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Climate Change and the Role of PV in the Energy Mix

Climate Change and the Role of PV in the Energy Mix. Eicke R. Weber Fraunhofer-Institute for Solar Energy Systems ISE, and Faculty of Mathematics and Physics, Faculty of Applied Sciences, Albert Ludwig University, Freiburg, Germany. Why do we need renewable energy:.

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Climate Change and the Role of PV in the Energy Mix

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  1. Climate Change and the Role of PV in the Energy Mix Eicke R. Weber Fraunhofer-Institute for Solar Energy Systems ISE, and Faculty of Mathematics and Physics, Faculty of Applied Sciences, Albert Ludwig University, Freiburg, Germany

  2. Why do we need renewable energy: • Tony Blair on the threat of global warming (climate change): • ‘ The threat, he said in a speech, poses a “challenge so far-reaching in its impact and irreversible in its destructive power that it alters radically human existence.”’ (NYT, Sept. 15, 2004) Is such a drastic statement justified?

  3. Strong correlation between [CO2 ] and average T in the last 500 kys Stable T in the last 10,000 years! 280 260 240 CO2 (ppmv) 2 220 0 200 -2 Temperature (°C) -4 -6 -8 -100 -400 -350 -300 -250 -200 -150 -50 0 Time before present [kys] Source: J. Petit et al., 1999, Nature 399, 429-436

  4. Temperature fluctuations in the last 100kys Time before present [kys] For reasons unknown, the last ca. 10,000 ys were extraordinary stable: “Holocene” Source: A. Ganopolski et al., 2001, Nature 409, 153-158

  5. Atmospheric CO2-Record, Mauna Lao C.D. Keeling und T.P. Whorf Carbon Dioxide Research Group, Scripps Institute, University of California, http://cdiac.esd.ornl.gov/trends/co2/sio-mlo.htm

  6. Atmospheric CO2-Record, South Pole P. Steele, P.B. Krummel und R.L. Langenfelds, CSIRO, Atmospheric Research, Aspendale, Victoria, Australia, http://cdiac.esd.ornl.gov/trends/co2/sio-mlo.htm

  7. Concentration of greenhouse gases in the last 150 years Source: T.S. Ledley et al., EOS 80, 453 (1999)

  8. Temperature variations in the last 1000 years Source: T.S. Ledley et al., EOS 80, 453 (1999)

  9. [CO2] 2004: 380 ppm, far above the highest peaks in 500 kys! When will the temperature follow the [CO2]? How high will it climb? Will we terminate the Holocene irreversibly? 280 260 240 CO2 (ppmv) 2 220 200 0 Temperature (°C) -2 -4 -6 -8 -400 -350 -300 -250 -200 -150 -100 -50 0 Time before present [kys]

  10. Allowed CO2 emissions for various scenarios: Data from Vostok Ice Core M. I. Hoffert et. al., Nature 395, 881 (1998)

  11. Globale climate change: the end of the holocene? Human influence on the composition of the atmosphere is well established. There has been a strong correlation between CO2-content of the atmosphere and the earth‘s temperature within the last > 500 kyrs. The CO2-concentration today is more than 380ppm, far above the highest value in the last 500 kyrs (ca. 290ppm); an increase to 500pm and more can be expected. Dramatic temperature increases and climate instabilities can bring about the END OF THE HOLOCENE by human influence!

  12. CO2-reduction in the energy sector Energy efficiency - in production, traffic, building sector Nuclear energy - non-renewable feedstock, final storage not clear, dangers during operation: no good solution for the global energy problem Clean coal technologies - requires carbon sequestration, unproven technology, energy inefficient, may pose danger of accidental release Wind - fluctuating production, limited number of suitable sites, Hydro - can be switched on instantaneously, suitable for storage, Good sites limited, production should be maximized Biofuels - interesting as liquid fuel for traffic, production energy intensive Solar energie (Photovoltaic, Solarthermal) - unlimited energy source PV: continuous price reduction through savings of scale

