Roger Angel. Steward Observatory. University of Arizona

Transcription

1 Physics/Solar talk Jan Telescope technology to harvest solar energy Roger Angel Steward Observatory Department of Astronomy University of Arizona

2 Wind, solar and hydro and geo - could provide all California s electricity 24 hours/day with no CO 2 emission (Scientific American October 09) similarly the nation and the world 40 GW

3 What s wrong with this picture? Solar and wind not cost competitive with fossil fuel generation: Conversion technologies too expensive both thermal and photovoltaic conversion at utility scale are around $5/watt installed

4 Nellis AFB 15 MW PV 18% efficient, 1-axis tracking

5 Thermal conversion: 20 year old 300 MW SEGS plant in California. trough reflectors make 370C, 14% overall efficiency. mirrors rotate about N-S axis to track sun

6 Goal is $1/watt installed Gives adequate annual return on each $1 invested: 7 x 365 watt hours = 2.5 $0.05/kWh 05/kWh get return of $0.125 or 12.5% of investment per year, for 20 year lifetime At this return, government subsidies not needed

7 composite approach for low cost Combine mirror collection with high efficiency concentrator PV cells Use triple junction PV cells 40% conversion efficiency Cells cost $0.16/watt when used at 1000x concentration Problem is shifted to providing concentrated sunlight and rest of system at $0.84/watt For 300W/m 2 yield, this translates to $250/m 2 for everything, say $100/m 2 for the opto- mechanical collector system

8 Advantage of triple junction PV cells QE of Spectrolab triple junction PV cell Stacked junctions tailored to generate the same current under sunlight. Higher voltage from bluer photons - E=h Current flows from back electrode up through cells to transparent front electrode,

9 Typical concentrator PV installation Rigid array of 1 cm single cells fed by individual 20 cm catadioptric concentrators (500 x) Passive conduction cooling Thousands of square miles of Celestrons?

10 Packaged this way, optomechanics cost for CPV cells still >> $1/watt 1 cm square cells fed individually by identical small optical concentrators Ensures same current for series connection avoids Christmas tree light failure Modules act like silicon panels, regular sunlight in, heat out the back by aluminum conduction But high manufacturing and packaging cost, still $5/watt or more

11 LBT, 100 m2, 0.01 arcsec images $1 million/m2

12 Current University of Arizona project new architecture for CPV with 3m x 3m reflectors

13 Use old astronomer trick to ensure uniform illumination of concentrated light paraboloid with spherical ball lens at focus Energy distribution ib ti on concentric receiving surface insensitive to pointing error Provides for lower-cost, flimsier tracker (a) 9 (b)

14 Image of 3 m square reflector feeds many cells, all with same flux

15 2.5 kw receiver

16 Experimental reflector 27% end to end efficiency measured with receiver at focus

17 2.5 m made for Raytheon

18 Results with UA 3 m behind Bear Down Moon

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20 Cooling water temperature Test results with Spectrolab 15 mm cell at 1000x concentration behind ball 56 watts from 2.25 cm 2 cell Cell very well cooled, - runs only 15C hotter than liquid coolant Very tolerant of mispointing, 10% loss for ¾ degree off-axis

21 Insensitive to tracking errors

22 Where are we with turning this into reality?

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28 Solar enough to supply the US

29 1 GW farm at $1/watt 2x6 trackers, same 3.1 m square reflectors

30 Glass in 1 year from 1 float glass factory yields energy of a 1.5 GW, 24 hour power station 700 tons/day = 1 m 2 /sec at 4 mm thick 30 square km of glass from one factory in one year At a grid yield of 200W peak/m 2, yield is 6 GW peak power equivalent to 1.5 GW 24 hour/day 100 float glass factories (doubling present count) would satisfy world s new energy needs with no CO 2

31 Component cost breakdown Estimated component costs, at GW level Components Mass kg/kw Cost Cost $/kg /watt Steel struts, weldments $ 0.10 Silvered glass dishes $ Triple-junction cells ,000 $ 0.16 Silica ball lens 1 40 $ 0.04 Remainder of receiver 1 90 $ 0.09 Aluminum heat exchanger $ 0.02 Copper wiring $ 0.03 Pumps, drives 1 50 $ 0.05 Inverters, controls - - $ Total 160 $ 0.68

32 Cost sanity check Pickup weighs 2.5 tons, costs $25,000 $10/kg retail, delivered to dealer 30 kw generator weighs 5 tons. At $10/kg this is $1.67/watt installed in farm In practice, generators are much simpler and should cost $6/kg when mass produced and installed at pickup truck volume

33 Startup formed last year Holds exclusive license to UA CPV technology Website rehnu.com 2 MW/year production starting 2012 First commercial 30 kw prototype in TEP test yard? First 2 MW plant for TEP?

34 Swing circle of 2x6 generator at proposed location Control sed Telephone pole 2x6 swing area

35 Conclusions $1/watt installed reachable at GW level profit motive will then ensure large scale adoption GW farms worldwide replacing coal give 10% reduction in global CO 2 emissions REhnu LLC started to commercialize the UA technology