the other building envelope materials that PV can replace. [1] BIPV doesn t only finction with PV cell; it comes with an entire system, which consists mainly of PV panels, balance of system (BOS), grid metering connection, inverters, and batteries if needed. BOS mainly includes cabling, wiring and structural elements that hold the system together. [2] The design and configuration of these components has to be made carefully, so it can function as a whole system. There are some issues that should be clarified before selecting PV as a part of the building material instead of the traditional building materials. These issues are as fallows: Cost, life expectancy, quality, constructability, structural and architectural characteristics 2.1 cost The cost effectiveness of the system is as important as the convenience of BIPV product, the building elements and the distributed sources of electrical energy. It can be very valuable to compare the cost of the alternative materials with BIPV system s cost before making any decision about building envelope materials, In practice, the sizing and pricing of PV installation is relative. The cost of the system can be calculated according to the size of the PV array area but also other components of the supporting system, such as BOS and inverters, should be included. There are also indirect costs associated with interconnection with the local utility grid, [1] Table 1 shows the cost of the different building envelope materials, If comparison is between PV and a high performance or high cost fa$ade element, such as polish stone granite, replacement of PV with this material can offset the Pv cost.

3 Table: 1 [3] $ll.s[aitwhlc ( ill [[ 1019 Costs of the conventional wall systems ($/m ) Rain screen over cladding 280 Stone cladding 450 Double-glazed cladding system Granite faqade pre-cast concrete cladding 928 Polished stone cladding Costs of PV cladding systems Rain screen cladding systems Curtain walling using glass/glass module I Based on c~stalline silicone technolo~. Balance ofsystem (BOS) is included. Also, according to BP Solar research, glass wall systems range from $560 to $800m2, polish stone walls range from $1200 to $2800m2 while photovoltaic range from $500 to $1500 m. [4] Lower system costs for other envelope systems are typical, The costs of building envelope material such as cavity walls are generally significantly lower when compared to the cost of PV systems. On the other hand, in an expensive fa$ade system such as polish stone cladding, the cladding cost may equal the cost of PV module and the cost can be offset. So, in the expensive faqade system, PV market is already competitive. Also, PV, as different than other expensive cladding material, will provide a return the investment to the building owners (especially for commercial buildings) by increasing in rent. [1] It shouldn t be forgotten that PV technology is still a developing technology and PV market is growing very fast. It is most likely that PV cost, will be equivalent to regular building envelope material in the near future. 2.2 Life expectancy Another important consideration for economy of the system is the life of the high performance building envelope element compared to PV system. The main concern for the PV system is PV module s 1ifetime. Present PV technology gives an approximate of years life expectancy. This affects the Life Cycle Cost Analyses of the building.

4 1020 Y /l,,s[/.sf,lillc/ll/( ( i/,1 // Table: 2 [1] Life Span for various building components (years) Brickwork Curtain-wall systems Steel cladding-plain Steel cladding- pre-coated Electrical distribution svstems Electrical installations in buildings External electrical eaui~ment i Life Span for PV module In addition to offsetting the cost, there are enhanced value that BIPV brings to building systems such as prestige and marketing opportunities for commercial and industrial building, architectural merits and aesthetics, satisfaction of the consumer s desire for environmentally sound products and satisfaction of the desire for increased autonomy. [1] These values cannot be quantified. However, it is very important to identi~ these values for better market development and customer attention. 2.3 Quality Unlike other building elements, PV modules cannot be distributed freely in the building envelope like other materials. Total available building surface for BIPV system is limited due to solar accessibility, which has direct affect on the efficiency of the system. Efficiency of the system is also relevant to the surface quality of the system. Better efficiency results in better quality of BIPV system. Therefore, the quality of the PV cell not only depends on the well-manufactured product but also on well sited cells on the building envelope. This can be obtained by determination of the following issues: Orientation of the building and PV system: The optimal inclination for solar radiation will give the better efficiency. In a way, PV systems also form the building envelope in the way they are integrated such as with inclined roof systems, atriums, vertical applications, as well as with inclined PVS with windows. [3] The amount of shading: Shading can be from surrounding building as well as trees or other objects. This shadow effect is varies depending the time of day.. The climatic region: This gives the characteristic of climatic condition such as available solar radiation, cloudy days, and humidity.

