Techno-Economic Evaluation of Low-Temperature Stirling Engine Powered Using Evacuated Tube Solar Collector

Low-temperature heat sources are ubiquitous. Harvesting this heat in an efficient and cost-effective way improve overall systems efficiency and reduce energy costs. Numerous studies shed light on these sources and technologies to utilize low-temperature heat. This paper evaluates the technical and economic feasibility of low-temperature Stirling Engine (SE) powered by hot water energy from evacuated tube solar water heater for distributed power generation when excess hot water energy is available. Evacuated tube solar collector provides hot water on-demand. When hot water is not consumed domestically, a SE is used to utilize the untapped heat from the solar water heater. The objective of this study is to evaluate the energy savings by using a SE to recover untapped heat from solar collectors. Thermal performance of the selected evacuated tube was measured experimentally under local weather conditions for different periods in summer and winter in the Mediterranean region and then simulated on hourly basis for a whole year to estimate the energy and hot water temperature output. Three different cases were taken to assess the potential of energy savings using SE to generate power namely, typical homes, office buildings and schools. SE is modeled using the most advanced third order design analysis method. Air, helium, and hydrogen are used as working fluids in the SE at different charging pressures. Results obtained from solar collector's thermal performance for the three cases are integrated with the results achieved from Stirling engine simulation of the various working fluids and pressures to evaluate the engine performance based on a dynamic approach. The study also investigates the economic feasibility of using Stirling engines for power generation from such low-temperature, intermittent heat sources. Results show that using hydrogen as working fluid is the most feasible. Typical schools show the most economical case to recover heat