Clear Sky Irradiance Year-to-Year Variations and Trends

Bill Marion

Research output: Contribution to conferencePaper


Solar radiation data for seven SURFRAD stations for the period 1996-2018 show an increase in irradiance under clear skies over the period, but the increase was not constant and shorter periods may have even experienced decreases in irradiance. A popular implementation of a clear sky model provided modeled irradiances for comparison with the SURFRAD data under conditions screened for clear skies. The use of the clear sky model, which did not consider year-to-year variances in atmospheric turbidity, was found problematic for resolving small changes in irradiance important for determining PV system degradation over three or five years, but less problematic for a period of ten years.
Original languageAmerican English
Number of pages4
StatePublished - 2021
Event2020 47th IEEE Photovoltaic Specialists Conference (PVSC) - Calgary, Canada
Duration: 15 Jun 202021 Aug 2020


Conference2020 47th IEEE Photovoltaic Specialists Conference (PVSC)
CityCalgary, Canada

Bibliographical note

See NREL/CP-5K00-75923 for preprint

NREL Publication Number

  • NREL/CP-5K00-79547


  • aerosols
  • clear-sky
  • data
  • irradiance
  • model


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