A solar heat energy collection system of the natural circulation type where the heat store is located above liquid cooled collectors. The system utilizes at least two liquids, the first is a non-freezing liquid which circulates between a heat store tank and the collectors, the second liquid is less dense than the first and immiscible therewith and acts as a heat store and also to supply the heat load. A third liquid less dense than the second and immiscible therewith may be utilized to supply the heat load. In this latter situation, the second liquid acts only as a heat store.