Enhancement strategies and engineering applications of photothermal conversion for evacuated tube solar collectors coupling heat pipes

The utilization of renewable solar energy is widespread across the globe. In solar energy systems, collectors are employed to capture solar radiation and convert it into more useable forms of energy. Among these collectors, the Evacuated Tube Solar Collector (ETC) has garnered significant attention due to its outstanding performance and cost-effectiveness. To further enhance the utilization of solar radiation, a Heat Pipe-Evacuated Tube Solar Collector (HP-ETC) is created by coupling a conventional ETC with a heat pipe. This paper systematically describes enhancement strategies for the photothermal conversion of HP-ETCs and their engineering applications. First, the common types of ETCs are summarized and their working principles and operation modes are analyzed. Subsequently, recent literature focused on improving the photothermal conversion performance of HP-ETCs is summarized, emphasizing the system working medium, heat pipe working medium, HP-ETC structure, solar concentrators, and phase change materials (PCMs). The engineering applications of HP-ETCs in solar water heating, desalination, solar cogeneration, and agricultural product drying are explored. In addition, using the HP-ETC solar water heater system with a specification of 15 tubes as an example, an economic and environmental benefit analysis was carried out from the perspective of the whole life cycle. Finally, based on existing studies, potential avenues and challenges for future research on HP-ETCs are discussed, with a view to providing reference values for the scientific development and engineering applications of solar collectors.