Ambient temperature correction of photovoltaic system performance data

The performance ratio (PR), which normalizes photovoltaic system energy production in terms of irradiance, is a widely used metric for monitoring, validating, and guaranteeing system performance. To improve the predictability of performance, the PR can be adjusted for additional environmental factors, such as temperature or soiling. This research compares the use of ambient temperature versus module temperature for performing a temperature adjustment of the PR calculation and the ASTM E2848-11 capacity test. Using one year of plant monitoring data for a 500 kW AC system near Las Vegas, Nevada, we applied multiple temperature correction methods to compare PR and ASTM results from measured and modeled values over both annual and monthly timescales. Though an ambient temperature correction increased performance predictability compared to the uncorrected PR, a module temperature adjustment provided the closest match between modeled and measured performance for both the PR and the ASTM methods.