Electrochemical storage systems are now universally regarded as one of the main tools for achieving the decarbonization of the Power System. This study falls within this context, presenting the results of the optimal sizing of an electrochemical storage system (ESS) intended to simultaneously provide various services to the Power System (PS). Several case studies were considered, referring to the installation of ESS coupled with renewable photovoltaic and wind power plants in the NORD market zone and in the FOGN limited production hub.

The sizing was carried out using an optimization tool developed by RSE, which defines the optimal size, from a technical-economic point of view, in terms of capacity, installed power, and optimal distribution of the installed power across the various services for an ESS intended to provide multiple services simultaneously to the ES.

The test cases are based on the results of the electricity markets in 2018, particularly the Day-Ahead Market (DAM), the Dispatching Services Market (DSM), and the Balancing Market (BM), as published by the Energy Market Operator.

The services considered include primary frequency regulation and secondary frequency regulation. The provision of the secondary frequency regulation service was evaluated through a simulation of the storage system’s participation in the BM, with a simplified strategy where bids are presented at a price equal to the annual average of the acceptance price limits: the maximum hourly price for upward bids and the minimum hourly price for downward bids, for the relevant point of exchange considered for the ESS installation. The offers were considered accepted during the hours when the bid price was competitive compared to the acceptance price limit. The provision of the primary frequency regulation service was instead evaluated according to the regulated price in force for this service. The assumptions of this study are: that ESS are allowed to provide the considered services; that the storage system participates in the Day-Ahead Market as a “price taker,” so that the resulting price from the different sessions is a given for sizing purposes; and that it also operates to reduce imbalances from coupled renewable generation, also valued according to current regulations.

The data relating to the frequency of the power system and the imbalances of photovoltaic plants were directly measured by RSE; the data relating to the secondary regulation signal and wind plant imbalances were the result of RSE’s analyses.

The time horizon used for the sizing simulations is 8,760 hours.

The results show that reducing imbalances from renewable sources is very convenient as long as they are substantial, as in the case of wind power; that participation in the DAM is always essential for technical reasons (respecting energy constraints); and that investments in small sizes are generally not cost-effective due to investment costs.