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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

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 ,


Figures robinson article

Figures:Robinson Article


Figures gore s version

Figures:Gore’s version


Figures robinson article1

Figures:Robinson Article


Wind energy

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


Summary of wind power

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

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


Ge 2 5mw generator

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


Basics of photo voltaics

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

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)


P and n type semiconductors

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.


P n junction and solar cells

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


P n junction

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


P n junction and solar cell action

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


Synopsis of solar cells

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%)


Solar cell costs

Solar Cell Costs

http://www.nrel.gov/ncpv/pv_manufacturing/cost_capacity.html


Essentials of pv design

Essentials of PV design


Discussion points robinson article

Engineering work-around # 2:

Martin Green’s record cell. The grid deflects light into a light trapping structure


Power characteristics si

Power characteristics (Si)

100 cm2 silicon

Cell under different

Illumination conidtions

http://www.solarserver.de/wissen/photovoltaik-e.html


Advanced designs multilayers

Advanced designs-multilayers

http://www.nrel.gov/highperformancepv/


Typical products

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/


Review for thursday

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

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

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


Fuel cell energy direct fuel cell

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.


Discussion points robinson article

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

  • 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


Hydrogen economy

  • 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


Discussion points robinson article

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


Discussion points robinson article

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


Discussion points robinson article

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


Discussion points robinson article

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


Discussion points robinson article

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


Storage possabilities

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


Doe report from 2004 is available at

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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