Development of a latent heat thermal energy storage unit for the exhaust of a recuperated solar-dish Brayton cycle

Abstract

Solar air Brayton cycles can provide heat and power to small communities with no access to the national grid. However, the temporal mismatch between the energy supply and demand can limit the amount of solar energy successfully transferred to the user. To increase this solar utilization factor, a high-temperature latent heat thermal energy storage unit for temperatures of up to 750 K, dedicated to a solar air Brayton cycle, is designed and tested under realistic operating conditions. The storage unit is charged employing the cycle exhaust and discharged after sunset to serve domestic heating applications. In agreement with the identified operating conditions, four storage material candidates are shortlisted and characterized. Thus, the so-called solar salt was selected as the most suitable material by means of 3D numerical analysis to meet a series of performance, durability, cost, and compactness requirements. The proposed latent heat thermal energy storage device was tested with 151 kg of solar salt and allowed for the storage of up to 17.5 kWh in a 10 h charging time. Overall, the numerical and experimental results reported in this work demonstrate the feasibility of the proposed device as a cost-effective and durable thermal storage solution in small-scale solar air Brayton cycles.