Solar Cells: when will they become economically feasible

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The cost of solar cells are rapidly falling through increases in efficiency and reductions in cost per area. But the installation costs have become the largest part of solar cells costs and their costs are not falling. How can these costs be reduced. These slides discuss the potentially installation costs for perovskite and organic cells, along with a general discussion of costs and efficiency. this general discussion covers roll to roll printing and a wide number of solar cells (e.g., quantum dots, cadmium telluride, cadmium indium gallium selenide).

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  • How do we get all the red area?
  • Why are best production efficiencies lower than best laboratory efficiencies?
  • The size of LCD substrates were increased by about 4 times in change from 1st generation to 5th generation LCD substrate equipment. We are now at Generation 10
  • Production of generation 7.5 panels (with generation 7.5 equipment) was just starting in 2008. Firms are now implementing generation 10 panels and equipment.
  • Subsequent generations of equipment are very large. Notice the size of the humans in the pictures.
  • The capital cost per area output of LCDs falls as the size of the substrates (and production equipment) are increased. the area increased by 3.7 times while the capital costs only rose by 2.37 times as we moved from Gen 5 to Gen 7.5.
  • This data is for one type of LCD manufacturing equipment, called dry etch equipment. The productivity of the equipment (square meters per hour-$) rose about 8 times (2.7 to 23) as firms moved from Gen II to Gen VI.
  • Solar Cells: when will they become economically feasible

    1. 1. A/Prof Jeffrey Funk Division of Engineering and Technology Management National University of Singapore For information on other technologies, see http://www.slideshare.net/Funk98/presentations
    2. 2.  What are the important dimensions of performance for solar cells and their higher level systems?  What are the rates of improvement?  What drives these rapid rates of improvement?  Will these improvements continue?  What kinds of new systems will likely emerge from the improvements in solar cells?  What does this tell us about the future?
    3. 3. Session Technology 1 Objectives and overview of course 2 Two types of improvements: 1) Creating materials that better exploit physical phenomena; 2) Geometrical scaling 4 Semiconductors, ICs, electronic systems 5 MEMS and Bio-electronic ICs 6 Nanotechnology and DNA sequencing 7 Superconductivity and solar cells 8 Lighting and Displays 9 Human-computer interfaces (also roll-to roll printing) 10 Telecommunications and Internet 11 3D printing and energy storage This is Part of the Seventh Session of MT5009
    4. 4.  Creating materials (and their associated processes) that better exploit physical phenomenon  Geometrical scaling ◦ Increases in scale ◦ Reductions in scale  Some technologies directly experience improvements while others indirectly experience them through improvements in “components” A summary of these ideas can be found in 1) forthcoming paper in California Management Review, What Drives Exponential Improvements? 2) book from Stanford University Press, Technology Change and the Rise of New Industries
    5. 5.  Creating materials (and their associated processes) that better exploit physical phenomenon ◦ Create materials that better exploit phenomenon of photovoltaic ◦ Create processes that enable these materials to better exploit phenomenon of photovoltaic  Geometrical scaling ◦ Increases in scale: larger substrates and production equipment lead to lower cost in much the same way that cost of LCDs and other displays have fallen (see other sessions for more details)  Some technologies directly experience improvements while others indirectly experience them through improvements in “components” ◦ Better solar cells lead to better modules and new ways of organizing electricity production
    6. 6. http://www.economist.com/news/21566414-alternative-energy-will-no-longer-be-alternative-sunny-uplands Solar cells are getting cheaper………… Partly because they are becoming more efficient
    7. 7. Why does this slide make me optimistic about solar?
