Photovoltaic Module Soiling Map
NREL scientists and engineers have generated a map that highlights soiling parameters of fielded photovoltaic panels at 255 locations—either soiling stations or photovoltaic sites—across the United States. Losses are quantified by insolationweighted soiling ratio (IWSR); an IWSR of 0.95 indicates 5% annual energy loss to soiling.
(e.g. 0.95=5% annual soiling loss)
The map shows locations of PV systems and soiling stations. Click on each site for:

Soiling Ratio (IWSR): the insolationweighted mean of all daily soiling ratios assuming perfect cleaning an no soiling between detected soiling intervals. The upper and lower bounds of the 95% confidence interval are also provided.

Tilt: The degrees of tilt of the primary axis of the system

Location: County and state

Mounting: Tracking or fixed system configuration

Annual Soiling Ratio: The soiling ratio along with upper and lower bound of the 95% confidence interval for each calendar year in the data set

Monthly Soiling Rate: Table providing a breakdown of the soiling rate data per calendar month for all valid soiling intervals for the given month in the data set. Rates are given in fractional units e.g. 0.001 represents 0.1% loss per day. Median soiling rates along with the upper and lower bounds of the 95% confidence interval are provided for each month as well as the number of soiling intervals that were used for the calculation.
Methodology
The data provided were extracted similarly to the method in A. Skomedal and M. Deceglie, “Combined Estimation of Degradation and Soiling Losses in Photovoltaic Systems,” IEEE Journal of Photovoltaics 2020 with exception of soiling stations and PV sites with soiling losses less than 1% which were extracted per M. Deceglie, L. Micheli, and M. Muller, "Quantifying Soiling Loss Directly from PV Yield," IEEE Journal of Photovoltaics 2018. Note that the above algorithms do not adequately address the impacts of pollen and biosoiling (see J. Bessa et al, "An Investigation on the PollenInduced Soiling Losses in UtilityScale PV Plants," IEEE Journal of Photovoltaics 2023).
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