Early Results From the Long-Term Testing of Inverters

The Florida Solar Energy Center (FSEC) has partnered with Sandia National Laboratories (SNL), the Southwest Technical Development Institute (SWTDI), and the California Energy Commissions Public Interest Energy Research (CEC PIER) in an effort to characterize the performance of PV inverters operating over extended periods of time. As part of this characterization, SNL executed an initial performance characterization in the laboratory to be repeated at one or two year intervals. These inverters were then sent distributed to the above test facilities for installation and long-term testing. To perform this long-term testing, FSEC built an inverter test facility made up of a configurable 10.1 kW PV array and four test beds. Each test bed was set up to monitor the following parameters: DC voltage, DC current, AC Voltage, AC Power and inverter temperature. Solar irradiance, ambient temperature, and several PV array temperatures were recorded by a separate, synchronized datalogger. Three inverters are currently being tested: the Fronius IG 3000, the Xantrex GT 3.0, and the SMA Sunny Boy 2500U. The three inverters were loaded with a PV array close to the maximum power limit allowed by the inverter, and the array power supplied to each inverter was within 100 W of one another. Since the PV array for each inverter used identical PV modules mounted in the same orientation, it was easier to develop a model to compare inverter performance based on energy output. In addition to energy output, other parameters were obtained such as inverter efficiency. An attempt was made to compare the results obtained at FSEC to those results compiled by the California Energy Commission.