A solar thermal power system includes a solar receiver and a thermal energy storage arrangement including thermal energy storage fluid to be circulated through the solar receiver to store thermal energy. The system includes a multistage steam turbine operable on variable pressure steam generated by primary and secondary arrangements, by utilizing the fluid. The primary arrangement generates and supplies a high pressure steam to a high pressure turbine inlet, and exits from a high pressure turbine outlet. The secondary arrangement having a reheat assembly, to generate an intermediate pressure steam from the fluid, received from the storage arrangement through the reheat assembly. The intermediate pressure steam and released steam from a high pressure turbine outlet are mixed and reheated in the reheat assembly to be supplied to an intermediate pressure turbine inlet.