PURPOSE: To absorb the solar heat and improve the thermal efficiency without using a conventional thermal medium by a method wherein a heat accumulation capsule having particles of thermal accumulation medium which may be carried is applied.

CONSTITUTION: A thermal accumulation capsule is formed to a spherical shape by a selective absorption film 1 made of such a material as carbon, iron oxide etc. absorbing a solar energy well, a thermal accumulation material 3 having a high specific heat, capable of accumulating much volume of calory or utilizing a melting heat, and an outer wall 2 made of material not decayed by the heat accumulation material 3 having a higher softening point than a melting point of the heat accumulator material 3 held between the film 1 and the material 3. In case that the solar heat collector 4, heat accumulator tank 5 and transferring pump 6 etc. are applied in the solar heat hot water heater which is connected by a closed circuit, a number of said capsules are stored in the heat accumulation tank 5, fed in a direction of arrow with water by pump 6 under an open condition of the valves 7,8, and only the heated water in the collector 4 is passed through the filter 11 and then taken out of the system.