100-Gigawatt-hour crushed-rock heat storage for CSP and nuclear

We are developing 100-GWh heat-storage systems for use with Concentrated Solar Power (CSP) and nuclear reactor systems. Crushed rock fills a container up to 20 m high and 250 m by 250 m with insulated floor, walls and roof structures. Heat is transferred from the heat source to the crushed rock and then to the power cycle using (1) heat transfer oils for lower-temperature power systems to 400°C or (2) nitrate salts for higher-temperature power systems to 600°C. In charging mode, hot heat transfer fluid is sprayed over crushed rock and drains through the rock to the collection pans at the bottom to be reheated. Sections of rock are heated sequentially. In discharge mode cold heat transfer fluid is sprayed over crushed rock and drains through the rock to the collection pan below to deliver hot fluid to the power cycle. This design minimizes the inventory and thus the cost of heat transfer oil or liquid nitrate salt. The large container size minimizes the surface to volume ratio and thus insulation and structural costs. Crushed rock is the lowest-cost storage material. The goal is to drive storage capital costs down to several dollars per KWh of heat.