Comparing standard translation methods for predicting photovoltaic energy production

Translation equations underpin all predictive models for the energy output of photovoltaics in the outdoor environment. These equations translate the performance of a PV device to an arbitrary temperature and irradiance, based on measurements taken under reference conditions. Little work has been done to compare and contrast the three translation methods recommended under IEC 60891. This is partly due to a lack of comprehensive test data, and partly due to the flexibility in the way these methods can be applied. Based on comprehensive outdoor test data, we have used software scripts to evaluate the performance of these three standard translation methods, where the choice of reference conditions has been optimized to produce the best result in different ranges of irradiance and temperature. This allows a fair comparison of their performance that is independent of the test site location. We map the performance of the three methods over a wide range of irradiance and temperature.