Self-reported field efficiency of utility-scale inverters

Accurate understanding of inverter performance in the field is essential for energy estimation of PV power plants. The self-reported field efficiencies of six utility-scale inverter models from four different manufacturers were studied. In total, 355 inverters were included in this analysis. Efficiency curves were calculated from AC and DC inverter measurements and compared to manufacturer and CEC efficiency curves, when available. Despite a large statistical sample, the expected and measured mean efficiencies differed by -4.1% to +1.5%. This suggests either a systematic sensor/measurement processing algorithm issue or a misunderstanding of field inverter efficiency as opposed to efficiency characterization in the lab. Careful field analysis and characterization of inverter-reported data appear to be the only methods to truly resolve this discrepancy.