Investigation of pyranometer and photodiode calibrations under different conditions

Irradiance sensors supply essential information in the business of planning and operating PV Systems. Errors and uncertainty in irradiance measurements propagate to uncertainty about performance and profitability. PV Performance Labs initiated the PVSENSOR project in 2014 to more fully characterize commercial irradiance sensors, with the objective of reducing such uncertainties. In this paper we focus on the calibration factors of 20 thermopile pyranometers and 10 photodiode pyranometers, all of which are used to measure hemispherical or global broadband irradiance. We discuss various calibration procedures that are in use, and explain our methods for collecting, selecting and comparing measurements collected in the lab and outdoors. The responsivities determined by these methods are compared to the calibration factors provided by the manufacturers.