Modeling renewable power systems on islands: Can renewables and energy storage fully replace fossil-fired power plants?

Non-interconnected islands face challenges in reaching a fully renewable energy supply, primarily due to insufficient renewable resources or oversized power systems that generate large amounts of excess power. By means of an optimization-based power plant dispatching model, this study depicts the way the storage system can be designed for a power mix in 2030, as balance between short-term storage such as batteries, and long-term storage system such as isothermal compressed air energy storage (I-CAES). Three key criteria guide policy mix decisions: the affordability of the storage cost, the acceptable level of energy curtailed and the amount of CO 2 emissions. The case study considers the French island of Guadeloupe, characterized by a high share of diesel and coal (more than 64% in 2023), significant biomass potential, and large seasonal variability in the demand – low during the dry season (110 MW) and high during the wet season (270 MW). Results show that the dry season requires storage with high charging capacity, while the wet season needs greater discharging due to higher home occupancy rates and increased energy consumption. By 2030, the renewable energy share reaches 99.6% to meet the dual objectives of cost-effectiveness and minimal curtailment. The remaining demand is met by diesel-fueled generation (7.4 GWh), resulting in low total emissions (5.4 kt CO 2 ) and low carbon intensity (3.1 kg CO 2 /MWh elec ). The best storage solution has long-lasting discharging duration, such as I-CAES system (253 MW/1518 MWh), with levelized cost of storage (LCOS) in the range 230–300 €/MWh, and 166 GWh of contribution to the electricity island's grid, or 9% of the yearly demand. • An optimization model balances renewables and storage for Guadeloupe island. • The policy mix is guided by energy and storage costs, curtailment and CO₂ criteria. • Storage design trades-off between short-term (batteries) and long-term (I-CAES). • The optimal case is made of 99.6% of renewables and I-CAES (LCOS 230–300 €/MWh). • Long-duration I-CAES reduces fossil use and supports year-round grid stability.