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Discussion points: Robinson Article

Discussion points: Robinson Article. General comments? What is the strongest argument? What is the weakest/most suspect? Did it change anyone’s thinking?. There are lots of other sites that you can find to argue with points in Gore’s movie e.g. www.cei.org/pdf/ait/AIT-CEIresponse.ppt ,.

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Discussion points: Robinson Article

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  1. Discussion points:Robinson Article • General comments? • What is the strongest argument? • What is the weakest/most suspect? • Did it change anyone’s thinking? There are lots of other sites that you can find to argue with points in Gore’s movie e.g. www.cei.org/pdf/ait/AIT-CEIresponse.ppt ,

  2. Figures:Robinson Article

  3. Figures:Gore’s version

  4. Figures:Robinson Article

  5. Wind Energy T typical availability of a wind farm is 17-38% for land-based plants and 40-45% for off-shore plants. An extensive site for Wind Information!! http://www.windpower.org/en/tour/wres/euromap.htm

  6. Summary of wind power • Power available is roughly: • P=2.8x10-4 D2 v3 kW (D in m, V in m/s) • I.e. you get much more power at higher wind speeds with larger turbines • 3-blade turbines are more efficient than multi-blade, but the latter work at lower wind speeds. • At higher wind speeds you need to “feather” the blades to avoid overloading the generator and gears. • Typical power turbines can produce 1 -3.5 MW

  7. Types of Windmills/turbines Altogether, there are 150,000 windmills operating in the US alone (mainly for water extraction/distribution) 7% efficiency, but work at low wind speeds According to wikipedia, as of 2006 installed world-wide capacity is 74 GW (same capacity as only 3.5 dams the size of the three-Gorges project in China). Up to 56 % efficiency with 3 blades, do very little at low wind speeds

  8. Blade diameter: 100m Wind range: 3.5m/s to 25m/s Rated wind speed: 11.5 m/s GE 2.5MW generator http://www.gepower.com/prod_serv/products/wind_turbines/en/downloads/ge_25mw_brochure.pdf

  9. Basics of Photo-Voltaics A useful link demonstrating the design of a basic solar cell may be found at: http://jas.eng.buffalo.edu/education/pnapp/solarcell/index.html • There are several different types of solar cells: • Single crystal Si (NASA): most efficient (up to 30%) and most expensive (have been $100’s/W, now much lower) • Amorphous Si: not so efficient (5-10% or so) degrade with use (but improvements have been made), cheap ($2.5/W) • Recycled/polycrystalline Si (may be important in the future)

  10. Basics of atoms and materials • Isolated atoms have electrons in shells” of well-defined (and distinct) energies. • When the atoms come together to form a solid, they share electrons and the allowed energies get spread out into “bands”, sometimes with a “gap” in between Energy Gap (no available states)

  11. p- and n-type semiconductors n-type p-type Conduction band Energy _ _ _ _ Gap _ _ _ _ Valence band Position • Separate p and n-type semiconductors. The lines in the gap represent extra states introduced by impurities in the material. • n-type semiconductor: extra states from impurities contain electrons at energies just below the conduction band • p-type has extra (empty) states at energies just above the valence band.

  12. p-n junction and solar cells n-type p-type Conduction band Energy _ _ _ _ Gap _ _ _ _ Valence band Position • When the junction is formed some electrons from the n-type material can “fall” down into the empty states in the p-type material, producing a net negative charge in the p-type and positive charge in the n-type

  13. p-n junction n-type p-type Conduction band Energy + _ _ _ _ Gap _ _ _ _ _ Valence band Position • When the junction is formed some electrons from the n-type material can “fall” down into the empty states in the p-type material, producing a net negative charge in the p-type and positive charge in the n-type

  14. p-n junction and solar cell action n-type p-type Conduction band Energy + _ _ _ _ Gap _ _ _ _ _ Valence band Position • When a light photon with energy greater than the gap is absorbed it creates an electron-hole pair (lifting the electron in energy up to the conduction band, and thereby providing the emf). • To be effective, you must avoid: • avoid recombination (electron falling back in to the hole). • Avoid giving the electron energy too far above the gap • Minimize resistance in the cell itself • Maximize absorption • All these factors amount to minimizing the disorder in the cell material

