Photovoltaic Power Plant Capacity Test Uncertainty

This paper presents uncertainty estimates for several typical capacity test approaches using a Monte-Carlo analysis of simulated data. Standard monofacial and extended bifacial versions of the ASTM E2848 evaluation procedures are applied, as are absolute (pre-defined reference conditions) and comparative (against a model per ASTM E2939) approaches. Seasonal variations from 4-6% at the sample site are observed. Uncertainty shifts from the measured capacity to the target capacity when field measurements are used to define reference conditions. An outboard rear irradiance sensor exhibits a lower capacity ratio uncertainty than an under-the array sensor.