Disclosed is a solar heat storage system that is provided with a heat exchange medium tank and a liquid heat exchange medium placed in said heat exchange medium tank, characterized in that: when light entering, with an incident angle 0o, at least one plane surface of the heat exchange medium tank is allowed to transmit through a plane surface of the heat exchange medium tank being almost parallel to the incident surface, the heat exchange medium tank shows a transmittance of light in the visible light region of 380-780 nm in wavelength of 50% or greater and an absorptivity of light in the infrared region of 780-2500 nm in wavelength of 10% or greater； the liquid heat exchange medium contains a dye, said dye having an absorption maximum within the visible light region of 380-780 nm in wavelength, at such a concentration as to give a light absorptivity of the liquid heat exchange medium of 5% or greater at the absorption maximum； and light having transmitted through at least one plane wall of the heat exchange medium tank at least partly enters the liquid heat exchange medium.
