Evaluation of Photodiode and Thermopile Pyranometers for Photovoltaic Applications: Preprint

Research output: Contribution to conferencePaper


Accurately determining PV module performance in the field requires measurement of solar irradiance reaching the PV panel at a high level of accuracy and known uncertainty. Silicon detectors used in various solar energy measuring instruments including reference cells are potentially an attractive choice for multiple reasons that include faster responsivity than thermopile detectors, cheaper costand lower maintenance. The main drawback though is the fact that the silicon detectors are only spectrally responsive in a narrow part of the solar spectrum. Therefore, to determine broadband solar irradiance a calibration factor that converts the narrowband response to broadband is required. Normally this calibration factor is a single number determined under standard conditions but then usedfor various scenarios including varying air-mass, panel orientation and atmospheric conditions. This would not have been an issue if all wavelengths that form the broadband spectrum responded uniformly to atmospheric constituents. Unfortunately the scattering and absorption signature varies widely across wavelengths and the calibration factor computed under certain test conditions is notappropriate for other conditions. This paper lays out the issues that will arise from the use of silicon detectors for PV performance measurement in the field. We also present a comparison of simultaneous spectral and broadband measurements from silicon and thermopile detectors and estimated measurement errors when using silicon devices for both array performance and resource assessment.
Original languageAmerican English
Number of pages6
StatePublished - 2012
Event27th European Photovoltaic Solar Energy Conference and Exhibition - Frankfurt, Germany
Duration: 24 Sep 201228 Sep 2012


Conference27th European Photovoltaic Solar Energy Conference and Exhibition
CityFrankfurt, Germany

NREL Publication Number

  • NREL/CP-5500-56540


  • direct normal irradiance
  • global horizontal irradiance
  • photodiodes
  • pyranometers
  • response


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