Screening analysis of metal hydride based thermal energy storage systems for concentrating solar power plants

Concentrating solar power plants represent a competitive option to produce electric power only if equipped with suitable thermal energy storage. Metal hydride material-based thermochemical hydrogen storage is a very attractive solution to store high temperature solar thermal energy. A literature review of some of the past and more recent investigations on using metal hydrides for thermal energy storage has been carried out. Based on findings from this review and new material property data, a preliminary material techno-economic analysis was performed to select the most promising candidate metal hydrides as well as to examine their behavior under different operating conditions. The performance was evaluated adopting simplified system models and the results were compared against the US Department of Energy targets including installed cost, exergetic efficiency, operating temperature and volumetric energy density. Selected sensitivity analyses for the most promising materials have also been carried out in order to evaluate the influence of solar plant and material properties on the overall system installed cost. Results demonstrated that the selected storage systems, based on currently available metal hydride high temperature materials (i.e. NaMgH3, TiH2 and CaH2), are able to achieve and exceed many of the targets such as volumetric energy density (25 kWhth/m3) and operating temperature (600 °C). Material modifications as well as heat exchange system improvements are also discussed in the paper, with the aim of reducing the overall thermal energy storage specific cost and helping to meet and exceed all of the targets.