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Solar modules on flat roofs – why worry about wind?
However, if we are interested in solar panels mounted on top of the roof, the zones are about twice as wide as the building is high (a » 2h). The zones for the roof itself and for roof-mounted solar panels are of different widths because the two are vulnerable to different phenomena. The roof is mainly vulnerable to the difference between the pressure within the building and that above the roof. Solar panels mounted on the roof, on the other hand, are vulnerable typically to the speed of the wind approaching the panel. Although the suction exerted by a flow separation dies off rapidly with increasing distance from the roof edge, wind speeds do not behave the same way. Therefore, the edge zones for roofs and for solar panels are different.
Figure 2: Wind zones for a flat roof
Now consider winds approaching the building obliquely, toward one of the corners. Oblique winds generate conical vortices above the roof. These vortices originate at the corner of the roof and radiate toward the middle of the roof. Rooftop corner vortices are identical to the vortices used by some fighter aircraft to generate lift at high angles of attack (see Figure 3).
Figure 3: Corner vortices on a rooftop and on an F/A-18 Hornet
Again, consider the roof zone map in Figure 2. The black areas in the corners are dominated by vortex development. The same phenomena that aerospace engineers employ to lift a fighter jet can destroy roof corners, so building codes require that these corners be especially strong.
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
