The study examines revenue stacking for a Stationary Electrochemical Storage System (SESS), assuming the provision of a set of services: balancing services, energy trading, and imbalance mitigation. To this end, a stochastic optimization approach is adopted to find the optimal sizing of the SESS in terms of nominal power and energy, and the optimal allocation of nominal power fractions to different services, aiming to minimize the payback period of the SESS investment. It is assumed that there is uncertainty only for the Tertiary Frequency Regulation (TFR), which refers to the acceptance/rejection of bids from the SESS’s balancing service provider on the Ancillary Services Market (ASM).

For TFR bids, several “acceptance scenarios” are estimated, along with their respective probabilities of occurrence, based on historical results of the ASM in terms of prices and energy exchanges. Simulation case studies are constructed with reference to the current Italian regulatory framework and historical market data. Overall, for high values of the nominal energy/nominal power ratio of the SESS, the nominal power is largely allocated to secondary frequency regulation and participation in the Day-Ahead Market, whereas for lower values of this ratio, it also includes imbalance mitigation.