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Solar modules on flat roofs – why worry about wind?
By David Carpenter, Dr. David Banks, and Dr. Scot Waye
The roofs of low-rise buildings offer attractive installation options for solar arrays because otherwise-underused spaces can be put to work powering the occupied spaces beneath the roof or generating valuable revenue through feed-in tariffs. Although such arrays may seem to spring up virtually overnight in many places, a local building code official must generally approve proposed solar installations before he or she will issue a permit. This approval process varies from one jurisdiction to another, but nearly all officials require that the structural engineer of record supply calculations demonstrating wind-worthiness of the installation.
Most local building codes reference a recognized model standard, such as Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-05), produced by the American Society of Civil Engineers. These codes are intended to produce estimates for design wind loads on buildings and were not intended to apply to roof-mounted solar panels. Applying building code calculations to rooftop solar panels, therefore, requires that the engineer interpret the code in a way that he or she believes to be most appropriate. Permitting officials may not be familiar with the unique challenges posed by rooftop solar and may require that rooftop installations meet inappropriate wind criteria. Consequently, permitting for solar panels and arrays is currently a patchwork of varying approaches. Some approaches are likely to result in over-designed, expensive mounting systems, while less conservative methods may jeopardize the integrity of the installation and the safety of its physical surroundings, particularly in the case of ballasted solar panels. Because neither scenario supports widespread deployment of solar energy, businesses developing rooftop solar products need a basic understanding of the wind environment on low-rise building roofs.
Links
Wind & Roof-Mounted Panels: A Common Scenario (Less Technical)
How to Calculate Wind Loads on Roof Mounted Solar Panels in the US
Wind Effects on Solar Panels Brochure
Renewable Energy Technical Papers
