U.S. August irradiance: Sunshine before the storm in the South


From pv magazine Global

Despite Hurricane Idalia at the end of the month, reduced onshore winds in the southern US enabled above-average sunshine during August. Further west, cloud associated with Tropical Storm Hilary decreased irradiance below monthly averages across southern California and the Rockies, according to data collected by Solcast, a DNV company, via the Solcast API.

During August, the Deep South saw a 20% increase in its Global Horizontal Irradiance (GHI) relative to the historical monthly average. This was accompanied by temperatures averaging 3 C above the typical for the season. The driver for these changes was reduced onshore winds compared to normal, reducing humidity and cloud cover.

In the final days of the month, the southern sunshine abruptly gave way to thick cloud, as Hurricane Idalia moved over the region. This animation shows the hurricane’s progression during August 29 and 30, bringing thick cloud from Louisiana to North Carolina.

Further west, Tropical Storm Hillary and its associated cloud systems led to significantly lower irradiance than usual for August, in a broad area from Baja, through Southern California, and along the Rockies to British Columbia.

Despite only lasting a few days, the effect of the cloud cover from Tropical Storm Hilary was significant, contributing to the reduced monthly irradiance on the west coast.

Solcast produces these figures by tracking clouds and aerosols at 1-2km resolution globally, using satellite data and proprietary AI/ML algorithms. This data is used to drive irradiance models, enabling Solcast to calculate irradiance at high resolution, with typical bias of less than 2%, and also cloud-tracking forecasts. This data is used by more than 300 companies managing over 150GW of solar assets globally.

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