This standard applies to solar thermal storage tanks (hereinafter referred to as direct thermal storage type, indirect thermal storage type, , heat storage tank). Therefore, it is not applicable to heat storage tanks that use heat storage media that utilize latent heat. The heat storage tank referred to here means a heat storage tank with a capacity of 1000 L or less, including for hot water supply and heat storage, and includes a heat storage tank in which an auxiliary heat source device is integrated into the heat storage tank. In addition, the performance of auxiliary heat source equipment shall be based on related standards.