Presentation on theme: "Solar thermal and combined heat and power"— Presentation transcript:
1 Solar thermal and combined heat and power Achintya Madduri, Mike He
2 Combined Opportunities: Low-cost media – water, mineral oil, molten saltsHeat engine (eg. Stirling) provides high efficiency,eg. better than ~ 2/3 of reversible limitStirling converter enables excellent durability, cycle- ability (contrast with IC engine)Ex.1: Solar Thermal Electric System
3 Stirling Engine Can achieve large fraction (70%) of Carnot efficiency Low cost possible for low temp design:bulk metal and plasticsSimple componentsFuel (heat source !) FlexibleReversibleIndependent scalable engine and storage capacity25 kW systems (SES), MW scale designs proposed by Infinia
4 Prototype 1: free-piston Gamma Displacer and power piston can independently be driven.44
6 Design Characterization Design SpecificationValueNominal Power Output2.500 kWHot Side Temperature180 oCCold Side Temperature30 oCDesign ParametersPressure30 barEngine Frequency20 HzRegenerator Hydraulic Diameter11umHeat Exchanger Hyd. Diameter (Air)144umRegenerator Wetted Area417.4 m2Heat Exchanger Wetted Area (Air)12.4 m2PerformanceNon-Regenerator Flow Loss108.6 WRegenerator Flow Loss143.2 WCompression Loss56.4 WHot Side Heat Exch Temp Drop2.81 oCCold Side Heat Exch Temp Drop3.30 oCRegenerator Effectiveness0.997Thermal-Mechanical Efficiency21.7%Fraction of Carnot65%
7 CHP Design Higher exit temperature (50 C) Lower electrical efficiency Higher system efficiencyDesign CharacteristicsValueNominal Power Output1.972 kWThermal-Mechanical Efficiency17.8%Fraction of Carnot62%Hot Side Temperature180 oCCold Side Temperature50 oC
8 Collector and Engine Efficiency Collector with concentrationG = 1000 W/m2 (PV standard)Schott ETC-16 collectorEngine: 2/3 of Carnot eff.No Concentration88
9 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
10 Concentrator for Evacuated Tube Absorber Conc. Ration C <= 1/sin(theta)Can accept full sky radiation +/- 90 degrees on tubular absorber with aperture of Pi*DReduce # tubes by PiInsolation increased by ~Pi, results in substantially increased thermal efficiency and/or increased temperature
11 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 ciruclated 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.
12 Evacuated Tube Absorber The heat pipes used in AP solar collectors have a boiling point of only 30oC (86oF). So when the heat pipe is heated above 30oC (86oF) the water vaporizes. Each heat pipe is tested for heat transfer performance up to 250oC (482oF) temperatures.
13 Thermal Storage Example Sealed, insulated water tankCycle through 50 C temperature swingThermal energy density of about 60 W-hr/kg, 60 W- hr/literConsidering Carnot (~30%) and non-idealities in conversion (50-70% eff), remain with10 W-hr/kgVery high cycle capabilityCost is for container & insulatorWater to perhaps 200 C; mineral oil to C
14 Ex.: Co-generation with thermal storage Combustion-to meetelectric demand (300 C ?)Electrical outputOn DemandThermal-Electric ConversionThermalReservoir(s)CThermal output ondemandOne tank system:cycle avg temp, orthermoclineTwo tank systemThermal-Electric conversion eff ~ >28% withhigh performance, longlife Stirling Converter
15 Costs and Scale Potential of Distributed CHP Thermal input to converter is perhaps 60-80% of combustion value without condensing heat exchanger, but perhaps >90% with condensing heat exchangerScale is substantial since 40,000 btu/hr thermal process in many homes translates to 13 kW thermal process, and to ~3 kWe generation at expected 25 % eff.:200M homes * 3kWe = 600 GWe
16 Costs and Scale Potential of Distributed CHP Hot Water System Cost Evaluation:$14 per 1000 cubic-feet/1 million BTU/gigajouleAt 25% efficiency this translates to a pure electric cost of 20 cents per kW-hourThis electric generation comes with a bonus of 10,000 BTU of thermal energy per kWe-hrThermal Storage:It take 35,000 BTU to heat a 60 gallon tank from 50° F to 120° FFor a reasonably sized, insulated water tank the loss due to conduction is 100 Btu/hr. Corresponds to a drop from 120° F to 115° F over 24 hours.
17 Economic Analysis of CHP Hot Water System For a Family of 4: gallons/day of hot water. This requires 35,000-60,000 BTU of thermal energy which comes at a cost of 47,000-80,000 BTU/day ($0.66-$1.12 per day) with an electric production of kWheIn contrast a traditional system would cost $1.54- $3.64 per day with $0.30 per kWhe-hr electric costThe corresponding savings per year would amount to ~$The computed value includes use as a dispatchable source to opportunistically match peak prices.
19 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
20 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 >.
21 Ex. 3: Waste heat recovery + thermal storage Waste heat streamC or higherThermal ReservoirElectric generationon demandHeat Engine ConverterDomestic Hot Water ?Huge opportunity in waste heat
25 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.
26 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)26
27 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 load9.32727
28 Free-Piston “Gamma” Engine (Infinia) Designed for > 600 C operation, deep space missions with radioisotope thermal sourceTwo moving parts – displacer and power piston, each supported by flexures, clearance sealsFully sealed enclosure, He working fluid, > 17 year lifeSunpower (Ohio) has designs with non-contacting gas bearings
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
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