Photovoltaic Calibrations at the National Renewable Energy Laboratory and Uncertainty Analysis Following the ISO 17025 Guidelines

The measurement of the photovoltaic (PV) performance with respect to reference conditions requires measuring the current versus voltage with respect to a given tabular reference spectrum, junction temperature, and total irradiance. This report briefly discusses the procedures implemented by the PV Cell and Module Performance Characterization Group at the National Renewable Energy Laboratory (NREL) to achieve the lowest practical uncertainty. We present a rigorous uncertainty analysis of these procedures following the International Organization for Standardization (ISO) 'Guide to the Expression of Uncertainty in Measurement.' This uncertainty analysis is required for our team's laboratory accreditation under ISO standard 17025, 'General Requirements for the Competence of Testing and Calibration Laboratories.' The report also discusses additional areas where the uncertainty can be reduced.