Concentrating PV at $1/watt. Field tests of a disruptive approach to reduce cost. Roger Angel Steward Observatory University of Arizona

Transcription

1 Concentrating PV at $1/watt. Field tests of a disruptive approach to reduce cost Roger Angel Steward Observatory University of Arizona

2 outline 1. Heritage - making astronomical telescopes at the University of Arizona 2. Solar as a renewable electricity source, cost-competitive with fossil fuels 3. Comparison of solar to electric conversion strategies: flat photovoltaic (PV) Concentrating thermal (CSP) Concentrating photovoltaic (CPV) 4. Arizona s disruptive concept for large scale, low-cost CPV 5. Field demonstration 6. Next steps and commercialization

3 1. Heritage making astronomical telescopes at the University of Arizona

4 Spin-casting liquid glass to make an 8.4 m diameter glass telescope mirror at the University of Arizona Mirror Lab

5 Polishing an 8.4 m diameter mirror at the Lab Inspection during stressed-lap polishing. Honeycomb cells visible beneath the surface.

6 Two of the 8.4m diameter mirrors on a tracking mount make the world s largest single astronomical telescope

7 The future: 25 m paraboloidal reflector made from seven 8.4 m segments for the Giant Magellan Telescope 3 m square paraboloidal reflectors to concentrate sunlight on photovoltaic cells

8 RRep Gabrielle Giffords with UA President Robert Shelton at experimental 3-m solar dish made at the Mirror Lab from back-silvered glass segments

9 2. Solar as a renewable electricity source, cost competitive with fossil fuels

10 Context for work Eliminate carbon dioxide emission as a by product of electricity generation Reduce dependence on foreign fuel Generate electricity from sustainable sources, solar and wind Goal Electricity delivered at cost parity with fossil fuel Method suitable for the required very large scale, 100,000 km 2 worldwide

11 Basic challenges in meeting cost parity goal Conversion cost for wind and solar Need ~$1/watt installed cost Storage to deal with intermittent sources Combine direct solar (day) with wind and stored solar heat (night) Pumped hydro storage for time shift Transmission up to 2000 miles needed from best solar and wind resources to population centers

12 Storage and transmission Storage 50 GW of pumped hydro storage is already in US and Europe, and making a profit Note that while hydro requires large river flow, pumped hydro does not. Its volume can be greatly expanded with relatively little environmental impact Transmission US example, Pacific Intertie 1000 miles, ± 0.5 MV miles with 10% loss viable (± 1MW, 14 grams of aluminum per watt) Conclusion: storage and transmission costs should not preclude sustainable transcontinental grid at parity cost. Conversion of sunlight to electricity is the area where cost reduction is most critical

13 Sun and wind - sources and needs Both have similarly low power density Solar flux = 1 kw/m 2 Wind kinetic energy at 10 m/sec = 0.5 kw/m 2 And similar intermittency, ~ 30% duty cycle Allowing for 30% intermittency and 30% conversion efficiency, replacing today s 10 TW of 24 hr power from fossil fuel will require harvesting over ~100,000 km 2

14 Wind Wind generation currently provides 30 times more power than solar, because of lower cost. Why does it cost less? Blade concentrates wind energy over large area (~10,000m 2 ) for conversion by dynamo Advantage: blade area << capture area Reduced cost Stow in extreme wind eases survival Steel mass is low, 150 kg/kw (land), 250 kg/kw (sea)

15 Solar comparison Harvest requires sunlight capture with PV panel or reflector extending over full area Mechanical support must be robust enough to survive large mechanical load on full area under extreme wind For current tracking systems, steel mass can exceed 300 kg/kw. Mass drives cost

16 more than enough desert sunshine to power the world NREL map of solar resource at direct incidence

17 3. Comparison of solar to electric conversion strategies: Photovoltaic flat panel - PV fixed or single axis tracking Concentration with thermal conversion - CSP single axis (trough) and dual axis (dish) with/without thermal storage Concentration with photovoltaics - CPV single axis (trough, low concentration) dual axis (dish, high concentration)

