Satellite-observed changes of surface spectral reflectances due to solar farming and the implication for radiation budget

Increased deployment of solar farms in the last decade is coincident with continued monitoring of
surface spectral reflectances by the moderate resolution imaging spectroradiometers (MODIS)
aboard NASA Aqua satellite. By analyzing the surface spectral reflectances retrieved at seven
MODIS shortwave bands, this study quantifies the changes of surface spectral reflectances caused
by solar farms commissioned in the southwestern US. Our case study using one solar farm
indicates a 20%–25% reduction of surface reflectance over the seven MODIS bands due to the solar
panel installation. Radiative transfer calculation shows that such a reduction in surface spectral
reflectance leads to a ~23% decrease in the upward shortwave broadband flux at the surface and a
~14%–18% decrease in the clear-sky reflected shortwave flux at the top of atmosphere (TOA).
Though the MODIS surface reflectance retrievals can be affected by other factors such as aerosol or
thin-cirrus contaminations, five out of six solar farm sites analyzed here show unambiguously
detectable changes of surface reflectances due to solar panel installations. The brighter the surface
is at a given MODIS band before the solar-farm construction, the larger the spectral reflectance
reduction tends to be. If all the bright deserts, which occupies about 4% of the global surface, were
covered with the solar panels similar to what has been studied here, the estimated instantaneous
TOA shortwave radiative forcing would be no more than 1.1 W m⁻².