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Jim Sites | CSU

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Visit the Solar Institute for details of the 2011 Solar Symposium: solar.gwu.edu/Symposium.html

Visit the Solar Institute for details of the 2011 Solar Symposium: solar.gwu.edu/Symposium.html

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  • 1. PV’s Leading Edge: The Direction of Maximum Impact Jim Sites Physics Department Colorado State University (1) Where are we? (2) What metrics indicate leading edge? (3) What next?April 26, 2011 James Sites
  • 2. The Typical Solar Cell Most existing PV panels, silicon and thin-film, consist of a semiconductor p-n junction, with top and bottom contacts, sandwiched between two pieces of glass. From NRELApril 26, 2011 James Sites
  • 3. Large Photovoltaic FieldsApril 26, 2011 James Sites
  • 4. Annual World PV Production 1982-present Production [Peak Gigawatts] 100 Leading Total PV Production (GW) edge 10 Average increase of 45%/yr for last 1 15 years! 0.1 0.01 0.001 1980 1985 1990 1995 2000 2005 2010 2015 Year Slide by Valerie JacobsonApril 26, 2011 James Sites
  • 5. Technology ComparisonApril 26, 2011 James Sites
  • 6. Additional Types of Solar-Cells Concentrated PV (CPV) Small, high-efficiency cells, often in tandem Organic PV (OPV) Lots of materials choices, inexpensive Dye Sensitized Solar Cell (DSSC) Liquid electrolyte (can be solid state) also inexpensive Intermediate Band-gap PV Utilizes intermediate band for lower energiesApril 26, 2011 James Sites
  • 7. Different Views of a Solar Cell? GRAIN BOUNDARY - potential barrier - recombination CONTACT - enhanced atomic diffusion VOID - gas transport CdTe GRAIN SURFACE - surface recombination - depletion layer - enhanced surface diffusion Electrical Engineering CdS Materials SnO x Science GLASS JUNCTION INTERFACE GRAIN INTERIOR - interface recombination - bulk recombination - S and Te interdiffusion Physics ManufacturingApril 26, 2011 James Sites
  • 8. Comparison of J-V Curves Voltage Efficiency = Electical Power fill- factor Light Power Commercial High-Eff CdTe (11%) Lab CdTe (16.5%) Current High-Eff Crystalline (27%) [Based on GaAs] Two efficiency issues: (1) lab vs ideal, (2) commercial vs labApril 26, 2011 James Sites
  • 9. Organize and Quantify Efficiency Losses Absolute efficiency loss and primary reason Commercial – Lab Efficiency Lab – Ideal Differences Efficiency Differences 1% 5% Voltage Lower electron lifetime Low electron lifetime (GBs); Low carrier density 2½% 2% Current Thick CdS; TCO/glass abs; Various: Reflection; CdS abs; Interconnect area loss TCO/glass abs; Collection 2% 3½% Fill-Factor High series resistance; Low electron lifetime (GBs)→ Uniformity issues voltage-dependent current Incremental progress expected Possible breakthough?April 26, 2011 James Sites
  • 10. Leading Edge Metrics (1) Efficiency (electrical power/light power) - defined at a specified temperature and illumination level, which can be misleading. - can vary significantly with temperature, illumination, and the PV module parameters. - however, the average efficiency (and from that the expected annual power) at a specified location can be calculated with reasonable accuracy.April 26, 2011 James Sites
  • 11. Variation in Effective Efficiency with Location Calculated average c-Si efficiency (relative to STC) throughout Europe T. Huld et al, Solar Energy 84, 324 (2010)April 26, 2011 James Sites
  • 12. Technology Comparison Calculated differential in relative power yield of higher band-gap CdTe compared to c-Si T. Huld et al, Solar Energy 84, 324 (2010)April 26, 2011 James Sites
  • 13. Leading Edge Metrics (1) Efficiency (electrical energy/light energy) - defined at a specified temperature and illumination level, which can be misleading. - can vary significantly with temperature, illumination, and the PV module parameters. - however, the average efficiency (and from that the expected annual power) at a specified location can be calculated with reasonable accuracy. (2) Cost - here also a caveat is needed: total cost includes installation and permitting, generally lower with higher efficiency. (3) Reliability (4) Additional practical considerations - scalability, impact on land area, grid integration.April 26, 2011 James Sites
  • 14. Technology Pros and Cons Arguments For Being Technology Arguments Against Leading Edge Has maintained production lead c-Si Good fundamental understanding Crystal growth and assembly relatively Solid efficiency and reliability expensive Credible roadmap to very large scale Very high efficiency Requires tracking system CPV Cell area small Only suitable for direct sunlight Good fundamental understanding Reasonable efficiency at modest cost Thin Films Complex structures; fundamental Impressive recent growth rate (a-Si, CdTe, understanding light Credible roadmap to very large scale CIGS) a-Si limited by efficiency CdTe and CIGS at low cost Fundamental understanding very light “Third Projections for very low cost OR very Difficulty producing high current and Generation” high efficiency high voltage in same cell No good roadmap to high efficiencyApril 26, 2011 James Sites
  • 15. Leading Edge Predictions (1) Almost certainly a mix of technologies, and all will come down in cost. (2) c-Si, especially from China, will remain highly competitive (3) Thin-film CdTe and CIGS will continue to increase their market share - CdTe straightforward to deposit; has momentum and potential for higher efficiency - CIGS is thin-film that suffers least from being polycrystalline; keep an eye on higher band-gap CIGS (4) Tandem CPV will have an impact in sunny areas; modest overall (5) Not clear that other approaches will gain traction (6) Successful countries will be those with both healthy manufacturing climate and intellectual infrastructureApril 26, 2011 James Sites