Renewables contributing to Primary Control Reserve: The role of Battery Energy Storage Systems

Extending the Primary Control Reserve to all the renewable generating plants could be an interesting solution to preserve the electrical power system stability. With this measure, the grid enhances its frequency regulation effectiveness and is consequently able to maintain stable operating conditions in case of sudden variations of either load or generation. In this scenario, instead of intentionally throttling the renewable plant output for providing upward reserve, the use of Battery Energy Storage Systems is introduced. This solution allows the renewable plant to maximize the primary source exploitation, reducing the costs for supplying the ancillary service. Taking into account the operative constraints of storage devices, the paper discusses a procedure to optimally design the storage system through a technical-economic analysis based on the investment profitability optimization. Some of the most diffused renewable generators are considered, such as wind plants, photovoltaic generators and hydroelectric run-of-river units. Results confirm how partially or entirely providing the primary reserve by means of storage systems (e.g., making use of Lithium-ion batteries) could be very interesting, especially in the case of renewable plants having access to incentives that increase the equivalent selling price of generated energy.