Intermittence of renewable power supply and high power generating costs are the major technical and economical obstacles to widespread commercial use of regenerative energy sources (RES). In contrast to photovoltaic (PV) or wind power, concentrated solar power (CSP) has the potential to provide dispatchable power on a defined capacity level by integrating large-scale thermal energy storage. Efficient, reliable and economic thermal energy storage (TES) technologies will thus improve economics and raise the market potential of CSP technology.
Recent strategies to further improve CSP technologies are aiming at plant concepts with higher concentration factors resulting in higher operation temperature with consequently higher overall conversion efficiencies. This implies the need for medium and high temperature thermal storage technologies that can easily be integrated into the CSP plant at low cost. Such TES systems are considered to be one of the key factors for providing low cost electricity from solar power.
A characteristic of thermal storage systems is their diversification with respect to temperature, power level and heat transfer fluid. The currently available commercial, pre-commercial or even pilot-scale heat storage systems suffer from insufficient energy density, limited efficiency and reliability. They demand investment costs which are still too high. Such shortfalls are obstacles to a more wide-spread use and market penetration of thermal energy storage in the CSP plant sector.
To close this gap, advanced approaches for thermal energy storage are needed which, on one hand, include materials with superior energy density, suitable thermo-physical and thermo-mechanical properties, cost effective design, reliable components, and efficient system integration. On the other hand, innovative storage concepts are to be developed which can be adapted and integrated into a large variety of CSP plant configurations. They should be flexible regarding heat transfer fluids, temperature and power levels.
Yet, there are not many thermal energy storage technologies available for a temperature range between 450°C and 1000°C that can be integrated into various CSP setups. Using reversible chemical reactions is a promising solution which has the potential for high storage densities at reasonable material cost (see Table B1.1). Also, this technology can be used for a wide temperature range by selecting an appropriate reaction system and tuning its pressure level in order to adjust the desired equilibrium temperature. Nevertheless, thermochemical energy storage (TCS) has not been demonstrated at a commercial or even prototype level as there are still important fundamental challenges to tackle. Ongoing research on TCS in the US being funded by DoE is contributing to the utilization of this technology in connection with solar power plants. The proposed TCSPower project intends to evaluate the potential of thermochemical energy storage for use with CSP plants and to verify the developed TCS storage reactor experimentally in 10kW scale with a storage capacity of about 100kWh.