18 Solar dish powers a printing press in late 1880s

19 PV and thermal are complementary Thermal storage has unique capability to handle late afternoon and evening load CPV likely to be cheaper during the day Solution may be separately optimized farms whose entire harvest goes to either daytime CPV production or to thermal storage CSP

20 Different challenges for PV and CPV to reach $1/watt PV - Direct illumination of large areas of semiconductor Challenge is to manufacture huge areas of semiconductor of reasonable efficiency CPV - Optical concentration onto much smaller semiconductor areas Semiconductor cost is 10x less Challenge is to reduce the optomechanics cost

21 Triple junction PV cells Cells in 3 layers on germanium substrate Blue photons absorbed in upper layer give higher voltage Highest conversion efficiency of any method Best triple junction cells now give 42.5%, increasing 1%/year Least expensive 1000x concentration Cost $0.15/watt Cells already in commercial production

22 CPV and CSP comparison for daytime generation Both use optical concentration to address basic problem - sunlight energy is dilute - expensive to convert Both require tracking CSP needs large engines for efficient conversion - premium on bringing large power to a single focus, from a collecting area of 10 m 2 to 10,000 m 2 Leads to higher costs/m 2 for dish collector or heliostat fields with reduced collection efficiency CPV allows huge flexibility in concentrating geometry and higher efficiency Collecting area being explored in current commercial implementations varies from 1 mm to 10 m diameter i.e m m 2 in area and energy collected

23 CPV has enormous promise Most energy per unit power 2300 kwh/kw/year from 2-d tracking in SW Longest hours of direct production - throughout the day Least environmental impact small area (4 acres/mw), no blading of land, no water consumed

24 But CPV volume currently < 1% of PV Cost for balance of system (BOS) >10x cost of cells (optical, mechanical, thermal, tracking) System architecture development neglected R&D has strongly favored cell development, not complete installed system

25 4. Arizona s disruptive concept for large scale, low-cost CPV Disruptive approach that does not exist in today s energy market Complete rethinking of opto-mechanical system for lowest cost concentration in large scale mass production Uses fact that in HCPV the collectors are inherently very much larger than the small cell converters System structured to separate large and small, for mass production by proven, sizeappropriate, high-volume methods

26 Solar reflector heritage from CSP Large back-silvered primary trough reflectors validated by 20 years of CSP experience High specular reflectivity maintained over 20 years Damage rate 0.3%/year (untempered) 0.01%/year (tempered) Float glass inexpensive, high volume cost projected to be $0.05/W

27 UA design uses back-silvered paraboloidal glass reflectors in spaceframe module Aimed at lowest mass and cost/m 2 to survive in 80 mph wind 2-axis tracker has eight 3 m dishes each focusing 9 kw sunlight Steel mass including foundation is 100 kg per kw of output

28 Early tests of dish manufacture - segmented 3 m reflector prototype

29 15 sec exposure at focus melts a quarter-sized hole in ¼ thick steel don t try this at home!

30 Most CPV systems do not use large dish concentration Typical systems use many 25 cm concentrator optics with individual 1 cm small cells Ensures equal power per cell, as needed for efficient series chain Concentrator/cell units are packaged into modules with aluminum heat sinks behind each cell for passive cooling Disadvantage: Modules emulate flat panels, but are more complex and must be tracked

31 UA solution allows use of large dish collectors Unique receiver optics take in strongly focused sunlight energy and apportion it equally to cells

32 the ball lens stabilizes against tracking error

33 Summary Arizona separation architecture Concentration by 3 m square glass dishes, massproduced at float glass $0.05/W Cells are packaged in compact receiver at 9kW (sunlight) focus Unique receiver optics ensure uniform high concentration illumination (1000x) over 36 cells Active cooling, using automobile and CPU technology, gives low - 1% - parasitic loss Module has multiple reflectors and receivers in balanced lightweight spaceframe, completely integrated as the elevation structure of alt-az tracker

