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Stirling Engine for Solar Thermal Electric Generation

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Stirling Engine for Solar Thermal Electric Generation Stirling Engine for Solar Thermal Electric Generation Mike Miao He Electrical Engineering and Computer Sciences University of California at Berkeley Technical Report No. UCB/EECS-2018-15 http://www2.eecs.berkeley.edu/Pubs/TechRpts/2018/EECS-2018-15.html May 1, 2018 Copyright © 2018, by the author(s). All rights reserved. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Acknowledgement I would like to thank Professor Seth Sanders for his mentorship and helping me to be a better engineer, for his perpetual good humor and kindness, and for always being available for his students. I would also like to thank Artin Der Minassians for his guidance and help. Thanks to Aron, Matt, Roger, Sarah, and Shai on the Cleantech-to-Market team for their research on the market viability of the technology. Thanks to Alan, Shong, Kelvin, Alex, and Samir and others for their help. Stirling Engine for Solar Thermal Electric Generation by Mike Miao He A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering { Electrical Engineering and Computer Sciences and the Designated Emphasis in Energy Science and Technology in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Seth Sanders, Chair Professor Randy Katz Professor Dan Kammen Summer 2016 Stirling Engine for Solar Thermal Electric Generation Copyright 2016 by Mike Miao He 1 Abstract Stirling Engine for Solar Thermal Electric Generation by Mike Miao He Doctor of Philosophy in Engineering { Electrical Engineering and Computer Sciences University of California, Berkeley Professor Seth Sanders, Chair Addressing the challenge of climate change requires the large-scale development of sig- nificant 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 heat- ing 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. i To my wife, Michelle, for loving me and supporting me throughout my graduate career. ii Contents Contents ii List of Figures iii List of Tables iv 1 Introduction 1 1.1 System Description . 1 1.2 Stirling Engine Background . 2 2 Motivation 5 2.1 Broader Context . 5 2.2 Applications . 11 3 Design and Optimization 21 3.1 Design Overview . 21 3.2 Analytical Design and Optimization . 22 3.3 Heat Exchangers . 23 3.4 Regenerator . 32 3.5 Displacer Piston . 34 3.6 Power Piston . 36 3.7 Adiabatic Simulation and Optimization . 39 3.8 Drive Train . 46 3.9 Losses and Inefficiencies . 48 3.10 Pressurization . 56 3.11 Prototype Design . 59 4 Electrical Conversion and Motor Control 61 4.1 Alternator Design . 61 4.2 Drive Controls . 69 5 Experimental Results 80 5.1 Assembly and Verification . 80 iii 5.2 Heat Exchanger Test . 81 5.3 Alternator Performance . 85 5.4 Loss Experiments . 85 5.5 Forward and Reverse Operation . 88 6 Conclusion 94 6.1 Future Work . 94 6.2 Final Words . 94 Bibliography 96 List of Figures 1.1 System Diagram . 2 1.2 Ideal Stirling Cycle P-V Diagram . 3 2.1 PV Installed Price . 6 2.2 PV Cumulative and Annual Installed Capacity . 6 2.3 Diesel Cogeneration Payback . 19 2.4 Diesel Cogeneration Market Segments . 20 3.1 Top and bottom CAD view of heat exchanger body. 24 3.2 Heat Exchanger Complete View . 25 3.3 Working Fluid Channel Flow Simulation . 28 3.4 Heat Exchanger External-Fluid Channel . 30 3.5 Heat Exchanger External-Fluid Channel Structural FEA . 31 3.6 Displacer isometric and section view . 34 3.7 Displacer deflection . 36 3.8 Power piston isometric and section view. 37 3.9 P-V Diagram from Adiabatic Simulation . 40 3.10 Optimization sweep over piston strokes . 42 3.11 Optimization sweep over regenerator stack length . 43 3.12 Working Fluid Stroke Length Sweep . 45 3.13 Crankshaft Unconnected . 46 3.14 Crankshaft Assembled . 47 3.15 Displacer linear bearing housing . 48 3.16 Assembled Engine with Wall . 57 iv 3.17 Pressure Vessel Drawing and Image . 58 3.18 Stirling Cycle Energy Flow Diagram . 59 3.19 Engine Photographs . 60 4.1 Magnet rotor disc . 62 4.2 Assembled winding structure . 63 4.3 Full rotor and stator assembly . 64 4.4 Flux density versus rotor angle and fourier components . 65 4.5 Aspect Ratio Optimization . 67 4.6 Normalized Aspect Ratio Optimization . 68 4.7 Custom Norm Level-Set . 75 4.8 Speed Control . 76 4.9 Control Block Diagram . 77 4.10 Control Schematic . 79 5.1 Engine Assembly Pictures . 82 5.2 Electric Heater . 83 5.3 Comparison of BackEmf from design and measurement . 86 5.4 Spinning Losses Experiment Descriptions . 87 5.5 Waveforms from Engine Test . 90 5.6 PV Diagrams in Heat Pump mode . 91 5.7 PV Diagrams in Engine mode . 92 List of Tables 2.1 Engine Capitol Costs . 14 2.2 Installed Price for Stirling vs PV . 14 2.3 Full-Value Installed Price for Stirling vs PV . 16 2.4 Diesel Generator Specifications . 17 3.1 Mesh longest path thermal resistances. 26 3.2 Heat exchanger thermal resistances. 29 3.3 Heat exchanger temperature drops. 30 3.4 Important regenerator properties. 33 3.5 Displacer properties . 36 3.6 Power Piston properties . 39 v 3.7 Stirling engine losses . 45 3.8 Bearing Components . 48 3.9 Peak Piston Forces . 48 3.10 Conduction path losses . 50 3.11 Stirling engine losses . 54 3.12 Temperature drops . 60 5.1 Heat exchanger conduction test temperature drops . 83 5.2 Heat exchanger temperature drops. 84 5.3 Heat Pump Equilibrium Thermal Test . 85 5.4 Heat Pump Equilibrium Thermal Test . 85 5.5 Spinning Losses Measurements and Predictions . ..
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