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SOLAR THERMAL AND COMBINED HEAT AND POWER Achintya Madduri, Mike He 1.

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Presentation on theme: "SOLAR THERMAL AND COMBINED HEAT AND POWER Achintya Madduri, Mike He 1."— Presentation transcript:

1 SOLAR THERMAL AND COMBINED HEAT AND POWER Achintya Madduri, Mike He 1

2 Combined Opportunities:  Low-cost media – water, mineral oil, molten salts  Heat engine (eg. Stirling) provides high efficiency,  eg. better than ~ 2/3 of reversible limit  Stirling converter enables excellent durability, cycle- ability (contrast with IC engine) Ex.1: Solar Thermal Electric System 2

3 Stirling Engine  Can achieve large fraction (70%) of Carnot efficiency  Low cost possible for low temp design:  bulk metal and plastics  Simple components  Fuel (heat source !) Flexible  Reversible  Independent scalable engine and storage capacity  25 kW systems (SES), MW scale designs proposed by Infinia 3

4 Prototype 1: free-piston Gamma 4

5 Prototype 2 – Multi-Phase “Alpha” 5

6 Design Characterization 6 Design SpecificationValue Nominal Power Output2.500 kW Hot Side Temperature180 o C Cold Side Temperature30 o C Design Parameters Pressure30 bar Engine Frequency20 Hz Regenerator Hydraulic Diameter11um Heat Exchanger Hyd. Diameter (Air)144um Regenerator Wetted Area417.4 m 2 Heat Exchanger Wetted Area (Air)12.4 m 2 Performance Non-Regenerator Flow Loss108.6 W Regenerator Flow Loss143.2 W Compression Loss56.4 W Hot Side Heat Exch Temp Drop2.81 o C Cold Side Heat Exch Temp Drop3.30 o C Regenerator Effectiveness0.997 Thermal-Mechanical Efficiency21.7% Fraction of Carnot65%

7 CHP Design  Higher exit temperature (50 C)  Lower electrical efficiency  Higher system efficiency Design CharacteristicsValue Nominal Power Output1.972 kW Thermal-Mechanical Efficiency17.8% Fraction of Carnot62% Hot Side Temperature180 o C Cold Side Temperature50 o C 7

8 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 8

9 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 9

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*D  Reduce # tubes by Pi  Insolation increased by ~Pi, results in substantially increased thermal efficiency and/or increased temperature 10

11 Evacuated Tube Absorber 11

12 Evacuated Tube Absorber 12

13 Thermal Storage Example  Sealed, insulated water tank  Cycle through 50 C temperature swing  Thermal energy density of about 60 W-hr/kg, 60 W- hr/liter  Considering Carnot (~30%) and non-idealities in conversion (50-70% eff), remain with 10 W-hr/kg  Very high cycle capability  Cost is for container & insulator  Water to perhaps 200 C; mineral oil to C 13

14 Ex.: Co-generation with thermal storage Combustion-to meet electric demand (300 C ?) Thermal-Electric Conversion Thermal Reservoir(s) C Electrical output On Demand Thermal output on demand One tank system: cycle avg temp, or thermocline Two tank system Thermal-Electric conversion eff ~ >28% with high performance, longlife Stirling Converter 14

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 exchanger  Scale 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 15

16 Costs and Scale Potential of Distributed CHP Hot Water System  Cost Evaluation:  $14 per 1000 cubic-feet/1 million BTU/gigajoule  At 25% efficiency this translates to a pure electric cost of 20 cents per kW-hour  This electric generation comes with a bonus of 10,000 BTU of thermal energy per kWe-hr  Thermal Storage:  It take 35,000 BTU to heat a 60 gallon tank from 50° F to 120° F  For 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. 16

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 kWh e  In contrast a traditional system would cost $1.54- $3.64 per day with $0.30 per kWh e -hr electric cost  The corresponding savings per year would amount to ~$  The computed value includes use as a dispatchable source to opportunistically match peak prices. 17

18 18

19 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

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 20

21 Thermal Reservoir Waste heat stream 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 21

22 Thermal System Diagram 22

23 Solar Dish: 2-axis track, focus directly on receiver (engine heat exchanger) Photo courtesy of Stirling Energy Systems. 23

24 Stirling Cycle Overview

25 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

26 DisplacerPower piston Temperatures: T h =175 o C, T k =25 o C 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 model254 W (thermal input) - 24 W (mechanical output) 26

27 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

28 Free-Piston “Gamma” Engine (Infinia) Designed for > 600 C operation, deep space missions with radioisotope thermal source Two moving parts – displacer and power piston, each supported by flexures, clearance seals Fully sealed enclosure, He working fluid, > 17 year life Sunpower (Ohio) has designs with non-contacting gas bearings 28

29 Collector Cost – no concentration  Cost per tube [1] < $3  Input aperture per tube 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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