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Deviations of Results for Energy Yield from Efficiency Rankings of Micro-Inverters
S. Krauter, J. Bendfeld
Power Conditioning, Small Grid-Connected PV Systems, Inverter
Operation, Performance, Reliability and Sustainability of Photovoltaics
Subtopic: Balance of System Components
Event: 32nd European Photovoltaic Solar Energy Conference and Exhibition
Session: 5AO.9.3
1508 - 1511
ISBN: 3-936338-41-8
Paper DOI: 10.4229/EUPVSEC20162016-5AO.9.3
0,00 EUR
Document(s): paper


To determine and rank the performance of micro-inverters, DC-AC conversion efficiency over the full range of load conditions (including inherent MPPT accuracy) is usually used as the principal indicator. However, for the end-user the AC energy yield fed into the grid is the most important value for benchmarking. To compare efficiency and yield of most micro-inverters available on the world market in 2014, an in- and outdoor test field at the University of Paderborn have been set up. The inverters have been fed by identical and calibrated crystalline silicon PV modules of 215 W at STC. To monitor accurately AC power output and yield, each of the micro-inverters has been equipped with a calibrated precision electricity meter. For micro-inverters that require control units for gridfeeding this has been purchased also. The test field is equipped with pyranometers in the module plane. The comparison includes energy yield over almost one year, efficiency-load characteristics, recovery times after low irradiance levels, cost consideration: While the market is quite new, the range of purchase costs varies considerably between the models in comparison, sometimes inverter costs are higher than module costs, particularly if an additional grid-connection or interface device is necessary for operation. The weighted conversion efficiency according to EU and CEC standards has been measured and compiled. While some inverters have been optimized for high irradiance levels, they ranked better at the CEC-efficiency, others performed very well also for low irradiance levels, thus ranking higher at in the EU-efficiency tables. These results deviated from the actual energy yield measurements, which showed a slightly different ranking. One device showed an extreme deviation of the efficiency rating from the yield results. An accurate but very slow MPPT algorithm that hardly could follow quickly changing irradiance conditions has possibly caused this effect. Apparently, some inverters are been optimized to show excellent EU and CEC efficiency ratings Further investigations are on the way, including temperature effects.