The article presents a case study on the effectiveness of photovoltaic farm and battery energy storage in one of the Polish foundries. In the study, we consider two investment options: stand-alone PV farm of 1MWp and the farm together with battery energy storage with a maximum capacity of 4MWh. The Payback Period and Net Present Value were used as measures of investment profitability. The paper provides a detailed presentation of the assumptions made, as well as the PV electricity production model of the farm and the optimization model that determines the operation cycle of the energy storage. The case study presented in the article shows that the PV farm is economically sensible and profitable, but the battery energy storage is too costly to give a positive economic effect. Energy storage is an important element that provides flexibility in the energy supply system, so it is necessary to find a technical solution that gives this flexibility. Such a solution could be a virtual power plant, which could include a foundry energy system with a RES installation inside.