This case study analyses the project developed by Lightsource BP in Spain, which consists of the provision of consultancy services to evaluate and define the energy storage strategy for an independent power producer (IPP) with extensive experience. The project includes the techno-economic modelling and regulatory assessment of reference battery energy storage (BESS) plants with capacities of 25 MW and 100 MW. The main objective is to provide a detailed analysis to establish an optimal energy storage strategy that complies with current regulations and maximises the economic viability of the project in the context of the Spanish market.