Optimal Photovoltaic Inverter Sizing Considering Different Climate Conditions and Energy Prices

State of the art, grid integrated photovoltaic inverters have the best efficiencies of approximately 98% at medium power ranges. Operations at lower and at higher power ranges decrease the efficiencies of these devices to some extent because of technical implications of the inverter. The nominal power of photovoltaic inverters is usually specified by the inverter manufacturer considering standard test conditions and/or normal operating conditions. If the inverters are oversized higher losses do appear as the inverter converts more energy at the lower power ranges and if the inverter is undersized higher energy losses appear as the inverter converts more energy at the higher power ranges. Especially due to the inverter's maximum power limitation a part of the disposable solar energy at very high incidences may be rejected by the solar inverters. Therefore a correct sizing defines an optimal solar generator size in relation to the inverter size which maximizes its yearly energy conversion. Due the inverters efficiency curve characteristic, an optimal sizing of the inverter depends on: (i) technological aspects of the solar inverter and photovoltaic modules, (ii) climatological aspects of the location where the inverter is installed and (iii) time resolutions considered for the simulations which have to be accomplished to obtain the yearly energy conversion. In the present work, different system configurations are simulated using the software PVsystTM in order to assess and compare an optimized system configuration for three different locations, Capivari de Baixo-SC (Latitude 28°S), Juazeiro do Norte-CE (Lat. 7°S) in Brazil and Freiburg in Germany (Lat. 48°N). The limits of the method are discussed and a method is proposed to assess to which extent the annual energy YIELD per unit of installed solar generator peak power can be improved and compared for different PV technologies. Considering a specific energy price, in either a net-metering or a feed-in tariff market (see e.g. [8]), the higher inverter investment cost due to an eventual over sizing of the inverter should be justified by a higher annual feed in revenue due to the higher amount of energy injected to the grid.