The energy saving and grid feed-in are shown in Fig. 7.Without an energy storage device, 1521 kWh grid energy can be saved by direct consumption of PV generation. If using an ideal 3 kWh FESS with 100% power efficiency, no windage losses and zero auxiliary power demand, the energy saving increases to 2464 kWh. Taking the losses into account, the saved grid consumption is 2146 kWh, 625 kWh higher than the system without an energy storage device. Nevertheless, the drawbacks of the FESS should be considered as well. This is evaluated by the reduction of grid feed-in energy.