Thermo-mechanical concepts for bulk energy storage

Grid scale electrical energy storage is considered facilitative for the increased deployment of renewable energy. Recent progress in the development of large scale thermal energy storage systems operated at medium and high temperatures has sparked the interest in the application of this technology as a storage sink for electricity. Life expectancies in the range of 20-30 years, low capacity-specific costs, a low environmental impact and flexibility regarding sites make thermo-mechanical energy storage a promising option for future bulk storage of electricity. A large number of concepts have been developed, which vary in storage efficiency, complexity and maturity. This paper provides an overview of the basic concepts for thermo-mechanical energy storage and describes various implementations and their characteristics. The utilization of waste heat, the combined delivery of heat and power during discharge and the integration of storage modules into power plants are described as additional options for some of these thermo-mechanical concepts.