This paper describes a novel concept for long-term thermochemical storage for solar heating and presents experimental validation in a large-scale laboratory prototype. The storage tank is intended for a closed-cycle calcium chloride system to provide space conditioning as well as hot water. Solar energy is stored in a concentrated liquid desiccant by desorbing water vapor in the collector. The stored energy is released by rehydrating the concentrated solution in a chemical heat pump. One of the key technical challenges to the long-term storage capacity is control of mass and heat transfer in the tank. This challenge arises because it is imperative to prevent mixing of solutions of different calcium chloride concentration, particularly during charge and discharge. Twodimensional optical measurements of velocity and mass fraction show that during indirect sensible charging of a prototype tank, mixing is minimal. The tank is thermally stratified and analysis of the data indicates that the storage can be maintained on the order of 175 days.