A first of its kind pilot-scale redox-based thermochemical storage system has been set up and operated under near-realistic conditions inside a solar power tower plant. The storage unit is made of inert honeycomb supports (cordierite) coated with 88 kg of redox active material (cobalt oxide). An experimental campaign has been carried out consisting of 22 thermochemical charge-discharge cycles. The heat absorbed or released by the chemical reaction became clearly evident through the temperature evolution inside the reactive material. It allows to store or release energy at constant temperature when crossing respectively the reduction/oxidation temperature of the Co3O4/CoO pair. A storage performance factor (P-F) was defined to evaluate how each experiment approaches the ideal behavior. During the complete campaign no measurable cycle-to-cycle degradation was observed and the system average capacity was very close to the ideal case of P-F = 0.84. The advantage of thermochemical storage could be quantified by comparing the storage capacity, to that of a sensible-only storage unit made of uncoated cordierite honeycombs. The thermochemical system offered almost double storage capacity (47.0 kW h) cf. the same volume of the sensible-only case (25.3 kW h). (C) 2016 Elsevier Ltd. All rights reserved.