Abstract: The energy storage problem of solar energy could be overcome with an ammonia based solar thermochemical energy storage system. It could allow production of solar thermal power on a continuous, 24-h basis. At the ANU ammonia based solar thermochemical systems have been investigated over a period of two decades. Following on past success with a prototype solar reactor and a small heat recovery reactor in open-loop energy transfer mode, tests with a closed loop were recently successfully carried out being world's first using the ammonia reaction. As an electrical endothermic reactor has been used, further tests will be completed using the prototype solar ammonia dissociation reactor instead. The successful experiments and a computer modelling of the heat recovery reactor indicate that the heat recovery reactor should be suitable for >700 W operation. Further modelling and experiments are to be followed by a scale up to a nominal 15 kW_sol input system using the full output of the ANU's 20 m² dish.