The Solar Thermal Group at the Australian National University has completed an experimental solar-driven ammonia-based closed-loop thermochemical energy storage system. The system uses a cavity receiver containing 20 reactor tubes filled with iron based catalyst material, which collects the radiation from a 20 m(2) dish solar concentrator. Reliable operation over a range of conditions including cloud transients has been demonstrated. Parallel theoretical investigations have established that maximising the potential for electrical power production from ammonia synthesis reactors, can largely be achieved through appropriate choice of average operating temperature in standard reactors. The possibility of operating the ammonia based system using trough concentrators has also been investigated theoretically, and the preliminary results indicate encouraging energy storage efficiencies in the region of 53%. (C) 2003 Published by Elsevier Ltd.