Silicon-photodiode pyranometers: operational characteristics, historical experiences, and new calibration procedures

Small, low-cost, silicon-photodiode pyranometers are now widely used for solar irradiance measurements associated with solar thermal and photovoltaic power systems, as well as for agricultural applications. Without correction, the irradiance values indicated by these pyranometers may differ from the "true" broadband solar irradiance by over 10%. This paper identifies the time-of-day dependent factors responsible for these systematic errors and describes new procedures that effectively compensate for the systematic influences. Application of the procedures should improve calibration methods and the accuracy of field measurements.