What you need to know about
wind effects on solar panels

You see, I’m bidding on a big job – several distribution center roofs, 1000 ft-wide nearly square boxes that are only 35 ft tall. Out in the center of such a large roof, far from the edges, there are no vortices, and the wind flows along the roof surface. Perhaps I can use the test results there, and will only need ballast for panels near the edges of the roof?

 

Well, there are three real problems with using the aerospace tunnel results for such a “middle of the roof” test. All three problems are the result of ignoring the critical nature of wind turbulence. Aerospace wind tunnels go to great lengths to prevent or remove turbulence (or eddies), since they need smooth flow to test their aircraft. Turbulent eddies are the dominant feature of the atmospheric boundary layer in which your panels will sit, so ignoring them is a bad idea.

So,

Rule #2 for measuring useful wind loads on roof-mounted solar panels:
You must test in gusty, turbulent airflow just like that on the roof of a building.

 

To understand the first problem with a smooth flow test, we need to discuss what the “90 mph design wind speed” implies. This speed is specified in your local IBC code, and it is the wind speed averaged over 3 seconds. A 3 second gust is a very big eddy, maybe 300 feet across, much bigger than your panels. During this 3 second span, your panels can expect to see shorter bursts over 110 mph which will fully load the panels.

 

Does that mean I should retest my model at 110 mph?

 

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Links

Solar Modules on Flat Roofs - Why Worry About Wind? (More Technical)

How to Calculate Wind Loads on Roof Mounted Solar Panels in the US

Wind Effects on Solar Panels Brochure

Renewable Energy Brochure

Renewable Energy Technical Papers