This paper shows how an additional provision of reactive power influences the economically optimized sizing of inverters for photovoltaic systems in Germany. At first, the results of an encompassing survey among 934 photovoltaic system operators show the current inverter sizing experiences for a region in South-East Bavaria. In a second step an analytical approach for the determination of the economically optimized inverter sizing is introduced, considering active as well as reactive power provision. The simulation results, shown in this paper, are based on real DC measurement data of modules at a test site in Germany, with a time resolution of 1 minute for a period of four years. It is shown that an additional reactive power provision leads to higher economically optimized inverter sizing compared to pure active power feed-in, depending on the actual reactive power supply method and the minimum power factor required.