Suggested Modifications for Bifacial Capacity Testing

Capacity tests such as those described in ASTM 2848 and IEC 61724-2 are widely used during the contracting and acceptance testing of photovoltaic systems. With the increasing deployment of bifacial photovoltaic modules, there is a need to develop a standardized approach to capacity test these systems. Although variability and bias error were inherently higher for the measured capacity of bifacial systems, they could be reduced to a level consistent with the monofacial reference system by appropriate incorporation of rear irradiance—either measured or modeled. Three field installations provided bifacial system capacity that was measured with a mean bias error and standard deviation within 1% over the 2–10-month observation period. Capacity test accuracy could be improved further by using the measured back-of-module temperature and the IEC 61724-2 test method for well curated systems.