  13. EJ/a TW 50 1400 Geothermal 40 Other Renewables Solarthermal (Heat only) 1000 30 Solar Electricity (PV und solarthermal) Wind 20 600 Biomass (modern) Biomass (traditional) 10 Hydropower 200 Nuclear Energy 0 Gas 2020 2100 2000 2040 Jahr Coal Oil Exemplary Path, global primary energy consumption Quelle: Wissenschaftlicher Beirat der Bundesregierung Globale Umweltveränderungen, 2003, www.wbgu.de

  14. Solar energy –PV and Solarthermal Wind Water, Geothermal, Biogas Regenerative Energy Mix Earth's ultimate recoverable resource of oil, estimated at 3 trillion barrels, contains 1.7 × 1022 joules of energy, which the Sun supplies to Earth in 1.5 days. The amount of energy humans use annually, about 4.6 × 1020 joules, is delivered to Earth by the Sun in one hour. The enormous power that the Sun continuously delivers to Earth, 1.2 × 105 terawatts, dwarfs every other energy source, renewable or nonrenewable G.W. Crabtree and N.S. Lewis, Physics Today, March 2007. 2020: Our need is estimated to be 20 TW!

  15. Solar energy –PV and Solarthermal Wind Water, Geothermal, Biogas Regenerative Energy Mix G.W. Crabtree and N.S. Lewis, Physics Today, March 2007: Earth's ultimate recoverable resource of oil, estimated at 3 trillion barrels, contains 1.7 × 1022 joules of energy, which the Sun supplies to Earth in 1.5 days. The amount of energy humans use annually, about 4.6 × 1020 joules, is delivered to Earth by the Sun in one hour. The enormous power that the Sun continuously delivers to Earth, 1.2 × 105 terawatts, dwarfs every other energy source, renewable or nonrenewable. 2020: Our need is estimated to be 20 TW!

  16. Required Area for PV Area required to produce 20 TW through PV: 6 sites, 250 x 250 km2 each producing 3.3 TW PV can easily supply a substantial part of the world energy needs

  17. Yearly installations of PV moduls from crystalline Si Actual Shipments Projection (2003) 2006: ca. 1.9 GWp Far above the most optimistic forecast! 2003: 600 MWp Source: 2000-2003 Strategies Unlimited, EPIA “solar generation” 2006

  18. 1.5 GWp Mono-Si Multi-Si - 2005 Thin Film Ribbon-Si - 2000 - 1995 - 1990 - 1985 - 1980 Development of the global PV-market 1990: 1/3 thin-film, c-Si, mc-Si 2006: 1.9 Gwp, >90% c-Si & mc-Si! Graph: G. Willeke, 2006

  19. Two technologies currently dominate the PV market: • Single Crystals: • highest efficiency • slow process • high costs • Poly (multi) crystalline: • low cost • fast process • lower efficiency Interesting further approaches: ribbon, sheet material, but: savings of scale? Sketches courtesy of W. Koch

  20. Plasma-textured surface: Low reflection and good „light trapping“ High-efficiency ISE solar cell structure for mc silicon Laser-fired contacts: Low contact resistance and high voltage Thermal oxide: Surface passivation and high internal reflectivity Wafer thickness: 99 µm Efficiency: 20.3% (1 cm2) world record for mc-Si!

  21. Efficiency 20,2% Wafer thickness 42 µm High-efficient ultra-thin solar cell

  22. anti reflection coating n Si emitter diffused p Si epi (base) 20 µm p+ Si epi (BSF) 2 µm low resistivity wafer Crystalline Si thin film solar cells Epitaxial wafer equivalent

  23. 102 103 10-3 10-2 10-4 1 2010 2020 Price learn curve of crystalline Si PV-modules [€/Wp] 100 hcell [%] = 10 15 18 20 22% 1980 1990 2000 10 (25%) 2004 (30%) 10-1 10 1 d [µm] = 400 300 200 100 50 Installed Peak Power (cumulative) [GWp] Graph: G. Willeke, ISE

