2 - Solar Cell Intro
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Transcript of 2 - Solar Cell Intro
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The energy problem
The world uses about 13 TW of power today.
We probably need to generate ~ 30 TW of power in 2050.
Within the next 10 years, the amount of oil we can extracteach year will probably start to decline.
If we do not dramatically reduce our emissions of carbondioxide, the average temperature of the planet will probablyrise by several degrees.
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Our options
Burn fossil fuels and sequester the carbon
Nuclear
Renewable energy
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Why solar cells are likely to provide a significant
fraction of our power
We need ~ 30 TW of power, the sun gives us 120,000 TW.
Solar cells are safe and have few non-desirableenvironmental impacts.
Using solar cells instead of burning coal to generateelectricity is a much easier way to reduce carbon emissionsthan replacing gasoline in vehicles.
Solar cells provide electricity exactly when we need it themost.
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Conventional p-n junction photovoltaic (solar)cell
e-
usable photo-voltage (qV)
Energy
e-
Jenny Nelson, The Physics of Solar Cells, 2003.
n-typep-type
max
= 32%heat loss
heat loss
h
h+
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Polycrystalline silicon solar cells
12 % efficiency$350/m2
Cost ($/W)Cell $2.50Making the module $1.00Inverter $0.50
Installation $4-5.00TOTAL $8-9.00
DOE numbers
Average cost of PV cell electricity: $.27/kW-hr
Todays grid electricity: $0.06/kW-hr
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Single crystal cells
Dick Swanson will show you how SunPower makes 21 % efficient cells.
What is the potential for using less silicon and reducing the costs?
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Multijunction cellsGrid
p
p
p
p
p
n
nn
++
++
p
n
p
p
nn
++
++
p
n
pn
++
++
Ge Substrate (0.67 eV)
GaAs (1.42 eV)
GaInP (1.90 eV)
Al InP
AlGaInP
GaInP
GaInP
n GaAs
GaAs:N:Bi (1.05 eV)
GaAs:N:Bi
GaAs:N:Bi
nn
SpectroLab has achieved 37 % efficiency
Costs are estimated at $50,000/m2, soconcentrators must be used.
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Quantum Dot Solar Cells
Energy levels are quantized. Electrons do not rapidly give upthere energy to phonons.
Art Nozik, Inorganic Chemistry, 44 (2005) p. 6893.
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The cheapest option
Efficiency: 0.3 %
We dont have theland and water toprovide the world
with energy thisway.
Can we artificiallyimprove theefficiency?
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Thin Film Cells
CIGS (CuInGaSe2)World record: 19.5 %
StableIs there enough In available?
amorphous SiWorld record: 12.1 %not completely stable
CdTeWorld record: 16.5 %
StableCd is toxic
A thin film of semiconductor isdeposited by low cost methods.
Less material is used.
Cells can be flexible.
Chris Eberspacher will tell you how Nanosolar prints CIGS cells.
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5 % efficient organic cells can be deposited fromsolution
P. Fairley, IEEE Spectrum. Jan. 2004 p.28