Transcript Slide 1

Wind Energy
The text gives (on page
407 in slightly different
units) the formula:
P = 0.3*D2 V3 (W.s3/m5)
D-turbine diameter
V- wind velocity
So a 9m/s wind provides
27 times the power that
a 3m/s wind provides!!
http://cenlamar.files.wordpress.com/2008/07/plan_3tiermap.jpg
Types of Windmills/turbines
7% efficiency,
but work at
low wind
speeds
Altogether, there are 150,000
windmills operating in the US
alone (mainly for water
extraction/distribution)
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
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
Types of Windmills (cont.)
Altamont Pass (CA)
http://www.ilr.tu-berlin.de/WKA/windfarm/altcal.html
6000 turbines, built 1980’s
San Gorgonio Pass (CA)
http://www.ilr.tu-berlin.de/WKA/windfarm/sgpcal.html
3500 turbines, built 1980’s
Costs of generating electricity
(http://www.iea.org/Textbase/npsum/ElecCostSUM.pdf $US quoted)
• Coal (Avg of 27 plants) $1K-$1.5K/kWe capital
– $45-60/MW.h (Inv. 50%, O&M 15%, Fuel 35%)
• Gas (23) $0.6-0.8K/kWe
– $40-63/MWh (Inv. 20%, O&M 7%, Fuel 73%)
• Nuclear (13) $1-$2K/kWe (DVB: probably more, esp. in USA)
– $30-50/MWh (Inv. 70%, O&M 13%, Fuel 10%)
• Wind (19)
$1-2K/kWe
– $45-140/MWh (O&M 12-40%)
– Load factor variability is a major factor in setting the costs of running a
wind plant (similar problems would hold true for solar as well).
• Solar (6) approaches $300/MWh
• Cogeneration (24) estimated $30-70/MWh
– Note the three separate cost categories and the different mix for
these.
• Compare all of these to gasoline ($2/gal => $55/MW.h)
Load (or capacity) factors
http://www.eia.doe.gov/cneaf/electricity/epa/epa_sum.html
Nuclear and Coal have very large “load factors” (these plants tend to run
most of the time, and provide “base load” capacity. Other types of plants,
like Natural gas, can be “fired up” more quickly and tend to be used to
accommodate peak loads (sometimes called “peaking plants”). Wind has a
typical capacity factor of only about 20% (solar is probably a little more, but
still much less than 50%).
COAL GASIFICATION CARBON-SEQEST. PLANT
(Approved to be sited in Edwardsport, IN)
http://www.heraldtimesonline.com/stories/2008/11/22/statenews.qp-0886723.sto?1227497481
Projected to open in 2012. Cost now projected to be $2.35B (up from original estimate of $1.3B) for 650MW
Capacity. (>$3600/kW; this is not cost-competitive with other technologies at present; it’s requiring big rate
hikes and heavy gov’t subsidies.) At that, it is only designed to capture “some of the 4Mtons of CO2 expected
to be produced per year.
Water wheels through the ages
ITAIPU (Brazil/Paraguay)
http://www.solar.coppe.ufrj.br/itaipu.html
ITAIPU (Brazil/Paraguay)
http://www.solar.coppe.ufrj.br/itaipu.html
Other approaches to Solar
http://www.cnn.com/video/#/video/tech/2008/06/10/obrien.algae.oil.cnn
Vertigro algae
Biofuels system.
Requires about
1000 gallons of
waer for each
gallon of biodiesel. But this
could be
promising!
Perfect sort of
thing for term
paper!
Basics of atoms and materials
Energy
Gap (no available states)
• 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
p- and n-type semiconductors
n-type
p-type
Conduction band
Energy
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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
n-type
p-type
Conduction band
Energy
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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
n-type
p-type
Energy
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+_
Conduction band
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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
n-type
p-type
Energy
+
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Conduction band
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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
Basics of Photo-Voltaics
• As with atoms, materials like
semiconductors have states of
particular energy available to their
electrons.
• Absorbing a photon of sufficiently
short wavelength (i.e. high enough
energy) can lift an electron from the
filled “valence” band of states to the
empty “conduction” band of states.
• If you can achieve a spatial separation
between the “elevated electron” and
the (positive) hole it left behind, you
have used the photon as a source of
EMF
• Blue light works, Red light doesn’t (to
oversimplify it a little bit)
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%)
• CIGS (5 -20 %)
Crude picture inside a solar cell
Limitations on efficiency:
•Reflection of light from front surface
•Not all light is short enough
wavelength (previous slide; some
panels now have multiple cells stacked
with lower layers senstive to lessenergetic photons)
http://en.wikipedia.org/wiki/Solar_cell
•Electron-hole recombination (i.e. some
of the electrons don’t get out into the
circuit; Hence single crystal Si is higher
efficiency than polycrys. Or
amorphous).
•Some light goes right through the
active layers (hence, sometimes you
see a reflective layer at the bottom)
Solar Cell Efficiency
http://en.wikipedia.org/wiki/Solar_cell
Typical types
Single Crystal
(highest efficiency)
Poly-crystalline
http://en.wikipedia.org/wiki/Solar_cell
Essentials of PV design
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 (42.8% is the record, as
of July 2007) 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)
Engineering work-around # 2:
Martin Green’s record cell. The grid deflects light into
a light trapping structure
Power characteristics (Si)
100 cm2 silicon
Cell under different
Illumination conidtions
Material
Level of
efficiency in
% Lab
Level of efficiency in %
Production
Monocrystalline
Silicon
approx. 24
14 to17
Polycrystalline
Silicon
Amorphous
Silicon
approx. 18
approx. 13
http://www.solarserver.de/wissen/photovoltaik-e.html
13 to15
5 to7
Solar Cell Costs
http://www.nrel.gov/pv/pv_manufacturing/cost_capacity.html
Costs have dropped from about $5.89/pk Watt output in 1992 to $2.73/pW in 2005
Solar House
This house in Oxford produces more electricity than it uses
(but only about 4kWh/yr!! According to the NREL, hardly worth selling)
http://www.nrel.gov/pv/pv_manufacturing/cost_capacity.html
Example of a retrofit
Typical products
Flood light system for
$390 (LED’s plus xtal.
Cells; claimed “150 W”)
15W systems for
$100 (was $150 in 2007)
http://www.siliconsolar.com/
Battery charges (flexible
Amorphous cells)
Advanced designs-multilayers
http://www.nrel.gov/highperformancepv/
Possible future technology: CIGS (Cu-In-Ga-Se) thin film cells. Presently they
Are less than 20% efficient (in lab, much less from production lines), but they
could be much less expensive and more durable than amorphous Si. E.G. Heliovolt
claims to have thin-film CIGS cells and claims to be at a $1/W price point.
( http://www.heliovolt.net/ )