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STIRLING ENGINE AND HIGH EFFICIENCY COLLECTORS FOR SOLAR THERMAL Mike He, Achintya Madduri, Seth Sanders 1.

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Presentation on theme: "STIRLING ENGINE AND HIGH EFFICIENCY COLLECTORS FOR SOLAR THERMAL Mike He, Achintya Madduri, Seth Sanders 1."— Presentation transcript:

1 STIRLING ENGINE AND HIGH EFFICIENCY COLLECTORS FOR SOLAR THERMAL Mike He, Achintya Madduri, Seth Sanders 1

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 2

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

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 4

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 5

6 Stirling Cycle Overview 1 2 3 4 6

7 Heat Exchanger Design ComponentTemperature Drop (C) Hot-side Liquid to Metal1.79 Hot-side Metal to Air1.26 Cold-side Liquid to Metal2.42 Cold-side Metal to Air1.09 7

8 Design characteristics Design CharacteristicsValue Nominal Power Output2.525 kW Thermal-Electric Efficiency21.5% Fraction of Carnot Efficiency65% Hot Side Temperature180 o C Cold Side Temperature30 o C Working Gas (Air) Pressure25 bar Engine Frequency20 Hz Electrical Output 60Hz, 3 φ Regenerator Effectiveness0.9967 Piston Swept Volume2.2 L 8

9 Design and Fabrication 9

10 Prototype Pictures 10

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

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 12

13 Evacuated Tube Absorber 13

14 Collector testing system 14

15 Questions 15

16 Cost Comparison – no concentration Component$/W Collector0.95 Engine0.5 Installation -Hardware0.75 -Labor1.25 Total $3.45 Component$/W PV Module4.84 Inverter0.72 Installation -Hardware0.75 -Labor1.25 Total $7.56 Solar ThermalPhotovoltaic Source: PV data from Solarbuzz With concentrator: expect substantial cost and area reduction due to efficiency increase 16

17 17

18 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

19 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

20 Thermal Reservoir Waste heat stream 100-250 C or higher Heat Engine Converter Domestic Hot Water ? Electric generation on demand Huge opportunity in waste heat Ex. 3: Waste heat recovery + thermal storage 20

21 Thermal System Diagram 21

22 Solar Dish: 2-axis track, focus directly on receiver (engine heat exchanger) Photo courtesy of Stirling Energy Systems. 22

23 Stirling Cycle Overview 1 2 3 4 23

24 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

25 DisplacerPower piston Temperatures: T h =175 o C, T k =25 o C 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 model254 W (thermal input) - 24 W (mechanical output) 25

26 Prototype 1: free-piston Gamma 26

27 Prototype 2 – Multi-Phase “Alpha” 27

28 Prototype Operation Power Breakdown (W) Indicated power 26.9 Gas spring hysteresis 10.5 Expansion space enthalpy loss 0.5 Cycle output pV work 15.9 Bearing friction and eddy loss 1.4 Coil resistive loss 5.2 Power delivered to electric load 9.3 28

29 Collector Cost – no concentration  Cost per tube [1] < $3  Input aperture per tube 0.087 m 2  Solar power intensity G 1000 W/m 2  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

30 Related apps for eff. thermal conv  Heat Pump  Chiller  Refrigeration  Benign working fluids in Stirling cycle – air, helium, hydrogen 30


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