Characterizing the operating conditions of bifacial modules

The crystalline Si bifacial PV module market has grown significantly in recent years due to the opportunity for increased performance in comparison to traditional PV modules because both sides of the cell can absorb solar radiation. Draft technical specification IEC TS 60904-1-2 (Measurement of current-voltage characteristics of bifacial PV devices) sets limits on permissible deviations of operating conditions, e.g. irradiance non-uniformity. One purpose of this work is to ensure correct evaluation of the real outdoor conditions experienced and to understand what is achievable in practice. A second scope is to ensure correct measurement of module operating conditions in long-term outdoor testing where conditions will be highly variable, but nevertheless must be accounted for in energy yield or rating calculations. Two bifacial modules of each of two different types (Type 1: glass-glass and Type 2: glass-foil) are studied. Rear-side albedo is studied for white ground sheets. The specific conditions studied are module temperature, rear-side irradiance non-uniformity and spectral irradiance.