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

6. Summary of wind power Power available is roughly: –P=2.8x10 -4 D 2 v 3 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 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). Altogether, there are 150,000 windmills operating in the US alone (mainly for water extraction/distribution) 7% efficiency, but work at low wind speeds Up to 56 % efficiency with 3 blades, do very little at low wind speeds

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

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 Conduction band Valence band Gap Energy Position _ _ _ _ p-type n-type 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 Conduction band Valence band Gap Energy Position _ _ _ _ p-type n-type 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 Conduction band Valence band Gap Energy Position _ _ _ _ p-type n-type 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 Conduction band Valence band Gap Energy Position _ _ _ _ p-type n-type 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. 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%) Synopsis of Solar Cells

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) http://www.solarserver.de/wissen/photovoltaik-e.html 100 cm 2 silicon Cell under different Illumination conidtions Material Level of efficiency in % Lab Level of efficiency in % Production Monocrystalline Silicon approx. 2414 to17 Polycrystalline Silicon approx. 18 13 to15 Amorphous Silicon approx. 135 to7

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

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

23. 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).

24. 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

25. 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 80 o C H 2 as the fuel (needs a reformer to make use of Methanol etc.) 300kW used for buses

26. 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 CH 4 (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.

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

28. The Hydrogen Hype 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 CH 4 No existing infrastructure The Realities H 2 burns with 0 2 to make water H 2 comes from the oceans (lots of it) Fuel cells can “burn” it efficiently/cleanly

29. Hydrogen Economy Need lots of research in areas such as: –Production –Transmission/storage –Distribution/end use 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).

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

35. Storage Possabilities Physisorbtion Chemical Reaction Chemisorbtion Encapsulation Weak binding energy -> Low T required Carbon nanotubes Porous materials Zeolites Reversible Hydrides PdH, LiH, … Large energy input to release H2 Slow Dynamics Very large energy input to release H2 Not technologically feasible H2 trapped in cages or pores Variation of physical properties (T or P) to trap/release H 2 4 H molecules in 5 12 6 4 cage Al H

36. DOE report from 2004 is available at: http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf 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)