Addressing the challenge of climate change requires the large-scale development of significant renewable energy generation, but also requires these intermittent energy sources to be balanced by energy storage or demand management to maintain a reliable electric grid. In addition, a centralized generation paradigm fails to capture and utilize thermal energy for combined heat and power, abandoning a large portion of the available value from the primary energy source. A solar thermal electric system utilizing Stirling engines for energy conversion solves both of these shortcomings and has the potential to be a key technology for renewable energy generation. The ability to store thermal energy cheaply and easily allows the reliable generation of output power even during absences of solar input, and operating as distributed generation allows the output thermal stream to be captured for local heating applications. Such a system also can achieve relatively high conversion efficiencies, is fabricated using common and benign materials, and can utilize alternate sources of primary energy in an extended absence of solar input.
This dissertation discusses the design, fabrication, and testing of a Stirling engine as the key component in a solar thermal electric system. In particular, the design addresses the low temperature differential that is attainable with distributed solar with low concentration ratios and is designed for low cost to be competitive in the energy space. The dissertation covers design, fabrication, and testing of a 2.5 kW Stirling Engine with a predicted thermal-to-mechanical efficiency of 20%, representing 60% of Carnot efficiency, operating between 180°C and 30°C. The design process and choices of the core components of the engine are discussed in detail, including heat exchangers, regenerator, pistons, and motor/alternator, and the process for modeling, simulation, and optimization in designing the engine. Finally, the dissertation covers the assembly and experimental testing that validates the design in terms of heat exchanger performance, losses, kinematics, and cycle work.
Stirling Engine for Solar Thermal Electric Generation
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