Energy storage with Power-to-Power systems relying on photovoltaic and hydrogen: modelling the operation with secondary reserve provision

Energy storage is increasingly required in order to cope with the fluctuations of renewable energy sources, especially in power generation. In many countries, the electric market is undergoing regulatory transformations that aim at increasing the type and number of technologies that can provide grid services, either alone or as virtual aggregates. In this context, this work investigates the economic profitability of Secondary Frequency Reserve (SFR) provision to the electric grid through integrated generation-and-storage systems. In particular, the case of Italy is assessed, where recent projects opened the Ancillary Service Market (ASM) to relevant generation units or aggregates of units, including programmable and non-programmable renewable sources, consumption units, and energy storage systems. The operation of a hydrogen-based Power-to-Power (P2P) system, designed to supply an electric load with locally generated electricity from a solar PV field, is studied when acting on both the Day-Ahead Market (DAM) and the ASM. A mixed-integer linear optimization problem is set up that minimizes the annual average cost of electricity to the load. The analysis considers a broad range of options in terms of electricity prices on the DAM and price-quantity combinations of accepted offers on the ASM. Results show that the economic advantages deriving from the utilization of P2P systems increase with more fluctuating prices. The provision of SFR services with an optimal bidding strategy and asymmetric bids allows one to reduce the average cost of electricity up to about 15 % with respect to the operation on the DAM only.