    8. 8.  Coal-fired power plants $2.10 a watt  Large hydroelectric systems can be cheaper ◦ Three Gorges Dam was supposedly about $1 a watt ◦ But actual costs are widely believed to be much higher  Natural gas-fired peaking power plants -$6 a watt  Large wind turbines -$2 a watt – but low capacity utilization (27%)  Solar panels currently selling for as low as US$0.70 a watt in large quantities ◦ But installation costs are $2-4$ per watt ◦ And capacity utilization is very low (18%)  Except for peaking plants (see next slide), we need much lower module and installation costs http://en.wikipedia.org/wiki/Price_per_watt; http://thebreakthrough.org/index.php/programs/energy-and- climate/how-fast-are-the-costs-of-solar-really-coming-down/
    9. 9. Electricity Usage by Time of Day in Florida
    10. 10.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    11. 11. Photovoltaic systemsSolar Cells in a Utility or on a Building
    12. 12. Thermal Energy SystemsVery Different from Solar Thermal Systems
    13. 13. Solar Cells Produce Electricity Based on Photovoltaic Effect
    14. 14.  1839: First recognized by the French physicist Alexandre-Edmond Becquerel  1883: First solar cell constructed from selenium by Charles Fritts  1946: modern junction semiconductor solar cell was first patented in 1946 by Russell Ohl  1954: first silicon solar cell was constructed by Calvin Fuller, Daryl Chapin, and Gerald Pearson  Subsequently other materials have been found some as recent as 10-15 years ago
    15. 15.  Semiconductor materials were found to exhibit the photovoltaic effect in the 1950s, 60s and 70s ◦ Silicon, including single crystalline, polycrystalline, and amorphous silicon ◦ Cadmium Telluride (CdTe) ◦ Copper indium gallium selenide (CIGS) ◦ Gallium arsenide  But also non-semiconductor materials, which were more recently found ◦ Photo-sensitive dyes (titanium oxide) ◦ Some organic materials ◦ Some of these materials can be used to make quantum dots or have Perovskite crystals
    16. 16.  Incoming solar radiation creates “electron-hole” pairs in material  These electrons and holes create electricity when they reach opposite terminals of device  Only photons whose energy exceeds band-gap of material create electron-hole pairs ◦ Other photons do not create electron-hole pairs ◦ Energy greater than this band gap is lost  There has been a search for materials that ◦ exhibit photovoltaic effect ◦ have appropriate band gap ◦ have little recombination of electrons and holes ◦ are inexpensive to acquire and process  Within a type of solar cell, there has been a search for the appropriate combination of material and process specifications Conduction band Band gap Valence band
    17. 17.  Materials with higher band gaps increase the amount of energy from each absorbed photon ◦ but reduce the percentage of incoming radiation that can be transformed into electrons and holes.  Thus, there is a tradeoff between low and high band gaps  Given the distribution of the solar spectrum ◦ the optimal band gap in terms of efficiency can be calculated ◦ the maximum theoretical efficiencies can be calculated (about 30%) ◦ Many materials have a maximum theoretical efficiency of about 30%
    18. 18. Examples of Efficiency Losses Reflection of photons by glass. Absorption of photons by glass (heat) Recombination of electron hole pairs before reaching terminals (crystalline materials have less recombination) Photons pass through material without generating electron- hole pairs But even if the best band-gap is used, there will be losses
    19. 19.  One way to overcome limitations of individual materials is to use multiple junctions ◦ Each has band gap that is appropriate for different part of solar spectrum  These solar cells can have ◦ much higher efficiencies than single junction ones ◦ but they also have higher costs as multiple layers must be deposited, patterned and etched  One way to reduce costs is to ◦ focus sunlight onto multi-junction cells using concentrators ◦ but concentrating mirrors require mechanical and electronic controls, gears and other potentially unreliable components  More on this later
