Metal hydride based thermal energy storage systems for solar driven plants

C. Corgnale, S. Sullivan, R. Zidan, P. Ward, M. Sulic, T. Motyka
Greenway Energy,
United States

Keywords: thermal energy storage, solar plant, low cost, high efficiency, process modeling, solar receiver, sCO2 plants


Concentrating solar power plants represent a competitive option to produce electricity only if equipped with suitable thermal energy storage systems. Metal hydride-based thermal energy storage systems have several advantages over other systems comprised of molten salt or phase change materials. Hydride systems can reach high exergetic efficiencies, low cost and volumetric energy densities on the order of 15-20 times higher than molten salt systems [1]. In addition, most of the corrosion issues associated with the use of phase change materials can be overcome with the adoption of metal hydrides, working only as solid phase materials. The metal hydride based system is comprised of a high temperature material which exchanges hydrogen with a low temperature metal hydride. During thermal energy storage, when the primary source (e.g. solar source) heat is available, the high temperature metal hydride releases hydrogen (exothermic reaction), which is absorbed in the low temperature metal hydride. The heat transfer fluid, which collects the primary source heat, exchanges the thermal power with the high temperature hydride, releasing hydrogen and storing energy. During the thermal energy release, the process is reversed. The high temperature metal hydride absorbs the hydrogen desorbed by the low temperature metal hydride. The high temperature heat, available from the exothermic hydrogen absorption, is exchanged between the metal hydride and the working fluid, to provide the power plant with the required thermal power. A recent techno-economic analysis demonstrated that some of the high temperature metal hydrides, currently available, have the potential to closely approach the US Department Of Energy (DOE) SunShot program targets for thermal energy storage [1]. For solar driven steam power plants, one of the most promising metal hydrides, working at temperatures adequate for steam power plants (about 400-500 °C), is Mg2FeH6 [1]. This material has several attractive properties (e.g. low raw material cost, high weight capacity and relatively high reaction enthalpy) that make it a very competitive and appealing system for thermal energy storage. In particular, a system comprised of Mg-Fe material, coupled with a suitable inexpensive low temperature hydride, represents a very promising economic energy storage concept. Results of modeling analysis of the proposed concept will be shown and discussed, demonstrating the technical feasibility of the proposed concept under several operating conditions and scenarios. Greenway Energy (GWE) is also partnering with Brayton Energy (prime recipient of the project) and the Savannah River National Laboratory (SRNL) within the DOE SunShot program, aiming to demonstrate a prototype integrated solar receiver-thermal energy storage system for a high temperature s-CO2 solar driven power plant. The overall system is comprised of a novel Ca-based metal hydride material, developed by SRNL and tested by GWE, coupled with a novel solar receiver concept developed by Brayton Energy. The initial outcomes of the novel prototype tests will be shown and discussed. Results of detailed analysis of the techno-economic performance of the system, operating at large scale, will also be presented and discussed. References [1] Corgnale C, et al. Renewable and Sustainable Energy Reviews 38(2014)821-833