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Stirling engine and high efficiency collectors for solar thermal

Stirling engine and high efficiency collectors for solar thermal. Mike He, Achintya Madduri, Seth Sanders. Motivation. Thermal storage is highly dense, cost-effective Flexible input – can use gas, solar, or electricity Storage medium is cheap Contributes to building slack

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Stirling engine and high efficiency collectors for solar thermal

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  1. Stirling engine and high efficiency collectors for solar thermal Mike He, Achintya Madduri, Seth Sanders

  2. Motivation • Thermal storage is highly dense, cost-effective • Flexible input – can use gas, solar, or electricity • Storage medium is cheap • Contributes to building slack • Predictable, controllable generation • Reversible process allows off-peak storage • Can reduce fossil fuel footprint • Can use solar input • Waste heat can be utilized

  3. System Schematic • Non-tracking collector • Low cost Thermal energy storage • Stirling engine generates electricity, waste heat

  4. Project Goals • Design, Build, and Test Stirling engine prototype to demonstrate efficiency and low cost • Design and test passive concentrator design for higher efficiency • Evaluate commercialization potential

  5. Novel Design Challenges • Designing for high efficiency, given low temperatures from distributed solar • High importance of low cost and long lifetime design • Improve commercially available collectors with passive concentrators

  6. Stirling Cycle Overview 4 1 2 3

  7. Heat Exchanger Design

  8. Design characteristics

  9. Design and Fabrication

  10. Prototype Pictures

  11. Collector and Engine Efficiency Collector with concentration G = 1000 W/m2 (PV standard) Schott ETC-16 collector Engine: 2/3 of Carnot eff. No Concentration

  12. Concentrator for Evacuated Tube Absorber • Passive involute-shaped concentrator • Produces concentration ratio ~pi in ideal case • Can reduce # tubes by concentration ratio • Lowers losses and/or increases operating temperature, improving efficiency

  13. Evacuated Tube Absorber

  14. Collector testing system

  15. Questions

  16. Cost Comparison – no concentration Solar Thermal Photovoltaic With concentrator: expect substantial cost and area reduction due to efficiency increase Source: PV data from Solarbuzz

  17. Electrical/Thermal Conversion and Storage Technology and Opportunities • Electricity Arbitrage – diurnal and faster time scales • LoCal market structure provides framework for valuation • Demand Charges avoided • Co-location with variable loads/sources relieves congestion • Avoided costs of transmission/distribution upgrades and losses in distribution/transmission • Power Quality – aids availability, reliability, reactive power • Islanding potential – controlling frequency, clearing faults • Ancilliary services – stability enhancement, spinning reserve

  18. Comparison of Water Heating Options “Consumer Guide to Home Energy Savings: Condensed Online Version” American Council for an Energy-Efficient Economy. August 2007. <http://www.aceee.org/Consumerguide/waterheating.htm >.

  19. Ex. 3: Waste heat recovery + thermal storage Waste heat stream 100-250 C or higher Thermal Reservoir Electric generation on demand Heat Engine Converter Domestic Hot Water ? • Huge opportunity in waste heat

  20. Thermal System Diagram

  21. Solar Dish: 2-axis track, focus directly on receiver (engine heat exchanger) Photo courtesy of Stirling Energy Systems.

  22. Stirling Cycle Overview 4 1 2 3

  23. Residential Example • 30 sqm collector => 3 kWe at 10% electrical system eff. • 15 kW thermal input. Reject 12 kW thermal power at peak. Much larger than normal residential hot water systems – would provide year round hot water, and perhaps space heating • Hot side thermal storage can use insulated (pressurized) hot water storage tank. Enables 24 hr electric generation on demand. • Another mode: heat engine is bilateral – can store energy when low cost electricity is available. Potential for very high cyclability.

  24. Gamma-Type Free-Piston Stirling Displacer Power piston • Temperatures: Th=175 oC, Tk=25 oC • Working fluid: Air @ ambient pressure • Frequency: 3 Hz • Pistons • Stroke: 15 cm • Diameter: 10 cm • Indicated power: • Schmidt analysis 75 W (thermal input) - 25 W (mechanical output) • Adiabatic model 254 W (thermal input) - 24 W (mechanical output)

  25. Prototype 1: free-piston Gamma

  26. Prototype 2 – Multi-Phase “Alpha”

  27. Prototype Operation

  28. Collector Cost – no concentration • Cost per tube [1] < $3 • Input aperture per tube 0.087 m2 • Solar power intensity G 1000 W/m2 • Solar-electric efficiency 10% • Tube cost $0.34/W • Manifold, insulation, bracket, etc. [2] $0.61/W • Total $0.95/W [1] Prof. Roland Winston, also direct discussion with manufacturer [2] communications with manufacturer/installer

  29. Related apps for eff. thermal conv • Heat Pump • Chiller • Refrigeration • Benign working fluids in Stirling cycle – air, helium, hydrogen

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