    20. 20.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    21. 21.  Depends on a lot of factors but to simplify….  Cost of electricity depends on ◦ amount of incoming solar radiation ◦ cost per “Peak Watt” of a module (based on a predetermined amount of incoming solar radiation) ◦ cost of installation including cost of capital, land, labor, etc.: becomes more important as cost of “modules” drop  Cost per “Peak Watt” depends on ◦ cost per area of solar cells ◦ efficiency of solar cells
    22. 22. Amount of incoming solar radiation
    23. 23. world electricity demand (18,000 TWh/y) can be produced from 300 x 300 km² =0.23% of all deserts distributed over “10 000” sites 3000 km Sources: Gerhard Knies, CSP 2008 Barcelona and Vinod Khosla 25 deserts as solar farms
    24. 24. Improvements in what technology might make this economically feasible? Source: Wikipedia Desertec
    25. 25. Source: Physica C: Superconductivity Volume 484, 15 January 2013, Pages 1–5. Proceedings of the 24th International Symposium on Superconductivity (ISS2011). CIGRÉ SC D1 WG38 Workshop on High Temperature Superconductors (HTS) for Utility Applications Beijing, China, 26 April 2013 Can these improvements make solar economical for Europe? Now 2 years 4 years
    26. 26. What About Cost Per Peak Watt of Modules? Depends on cost per area and Efficiency Cost per area ($/m2) 50 100 200 Cost per Area 200 100 50 0 2 4 6 8 10 12 14 16 18 20 22 Cost($)perPeakWatt 1.5 1 .5 0 Efficiency
    27. 27. Improvements in either Cost per area or Efficiency can lead to a Lower Cost per Peak Watt Cost per area ($ per square meter) 50 100 200 Cost per Area 200 100 50 0 2 4 6 8 10 12 14 16 18 20 22 Cost($)perPeakWatt 1.5 1 .5 0 Efficiency Improvements in Improvements in efficiency or cost per area lead to lower costs per peak watt
    28. 28.  Rapidly falling costs and prices  Sometimes faster than expected, other times slower than expected  Subsidies distort prices ◦ Not just subsidies for installations (U.S., Germany, Japan, Spain) ◦ But also alleged subsidies for producers (China)  Alleged subsidies have led to ◦ Large exports of solar cells from China ◦ Trade dispute ◦ Smaller value added for solar cell producers both in absolute and percentage terms
    29. 29. http://www.economist.com/blogs/graphicdetail/2012/12/daily-chart-19
    30. 30. Cost Data for Different Types of Solar Cell Materials
    31. 31. http://cleantechnica.com/2013/01/22/chinese-solar-imports-drop-but-prices-continue-to-fall/
    32. 32.  Hard to separate long term and short term trends  Likely that Chinese subsidies for Chinese producers have caused short term fall in prices  Thus prices may go up when subsidies are gone ◦ This may be why Suntech went bankrupt in March 2013  Rising use of natural gas in U.S. has also reduced demand for solar panels and thus prices in the U.S. ◦ Firms must reduce prices or have unused capacity, so most firms will sell below costs  Subsidies also make it hard to understand which technology might be the cheapest in the future Sources: http://sync.democraticunderground.com/112739038; http://www.nytimes.com/2013/03/21/business/energy-environment/chinese-solar- companys-operating-unit-declares-bankruptcy.html?_r=0
    33. 33.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    34. 34.  Maximum Theoretical Efficiency ◦ Similar for a wide range of materials ◦ Black body limit  Best Laboratory Efficiencies ◦ Best efficiencies for cells produced in a laboratory  Best production efficiencies ◦ Best efficiencies for cells (or modules) produced in a factory
    35. 35. Technology Production Facilities Laboratories Theoretical Limits Crystalline Silicon 18% 25% 29% Micro-crystalline silicon 14% 20% 29% Cadmium-Indium Gallium Selenide (CIGS) 11% 20% 29% Cadmium Telluride (CdTe) 11% 17% (20.4%) 29% Amorphous Silicon 8% 13% 20% Organic Cells 2% 8% (11.1%) 31% Dye-Sensitized Cells 12% 31% Best Solar Cell Efficiencies and Theoretical limits (for single materials in 2010) Sources: U.S. DOE, 2010; Wang Qing and Palani Balaya (personal communication)
    36. 36.  Crystalline materials have lower recombination of holes and electrons ◦ Also high efficiencies for other crystalline materials (e.g., GaAs)  More research on silicon ◦ Longer history of silicon research than other materials ◦ Silicon’s current dominance (cheaper equipment and demand-based subsidies) reinforces this perspective  Do the other materials have more potential for improvements? And if so, how much?
