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)

Other approaches to Solarhttp://www.cnn.com/video/#/video/tech/2008/06/10/obrien.algae.oil.cnn

Vertigro algaeBiofuels 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!

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

_

+

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)

Vout~0.5 V

(for Si)

Crude picture inside a solar cell

http://en.wikipedia.org/wiki/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 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)

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.

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.

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).

~0.1 nm (10-10m) ~1 fm (10-15m)

Z- # protons

A- # nucleons (p + n)

ZACh

Known Nuclides

http://sutekh.nd.rl.ac.uk/CoN/

Z=

# protons

A-Z= # neutrons

Note: all nuclides that are not black on this chart, decay through the emission of some type of nuclear radiation:

nn

Radioactive Decay• Rate of emission (decay) is proportional to the

number of nuclei present (=> exponential decay). N = Noe-t

• In most cases the energy of the emitted particle is on the order of MeV.

: emitted particle is a 4He nucleus– Changes Z (-2) and A (-4)– Very short range in tissue

: emitted particle is an electron or positron– Changes Z (+/-1) but not A– More penetrating than , but still short range

emitted particle is a photon– Changes neither Z nor A.– Very penetrating, so not easily shielded.

Nuclear Fission

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fission.html

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

Nuclear Reactors (LWR’s)

http://reactor.engr.wisc.edu/power.html

Boiling water reactor (BWR)33% of US reactors are of this type

Pressurized water reactor (PWR)67% of US reactors are this type

Fission products

http://www.euronuclear.org/info/encyclopedia/f/fissionproducts.htm

http://en.wikipedia.org/wiki/Fission_products

Radioactive wastes

http://www.uic.com.au/nip09.htm

American Nuclear Plants

http://www.nrc.gov/info-finder/reactor/

Nuclear Waste depots

http://www.ocrwm.doe.gov/info_library/newsroom/photos/photos_natlmap.shtml

Waste depots Nuclear Plants

Temporary Storage

http://library.thinkquest.org/17940/texts/nuclear_waste_storage/nuclear_waste_storage.html

Yucca Mountain (100 mi NW of Las Vegas)

http://www.ocrwm.doe.gov/ymp/about/why.shtml

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.state.nv.us/nucwaste/states/us.htm

Rail shipping cask for spent nuclear fuel

http://en.wikipedia.org/wiki/Image:Shipping_Cask_01.jpg

http://ww.ymp.gov/factsheets/images/0500_left.jpg

Nuclear Plants world wide

http://en.wikipedia.org/wiki/Radioactive_waste

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!

Nuclear Fusionhttp://www.nuc.berkeley.edu/fusion/fusion.html

The reaction shown is the easiest to use, but D-D is also possible and is whatwe discussed in class, simply because it is easier to get the fuel and the mathis a bit easier. 2*MD= 4.027106 amu vs. 3He + p = (3.0160293+1.007825) amu + ~2MeV or 3H + n = (3.0160492+1.008665) 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.

ITER

http://www.iter.org/index.htm

Proposed 500MWFusion testFacility. First plasma expected2016.

“InternationalThermonuclearExperimental Reactor”

Inertial confinement

http://www.nuc.berkeley.edu/thyd/icf/target.html

Temperature/Density sweet spot

http://en.wikipedia.org/wiki/Fusion_power

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.