Performance assessment of an oil-based packed bed thermal energy storage unit in a demonstration concentrated solar power plant

Small scale concentrated solar power plants (1–5 MW_e) are a suitable alternative for regions with limited space for land occupation or applications requiring a low capital investment. A successful approach for these plants is the use of Linear Fresnel collectors together with organic Rankine cycles, mainly, due to their lower investment cost and flexibility in operation. To improve the dispatchability of the plant, a thermal energy storage is normally incorporated. The well-known thermal energy storage technology based on a double tank configuration using molten salts is not suitable for these systems, due to the operation temperatures. A promising alternative is the use of a packed bed thermal energy storage system, as they allow a wide operation temperature range and the implementation of low-cost heat storage materials. This work investigates a packed bed using Magnetite ore as heat storage media and a thermal oil, Delcoterm Solar E15, as heat transfer fluid. This oil is also used in the Linear-Fresnel-type solar field. The performance of this thermal energy storage solution is addressed for the particular case of the 1 MW_e concentrating solar plant available in Ben Guerir (Morocco). The present work is part of the ORC-PLUS project, which targets to provide this plant with a thermal energy storage system able to supply up to 16 MWh_t to the power block. Overall, this work aims at demonstrating the potential in terms of thermal performance and cost-effectiveness of a packed bed thermal energy system for small-scale CSP plants using thermal oil as heat transfer fluid.