The increasing use of renewable energy sources is leading to the retirement and decommissioning of fossil-fuel thermal power plants, starting with the older ones. This shift has an immediate impact on the transmission system operator, who has traditionally relied on large, dispatchable plants. As a result, the operator is often forced to bring some conventional generation units, previously excluded from the energy market, back online to ensure system balance and safety. Additionally, due to the fluctuations introduced by non-dispatchable renewable energy sources (NRES), the operator requires even more flexible balancing resources, which only certain types of conventional plants can provide. In this context, hydroelectric pumping and other storage technologies offer or could offer valuable resources. However, none of these technologies currently meet all the network’s needs in terms of services.

This work presents an initial version, developed in MATLAB – Simulink®, of a dynamic model for a plant that combines hydroelectric pumping with electrochemical storage (batteries), flywheels, and more complex control logic for providing flexibility services. The goal is to enhance the system’s capacity to accommodate generation from NRES. The model has been applied to the Foxi Murdegu marine pumping plant (Sardinia), for which RSE has developed a feasibility study. The model was detailed for the pumping system, while simplifications were applied to the batteries and flywheels. The effectiveness of various configurations (from a standalone pumping plant to full integration of the three components) was also assessed in terms of wear and aging of the components (loss of useful life). Initial results indicate that both appropriately sized batteries and flywheels can completely relieve the pumping plant from frequency regulation duties. However, an optimized control strategy is needed to avoid premature component aging.

A preliminary methodological framework was then described, based on Multi-Criteria Analysis (MCA) for the localization, characterization, and ranking of potential new traditional and marine pumping plants. This framework aims to provide flexibility services in power and energy to the system, considering various sustainability aspects (economic, environmental, etc.). Criteria were defined for assessing flexibility service requirements, project economic feasibility, and ease of approval and implementation. Indicators and their quantification were described, and examples of utility functions characteristic of the method were proposed.