Urban land, aerosols could accelerate hail storm formation


From pv magazine USA

Urban landscapes and man-made aerosols have the potential to accelerate the formation of hail storms, according to a recent study by the U.S. Department of Energy’s Pacific Northwest National Laboratory.

The team, led by atmospheric scientist Jiwen Fan, created two storm models. One was for an area near Houston, Texas, while the other was in Kansas City, Missouri. The team simulated multiple versions of two storms, with and without the presence of cities and aerosols, in order to isolate the effects of these two distinct factors. They were always tested in tandem, as models of cities and aerosols independent of one another already exist.

The researchers found that urban land and aerosols worked together to amplify the frequency of large hail by roughly 20% in Kansas City. The Houston storm was “gentler” by comparison, but still resulted in amplified, longer-lasting rainfall that developed sooner than expected.

The Houston storm was not modeled as a hailstorm, but as a sea breeze-induced thunderstorm. The study followed earlier research that concluded that cities are warmer than surrounding areas because buildings absorb and retain the sun’s heat differently than trees and agricultural land, and also block wind flow.

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The Kansas City model is one that could prove particularly troubling for the solar industry. In the PNNL model, heat from the city was carried downwind, where it met the storm just after its formation at the northern urban-rural boundary. When warmer, drier air met with cooler, moister rural air, it intensified convergence.

This  eventually led to a more violent storm that moved toward urban land. When the aerosols were modeled alongside the urban landscape, the two combined to amplify hail, producing a more hazardous hailstorm.

Hail has long been a concern for utility-scale solar installations in rural areas. In 2019, a hailstorm in Pecos County, Texas, damaged more than 400,000 panels at the 178 MW Midway Solar Project. The Pecos storm was one of a handful of extreme weather events in the past two years which have hardened the market for property and casualty insurance for solar projects. Premiums have risen by as much as 400% over that time.

The researchers found that urban landscapes and aerosols are capable of pushing more violent storms toward cities. This could create additional uncertainty when it comes to insuring urban distributed solar projects. While the financial risks for a distributed solar project are less than those of utility-scale installations, insuring them against hail could still prove difficult if urban hailstorms become more common and violent. A single PV project could be subjected to multiple extreme storms over its lifespan.

Please check out our webinar video, “Can your solar project weather a hailstorm?

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