PV system power loss and module damage due to partial shade and bypass diode failure depend on cell behavior in reverse bias

Power loss due to partial shade was compared for two types of commercial photovoltaic modules. We also tested both types of modules with bypass diodes removed to simulate diode failure. Modules with uniformly low reverse bias voltage (VBR) cells (of -4V) lost significantly less power compared to modules with high VBR cells (of -15V) when subjected to partial shade. Differences in power loss were even larger when bypass diodes were removed. Associated with higher power loss, we observed several types of degradation on modules with high-VBR cells. A model to simulate power loss in an array due to partial shading that uses VBR as the main parameter was found to be in good agreement with measured power losses in the field.