34 5. Field demonstration

35 Current state of construction of 20 kw prototype at the University of Arizona. The full scale mechanical tracker weighs 2 tons including foundation, and tracks 99% of the time within 0.1 accuracy

36 Prototype with ball-lens receiver and radiator at the focus of a partial (4-segment) reflector The ball lens images the segments onto a partially populated receiver array with 4 pairs of optical funnels and cells

37 DOE Undersecretary Zoi inspects one of the 4 reflector segments

38 Eight triple junction PV cells used at the 1000x concentration

39 Eight cells and funnels mounted on a cooled, faceted cup (ball lens removed)

40 On-sun data from the 8-cell receiver I-V curve showing a maximum power point of 511 W The 8 cells are connected in series in the receiver

41 Off-axis response measured for the 8-cell receiver is very broad, given the 1200x geometric concentration

42 Consistent power > 500W over 100 hours of sun-tracking

43 Tracking advantage: > 80% of max power for 8 hours, 7 weeks before the winter solstice. More kwh per kw

44 Summary of current status Dish shaping technology proven in back-silvered segments Prototype receiver with eight 15 mm triple junction cells at 1200x (geometric). First test 9/2010 with partial segmented reflector gave 500+ watts (25A, 20V) Cell temperature 20C above ambient 25% end-to-end sun to DC efficiency (with 2 year old cells). 30% efficiency projected for current cells and better coated optics. Spaceframe tracker for 8 reflectors (20 kw) shows excellent pointing stability (99% < 0.1 ) very low mass. Total steel mass including foundation measured at 2 tons, i.e. 100 kg/kw.

45 6. Next steps and commercialization joint development by the University of Arizona and REhnu LLC next 12 months June implement and test on-sun full 3 m dish with full 36 cell 2.5 kw receiver Jan 2012 populate existing tracker with 8 dishes and receivers to demonstrate full module operating at 20 kw

46 3.1 m square mold (right) to shape the flat float glass sheets (back) in the furnace (left)

47 Initial fabrication test at the Mirror Lab of a 3.1 m square glass dish, made from a single sheet of glass

48 Evolutionary path to 1 dish/minute Technology evolution from for 1 GW/year Dish construction: segmented monolith Furnace heat transfer: convective radiative Silvering: chemical sputtering shaping and coating: batch processing in-line Next year build an in-line sputter coating plant and a shaping furnace, both rated for 2 8 MW/year Later our deep dish shaping technology will be combined with existing high volume trough reflector technology

49 20 kw modules will be assembled on-site from separate shipments of dishes, steel struts, receivers etc. and transported out for mechanized installation Assembly facility for generator units

50 Bottom up cost estimate for production at GW scale: $0.80/watt installed, leaving $0.20 margin Steel components $0.10 Margin $0.20 Reflectors $0.04 Cells $0.16 Assembly & installation $0.12 Silica balls $0.04 Inverter & controls $0.15 Cooling & wiring $0.10 Remaining receiver $0.09

51 If the 20 kw, 3200 kg module units were built at the same cost per kg as a pickup truck ($10/kg), the cost of power would be $1.60/watt. Spaceframe modules are structurally much simpler than pickups, so $1/watt is credible.

52 Startup formed in 2009 Holds exclusive license to UA CPV technology Will build ten 20 kw modules next year followed by 100 module (2 MW) farm in 2013 Website: rehnu.com

53 Large commercial impact Commercialization path Potential for lower energy cost in daytime at utility scale than CSP and flat PV panels REhnu LLC startup formed specifically to develop the technology Exclusive license for commercialization of University of Arizona technology REhnu s goal >1 <$1/watt installed by 2018 Spaceframe and receiver risks mostly retired Key R&D to ensure rapid investment and commercialization Demonstrate clear technology and manufacturing path to GW scale Key challenge Quickly prove reliability to attract major investment