Disclosed is a thermal storage tank for the long term storage of a thermal storage medium whose energy is available on demand for satisfying cooling or heating loads. The tank may be earth excavated and include side walls of a lightweight, high strength concrete that retains its thermal insulating characteristics...http://www.google.es/patents/US5201606?utm_source=gb-gplus-sharePatente US5201606 - Thermal storage tank and associated top structure
