A comparative study of sensible energy storage and hydrogen energy storage apropos to a concentrated solar thermal power plant

To achieve dispatchable and reliable power generation through renewable sources, energy storage is often indispensable. This paper attempts a quantitative investigation and comparison between two different energy storage technologies, Thermal Energy Storage System (TESS), which is already mature, and Hydrogen Energy Storage System (HESS), applied to a common concentrated solar thermal power (CSP) plant. A solar field (SF) comprising parabolic troughs and molten salt as a heat transfer fluid is conceived with a power block running on the Rankine cycle. An integrated TESS system is first considered, and the SF size is iteratively determined, so that plant with TESS has a capacity factor of 100 % for a typical summer day, thereby standardizing the TESS performance. The TESS is then replaced with the HESS, keeping the same SF capacity. The plant capacity and storage performances are then compared with simplistic assumptions. The results show superior TESS performance, while HESS delivers only 58 % capacity factor. TESS also delivers superior energy and power density (68 kWh/m³ and 4.5 kW/m³ for TESS, as opposed to 26 kWh/m³ and 1.8 kWh/m³ for HESS, respectively). However, the specific energy and power for both are comparable (approx. 93 Wh/kg and 6 W/kg, respectively). Although electrolyzer and fuel cell efficiencies individually outperform Rankine efficiency, HESS lags in performance with CSP configuration due to multiple steps of energy conversion.