2/12/2015 Inverter sizing of gridconnected photovoltaic systems in the light of local solar resource distribution characteristics and temperature

http://www.sciencedirect.com/science/article/pii/S0038092X05003099 1/1

doi:10.1016/j.solener.2005.08.012

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Solar EnergyVolume 80, Issue 1, January 2006, Pages 32–45

Inverter sizing of grid-connected photovoltaic systems in the light oflocal solar resource distribution characteristics and temperatureBruno Burgera, 1, , Ricardo Rütherb, ,

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AbstractInverter sizing strategies for grid-connected photovoltaic (PV) systems often do not take into account site-dependent peculiarities of ambient temperature, inverter operating temperature and solar irradiationdistribution characteristics. The operating temperature affects PV modules and inverters in different waysand PV systems will hardly ever have a DC output equal to or above their STC-rated nominal power.Inverters are usually sized with a nominal AC output power some 30% (sometimes even more) below thePV array nominal power. In this paper, we show that this practice might lead to considerable energy losses,especially in the case of PV technologies with high temperature coefficients of power operating at sites withcold climates and of PV technologies with low temperature coefficients of power operating at sites withwarm climates and an energy distribution of sunlight shifted to higher irradiation levels. In energy marketswhere PV kW h’s are paid premium tariffs, like in Germany, energy yield optimization might result in afavorable payback of the extra capital invested in a larger inverter.

This paper discusses how the time resolution of solar radiation data influences the correct sizing of PVplants.

We demonstrate that using instant (10 s) irradiation values instead of average hourly irradiation valuesleads to considerable differences in optimum inverter sizing. When calculating inverter yearly efficiencyvalues using both, hourly averages and 1-min averages, we can show that with increased time resolution ofsolar irradiation data there are higher calculated losses due to inverter undersizing. This reveals that hourlyaverages hide important irradiation peaks that need to be considered.

We performed these calculations for data sets from pyranometer readings from Freiburg (48°N, Germany)and Florianopolis (27°S, Brazil) to further show the peculiarities of the site-dependent distribution ofirradiation levels and its effects on inverter sizing.

KeywordsInverter sizing; Grid-connected PV systems

Corresponding author. Tel.: +55 48 331 5174; fax: +55 48 331 7615.Tel.: +49 761 4588 5237; fax: +49 761 4588 9237.

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