Rock bed storage for solar thermal power plants: Rock characteristics, suitability, and availability

It is proposed that air-rock packed beds are suitable for thermal storage in solar power plants at temperatures of approximately 500-600 °C. However, little has been published in the field of thermal energy storage on the suitability of rock for this particular application. Desirable characteristics of rock for this application are presented, and the different rock types are discussed in the light of these requirements. A survey of the literature in other fields on rock characteristics shows which rock is most likely to be suitable. Results from thermal cycling tests (more than 900 cycles at rates of 2 °C/min) on a variety of rock samples are reported. Dolerite withstood this process well; some gneisses did but others did not. Geological maps showing the availability of potentially suitable rock in solar-rich regions of South Africa are presented. There are potentially suitable rock types (for example dolerite, granite, gneiss) in parts of the country which are deemed to have a good solar resource. Dolerite, which is found in copious quantities in insolation-rich regions, should be well-suited to packed bed thermal storage.