Electricity Storage, Reality and Perspectives

What can be done to do better? PHES plants along with storage of compressed air in very large underground cavities are and will remain insufficient. There is an unbeatable reason for this, pertaining to the laws of physics: the energy density of these forms of energy is insufficient. Only chemical energies, such as synthetic gases, hydrogen (produced by water electrolysis to avoid emitting CO₂) and methane (produced by hydrogen methanation) present energy densities that would be capable of satisfying the needs. But the very small overall efficiencies of these conversion chains [electricity → synthetic gas → electricity] increase the cost of the electricity retrieved to such a degree that their economic model is not viable. There is a potential for improvement but the overall efficiency will still be limited because of the large number of energy transformations involved. Considerable investment cost reductions would also be necessary so that the economic viability of these solutions is quite unpredictable in the near term. Increased R&D in promising storage solutions, whether already identified or groundbreaking, remains a necessity but does not allow, today, to place mass storage capacities on the horizon when making strategic evaluations, in particular for the present PPE (Programmation pluriannuelle de l'énergie).