A single thermal energy storage tank is used so that costs can be reduced and an installation space can also be reduced compared to a case where two tanks, i.e., a high temperature tank and a low temperature tank are provided. In addition, the single thermal energy storage tank includes a porous block so that passage of molten salt can be more easily performed and flow pressure drop can be reduced. In addition, the porous block is configured by stacking a plurality of unit blocks so that the capacity of the single thermal energy storage tank can be easily adjusted. Furthermore, a plurality of single thermal energy storage tanks are connected in parallel so that the plurality of single thermal energy storage tanks can be selectively used according to an operation load and thus the solar thermal power generation system can easily cope with the operation load.