Use of molten salts tanks for seasonal thermal energy storage for high penetration of renewable energies in the grid

Energy storage is acknowledged a key technology to meet the challenges posed by the energy transition. Short-term grid-connected storage, based on Li-Ion batteries, is becoming commonplace but seasonal energy storage at grid-scale will be needed for deep decarbonisation of the electrical power system. Pumped hydropower is considered to be the only mature technology for such applications, but this paper demonstrates that two-tanks molten salts systems, that are used today in commercial concentrating solar power (CSP) plants, can also be considered a mature technology that can be used at large scale for seasonal energy storage. This was established by evaluating the annual heat losses of molten salts tanks using validated models of these systems. The results show that the heat losses in a very well insulated molten salts tanks are around 1 K/day, which would result in good economic performance of the power block even if storage was required for up to months.