For a PV system without a FESS, the self-sufficiency ξ reaches 36.8% as shown in Fig. 8. With a FESS, ξ increases to 59.6% for an ideal one and 51.9% considering the losses and auxiliary power. This is an absolute increase of 15.1% from no FESS to a FESS with losses. Compared to the self consumption of 30.2% for the PV system without the FESS, 61.4% is reached with the use of a FESS with losses. The energy efficiency of the FESS is only 40% due to the losses especially during long term high speed idling