1000-MW CSP with 100-gigawatt-hour crushed-rock heat storage to replace dispatchable fossil-fuel electricity

Abstract

We are developing 100-GWh heat-storage systems for use with 1000-MW Concentrated Solar Power (CSP) and nuclear reactor systems with capital cost goals of several dollars per kWh of heat storage—a factor of 50 under lithium ion batteries per unit of electricity. The capabilities of a 100-GWh heat storage system are similar to the Tennessee Valley Authority Raccoon Mountain pumped hydro facility that can provide 1652 MW(e) for 22 hours to address daily to weekly storage. The low capital cost of the Crushed Rock Ultra-large Stored Heat (CRUSH) system is only possible in large-capacity systems; thus, the CSP system average 24/7 heat inputs may exceed 1000 MW to match the heat storage capacity. Hot oil or nitrate salt is pumped from multiple solar farms or towers to the central CRUSH system and associated power block. The peak power block output may be 2 to 4 times average output with large economics of scale relative to the smaller power blocks associated with existing CSP systems. The cost savings from the large storage and the power block exceed the cost of hot oil or hot nitrate salt insulated pipelines over 10+ kilometers. The heat is stored in crushed rock in piles 20 m high and up to 250 m by 250 m on a side within an insulated floor and building structure. The sides of the rock pile are sloped rock that allow rock expansion and contraction with temperature without generating mechanical forces against walls. Heat is transferred from CSP 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 pans below to deliver hot fluid to the power cycle. Heat storage costs are minimized by three features. Crushed rock is the lowest-cost storage material. The large building size minimizes the surface-to-volume ratio and thus building, insulation and foundation costs. The inventory and thus cost of oil and nitrate salt is minimized by using these fluids to transfer heat from CSP collectors to storage and then to the power block—but not for heat storage.