PARTIALLY SHADED OPERATION OF MULTI-STRING PHOTOVOLTAIC SYSTEMS

New shade mitigation technologies are available claiming improved performance under shaded conditions. A typical multi-string photovoltaic (PV) system was operated under partial shading conditions with and without these DC-DC converters. Power loss was attributed to low irradiance on shaded modules, current mismatch within shaded PV strings, and voltage mismatch between parallel strings. Indirect loss from voltage mismatch contributed up to 40% of the total power loss from shading. A representative residential solar installation was evaluated for potential benefit from DC-DC equipment. Detailed shading site survey information was collected and used to modify a PV production model. Using various assumptions on the severity of shade in this PV model, the application of DC-DC converters improved annual modeled power production by 5%-10% and recovered 24%-48% of the power lost due to shading.