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Due to the great potential of ionic liquid (ILs) for solar energy storage, this work combines computer-aided ionic liquid design (CAILD) and a TRNSYS simulation to identify promising IL candidates as simultaneous thermal storage media and heat transfer fluids. First, a mixed-integer nonlinear programming (MINLP) problem is formulated to search for optimal IL structures, where the thermal storage density integrating the IL density, heat capacity, melting point, and desorption temperature is employed as the objective function and the physical properties, i.e. thermal conductivity and viscosity, are implemented as optimization constraints. After that, TRNSYS simulations of a solar energy power system with the designed ILs as thermal fluids are conducted during a typical meteorological year to further study the practical performance of the IL candidates. Through the analyses of annual system operation performance as well as the long-term cost savings of such a system, the application feasibility and sustainability of the designed ILs for solar energy storage are well interpreted.

2018 Elsevier Ltd The heat transfer properties of phase change materials (PCMs) are of importance for the efficiency assessment on the heat storage and release in solar thermal systems. Previous research results demonstrate that the increase of thermal conductivity of PCMs can enhance the thermal performance in solar thermal systems; however, the corresponding mechanism is not clear. To this end, this work investigates the influence of PCMs properties on storage performance of solar thermal systems. First, experimental testing was conducted to verify the effectiveness of a thermal simulation model in the heat storage and release process. Then, the proposed simulation model was used to investigate the performance of several commonly used PCMs in the process of melting and solidification. The influence of thermal conductivity and phase transition temperature on the thermal storage properties was analyzed. The analysis results demonstrated that the influence of phase transition temperature on the thermal system performance was greater than that of the thermal conductivity in short time, while the thermal conductivity contributed greater influence on the system performance in long time. The phase transition temperature hardly affected the total system efficiency if given enough heat transfer time. The findings in this work may provide a theoretical reference for the selection of heat storage materials.