Module-Level Power Electronics under Indoor Performance Tests

In the last decade, very few papers with outdoor measurement test results were published, which demonstrated a benefit of module-level power electronics (MLPE) higher than the measurement uncertainty. Due to the expected small difference in efficiency between conventional string-inverter based and MLPE systems, indoor measurements are required to exclude natural variation of solar irradiance in outdoor tests. Therefore, indoor efficiency measurements were performed on MLPE. Afterwards, the indoor measured efficiency of the single PV module DC/DC power optimizers were multiplied with the DC/AC inverter measurements. The final system efficiency with the maximum average value resulted in 94.78 % and with the power weighted efficiency in 94.37 %. Accordingly, if mismatches are neglected, the analysed MLPE system is expected to yield approximately 2.82 % less energy than a comparable stringinverter based system in unshaded conditions. However, in the case of shading, the tested system with heavy-shading orthogonal to the cell strings was estimated to yield approximately 3.5 % more energy on a clear-sky day in March in Winterthur, Switzerland. The performances determined in the tests are significantly lower than the efficiencies provided by the datasheet of the power optimizers (around -2.29 %). However, they are still presumed to provide significant additional yields for PV systems with mediumand heavy-shading conditions.