Optimized Operation of an Electric Vehicle DC Fast Charging Station in Combination with Storage and Photovoltaics

Fast charging stations significantly reduce the time to charge electric vehicles. Adequately placed, fast charging stations can enable electric vehicles to cover even larger distances by avoiding extremely long charging breaks. In this way, fast charging stations contribute to strengthen the competitiveness of electric vehicles compared to vehicles with combustion engine. However, the high load of fast charging stations may possibly have negative effects on the power grid. Operators of fast charging stations might be incentivized to adjust time and amount of purchased energy to the current state of the power grid, if it reduced energy costs for them. Energy purchasing can thus be influenced by the structure of the electricity tariff based on which energy costs are calculated. This paper examines how to minimize energy costs of a fast charging station under different conditions. In order to minimize energy costs, a stationary storage and a photovoltaic system are placed between the power grid and the fast charging station. As stationary storage, a vanadium redox flow battery is assumed. Own consumption of photovoltaic electricity reduces the amount of energy to be purchased and hence lowers energy costs. ... mehrThe stationary storage contributes in two ways to reducing energy costs: First, it increases own consumption of photovoltaic electricity. Second, the stationary storage allows to manage time and amount of energy purchases from the grid according to the electricity tariff in effect. Different designs of electricity tariffs lead to different energy cost optimal operation strategies of the stationary storage: A price per kWh variable in time implies charging of storage at lowest possible prices. Then, the storage is discharged at highest possible prices in order to avoid or reduce energy purchases from the grid at this time. In contrast, a price per kW peak offers an incentive to distribute energy purchases as equally as possible over time. However, energy cost savings must exceed the additional costs induced by the storage and photovoltaic system. Otherwise, energy cost savings do not imply an actual monetary benefit for the operators of a fast charging system. Results of this paper show that overall savings are feasible under certain circumstances. For maximum savings the stationary storage is to be operated in a specific manner: The state of charge curve in most cases follows an M-shaped pattern per day. The first peak of this pattern is reached early in the morning and the second one in the afternoon.