Analysis of DC-coupled system efficiency losses and their financial effects for a PV-based EV charging station

Abstract

Photovoltaic (PV)-powered electric vehicle charging stations (EVCS) are expected to play a critical role in achieving carbon neutrality in the transport sector, as PV power has a great ability to reduce CO 2-emission. By integrating PV into an EVCS, solar energy can supply a considerable portion of the electric vehicle (EV) energy demand. Besides a good energy management strategy (EMS) for the system, the efficiency of the system is an important aspect that needs to be discussed. Be it EV charging/discharging, energy exchange with the grid or battery use - power losses occur in the system. Previous studies have mostly only discussed the effects of EMS on energy losses in the system. In this paper we conduct a systematic analysis of the converter efficiency and its effect on the energy losses for an EVCS integrated with PV, stationary battery (BAT), and grid connection. A DC- and an AC-coupled EVCS are compared on the basis of example systems. Converter efficiency for PV, grid, BAT, and EVs and BAT efficiency are considered for the analysis. A comprehensive comparison of system efficiency and energy losses over different seasons and a full year is presented and discussed. Finally, we discuss the financial losses influenced by the efficiency losses in the system over the year. It is shown, that the overall system efficiency is almost the same for both EVCS with about 92%. The DC-coupled EVCS's higher number of converters leads to a higher sum of energy loss compared to the AC-coupled EVCS, even including the onboard-charger of the EVs. For the AC-coupled EVCS, more than 50% of the energy loss occurs due to the EV's onboard-charger. These losses are paid for by the EV user. However, even if the EVCS operator also owns the EV fleet, regarding the example system looked at, the AC-coupled EVCS is about 10% more profitable.