From providing electricity for satellites to powering solar calculators, photovoltaic (PV) cells capture the sun’s energy for many purposes. But what is the reality of using solar cells to generate electricity for buildings? This is a critical issue since buildings use more than one-third of the total energy consumed in the United States. In the past, PV installations didn’t have much fashion sense, as their support structures tended to dominate rooflines. Today’s PVs, however, have been integrated into materials such as standing seam steel roof panels, insulated-panel flat roof systems, shingles, spandrels, sunshades and glazings. Building-integrated photovoltaics (BIPVs) extend the architect’s palette rather than limiting it.
“Why should a PV array look like a 15-year-old’s science project?” asks Joe Morrisey, sales director for Atlantis Energy. Although the idea of BIPVs is not unique to Atlantis, this manufacturer creates window and roof panels that correspond to typical commercial and residential standards, allowing builders to literally replace conventional windows and roofs with units that not only let in light or keep out rain, but also create electric power at the same time.
Besides design features, PV cell efficiency and size to output ratios have also come a long way. Early PVs could only convert about one to two percent of the sunlight’s energy into electrical power. By contrast, today’s PV panels have improved on these figures by a factor of ten. And, depending on the BIPV product type and the climate in a given region, the power produced in full sunlight can vary from five to ten watts per square foot of collector.
Installation is another big part of the equation required to make BIPVs work in the real world. The architecture firm of Skidmore Owings & Merrill (SOM), headquartered in Chicago, is a leader in BIPV implementation. According to SOM designers, it is critical to get both the general contractors and clients on board early. Rather than hiring a BIPV expert, it is much more cost-effective to build enthusiasm and interest among the trades and provide them with the necessary training. If this is not done, bid amounts may double or triple to make up for perceived challenges.
“We are working with roofing contractors to have them install the photovoltaic material,” says Morrisey, whose company’s roof and window PV panels are built to the same size specifications as regular roof and window materials and have simple electric connections. “Eighty percent of the work to install one of our roofs is the same work required to install a regular roof, and the remaining 20 percent is electrical work that any electrician can perform.”
Lastly, aside from using BIPVs primarily for marketing purposes like the retailer IKEA has done recently, are the increased costs associated with these systems justified? While the cost per BIPV generated kilowatt-hour has dropped, it is still ten to 100 percent higher than commercial power and 20 to 50 percent higher than standard PV panels. Often, these increased costs can be recovered because the photovoltaic units are replacing window and roofing material that would have to be purchased anyway in new construction. Moreover, the design of the roof panels, which requires about two inches of airspace underneath the photovoltaic panels, creates an insulating layer that reduces home heating and cooling expenses, and also causes snowfall to melt off the roof much faster than off a conventional roof. Similarly, PV windows are tinted and can therefore reduce air conditioning costs. According to Morrisey, it is already possible (in volume orders) to equip a home with two kilowatts of BIPV power for as little as $20K per house, before any subsidies or rebates. BIPVs are also useful in reducing costly demand charges, which are based on peak power use during a given month.
“If the BIPV technology exists, it must be possible,” says Steven Strong of Solar Design Associates to skeptics. He has been able to retrofit existing tract homes in the Northeast to make them energy-autonomous. Furthermore, Atlantis’ Morrisey points out that BIPVs create “multiple values,” including electric power, construction material, thermal insulation, and—the fact that they don’t make the neighborhood look like a science project.
Thanks to EcoWorld for allowing some material for this column to be taken from an article on their website (www.ecoworld.com).