    37. 37. Perovskite Dye Sensitized CZTSSe Organic QD
    38. 38.  Quantum dots (discussed in Session 5)  Organic materials  Perovskite cells
    39. 39. Increases in best laboratory efficiencies of organic and dye-sensitized solar cells http://www.asiabiomass.jp/english/topics/1208_05.ht ml
    40. 40. http://electronicdesign.com/article/components/organic-solar-cell-architecture-taps-next- performance-plateau Increases in best laboratory efficiencies of organic solar cells
    41. 41.  Many types of organic materials, but they all contain carbon ◦ Many substitutions are tried  One substitution is fullerenes  Placing them in the right place is important  Synchrotron is used to analyze the energy levels and thus the right places to place the fullerenes
    42. 42. Worldwide OPV production forecast Source: Solar&Energy, Recent Organic Solar Cell Technology and Market Forecast (2010 - 2015
    43. 43. 2000 2005 2010 2015 16 14 12 10 8 6 4 2 Rapid Improvements in Efficiency of Perovskite Solar Cells Perovskite Organic Dye Sensitized Amorphous Silicon Perovskite-based solar cells, Hodes G, science 342, 317 (2013, Oct): 317-318
    44. 44.  Perovskite cells are a hybrid of organic and inorganic materials and they have a certain type of crystal structure ◦ Thus may use materials classified as other types of solar cells ◦ Key difference is in crystalline structure  Efficiencies similar to crystalline silicon are possible due to its single crystalline structure  First two cells in 2009 and 2010 were liquid junction cells that were not stable Perovskite-based solar cells, Hodes G, science 342, 317 (2013, Oct): 317-318; http://www.technologyreview.com/news/521491/a-new-solar-material-shows-its-potential/
    45. 45.  Recent ones have high diffusion lengths and long lifetimes for holes and electrons (i.e., low recombination)  Researchers have shown that it is relatively easy to modify the material so that it efficiently converts different wavelengths of light into electricity  May be possible to form a solar cell with different layers, each designed for a specific part of the solar spectrum (i.e., multi-junction cell) Perovskite-based solar cells, Hodes G, science 342, 317 (2013, Oct): 317-318; http://www.technologyreview.com/news/521491/a-new-solar-material-shows-its-potential/
    46. 46.  Low-temperature deposition methods ◦ typically solution-based spin coating as compared to sputtering or vapor deposition  One-fifth the cost of current silicon-based solar cells on an area basis, due to the simpler manufacturing process  No rare materials or toxic (lead is worst material)  If lifetime related problems are solved and if lab efficiencies reach 20%, costs of $0.20 per peak Watt are expected Perovskite-based solar cells, Hodes G, science 342, 317 (2013, Oct): 317-318; http://www.solarika.org/blog/-/blogs/new-hope-for-cheaper-solar-cells-using-perovskites
    47. 47.  http://www.youtube.com/watch?v=oQ2bz6jl bz0
    48. 48.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    49. 49.  One way to overcome limitations of individual materials ◦ Each has band gap that is appropriate for different part of solar spectrum  These solar cells can have ◦ much higher efficiencies than single junction ones ◦ but they also have higher costs as multiple layers must be deposited, patterned and etched  One way to reduce costs is to ◦ focus sunlight onto multi-junction cells using concentrators to reduce amount of photovoltaic material ◦ but concentrating mirrors require mechanical and electronic controls, gears and other potentially unreliable components and they can only be currently used in cloudless skies
    50. 50. Two-Junction Solar Cells
    51. 51. Ideally as you increase the number of band gaps the efficiency increases
    52. 52.  For the highest efficiency solar cells, $50,000 per square meter  High costs come from maintaining crystalline structure even with 20 layers  Grown as one large crystal
    53. 53.  Organic materials can be roll printed or sprayed on top of each other  Organic tandem cells have the same efficiencies as do single- junction organic cells  But this may change
    54. 54.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    55. 55.  Type of material ◦ Availability in earth’s crust, Processing requirements  Number of layers ◦ More layers means more processing steps  Temperature of processing ◦ Higher temperatures means higher costs (e.g., semiconducting materials, crystalline silicon) ◦ http://www.youtube.com/watch?v=F2KcZGwntgg (from 1:50) ◦ Organic materials can be roll printed  Thickness of materials ◦ More difficult to reduce thickness of epitaxial formed silicon (crystalline silicon) than thin-film deposited materials (CIGS, CdTe, amorphous silicon)  Scale of substrates and production equipment ◦ Same as with LCDs and semiconductor wafers
