Fast-charging infrastructure along highways experiences both a low occupation rate and high electricity costs owing to high power peaks. To reduce electricity costs, this paper examines the cost reductions possible using different sizes of battery energy storage systems (BESS) and photovoltaic (PV) systems at a gas station with fast-charging infrastructure on a German highway. An energy management system optimizes the overall operation via peak-shaving, optimized usage of dynamic tariffs, increased energy self-consumption, and the participation in the balancing energy market, enabling savings. However, the optimal sizing of BESS and PV system differ, depending on the objective for the target application. The lowest energy costs can be achieved using the maximum BESS and maximum PV size within the experiment’s constraints. The greatest internal rate of return is accomplished by the medium sized PV system without any BESS. Finally, assuming a linear deduction of investments, the lowest overall costs can be achieved by a medium sized BESS in combination with the highest-powered PV system.