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SENER, under the Baseload CSP FOA, aimed to develop a highly efficient, low-maintenance and economical thermal energy storage (TES) system using solid graphite modular blocks for CSP plants.


The main objective was to evaluate a TES system able to store energy at temperatures greater than 800°C and that is robust enough to withstand the thermal cycles foreseen in a lifespan of 30 years with no parasitic energy consumption. SENER refined the layout of the TES system, which was too large with too much piping to be economical.

The graphite material used in this project appeared to be superior to concrete for use as a TES storage medium. The modified the graphite composition to increase the thermal conductivity and reduce the cost of the graphite, as these are the two biggest drivers in the cost of the system.

SENER is developing solid thermal energy storage (TES) systems that use heat-transfer fluids formed by combining high-thermal-capacity solids, such as graphite, with gases.


The system developed under this award had extra capacity for higher temperatures and/or larger thermal differences compared with previous storage systems. The use of graphite allowed for temperatures in the storage media approaching 1650°C. This technology can extend the operating range of thermal storage to significantly beyond that of molten salt (1650°C vs. 565°C), which could also have direct application to solar power towers.


The conceptual design has been developed for a thermal energy storage system, technically suitable for high temperature (650ºC), high thermal difference (200ºC to 650ºC) and long useful life, with a target cost per energy unit stored of $21/kWh. 

Final Report

Villarroel, Eduardo et al. High Efficiency Thermal Storage System for Solar Plants (HELSOLAR). No DE-EE0003592, 2013. doi:10.2172/1068058. 

​Learn about other DOE competitive awards for concentrating solar power research that are in progress.