Trust but verify: procedures to achieve accurate efficiency measurements for all photovoltaic technologies

The measurement of the photovoltaic (PV) performance with respect to reference conditions requires measuring the performance with respect to a given tabular reference spectrum, junction temperature, and total irradiance. This paper discusses the procedures implemented by NREL's PV Cell and Module Performance Characterization Group to achieve the lowest practical uncertainty. This paper describes the process of trusting and verifying software, hardware, calibrations, procedures, and results. As an ISO 17025 accredited calibration facility, the quality system that is in place is designed to assure customers that the results are valid within specified uncertainty limits and are traceable. The process of trusting performance claims but desiring an independent verification permeates the PV business and society.