Cost-effective Electro-Thermal Energy Storage to balance small scale renewable energy systems

Abstract

To decarbonise the energy production system, the share of renewable energy must increase. Particularly for small-scale stand-alone renewable energy systems, energy storage has become essential in providing electricity when the demand is high, for example, during the night. Although there are many different storage technologies, only a few are suitable for small-scale stand-alone renewable systems. Those systems must be modular and scalable to be deployed according to the capacity needed. Currently, batteries are among the leading grid storage technologies, but the demand, particularly for Lithium-ion batteries, is also high because of the electrification needs of the transportation sector. Therefore, the question of material availability might become an issue in the future, as Lithium is a scarce and critical element. As an alternative, we introduce a new modular electro-thermal energy storage (ETES) technology that is suitable for various storage needs. This storage unit can utilise various thermal storage materials (thermal oil, molten salt, and sand) at high capacities and improved efficiencies. Our design consists of the embedment of Stirling engines and an electric heater into a thermally insulated storage tank. The source electricity is first converted to heat stored in the storage tank and then converted back to electricity when needed. Among the thermal energy storage materials studied here, sand enabled the storage system's efficiency to reach 85% thanks to its wide range of operating temperatures. The cost is projected to be up to six times lower than that of current Lithium-ion batteries. This new electro-thermal energy storage provides a promising cost-efficient, high capacity alternative for stand-alone energy systems.