Between April 2001 and September 2002, the Florida Solar Energy Center conducted research to evaluate the performance of several utility-interactive inverters. The major issues to be identified were the efficiency of the inverters and their ability to follow the maximum power point of the photovoltaic (PV) array. Existing PV testing facilities at FSEC were modified to carry out this analysis. This facility, called the Photovoltaic Inverter Test Facility, is capable of providing approximately four kWp of array power to the inverter. Data on inverter performance were collected using a Campbell 10X datalogger. The parameters collected included the following: irradiance, PV array temperature, inverter temperature, PV voltage, PV current, AC voltage, AC current, and AC Power. Because of the voltage windows and power requirements of the different inverters, the array was designed to be easily reconfigured to meet those requirements. Each of the inverters was installed and allowed to run for several weeks under both clear and cloudy conditions. At the end of the test period, inverter efficiencies were calculated from the collected data. The ability of the inverter to follow the maximum power point of the array was evaluated in two ways. In the first method, DC voltage and current were measured while the inverter was operating, then the array was disconnected from the inverter and the maximum power point of the array was immediately taken. By comparing the measured DC voltage and current to the maximum power point of the array, one could determine the effectiveness of the inverter algorithm. Unfortunately this method requires steady-state conditions and does not show the effectiveness of the algorithm in cloudy conditions. To determine its effectiveness in cloudy conditions, DC voltage and current were compared to the expected maximum power. The expected array maximum power point was calculated from IV curves of the array, irradiance measurements, and array temperature measurements. DC to AC efficiency curves were derived from the data as well. Results from the inverters were mixed, but several showed room for improvement.

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