Thermal storage in an important operational aspect of a solar thermal system which enables it to deliver power or energy when there is no sunlight available. Current thermal storage systems in solar thermal systems work based on transferring the generated heat from sunlight to a thermal mass material in an insulated reservoir and then withdraw it during dark hours. Some common thermal mass materials are stone, concrete, water, pressurized steam, phase changing materials, and molten salts. In the current paper, a hybrid thermal energy storage system which is based on two metal hydrides is proposed for a solar thermal system. The two hydrides which are considered for this system are magnesium hydride and lanthanum nickel. Although metal hydride Energy Storage Systems (ESS) suffer from slow response time which restricts them as a practical option for frequency regulation, off peak shaving and power supply stabilization; they can still demonstrate significant flexibility and good energy capacity. These specifications make them good candidates for thermal energy storage which are applicable to any capacity of a solar thermal system just by changing the size of the ESS unit.

The implementation of efficient and cost effective thermal energy storage in concentrated solar power (CSP) applications is crucial to the wide spread adoption of the technology. The current push to high-temperature receivers enabling the use of advanced power cycles has identified solid particle receivers as a desired technology. A potential way of increasing the specific energy storage of solid particles while simultaneously reducing plant component size is to implement thermochemical energy storage (TCES) through the use of non-stoichiometric perovskite oxides. Materials such as strontium-doped lanthanum cobalt ferrites (LSCF) have been shown to have significant reducibility when cycling temperature and oxygen partial pressure of the environment [1]. The combined reducibility and heat of the oxidation and reduction reactions with the sensible change in temperature of the material leads to specific energy storage values approaching 700 kJ kg −1 . A potential thermochemical energy storage system configuration and modeling strategy is reported on, leading to a parametric study of critical operating parameters on the TCES subsystem performance. For the LSCF material operating between 500 and 900°C with oxygen partial pressure swings from ambient to 0.0001 bar, system efficiencies of 68.6% based on the net thermal energy delivered to the power cycle relative to the incident solar flux on the receiver and auxiliary power requirements, with specific energy storage of 686 kJ kg −1 are predicted. Alternatively, only cycling the temperature between 500 and 900°C without oxygen partial pressure swings results in TCES subsystem efficiencies up to 76.3% with specific energy storage of 533 kJ kg −1 .