NREL Pyrheliometer Comparisons: September 23-October 4, 2019 (NPC-2019)

Ibrahim Reda, Afshin Andreas, Aron Habte, Peter Gotseff, Mark Kutchenreiter, Marta Stoddard

Research output: NRELTechnical Report


Accurate measurements of direct normal (beam) solar irradiance from pyrheliometers are important for developing and deploying solar energy conversion systems, improving our understanding of the Earth's energy budget for climate change studies, and for other science and technology applications involving solar flux. Providing these measurements places many demands on the quality system used by the operator of commercially available radiometers. Maintaining accurate radiometer calibrations that are traceable to an international standard is the first step in producing research-quality solar irradiance measurements. In 1977, the World Meteorological Organization (WMO) established the World Radiometric Reference (WRR) as the international standard for the measurement of direct normal solar irradiance (Frohlich 1991). The WRR is an internationally recognized, detector-based measurement standard determined by the collective performance of six electrically self-calibrated absolute cavity radiometers comprising the World Standard Group (WSG). Various countries, including the United States, have contributed these specialized radiometers to the Physikalisch-Meteorologisches Observatorium Davos - World Radiation Center (PMOD/WRC) to establish the WSG.
Original languageAmerican English
Number of pages45
StatePublished - 2019

Bibliographical note

Revised December 2020

NREL Publication Number

  • NREL/TP-1900-75123


  • Absolute Cavity Radiometer
  • NPC
  • WRR


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