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Stirling engine and high efficiency collectors for solar thermal

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Presentation on theme: "Stirling engine and high efficiency collectors for solar thermal"— Presentation transcript:

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 6

7 Heat Exchanger Design Component Temperature Drop (C)
Hot-side Liquid to Metal 1.79 Hot-side Metal to Air 1.26 Cold-side Liquid to Metal 2.42 Cold-side Metal to Air 1.09

8 Design characteristics
Value Nominal Power Output 2.525 kW Thermal-Electric Efficiency 21.5% Fraction of Carnot Efficiency 65% Hot Side Temperature 180 oC Cold Side Temperature 30 oC Working Gas (Air) Pressure 25 bar Engine Frequency 20 Hz Electrical Output 60Hz, 3φ Regenerator Effectiveness 0.9967 Piston Swept Volume 2.2 L

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 11 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

13 Evacuated Tube Absorber
The operation of the solar collector is very simple. 1. Solar Absorption: Solar radiation is absorbed by the evacuated tubes and converted into heat. 2. Solar Heat Transfer: Heat pipes conduct the heat from within the solar tube up to the header. 3. Solar Energy Storage: Water is circulated through the header, via intermittent pump cycling. Each time the water circulates through the header the temperatures is raised by 5-10oC / 9-18oF. Throughout the day, the water in the storage tank is gradually heated.  Introduction, How Evacuated tubes work, rated temperature and water tank.

14 Collector testing system

15 Questions

16 Cost Comparison – no concentration
Solar Thermal Photovoltaic Component $/W Collector 0.95 Engine 0.5 Installation -Hardware 0.75 -Labor 1.25 Total $3.45 Component $/W PV Module 4.84 Inverter 0.72 Installation -Hardware 0.75 -Labor 1.25 Total $7.56 With concentrator: expect substantial cost and area reduction due to efficiency increase Source: PV data from Solarbuzz

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

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

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

21 Thermal System Diagram

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

23 Stirling Cycle Overview
4 1 2 3 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.

25 Gamma-Type Free-Piston Stirling
Displacer Power piston Temperatures: Th=175 oC, Tk=25 oC Working fluid: 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

26 Prototype 1: free-piston Gamma
Displacer and power piston can independently be driven. 26 26

27 Prototype 2 – Multi-Phase “Alpha”

28 Prototype Operation Power Breakdown (W) 26.9 10.5 0.5 15.9 1.4 5.2 9.3
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 28

29 Collector Cost – no concentration
Cost per tube [1] < $3 Input aperture per tube m2 Solar power intensity G W/m2 Solar-electric efficiency 10% Tube cost $0.34/W Manifold, insulation, bracket, etc. [2] $0.61/W Total $0.95/W Solar-Thermal Collector Up to 250 oC without tracking [1] Low cost: glass tube, sheet metal, plumbing Simple fabrication (e.g., fluorescent light bulbs) ~$3 per tube, 1.5 m x 47 mm[1] No/minimal maintenance (round shape sheds water) Estimated lifespan of years, 10 yrs warranty [2] Easy installation – hr per module [2] [1] Prof. Roland Winston, also direct discussion with manufacturer [2] communications with manufacturer/installer 29 29

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


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