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

_

+

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

_

+

• 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)