Abstract
•A new configuration of a hybrid heat storage unit was proposed.•The paired metal hydride unit integrated with a heat recovery system based on PCM.•The effects of the PCM's proprieties on the system performance was carried out.•The PCM enhances the thermal efficiency of the hybrid heat storage unit by 30%.•An optimal performance analysis of the hybrid heat storage unit was carried out.
In order to generate electricity at night and on cloudy days, concentrated solar power (CSP) plants need a sufficient thermal energy storage (TES) unit. The most effective TES unit that combines thermochemical and latent heat storage techniques. In the present paper, for CSP plants, a new MH/PCM-TES unit design is proposed. This unit consist of paired metal hydride (MH) tanks that are connected. The high-temperature metal hydride (HTMH) tank filled with Mg2Fe alloy is used to store solar heat, while the low-temperature metal hydride (LTMH) tank filled with Na3Al alloy is used to store hydrogen that desorbed by the HTMH tank during heat charging process. The thermochemical heat released by the LTMH tank is stored as latent heat in a PCM truncated heat exchanger for reuse during desorption pocess. A two-dimensional mathematical model is established and a numerical code written in Fortran-90 is developed to study the performance of the proposed hybrid heat storage unit. The volumetric storage capacity, the specific power, and the energy efficiency are used as key performance indicators of the new MH/PCM-TES unit. The effects of the PCM's thermo-physical proprieties and the operating temperatures are investigated and discussed. The obtained numerical results demonstrated that the heat charging/discharging temperature and thermo-physical properties of PCM (melting temperture, density, thermal conductivity, specific heat) had a substantial effect on the used key performance indicators. In addition, it was found that the use of PCM with the LTMH tank enhances the energy recovery efficiency of the hybrid heat storage unit by about 30%.