  24. Comparison PV-production and consumption (load)

  25. Comparison PV-production and spot market price, European Energy Exchange (EEX) Highest price around noon, corresponds to highest feed-in of PV-power In CA: PV costs ca. $ 0.25/kwh, PGE Time-of-use Rate: $ 0.32/kWh (1-7pm)

  26. Competitiveness of PV in Germany On July 28, 2006, the electricity cost on the spot market climbed to €0.54/kwhr, further increase was limited by the availability of PV power […]

  27. Source: Wacker 2nd SoG-Si workshop 2005

  28. Possible solutions of the Si feedstock shortage: • Increased production of semiconductor-grade Si: for 2010, ca. 40 kt/a expected; • Thinner cells (but: limits cell size!); • Thin-film c-Si cells on various substrates • (of special interest: metall. grade mc-Si!); • Thin film cells, such as a-Si, CIS, CIGS, CdTe (but: limited efficiency, >10% difficult!) • Purified metallurgical-grade Si (‚dirty Si‘)

  29. Impact of Ni, Fe, and Cu on lifetime in p-Si Better Solar Cells • Electrical properties are very sensitive to small amounts of impurities. Worse Solar Cells

  30. Some PV cell materials were found by NAA analysis to have extraordinary large T-Metals concentrations • If such a high concentration of metals were all electrically active, the efficiencies of multicrystalline solar cells would be far below 10%! • As such material can achieve diffusion lengths between 20 and >250 microns, the chemical state and spatial distribution of transition metals determines their electrical activity, rather than the metal concentration!

  31. Advanced Light Source, Lawrence Berkeley Nat. Lab. FeSi2 distribution along grain boundary in multicrystalline silicon sheet material Multicrystalline Silicon Solar Cell Applications of synchrotron radiation for studies of metal impurities in silicon

  32. µ-XAS • (X-ray absorption microspectroscopy): • Chemical state of metal-rich nanoclusters. • µ-XRF • (X-ray fluorescence microscopy): • Distribution, elemental composition, size, morphology of metal-rich nanoclusters. mm • XBIC • (X-ray beam induced current): • Maps underperforming regions, • analogous to LBIC. • SR-XBIC • (Spectrally-resolved XBIC): • Quantifies impact of metals on minority • carrier diffusion length, • analogous to SR-LBIC. mm Synchrotron x-ray techniques for the study of metals in mc-Si WHAT DOES THE SYNCHROTRON:

  33. Distribution of metal species depends on metal, process history GB T. Buonassisi, A.A. Istratov et al.,Prog. Photovolt.: Res. Appl., 2006

  34. Interstitial Substitutional Metals, complexes Metal Silicide Nanoprecipitates Inclusions (Foreign Particles) The concept of metal defect engineering in solar cells Generally, a high density of interstitial metals or metal–silicide nanoprecipitates affects the minority carrier diffusion length stronger than a low density of large metal precipitates / inclusions T.Buonassisi, A.A.Istratov, M.A.Marcus, B.Lai, Z.Cai, S.M.Heald, E.R.Weber, Nature Mat. 4, 676 (2005).

  35. Goal of defect engineering of metal impurities Improvement through change in the state/distribution of metals Interstitial Substitutional Metals, complexes • Gettering improves material by removing metals from the device area. • Defect engineering improves material by converting metals into their least recombination active state, while keeping the metals in the device area Inclusions (Foreign Particles) Metal Silicide Nanoprecipitates

  36. Properly chosen annealing sequence decreases spatial density of metal clusters and improves the minority carrier diffusion length Quenched: LD = 7-8 µm Quenched&Re-annealed: LD = 18-21 µm Mc-Si intentionally contaminated at 1200oC, either quenched in silicone oil, or quenched and then reannealed again at 655oC, or slowly cooled in the furnace. Slow-cooled: LD = 19-35 µm T.Buonassisi, A.A.Istratov, M.A.Marcus, B.Lai, Z.Cai, S.M.Heald, E.R.Weber, Nature Materials, 4, 676, (2005)

