Energy modelling and rating - (a personal overview)

There are two main requirements for PV model accuracy - 1) Power Modelling : “Measured vs. predicted PMAX W” at each measurement (under variable weather conditions). 2) Energy Rating : “Measured vs. predicted energy yield (kWh/kWp)” summed over a time period such as 1 year. The relative spread in measured energy yield (kWh/kWp) from systems of different technologies has been reducing over the years to less than f a few % as power tolerances have decreased (from more accurate measurements by the manufacturers) and lower marketing tolerances including allowances for degradation [1][2]. PV technologies are also now optimised with better low light performance [3]. Predicted energy yields from PV simulation programs have been found to be very dependent on the default loss assumptions and user estimates for module mismatch, soiling, measured/nominal Pmax etc. [4]