Thermochemical (TC) heat storage is an interesting technology for future seasonal storage of solar heat in the built environment. This technology enables high thermal energy storage densities and low energy storage losses. A small-scale laboratory prototype TC storage system has been realized at ECN, applying an open sorption system concept. The packed bed contains 17 dm(3) of sorption material and is capable of generating 150 W of thermal power. An effective energy storage density of approximately 0.5 GJ/m(3) was obtained. (c) 2013 Elsevier Ltd. All rights reserved.