Method for estimating the power conversion output in photovoltaic systems with more than one maximum power point tracking device

The commonly-used photovoltaic system performance estimators allow for only a single inverter input. New products, however, have multiple inverter inputs. To use these estimators with the newer products, a “Straight-Sum” method is typically employed: each string is treated as an independent array and the results are mathematically summed. The resultant estimated system yield includes an error associated with the efficiency curve shape. To calculate this error, a new performance estimate method is described here. For the Dow™ POWERHOUSE™ system, the Straight-Sum method was found to under-represent performance by 2.7-4.0%, depending on array location and orientation.