Design and analysis of a novel low-temperature solar thermal electric system with two-stage collectors and heat storage units

Abstract

The proposed low-temperature solar thermal electric generation is based on the compound parabolic concentrator (CPC) of small concentration ratio and Organic Rankine Cycle (ORC). The technologies of CPC and ORC are analyzed, and feasibility of the system is demonstrated. In particular, two-stage collectors and heat storage units are adopted to improve heat collection efficiency. Organic fluid is preheated by flat plate collectors (FPCs) prior to entering a higher temperature heat exchanger connected with the CPC. The two-stage heat storage units are composed of two types of phase change material (PCM) with diverse melting temperatures. The novel configuration is carefully designed to react to different operating conditions. The fundamentals are illustrated for both simultaneous and separate processes of heat collection and power conversion. Mathematic models are built for heat transfer and thermodynamics of the innovative system. Coupling relationship among the proportion of FPC to CPC, the melting temperature of the first-stage PCM and the overall collector efficiency is established. The benefits of the preheating concept and cascaded heat storages are investigated in detail in comparison with the single-stage system. The results indicate that the increase in collector efficiency of the two-stage system is appreciable.