UNDERGROUND PUMPED-HYDRO ENERGY STORAGE USING CARBON DIOXIDE IN SHALLOW LINED ROCK CAVERNS; APPLICATION TO LONG-DURATION STORAGE AS THE ENERGY CONVERSION OF A PUMPED THERMAL ELECTRICITY STORAGE

International audienceA fast-paced energy transition needs a better penetration of renewables, of heating and of cooling in the worldwide energy mix. With three novelties 1-of using shallow high-pressure LRC (Lined Rock Cavern) excavated close to storage needs, 2-of using a slow-moving CO2 piston applying constant pressure on the hydro part of UPHES (Underground Pumped Hydro Energy Storage) and 3-of relying on inexpensive thermal stores for the long-duration storage of electricity, CO2 UPHES coupled with PTES (Pumped Thermal Electricity Storage) could become a game-changer by allowing the complete integration of intermittent renewable sources. The RTE of the latter system, devoid of the 4 gas machineries of conventional PTES, is targeted to 60-70% and its Capex cost for pure electricity storage is calculated at 2160 USD/kW + 10 USD/kWh (meaning a compounded Capex of 20 USD/kWh only). Thanks to an attractive COP of heat displacement, expected to reach 10 depending on required temperatures, the CO2 UPHES as well as UPHES-PTES hybrid storage could also allow a low cost, low investment (compounded Capex of 4 USD/kWh) and low-emission integration of intermittent renewables with future district heating and cooling networks