5 1Iw.Sl{vtclimlllle ( ilj fl 1021 So, PV modules cannot be considered as replacement for every part of the building envelope, In order to maximize the life cycle economics of a BIPV project determination of the performance quality for the different part of the building should be made during the building design, 2.4 Constructability In construction terms, BIPV systems have to address all the issues that traditional wall systems does such as appearance, windioading, weather protection, life time of the materials, risk of failure, safety and cost. [1] PV systems are different from traditional building materials, in that they have to deal with cabling and maintenance of the system. Physical characteristics of the PV product should also match with the architectural design consideration such as color, size, and even material type. For better market development, architects and manufacturers of PV products should work together to produce architecturally acceptable BIPV systems, PV product can be custom-made to fit into different design alternatives, or standard size and type modules can be used in the design. Color, shape and transparency of the PV can be varied according to different design alternatives. Integration concept not only satisfies architectural design, but also has to meet building industry s criteria, [5] Actually, PV, as a building material, is a new challenge for building industry, New attractive design alternatives can be created with a respect to environmental concerns. For architects there are many options that they can integrate PV systems into the building such as day-lighting, shading or fapade elements. 2.5 Structural and architectural characteristics Color: PV cell can be produced in different colors, range of black, blue or brown, etc. [6] Also PV panels can be design in different colors. Visible back layer can be colored so PV panels have combination of PV cells color and back coloring. [5] Like other building material such as fritz glass, stone or metal, tinted and conditioned surfaces also give different textures to PV panels.. Shape: PV panels are produced in various sizes where can be used as different building elements such as different sized rectangular spandrel units, roof tiles, or windows elements. [5] Even though manufactures of the PV offer standard products, they also produce custom-made products to fit in to various building design alternatives with more cost.. Transparency: Transparency can be achieved in two different ways. One is to spacing PV cells within the laminated glass layers from a distance each other. Second is to use transparent cells. Transparency on the cell is achieved by making pinholes in each cell. Different density and size of the pinholes give different degrees of transparency. [5] Transparency gives architects variety of design opportunities. They can create an attractive building skin and also provide the natural light inside of the building

6 without glare problem. Also with a distance-replaced cell, shade patterns can be created inside of the building, which change different time of day. [1] 2.5,1 Thermal characters Acoustic and thermal properties can be improved by adding glass layers on the back-side of the panels. Insulation of the system: In most cases PV itself can act as an insulation material. Some studies show that thermal radiation can be reduced by 35 Aand 31% if PV added on the design. [5], Heating: Transmitted solar radiation thorough PV cell heat up the module. With a design strategy this heat can be use for heating to space or water. This kind of systems called hybrid electric/thermal (PV/T) system. These systems also reduce the cost of the overall building system and energy demand. [3] Ventilation: With a stack effect, natural ventilation behind the PV module can be attained. This creates the airflow behind the PV module, This airflow helps to reduce the PV temperature, which increases the efficiency of the module. [5] 3 Non-quantifiable values for PV as a building material BIPV systems should not be compared with other non-pv product without mentioning the non-quantifiable values of the system. BIPV system works as a multifunctional building material, They aren t designed just to be a fa~ade or roof elements of the building envelope. They also generate electricity, and, in some cases work as day lighting elements. Non-quantifiable values have effects on the building owner, the occupant of the building and on society as a whole. For example, a commercial building owner might be able to collect higher rents because of the high profile element of the building. The occupant of the building might take advantage of the prestige value of the building and its marketing benefits in addition to the value of the electrical energy. [2] BIPV system also has benefits for electricity industry. It decreases the need for utility capacity and decreases potential losses in the distribution system. With cost reducing tariffs that may be offered by utility, occupants can also take advantage of these benefits by reducing their electricity costs. Society also benefits from BIPV in terms of a reduction in greenhouse gas emissions from fossil fuel generation. Also, enhanced building aesthetics and the improvement of a local industry are benefits for society. Conclusion PV technology is still a developing technology and PV market is growing very fast. It is most likely that PV cost, will be equivalent to regular building envelope

7 material in the near future. Even in today s market PV can be compatible if compares with expensive cladding systems. Simple comparison between F Vand other existing systems is no longer proper to determine competitiveness of one system versus another. An appropriate strategy would be to compare PV systems with each other. lf PV is considered as a building material, it is critical to underline the PV as a multifunctional material and explain the un-quantified values, Acknowledgement The author likes to thank Prof. Patrick DoIan from College of Architecture at Illinois Institute of Technology for his guidance and support. References [1] Watt M,, Kaye J., Travers D., MacGill I., Opportunities for the Use of Building Integrated Photovoltaics in NWS, March 1999 [2] Eiffert P., Kiss G,, Building Integrated Photovoltaic Designs for Commercial and Institutional Structures, A Sourcebook for Architects, February 2000 [3] Randall T., Photovohaics and Architecture, 2001 [4] BP Solar, Annual Report, Building-Integrated Photovoltaic Power System, 1998 [5] IEA-PVPS, Added Values of Photovoltaic Power Systems, 09:2001 [6] Humm O, Toggweiler P, Photovoltaics in Architecture