Research and Development for Novel Thermal Energy Storage Systems (TES) for Concentrating Solar Power (CSP)

Abstract

Executive Summary:The overall objective was to develop innovative heat transfer devices and methodologies for novel thermal energy storage systems for concentrating solar power generation involving phase change materials (PCMs). Specific objectives included embedding thermosyphons and/or heat pipes (TS/HPs) within appropriate phase change materials to significantly reduce thermal resistances within the thermal energy storage system of a large-scale concentrating solar power plant and, in turn, improve performance of the plant. Experimental, system level and detailed comprehensive modeling approaches were taken to investigate the effect of adding TS/HPs on the performance of latent heat thermal energy storage (LHTES) systems. Experimental results proved the superior performance of HPs to increase the heat transfer rates compared to finned and non-finned cases. Quantitatively, inclusion of heat pipes increased PCM melting rates by approximately 60%, while the fins were not as effective. During solidification, the heat pipe-assisted configuration transferred approximately twice the energy between a heat transfer fluid and the PCM, relative to both the fin-assisted LHTES and the non-heat pipe, non-fin configurations.Comprehensive multiphase multi-dimensional simulations were conducted to provide a better understanding of the fundamental physical phenomena involved in thermal energy storage in a phase change media with embedded TS/HPs, and also to provide input for the system level model. A system level model, leveraged by the input from the comprehensive model, was developed to predict the response of large-scale TS/HP-assisted LHTES systems in a computationally-effective manner. Consistent with the experimental results, the results of the system level model also demonstrated a significant increase in heat transfer rates associated with HP-assisted LHTES systems.The developed system level model was employed to predict the performance of a large-scale LHTES system utilizing multiple PCMs in a cascaded configuration. It was shown that the maximum exergy recovery can be achieved by using a cascaded configuration. Optimization studies were performed using the system level model and the preferred configurations of HPs in the LHTES systems were identified. Exergy analysis of LHTES systems was carried out considering the practical constraints imposed on the system in solar applications. Novel guidelines were proposed for design and optimization of LHTES systems for solar applications. Economic aspects of TS/HPassisted LHTES systems were also investigated and it was shown that these systems are cost competitive with the state of the art thermal energy storage systems currently in use. DE-FG36-08GO18146Research and Development for Novel TES Systems for CSP University of Connecticut 3 Background:Energy storage capability is desirable in solar and wind electric power applications due to the intermittent nature of the energy generated. In solar thermal generation, thermal energy storage is the preferred energy storage mode [1]...