Solar thermal electricity generating systems with thermal storage

A solar power system comprising:

• a solar receiver, in which steam is generated using insolation directed thereon;
• a plurality of heliostats that direct insolation onto the solar receiver;
• a thermal storage system having first and second reservoirs for holding a thermal storage fluid therein, the first and second reservoirs being connected together by one or more conduits such that the thermal storage fluid can flow between the first and second reservoirs;
• a heat exchanger in thermal communication with the one or more conduits and arranged such that enthalpy can be transferred to or from thermal storage fluid flowing in the one or more conduits;
• an electricity generating system that uses the generated steam to produce electricity;
• an auxiliary heater that heats the thermal storage fluid using one of electricity and a fossil fuel, the thermal storage fluid including a molten salt and/or a molten metal;
• and
• a controller that controls the thermal storage system, the heat exchanger, and the auxiliary heater, wherein the controller comprises electrical circuitry that is configured to:
• during a first time period, charge the thermal storage system using enthalpy transferred from steam from the solar receiver via the heat exchanger;
• during a second time period, charge the thermal storage system using heat from the auxiliary heater;
• and
• during a third time period, discharge the thermal storage system to generate steam from enthalpy stored in the thermal storage system to produce electricity.