Discussion points: Robinson Article
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Transcript of 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 moviee.g. www.cei.org/pdf/ait/AIT-CEIresponse.ppt ,
Figures:Robinson Article
Figures:Gore’s version
Figures:Robinson Article
Wind Energy
http://www.windpower.org/en/tour/wres/euromap.htm An extensive site for WindInformation!!
T typical availability of a wind farm is 17-38% for land-based plants and 40-45% for off-shore plants.
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
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
GE 2.5MW generator
http://www.gepower.com/prod_serv/products/wind_turbines/en/downloads/ge_25mw_brochure.pdf
Blade diameter: 100mWind range: 3.5m/s to 25m/sRated wind speed: 11.5 m/s
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)
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
EnergyGap (no available states)
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.
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
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
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+
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
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+
• 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
Solar Cell Costs
http://www.nrel.gov/ncpv/pv_manufacturing/cost_capacity.html
Essentials of PV design
Engineering work-around # 2:
Martin Green’s record cell. The grid deflects light into a light trapping structure
Power characteristics (Si)
http://www.solarserver.de/wissen/photovoltaik-e.html
100 cm2 silicon Cell under differentIllumination conidtions
Material Level of
efficiency in % Lab
Level of efficiency in % Production
Monocrystalline Silicon
approx. 24 14 to17
Polycrystalline Silicon
approx. 1813 to15
Amorphous Silicon
approx. 13 5 to7
Advanced designs-multilayers
http://www.nrel.gov/highperformancepv/
Typical products
40W systems for $250, 15 W for $120
Battery charges (flexibleAmorphous cells)
http://www.siliconsolar.com/
Typical pattern for crystallinecells
Typical patterns for amorphouscells
Flood light system for $390 (LED’s plus xtal. cells)
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).
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
Ballard Power Systems (PEM)
•85kW basic module power (scalable from 10 to 300kWThey 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
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 delivers250kW according to their press releases). Mostof the units installed to date are of this size.
http://www.netl.doe.gov/publications/proceedings/03/dcfcw/dcfcw03.html
http://www.netl.doe.gov/publications/proceedings/03/dcfcw/Cooper%202.pdf
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 CH4
• No existing infrastructure
The Realities
•H2 burns with 02 to make water
•H2 comes from the oceans (lots of it)
•Fuel cells can “burn” it efficiently/cleanly
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).
http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf
http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf
http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf
http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf
http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/4_science_stevens_04.pdf
Storage Possabilities
Physisorbtion
Chemical Reaction
Chemisorbtion
Encapsulation
Weak binding energy -> Low T requiredCarbon nanotubesPorous materialsZeolites
Reversible Hydrides PdH, LiH, …
Large energy input to release H2Slow Dynamics
Very large energy input to release H2Not technologically feasible
H2 trapped in cages or poresVariation of physical properties
(T or P) to trap/release H24 H moleculesin 51264 cage
Al
H
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)