  15. Synopsis of Solar Cells • Need to absorb the light • Anti-reflective coating + multiple layers • Need to get the electrons out into the circuit (low resistance and recombination) • Low disorder helps, but that is expensive • Record efficiency of 42.8% was announced in July 2007 (U. Delaware/Dupont). • Crystalline Si: highest efficiency (typically 15-25%), poorer coverage, bulk material but only the surface contributes, expensive (NASA uses them). • Amorphous Si: lower efficiency (5-13%)

  16. Solar Cell Costs http://www.nrel.gov/ncpv/pv_manufacturing/cost_capacity.html

  17. Essentials of PV design

  18. Engineering work-around # 2: Martin Green’s record cell. The grid deflects light into a light trapping structure

  19. Power characteristics (Si) 100 cm2 silicon Cell under different Illumination conidtions http://www.solarserver.de/wissen/photovoltaik-e.html

  20. Advanced designs-multilayers http://www.nrel.gov/highperformancepv/

  21. Typical products Flood light system for $390 (LED’s plus xtal. cells) 40W systems for $250, 15 W for $120 Typical pattern for crystalline cells Battery charges (flexible Amorphous cells) Typical patterns for amorphous cells http://www.siliconsolar.com/

  22. Review for Thursday • Solar Cells • Need to get the electrons out into the circuit (low resistance and recombination) • Low disorder helps with both (hence crystal is more efficient than amorphous) • Crystalline Si: highest efficiency (typically 15-25%), poorer coverage, bulk material but only the surface contributes, expensive (e.g. NASA). • Amorphous Si: lower efficiency (5-13%), less stable (can degrade when exposed to sunlight).

  23. Fuel Cells- sample schematics http://www.iit.edu/~smart/garrear/fuelcells.htm For more details on these and other types, see also: http://www.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html

  24. Ballard Power Systems (PEM) • 85kW basic module power • (scalable from 10 to 300kW • They say) for passenger cars. • 212 lb (97 kg) • 284 V 300 A • Volume 75 liters • Operates at 80oC • H2 as the fuel (needs a • reformer to make use of • Methanol etc.) • 300kW used for buses

  25. Fuel Cell Energy (“Direct Fuel Cell”) • Appears to be a molten • carbonate systme based on • their description • Standard line includes units • of 0.3,1.5 and 3 MW • Fuel is CH4 (no need for • external reformer) can also • use “coal gas”, biogas and • methanol • Marketed for high-quality power • applications (fixed location) This is a nominal 300kW unit (typically delivers 250kW according to their press releases). Most of the units installed to date are of this size.

  26. http://www.netl.doe.gov/publications/proceedings/03/dcfcw/dcfcw03.htmlhttp://www.netl.doe.gov/publications/proceedings/03/dcfcw/dcfcw03.html http://www.netl.doe.gov/publications/proceedings/03/dcfcw/Cooper%202.pdf

  27. H2 burns with 02 to make water • H2 comes from the oceans (lots of it) • Fuel cells can “burn” it efficiently/cleanly The Hydrogen Hype The Realities • Can’t mine it, it is NOT an energy source • Why not just use electricity directly? • Even as a liquid, energy density is low • Storage and transport are difficult issues • More dangerous (explosive) than CH4 • No existing infrastructure

  28. Hydrogen seems to be an attractive alternative to fossil fuels, but it cannot be mined. You need to treat it more like electricity than gasoline (i.e. as a carrier of energy, not as a primary source). Hydrogen Economy Need lots of research in areas such as: Production Transmission/storage Distribution/end use

  29. http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdfhttp://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf

  30. http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdfhttp://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf

  31. http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdfhttp://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf

  32. http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdfhttp://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf

  33. http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdfhttp://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf

  34. H Al 4 H molecules in 51264 cage Storage Possabilities Weak binding energy -> Low T required Carbon nanotubes Porous materials Zeolites Physisorbtion Reversible Hydrides PdH, LiH, … Large energy input to release H2 Slow Dynamics Chemical Reaction Very large energy input to release H2 Not technologically feasible Chemisorbtion H2 trapped in cages or pores Variation of physical properties (T or P) to trap/release H2 Encapsulation

  35. MIT web site on photo-production: http://web.mit.edu/chemistry/dgn/www/research/e_conversion.html Nature and Physics Today articles: Nature Vol. 414, p353-358 (2001) Physics Today, vol 57(12) p39-44 (2004) DOE report from 2004 is available at: http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf

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