Costs of generating electricity http:www'iea'orgTextbasenpsumElecCostSUM'pdf $US quoted

1
Costs of generating electricity(http//www.iea.or
g/Textbase/npsum/ElecCostSUM.pdf US quoted)

• Coal (Avg of 27 plants) 1K-1.5K/kWe capital
• 45-60/MW.h (Inv. 50, OM 15, Fuel 35)
• Gas (23) 0.6-0.8K/kWe
• 40-63/MWh (Inv. 20, OM 7, Fuel 73)
• Nuclear (13) 1-2K/kWe (DVB probably more,
  esp. in USA)
• 30-50/MWh (Inv. 70, OM 13, Fuel 10)
• Wind (19) 1-2K/kWe
• 45-140/MWh (OM 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 gt
  55/MW.h)

2
Other approaches to Solar
http//www.cnn.com/video//video/tech/2008/06/10/o
brien.algae.oil.cnn
Vertigro algae Biofuels system. Requires about
1000 gallons of water for each gallon of
bio-diesel. But this could be promising! Perfect
sort of thing for term paper!
3
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

4
Basics of Photo-Voltaics
Vout0.5 V (for Si)

• 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 doesnt (to
  oversimplify it a little bit)

5
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
  less-energetic photons)
• Electron-hole recombination (i.e. some of the
  electrons dont 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)

http//en.wikipedia.org/wiki/Solar_cell
6
Basics of Nuclear Energy
Recall the basic structure of the atom that we
have seen on several occasions in this course.
Electrons orbit about the nucleus in states
with particular energies, and electrons jump
between those states by emitting or absorbing
photons with energies on the order of eV. This
electrical binding energy is, essentially the
source of all CHEMICAL energy.
7
Basics of Nuclear Energy
0.1 nm (10-10m)
1 fm (10-15m)
Z- protons A- nucleons (p n) ZACh
Nuclear energy, not surprisingly, involves the
binding energy of the neutrons and protons in the
nucleus of the atom. The energies involved are
MeV (106 times stronger), AND can involve
changing both the isotopic and chemical nature of
the atoms involved, since the chemistry is
determined by the number of protons (Z) in the
nucleus and the isotope by the number of neutrons
and protons (A).
Recall the basic structure of the atom that we
have seen on several occasions in this course.
Electrons orbit about the nucleus in states
with particular energies, and electrons jump
between those states by emitting or absorbing
photons with energies on the order of eV. This
electrical binding energy is, essentially, the
source of all CHEMICAL energy.
8
Known Nuclides
Z protons
Note all nuclides that are not black on this
chart, decay through the emission of some type of
nuclear radiation a, b, g, n
A-Z neutrons
http//sutekh.nd.rl.ac.uk/CoN/
9
Radioactive Decay

• Rate of emission (decay) is proportional to the
  number of nuclei present (gt exponential decay).
  N Noe-lt
• In most cases the energy of the emitted particle
  is on the order of MeV.
• a emitted particle is a 4He nucleus
• Changes Z (-2) and A (-4)
• Very short range in tissue
• b emitted particle is an electron or positron
• Changes Z (/-1) but not A
• More penetrating than a, but still short range
• g emitted particle is a photon
• Changes neither Z nor A.
• Very penetrating, so not easily shielded.

10
Nuclear Fission

• E mc2
• 1 amu (roughly the mass of a proton or neutron)
  934 MeV 1.49x10-10 J
• Mass of 235U is quite close to 235 amu

http//hyperphysics.phy-astr.gsu.edu/hbase/nucene/
fission.html
11
Nuclear Reactors (LWRs)
Pressurized water reactor (PWR) 67 of US
reactors are this type
Boiling water reactor (BWR) 33 of US reactors
are of this type
http//reactor.engr.wisc.edu/power.html
12
Fission products
http//en.wikipedia.org/wiki/Fission_products
http//www.euronuclear.org/info/encyclopedia/f/fis
sionproducts.htm
13
Radioactive wastes
http//www.uic.com.au/nip09.htm
14
American Nuclear Plants
http//www.nrc.gov/info-finder/reactor/
15
Nuclear Waste depots
http//www.ocrwm.doe.gov/info_library/newsroom/pho
tos/photos_natlmap.shtml
16
Waste depots
Nuclear Plants
17
Temporary Storage
http//library.thinkquest.org/17940/texts/nuclear_
waste_storage/nuclear_waste_storage.html
18
Yucca Mountain (100 mi NW of Las Vegas)
Present specification is to safely hold
high-level waste for 10,000 years, there is an
effort to force this to be extended to much
longer times (recommended by the National Academy
of Sciences). Designed for 77 kTons, presently we
have 57kTons in temp. storage at reactors!!
http//www.ocrwm.doe.gov/ymp/about/why.shtml
19
http//www.state.nv.us/nucwaste/states/us.htm
20
Rail shipping cask for spent nuclear fuel
http//en.wikipedia.org/wiki/ImageShipping_Cask_0
1.jpg
http//ww.ymp.gov/factsheets/images/0500_left.jpg
21
Nuclear Plants world wide
http//en.wikipedia.org/wiki/Radioactive_waste
22
Summary of problems with Nuclear Fission

• Very expensive to build power plants (at least
  the way it is done in the USA).
• Potential for weapons proliferation by diversion
  of 235U or byproducts to undesirables
• Handling of the waste (both from health and
  proliferation points of view).
• Very small probability of a very bad accident
  (Chernobyl, although an event just like that is
  impossible with western designs).
• New reactor designs, fuel cycles (Thorium), waste
  processing, etc. could provide ways out of many
  of these but will take research and significant
  investments!

23
Nuclear Fusion
http//www.nuc.berkeley.edu/fusion/fusion.html
The reaction shown is the easiest to use, but D-D
is also possible and is what we discussed in
class, simply because it is easier to get the
fuel and the math is a bit easier. 2MD
4.027106 amu vs. 3He p (3.01602931.007825)
amu 2MeV or
3H n (3.01604921.008665) amu
3MeV NOTE 3He and p are stable 3H has a
half-life of 12 years, n of 15 minutes. This
process produces no long-lived radioactivity
directly, unlike fission.
24
ITER
Proposed 500MW Fusion test Facility. First
plasma expected 2016. International Thermonucle
ar Experimental Reactor
http//www.iter.org/index.htm
25
Inertial confinement
http//www.nuc.berkeley.edu/thyd/icf/target.html
26
Temperature/Density sweet spot
http//en.wikipedia.org/wiki/Fusion_power
27
Summary of problems with Nuclear Fusion

• Have not yet figured out how to do it (need very
  extreme conditions)!
• Radiation damage to equipment will be a severe
  problem.
• Spent fuel waste has a short half-life but you
  still activate lots of material, so it is not
  free of nuclear waste altogether.