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Low-cost and Low-Maintenance Soiling Spectral Deposition Detector

National Renewable Energy Laboratory

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Technology Marketing Summary

As dust, dirt, and other debris accumulate on the surface of photovoltaic (PV) modules, light transmission to the absorber layer of the PV module may be blocked – resulting in up to a 50% (or more, in extreme conditions) reduction in a PV module’s ability to generate electrical power.  This detrimental effect to PV performance is known as soiling loss and is a major consideration for photovoltaic applications in industry, particularly those located in arid geographic regions where rainfall is not as likely to help keep PV surfaces clean.  Moreover, manual cleaning of PV modules can be quite expensive (~$0.20/W) and should only be performed when necessary.  Thus, identifying the effect, forecasting the likelihood, or determining amount of soiling present on a PV module is essential in planning maintenance schedules that allow for maximum power production and limiting operating costs.


Researchers at NREL have developed a low-cost, reliable, and accurate device for measuring soiling accumulation on PV modules.  Where most soiling measurement stations depend on water cleaning or covering of a separate, clean photovoltaic device to compare the measured output of a soiled one, NREL’s new technology does not require cleaning and relies on a different measurement to estimate the full spectral transmittance of soiling.  It estimates soiling loss by periodically using a collimated light source to emit discrete wavelengths through a soiled transparent surface and then measuring the throughput signal with a detector on the opposite side.  The relationship of the signal reduction to the known light transmission allows for very accurate determination of the soiling effects on the surface of the device.

  • Reliable soiling measurements for photovoltaic maintenance
  • Power savings
  • Increased economic revenue from solar energy
Applications and Industries
  • Photovoltaic Systems world wide
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
ROI 17-85PrototypeAvailable06/28/201806/28/2018

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To: Bill Hadley<>