New clean energy products for residential roofs
April 04, 2012— Ottawa, Ontario
A new generation of flexible photovoltaic products may soon help protect Canadian homes from the elements while generating renewable solar energy.
Building-integrated photovoltaic (BIPV) systems integrate photovoltaic panels directly into the building envelope. One of the most common BIPV systems is the flexible thin film amorphous silicon PV panel. “Even though these products have half the efficiency of crystalline silicon solar panels, they offer several advantages including a large coverage area, high performance under diffused light, and easy integration onto a roof in comparison to rack-mounted or independent crystalline silicon panels,” says Dr. Sudhakar Molleti of NRC.
For two seasons, an NRC team evaluated flexible photovoltaic solar panels at this test house operated by the Canadian Centre for Housing Technology. The Centre is a joint initiative of NRC, Natural Resources Canada, and the Canada Mortgage and Housing Corporation.
BIPV systems “are mostly commonly used on the flat commercial roofs with large surface area typical of a ‘Big Box’ store, but are not yet designed for residential roofs,” adds Dr. Molleti. As part of a demonstration project supported by Natural Resources Canada, and with help from the roofing manufacturer Soprema Canada, an NRC team headed by Dr. Molleti and Marianne Armstrong recently installed a 2 kW BIPV system at the Canadian Centre for Housing Technology, replacing the existing asphalt shingles. The project’s aims were to measure the potential energy generation and evaluate the durability of the system on a residential roof.
“The outcomes of our research could either help pave the way to opening up residential markets for the new roofing products, or identify technical barriers that could discourage the adoption of such technologies in Canadian climates,” says Dr. Molleti.
So far, after two seasons of testing, the results look promising in terms of electricity generation. Over a 23-week period from September 9, 2011 to February 17, 2012, the BIPV solar panels generated a total of 557 kilowatt hours (or 19 kilowatt hours per square metre). Extrapolated over a full 12 months, “the potential is close to 1200 kilowatt hours per year,” says Armstrong.
"With virtually every shingled roof being replaced every 15–20 years, there is a built-in opportunity to achieve major retrofit inroads with these technologies."
- Dr. Sudhakar Molleti
Besides tracking power generation, Dr. Molleti’s team conducted wind uplift tests on the BIPV panels, using NRC’s dynamic roof testing facility. The experiments showed that during high winds, flexible solar panels may peel away from the underlying roofing membrane they’re attached to, so certain design changes may be required.
“There are currently no Canadian guidelines available on how to apply flexible-film photovoltaic panels or the rack-mounted crystalline silicon photovoltaic panels on a residential roof,” notes Dr. Molleti. In future research, he and his colleagues hope to explore in detail how to optimize the installation of BIPV panels on residential roofs.
In addition, “we are interested in comparing the performance of flexible roofing membranes with solar shingles and crystalline silicon PV panels,” says Dr. Molleti. Such a comparison would examine a range of parameters including energy efficiency, cost and durability.” The NRC data would ultimately be used to help “owners, practitioners and contractors install BIPV panels with confidence.”
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