Energy Recovery Through Massive and Reversible Underground Storage (O2, CO2, CH4)

Ambitious targets for renewable penetration in the electricity production mix in France goes with the emergence of new challenges, such as the integration of intermittent electricity into the transmission and distribution grid. The major hurdle on this path however is the energy storage that would help to smooth electricity production with energy shifting from high production demand times to peak demand times. The large volumes available underground offer scope for energy storage through "Power-to-Gas" systems that are suited to massive on-grid energy storage. This technology comprises two alternative paths: power-to-hydrogen and power-to-methane. In the power-to-methane path, hydrogen (H2) reacts with carbon dioxide (CO2) to produce methane (CH4). CO2 sources considered so far to supply methanation reactors are mostly from power plants or industrial processes running of fossil fuels. If power-to-methane is deployed at large scale, it could face CO2 supply issues, especially in a scenario of low carbon emitting industry and energy production. The Electro-Methanation-Oxy-Fuel (EMO) is a "Power-to-Gas-to-Power" concept based on the power-to-methane path that addresses this challenge by proposing a closedloop solution that recycles CO2 released at power generation step. In this concept, the oxygen (O2) co-produced during the electrolysis is used as combustive for power generation in an oxy-combustion turbine. Due to its relative purity, the emitted CO2 is then easily captured and reused in methane production. The process implies the temporary storage of large amount of fluids (O2, CO2 and CH4). Solution-mined caverns in salt could be used for massive and reversible storage of O2 and CO2. Critical aspects of the EMO process that will be discussed in this paper are the availability of cavern capacity in France, the dynamic behaviour of the individual process steps, and especially the economics as well as the efficiency of the concept.