The Building Side of Building Integrated Photovoltaics
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BIPV offers the PV industry exciting market opportunities and design innovations. However, integrating BIPV products and services into the building design and construction industry is challenging.
Building integrated photovoltaic (BIPV) systems provide many benefits beyond the generation of energy. With BIPV a building owner can stand underneath a canopy and enjoy the play of light through the PV cells or modules; a company can use its building facade to advertise its green credentials; a homeowner can more easily gain acceptance from its neighbors or homeowner association because the PV system’s visual impact is minimized. Additionally, BIPV promises to make the building process itself more sustainable: Total material consumption is reduced through the use of multifunctional building features, such as facades, skylights, roofs, carports or canopies that double as clean power generators.
“BIPV has become one of the most powerful visual manifestations of green design,” says Steven Strong, president of Solar Design Associates, a pioneering BIPV services provider located in Harvard, Massachusetts. “While there are literally hundreds of options to improve a building’s performance and reduce its environmental footprint, most are invisible when you are done. BIPV is unique in its visibility. Innovative architects are now adding BIPV to their design pallet and the creative process. With continued progress in component and systems development, BIPV is destined to become ubiquitous in the built environment.”
If BIPV is to succeed on a large scale, there is much to learn and plenty of room for improvement. This is true not only for solar professionals—product manufacturers, PV system designers and integrators—but also for the building design and construction industry in general. Architects, engineers, general and electrical contractors, and glaziers are in the early stages of their BIPV learning curves.
Building integrated photovoltaic materials and applications are not new. Solar Design Associates pioneered the BIPV concept 30 years ago with the completion of the Carlisle House, an all electric, net zero energy application in Carlisle, Massachusetts. One of the first BIPV facades was completed in 1991 for the Aachen Municipal Utility in Aachen, Germany. This project demonstrated that energy generation could be successfully integrated with a building facade curtainwall system. Today’s BIPV applications beg for a holistic understanding, one that captures the multiple functions BIPV can provide. These include power generation, material replacement, architectural integration and the creation of shade.
Power generation and energy harvest. The BIPV component should generate power effectively and harvest a meaningful amount of energy for the building. Challenges are the building’s orientation, overall energy consumption and the power density of the BIPV system. A wide variety of technologies with associated power densities are available from 4 W to 16 W per square foot. Each project has a different answer as to what is meaningful and cost effective energy generation.
Conventional material replacement. BIPV components replace conventional building materials, such as roof tile, roof membrane, facade cladding, or facade or skylight glazing. This can lower total material costs and reduce the construction time for a building project, while minimizing the consumption of materials and natural resources. If you compare the cost and installation time for a BIPV skylight, for example, with the same quantity of skylight glass and a separate conventional PV system, the BIPV skylight has a lower total cost. Further, the BIPV skylight should have less environmental impact since fewer materials are used to achieve the same result: power generation, building enclosure and natural daylighting.
Aesthetic integration with architecture. A building’s BIPV component must integrate with its overall design. Since aesthetics are more subjective than objective, opinions differ on this point. In general, BIPV components should be complementary and harmonious with the architecture. BIPV components provide a range of aesthetic options, from being hidden among roof tiles to being visible shade elements.
Shading benefits. The BIPV system itself, of course, takes advantage of direct sun—but it also can shield building surfaces and openings from unwanted solar heat gain. You can argue that a conventional PV array mounted above a roof surface reduces solar heat gain, but BIPV louvers at window openings are even more effective.