Thermodynamic Superiority of Calcium Hydroxide-Based Thermochemical Energy Storage over Ammonia-Based Systems in Concentrated Solar Power

Thermochemical energy storage technology is a promising step in the development of renewable energy and the transition to sustainable energy systems. Thermochemical energy storage systems store thermal energy through reversible chemical reactions and can provide a stable and continuous energy source with appropriate efficiency. This study investigates and compares the performance of two promising thermochemical energy storage systems when integrated with a concentrated solar thermal power plant. Calcium hydroxide- and ammonia-based thermochemical energy storage systems, due to their suitable temperature range and energy density, are coupled with a 20 MW concentrated solar plant. Results show that, in terms of roundtrip efficiency, the calcium hydroxide-based system performs better, achieving 93.6 % thermal-to-thermal efficiency with the capability of generating 2.28 MW of electrical power, while the ammonia-based system achieves 84 % thermal-to-thermal efficiency with a capability of 2.04 MW of electrical power. From a second- law thermodynamics perspective, during the charging phase, the endothermic reactor in the ammonia-based system demonstrates better performance, with approximately 10 % higher exergy efficiency compared to the calcium hydroxide-based system. During the discharging phase, reactors in both systems show similar performance. For the proposed integrated configurations, a heliostat field is designed with an area of 0.055 km2 and an efficiency of 72.44%.