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Photovoltaics for the Terawatt Challenge

Photovoltaics for the Terawatt Challenge. Christiana Honsberg Department of Electrical Computer and Energy Engineering Director, QESST ERC Arizona State University. Outline. Terawatt Challenge What is it? Photovoltaics for the TW challenges Importance of rapid growth

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Photovoltaics for the Terawatt Challenge

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  1. Photovoltaics for the Terawatt Challenge Christiana HonsbergDepartment of Electrical Computer and Energy Engineering Director, QESST ERCArizona State University

  2. Outline • Terawatt Challenge • What is it? • Photovoltaics for the TW challenges • Importance of rapid growth • Recent milestones in PV • But what about ….. • Myths of photovoltaics: land area; efficiency; energy payback time; materials availability; time to impact; duck curves, etc • Future prospects • Education ASU-UA-NAU Student Solar Conference 04/01/2014C. Honsberg 2

  3. Terawatt Challenge • Terawatt Challenge: Encapsulates the dichotomy surrounding energy– essential for improved quality of life, but also tied among the most serious global challenges. ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 3

  4. Terawatt Challenge • Why is compound annual growth rate important? ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 4

  5. Terawatt Challenge • In the nearly two decades since the TW challenge paper, renewables have reached multiple milestones • In US, renewable compound annual growth rate 4.8% from 2000-2012 (NREL data) NREL,2012 Renewable Energy Data Book ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 5

  6. Photovoltaic Milestones • Germany, Spain, Italy have yearly installed PV capacity > yearly increase in electricity demand. • In Germany, PV is 50% of summer peak electricity demand ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 6

  7. Learning Curves for Photovoltaics • PV learning curves show compound annual growth rate (CAGR) of ~30% over the last several decades • Extending the growth rates shows ability of PV (renewables more generally if these are included) to make a substantial impact on electricity generations ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 7

  8. Potential for PV in the US

  9. Photovoltaic Milestones • ASU – reached 50% of total electricity supplied by PV ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 9

  10. Arizona Context ASU-UA-NAU Student Solar Conference 04/01/2014C. Honsberg 10

  11. Photovoltaics “FAQ” • Energy payback time • Land use • Cost • What do you do at night for power? • Materials availability • For silicon, limitation is silver in grids, which cause a limitation at 2 TW • Availability subject to efficiency, thickness APS Tutorial Nanostructured Photovoltaics C. Honsberg 11

  12. Duck Curves • Power after sun goes down a concern for utilities. • Can mitigate by load management. ASU-UA-NAU Student Solar Conference 04/01/2014C. Honsberg 12

  13. PV for the Terawatt Challenge • PV technology must be high efficiency, efficient use of materials, scalable, reliable, and enable path for future improvements • High efficiency; overcome limits; thin ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 13

  14. Present State of PV: efficiencies

  15. Fraction of Efficiency Achieved APS Tutorial Nanostructured Photovoltaics C. Honsberg 15

  16. Types of PV Systems • Optical configuration of photovoltaic systems: One-sun or flat plate; concentrating systems; tracking APS Tutorial Nanostructured Photovoltaics C. Honsberg 16

  17. Scope of QESST ERC

  18. Multiple Junction (Tandem) Solar Cells Concentration or stacking multiple solar cells increases efficiency To reach >50% efficiency, need ideal bandgap 6-stack tandem, (assuming ~75% of detailed balance limit). Hard to get compatible materials with the right bandgaps. APS Tutorial Nanostructured Photovoltaics C.Honsberg 18

  19. # junctions in solar cell 1 sun h Max con. h 1 junction 30.8% 40.8% 2 junction 42.9% 55.7% 3 junction 49.3% 63.8%  junction 68.2% 86.8% What do efficiency calculations tell us? Approaches to high efficiency: • Concentrate sunlight. “One sun” = 1kW/m2, max concentration ~46,000. • No entropy penalty for concentrating sunlight, but etendue limits to acceptance angle and concentration. • Optically split solarspectrum (i.e. tandem) • No entropy penalty • Efficiency controlled by existence of materials • Beneficially circumventone of the assumptionsin thermodynamics APS Tutorial Nanostructured Photovoltaics C.Honsberg 19

  20. Tandem Solar Cells • Key issue for III-Vs: need precisely controlled band gaps which are lattice matched • “Missing” low band gap material • Approaches: • Lattice matched; Ge-GaAs-GaInP • Metamorphic;Ge-GaInAs-GaInP • Metamorphic; GaInAs-GaAs-GaInP • Band gaps for 4-tandem arepoorly lattice matched;5 band gapsand six band-gaps are better matched APS Tutorial Nanostructured Photovoltaics C.Honsberg20

  21. Ge-based tandem solar cells • Metamorphic solar cell reached 40.7% at ~200X. APS Tutorial Nanostructured Photovoltaics C.Honsberg21

  22. Carrier-Selective Contacts Carrier-selective contacts enable ideal VOC

  23. CSC Implementation: a-Si/c-Si solar cell Demonstrated 746 mV on 50 µm wafers

  24. InAs QDs on GaAsSb barriers • InAs QDs achieved on GaAsSb material • Increasing Sb composition decreases QD size and increases QD density InAs QDs on GaAs (5 ML) / GaAs1-xSbx (5nm) buffer layers with x = 23%, with density 2.6 x 106 cm-2 InAs QDs on GaAs APS Tutorial Nanostructured Photovoltaics C.Honsberg24

  25. GaAs (50nm) GaAsSb (20nm) δ-doping InAs QDs GaAsSb (20nm) S.I. GaAs substrate 8nm (b) (c) Experimental GaAsSb/InAs QD material • Doping of QD layers to control occupancy of the QD. GaAsSb/GaAs interface

  26. Tandem Solar Cells • Monolithic III-V tandem solar cells; Series connected; three junctions • High efficiency used in high concentration, two-axis tracking systems • High concentration meanssmall area (and lower cost) needed for solarcells • Trade balance of systemsand solar cell cost. APS Tutorial Nanostructured Photovoltaics C.Honsberg 26

  27. Experimental GaAsSb/InAs QD material

  28. Path for Continual Improvement • Ideal solar cell consists of a light-trapped, thin solar cell • Nanostructured surfaces allow light trapping and advanced concepts (e.g., multiple exciton devices) ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 28

  29. Student Led Pilot Line • Silicon pilot line capabilities for interaction among students, industry and researchers • 10 Fulton Undergraduate Research Initiative Projects • 2 honors thesis • 4 capstone projects

  30. Questions? ASU-UA-NAU Student Solar Conference 04/01/2014 C. Honsberg 30

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