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Partially shaded rooftop photovoltaic systems operate with non-uniform conditions within the photovoltaic array, which lead to power losses. Module-level power electronics can potentially improve the performance of such photovoltaic systems. However, the potential performance increase compared to standard string inverter systems depends on the site-specific details of the installation. To investigate this, power optimizer and string inverter efficiency measurements were conducted in the ZHAW indoor laboratory. With these results, simulations were performed for a module-level power electronics system, for which power optimizers were used at every module, and a standard string inverter photvoltaic system. As a performance comparison, the P370 power optimizer and 3500H inverter was used for the module-level power electronics system and partial shading by a chimney was considered. For the standard string inverter system, the string inverter SUN2000- 3.68KTL-L1, without the use of module-level power electronics was chosen. The results of the annual simulations showed a gain of the module-level power electronics system between 0.9 % and 1.4 % (14-modules) or -0.2 % and 0.8 % (13-modules), depending on the position of the chimney. Furthermore, the shading adaption efficiency, a method of quantifying the annual performance for shading situations by applying weightings to a few indoor measured performance values of power electronic components, is described.

The low-voltage distribution grid in Dettighofen, Germany was analysed regarding load flows and the voltage behaviour because of decentralised photovoltaic (PV) power generation. High load flow fluctuations of 400kW within 25 min were observed in the more critical western part of the grid. During the night, the average base and the peak load obtained from the medium voltage grid was 55.8 and 150 kW, respectively. On certain days, the transformer (400 kVA) fed with rated power into the medium-voltage grid. The relative voltage rise on the transformer was between 2% and 3%. A critical situation was found at a distribution box with two long stubs and a total PV installation power of 99.3 kWp. The load flows caused a relative voltage rise of 4.5% on a day with clear sky, and there was a voltage peak slightly above 110% on a day with high fluctuating irradiance. In a second step, load flow simulations with NEPLAN were performed to analyse three different voltage reducing measures. The relative voltage rise could be reduced by 3% with an active power curtailment ratio of 70% together with reactive power control (cosφ of 0.95 and cosφ of 0.9 at p>13.8kW). Peak shifting with battery storage leads to the same reduction if the power that exceeds 40% of the rated PV power is shifted. The average costs of limiting the active power to 70% are 1.45 ct/kWh compared with €3.11/kWh for peak shifting with commercial available lead-acid batteries. This is due to the low number of storage cycles resulting in high costs.