A regenerative heat storage system for central receiver technology working with atmospheric air

Abstract

Solar thermal power plants (STPP) are focused on reducing costs while increasing performance. In this context central receiver (CR) technology working with volumetric receiver shows a high potential to improve efficiencies by allowing higher operating temperatures. This technology requires the implementation of efficient thermal energy storage (TES) that allows predictable electricity delivery to the grid. Moreover, to compete with the advantage of molten salt technology storage, the CR technology based in air as heat transfer fluid (HTF) must identify TES solutions that enable efficient thermal storage times, that could be considered dispatchable, and competitive specific costs under 20 €/kWhth. It may be considered that the reference solution for thermal storage in STPP-CR with open volumetric receiver continues being the TSA project developments, also adopted in the experimental plant in Jülich. Knowing the present market situation, CIEMAT-PSA developed a lab-scale packed bed storage system, with the main objective of identifying economically competitive materials and configurations for efficient regenerative heat storage. For the newer configurations, CIEMAT-PSA has 4-Al2O3 commercial balls with two diameters – 9 and 13 mm –, and two densities – 2.3 and 3.5 g/cm3 – that allows different configurations to be analyzed. Dynamics tests with 9 mm Al2O3 balls and 2.3 g/cm3 have been carried out for air inlet temperatures near 400ºC until 640ºC. In addition, a simplified dynamic model, whose formulation is widely assumed in the literature as reasonable to represent the realistic thermal performance, will be used, in order to compare the experimental and predicted temperature profiles, during the charging process.