Underwater CAES assessment: economic and engineering references for energy mix sizing in islands grids

This study investigates the system benefits of the integration of an underwater CAES storage technology to support variable renewables integration. The case study is the French island of Guadeloupe, where power specificities are the high share of fossil fuels, i.e. diesel and coal, and the significant seasonal variability of the load. An optimization model is built to test energy scenarios targeting 100% renewables on the island such as to minimize the waste of energy, i.e. the power curtailed, subject to hourly supply-demand balance. The underwater Isothermal-CAES storage system under consideration seems suitable for coupling with large-scale fluctuating energy renewable power plants and to attain carbon emission targets, due to higher efficiency rate (70%) than conventional CAES, and to free of natural gas requirements. The model shows that using I-CAES storage allows the system to avoid curtailment of fluctuating renewables, and that fast adjustment speeds and the resilience to frequent start-ups and shut-downs effects are the suitable features for attaining political energy targets of the island in 2030.