    56. 56.  Fewer layers  Less materials  Lower temperature and simpler processes ◦ Organic materials, CIGS, and Perovskite can be roll printed onto a substrate  Perhaps lower scale right now so greater potential for increases in scale ◦ Many forms of thin film already use large scale production equipment ◦ But large scale equipment has not been implemented for some technologies, particularly roll printing ◦ Roll printing is applicable to some processes and many processes for organic solar cells
    57. 57. Roll Printing of Organic Solar Cells
    58. 58. Roll printing of organic solar cells Notice the simplicity Also notice the small size of the solar cells – still a long way from reaching its optimum scale Discussed more in two weeks Organic solar cells, roll-to roll printing 16 May 2013 http://reneweconomy.com.au/2013/on-a-roll-csiro- printing-australias-largest-solar-cells-58992
    59. 59.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    60. 60. http://www.economist.com/node/21543215 Source: Television Making: Cracking Up, Economist, January 21st, 2012, p. 66 Most cost reductions of LCD panels came from larger scale substrates and equipment. Similar effect for Solar
    61. 61.  Equipment costs per area of output fall as size of equipment is increased, similar to chemical plants  For chemical plants ◦ Cost is function of surface area (or radius squared) ◦ Output is function of volume (radius cubed) ◦ Thus, costs increase by 2/3 for each doubling of equipment capacity  For LCD Substrates, IC Wafers, and Solar Substrates ◦ Processing, transfer, and setup time (inverse of output) fall as area of substrate increases since entire area can be processed, transferred, and setup together
    62. 62. Another Benefit from Large Panels is Smaller Edge E Panel Equipment Effect Effects: the equipment must be much wider than panel to achieve uniformity Ratio of equipment to panel width falls as the size of the panel is increased
    63. 63. Increases in LCD Substrate Size Source: www.lcd-tv-reviews.com/pages/fabricating_tft_lcd.php
    64. 64. Scale of photolithographic aligners (upper left), sputtering equipment (top right), and mirrors for aligners (lower left) for LCD equipment Source: http://www.canon.com/technology/ canon_tech/explanation/fpd.html
    65. 65. http://www.electroiq.com/articles/sst/print/volume-50/issue-2/features/cover- article/scaling-and-complexity-drive-lcd-yield-strategies.html
    66. 66.  Solar cells also benefit from increases in scale of production equipment  Crystalline silicon solar cells are made in wafers, just like semiconductor chips ◦ Their costs fall as wafers and production equipment are made larger, but improvements are difficult  Thin-film solar is made on substrates, like LCDs ◦ Their costs fall as substrates and production equipment are made larger  CIGS and organic solar cells can be roll printed ◦ Materials can be deposited and patterned using roll-to roll printing ◦ Consider Self-Aligned Imprint Lithography (SAIL)
    67. 67. $0.0 $0.5 $1.0 $1.5 $2.0 $2.5 $3.0 Web preparation Sputter Gate 1 Metal Align and Expose SiN, a-Si, N+ dep Align and Expose Si RIE & Resist Strip Ultrasonic Clean Align and Expose Sputter Dep/ ITO Align and Expose Sputter Dep Interconnect Align and Expose Web cost $0.0 $0.5 $1.0 $1.5 $2.0 $2.5 Condition web (de-hydro) Gate metal deposition (Al) PECVD oxide/nitride/Si/N+ deposition SD metal deposition (Cr) Imprint SAIL structure Wet etch Cr RIE etch n+&Si&SIN RIE etch oxide Plasma etch Al Thin down 2P (clear gate-pad) Pre-Cr-etch Cleaning RIE etch n+&Si&SIN Thin down 2P (clear gate-pad) Wet etch Cr RIE etch n+ Under-cut Al (1-3 um) RIE etch oxide Strip-off 2P Web cost costper ft2 $0.00 $2.00 $4.00 $6.00 $8.00 $10.00 $12.00 $14.00 $16.00 $18.00 Photolithography SAIL Cost of Patterning Backplane materials costs for R2R photolithography & SAIL R2RSAILR2Rphotolith(AGI) Multiple photoresist applications dominate photolithography process materials costs
    68. 68. 2 3 4 5 6 7 8 9 10 10 -3 10 -2 10 -1 10 0 equipmentcost[M$]/throughput[cm2 /S] generation equipment cost scaling comparison: panel stepper vs R2R imprinter 100 mm R2R imprinter 330 mm R2R imprinter R2R Imprinters are much cheaper than Panel Stepper used in Photolithography (and benefits from increases in scale) Source: Roll-to-Roll Manufacturing of Flexible Displays, Hewlett Packard, Phicott
    69. 69. 1 2 3 4 5 6 7 8 9 10 10 -2 10 -1 10 0equipmentcost[M$]/throughput[cm2 /S] generation equipment cost scaling comparison: panel CVD vs R2R CVD 330 mm R2R PECVD 1 m R2R PECVD Source: Roll-to-Roll Manufacturing of Flexible Displays, Hewlett Packard, Phicott PECVD (plasma enhanced chemical vapor deposition) is also cheaper when doing R2R Printing (and benefits from increases in scale)