  37. metal clusters in ‘dirty Si’: multiple metal species! Correlation of EXAFS of the precipitates in the slow cooled mc-FZ-silicon and different reference materials a good match for Ni-EXAFS and NiSi2 poor match for Fe- EXAFS and FeSi2 very poor match for Cu- EXAFS and Cu3Si The investigated metal clusters are not formed through co-precipitation of NiSi2, FeSi2 and Cu3Si. M.Heuer, T.Buonassisi, et al., Phys. Rev. B 73, 235204 (2006)

  38. Modeling results: The refinements achieved good fits for every measured spectrum ending up in R-values between 2 and 5%. -NiSi2 structure  Fe on Ni-site (4a)  Cu on Si-site (8c) M.Heuer, T.Buonassisi, et al., Phys. Rev. B 73, 235204 (2006)

  39. Averaged alpha-NiSi2- structure with mixed site occupancies M.Heuer, T.Buonassisi, et al., 2006

  40. Maximum efficiency of semiconductor solar cells with one pn-junction • W. Shockley,H.-J. Queisser (1961) • Theoretical limit 33% • J. Zhao, A. Wang,M.A. Green (1999) • Best lab value (c-Si): 24,7% 1600 1400 Unused energy of 2 High-energy photons 1200 Utilized energy 1000 Power Density [W/m µm] 800 600 Low-enegy photons cannot create carriers 400 200 0 500 1000 1500 2000 2500 Wave length [nm]

  41. Efficiencies beyond the Shockley-Queisser limit • Maximum efficiencies • (theoretical, without optical concentration): • 2-jct. cells: 45.3% • 3-jct. cells: 51.2% • 4-jct. cells: 54.9% • ...

  42. High-efficiency ISE triple-junction solar cells Ga0.65In0.35P tunnel diode Ga0.83In0.17As tunnel diode Ge substrate

  43. Triple-junction solar cell for high optical concentration, h > 35% GaInP/GaInAs/Ge solar cell with h = 35.2 %at C = 500

  44. High-concentration PV tracker systems Solar Systems (AUS) Amonix (US) Concentrix Solar (D)

  45. ZnO:Al i- ZnO CdS Cu(In,Ga)Se 2 Mo P 1 P 2 P 3 Glass CI(G)S – Solar Cell,schematic Record efficiency: 18% (small area) Best module efficiency: ca. 11% Source: ZSW (Stuttgart)

  46. Aluminum Absorber Polymer Anode ITO Substrate Organic Solar Cell h record = 4,8% h FMF, ISE= 3,7% Akzeptor Donor

  47. PV will grow in the coming decades 10 - 100 times in volume, from a $15 B market into a $100 - 300 B market, replacing fossil fuels, reducing climate gases, and providing energy for the world, including developing countries such as China and India. PV provides valuable peak power, today it is already economically competitive in certain areas; lower cost of PV and rising cost of fossil fuels will increase the competitiveness in the future. Crystalline Si will remain the dominant PV technology for a long time, the current shortage will be overcome by increased production of pure Si and the introduction of purified metallurgical-grade Si: ‘dirty Si’. Conclusion: the big picture for solar energy

  48. The reliable, practically unlimited solar energy will be the key contributor to the future renable energy mix. Organic solar cells, other ‘3rd generation’ concepts will serve interesting market niches, but are not l likely to affect the global picture. Solar thermal energy can be a big contributor, first for distributed energy and may be later for power plants. Thin film modules out of a-Si, CIS, or CdTe have an interesting market opportunity today, their long-term success will depend on efficiency improvements and cost reduction. Conclusion: the big picture for solar energy II

  49. Thanks to: Tonio Buonassisi * Matthew D. PickettMathias Heuer ** Andrei A. Istratov *** Dept. of Materials Science and EngineeringUniversity of California, Berkeley, USAand Materials Science Division, Lawrence Berkeley National Lab*now: Evergreen Solar, soon: MIT, **now: Leipzig University, * * * now: Siltronic

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