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 electricityStorage medium is cheapContributes to building slackPredictable, controllable generationReversible process allows off-peak storageCan reduce fossil fuel footprintCan use solar inputWaste heat can be utilized
3 System Schematic Non-tracking collector Low cost Thermal energy storageStirling engine generates electricity, waste heat
4 Project GoalsDesign, Build, and Test Stirling engine prototype to demonstrate efficiency and low costDesign and test passive concentrator design for higher efficiencyEvaluate commercialization potential
5 Novel Design Challenges Designing for high efficiency, given low temperatures from distributed solarHigh importance of low cost and long lifetime designImprove commercially available collectors with passive concentrators
7 Heat Exchanger Design Component Temperature Drop (C) Hot-side Liquid to Metal1.79Hot-side Metal to Air1.26Cold-side Liquid to Metal2.42Cold-side Metal to Air1.09
8 Design characteristics ValueNominal Power Output2.525 kWThermal-Electric Efficiency21.5%Fraction of Carnot Efficiency65%Hot Side Temperature180 oCCold Side Temperature30 oCWorking Gas (Air) Pressure25 barEngine Frequency20 HzElectrical Output60Hz, 3φRegenerator Effectiveness0.9967Piston Swept Volume2.2 L
11 Collector and Engine Efficiency Collector with concentrationG = 1000 W/m2 (PV standard)Schott ETC-16 collectorEngine: 2/3 of Carnot eff.No Concentration1111
12 Concentrator for Evacuated Tube Absorber Passive involute-shaped concentratorProduces concentration ratio ~pi in ideal caseCan reduce # tubes by concentration ratioLowers 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.
16 Cost Comparison – no concentration Solar ThermalPhotovoltaicComponent$/WCollector0.95Engine0.5Installation-Hardware0.75-Labor1.25Total$3.45Component$/WPV Module4.84Inverter0.72Installation-Hardware0.75-Labor1.25Total$7.56With concentrator: expect substantial cost and area reduction due toefficiency increaseSource: PV data from Solarbuzz
18 Electrical/Thermal Conversion and Storage Technology and Opportunities Electricity Arbitrage – diurnal and faster time scalesLoCal market structure provides framework for valuationDemand Charges avoidedCo-location with variable loads/sources relieves congestionAvoided costs of transmission/distribution upgrades and losses in distribution/transmissionPower Quality – aids availability, reliability, reactive powerIslanding potential – controlling frequency, clearing faultsAncilliary 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 streamC or higherThermal ReservoirElectric generationon demandHeat Engine ConverterDomestic Hot Water ?Huge opportunity in waste heat
24 Residential Example30 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 heatingHot 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 DisplacerPower pistonTemperatures: Th=175 oC, Tk=25 oCWorking fluid: ambient pressureFrequency: 3 HzPistonsStroke: 15 cmDiameter: 10 cmIndicated 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.2626
28 Prototype Operation Power Breakdown (W) 26.9 10.5 0.5 15.9 1.4 5.2 9.3 Indicated power26.9Gas spring hysteresis10.5Expansion space enthalpy loss0.5Cycle output pV work15.9Bearing friction and eddy loss1.4Coil resistive loss5.2Power delivered to electric load9.32828
29 Collector Cost – no concentration Cost per tube  < $3Input aperture per tube m2Solar power intensity G W/m2Solar-electric efficiency 10%Tube cost $0.34/WManifold, insulation, bracket, etc.  $0.61/WTotal $0.95/WSolar-Thermal CollectorUp to 250 oC without tracking Low cost: glass tube, sheet metal, plumbingSimple fabrication (e.g., fluorescent light bulbs)~$3 per tube, 1.5 m x 47 mmNo/minimal maintenance (round shape sheds water)Estimated lifespan of years, 10 yrs warranty Easy installation – hr per module  Prof. Roland Winston, also direct discussion with manufacturer communications with manufacturer/installer2929
30 Related apps for eff. thermal conv Heat PumpChillerRefrigerationBenign working fluids in Stirling cycle – air, helium, hydrogen