    70. 70.  Installation costs are now more than the module costs on a per Watt basis  Lower on a per Watt basis with ◦ large-scale than small-scale systems ◦ High-efficiency than low-efficiency modules  Lower on a per-area basis with thin- film or rolled materials than with thick materials (crystalline silicon) ◦ Just unroll a roll of organic solar cells
    71. 71.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    72. 72.  Can further decrease costs  It is easier to reduce thickness of thin-film materials than crystalline silicon ◦ their thickness depends on deposition of materials ◦ thickness of crystalline silicon materials depends on cutting silicon ingots into wafers  But it can also lead to lower efficiencies ◦ Less active material increases the chances that photons will pass through the material before they create an electron-hole pair  What if we can increase the amount of time that a photon spends within the material for a given thickness? ◦ Thus enabling reductions in thickness
    73. 73. Rationale: Light trapping increases the optical thickness of a silicon cell by 10--‐50 times Hence, theoretically it is possible to achieve similar efficiencies with a thinner layer material
    74. 74.  How do solar cells work?  Improvements in cost of electricity from solar cells  Improvements in Efficiency  Multi-junction cells  Improvements in cost per area  Increases in scale  Reductions in thicknesses  Conclusions
    75. 75.  Cost of electricity from solar cells is dropping rapidly  Silicon is most widely used material ◦ Will further cost reductions for silicon occur? ◦ Or have we reached the limits?  Large number of materials and processes suggests that many improvements can still be achieved ◦ Rapid increases in efficiency are still occurring for some materials: organic, quantum dot, perovskite, multi-junction solar cells ◦ Scale up of substrates and equipment have not been done for some materials
    76. 76.  Other improvements are also occurring ◦ Reducing thickness of materials  Installation costs are becoming larger as a percentage of total costs ◦ How can they be reduced? ◦ With roll printed solar cells, or with higher efficiency solar cells?
    77. 77.  Appendix
    78. 78. 2 September 2004© Scholtes 2004 Page 89Source: U.S. Department of Energy, 1998 120 100 80 60 40 20 0 1975 1980 1985 1990 1995 2000 2005 Year 1982 Trend predicted 1981 1984 1985 1986 1987 1991 1995 Actual DollarsperBarrel 1983
    79. 79. Ban Best Laboratory and Maximum Theoretical Efficiencies v Band-Gap of Material
    80. 80. 0.5 1 1.5 2 2009 2010 2011 2012 2013 2014 2015 Micro (Poly) Crystalline Silicon Cost (USD) per Peak Watt of Solar Cells Cadmium Indium Gallium Selenide (CIGS – thin film) Source: Lux Research (2011) Thin Film Silicon Cadmium Telluride (thin film) USD
    81. 81. http://thinkprogress.org/climate/2011/12/11/387108/solar-power-much-cheaper-than-most- realize-study/?mobile=nc
    82. 82. http://thinkprogress.org/climate/2011/12/11/387108/wp-content/uploads/2011/06/Screen-shot-2011-06-08- at-3.20.01-PM.png
    83. 83. http://cleantechnica.com/2012/03/14/ultra-thin-solar-cell-company-unstealths-aims-to-cut-cost-of-solar- cells-in-half-images/
    84. 84.  http://revolution-green.com/2013/07/17/solar-at-30-cents-per-watt/  http://blogs.berkeley.edu/2013/06/18/the-california-solar-initiative-is-ending-what- has-it-left-behind/  http://www.resilience.org/stories/2013-08-16/it-keeps-getting-cheaper-to-install- solar-panels-in-the-u-s  http://energyathaas.wordpress.com/2013/06/17/the-california-solar-initiative-is- ending-what-has-it-left-behind/  http://thinkprogress.org/climate/2011/12/11/387108/solar-power-much-cheaper- than-most-realize-study/
    85. 85.  Implications of learning curve (cost of producing product falls as cumulative production increases)  Although learning curves don’t exclude non-factory activities, linking cost reductions with production ◦ focuses policy, other analyses on production of final product ◦ implies that research done outside of factory is either unimportant or being driven by production of final product ◦ for solar, has encouraged demand-based policies that subsidize installation of solar cells ($130B just in Germany) as opposed to more R&D, which has encouraged focus on existing technologies  We should first understand direct drivers of cost reduction, then develop good policy
    86. 86. http://electronicdesign.com/article/components/organic-solar-cell-architecture-taps-next- performance-plateau Increases in best laboratory efficiencies of organic solar cells
    87. 87. Increases in best laboratory efficiencies of organic and dye-sensitized solar cells http://www.asiabiomass.jp/english/topics/1208_05.html
    88. 88. Worldwide OPV production forecast Source: Solar&Energy, Recent Organic Solar Cell Technology and Market Forecast (2010 - 2015

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