Novel techniques to enhance the performance of Stirling engines integrated with solar systems

Abstract

In this paper, we present three novel techniques for enhancing Stirling engines (SE). Conventional SE regenerators are replaced with Phase-Change material (PCM) regenerators to increase regenerator and engine performance. The plate receiver of a Solar-Dish Stirling engine (SDSE) is replaced with a glass receiver to increase direct radiation absorption and reduce losses. An SDSE system is coupled with a PCM Thermal Storage Reservoir PCMTSR)) to store the rejected heat during daylight and extract stored energy to produce power during the night. Either ambient air or geothermal water is used to cool down the engine during night operation. Theoretical models were constructed to determine the effects of the proposed modifications on SE performance. Installing a PCM regenerator with 0.6 porosity and 10 mm length increased the regenerator effectiveness by 3.8% and the SE efficiency by 4.2%. However, high-porosity PCM regenerators suffered from engine frequency limitations: PCM regenerators with 0.9 porosity limited the SE to 12Hz. Installing a glass receiver in SDSE systems caused a 10% SE efficiency and a 37.9% system efficiency gain at 700 W/m2 solar radiation. An air-cooled SDSE-PCMTSR system produced 22.6% of the daily energy output during the night, while its geothermal-cooled counterpart produced 73% during the night.