Solar Power

1
Solar Power
Photovoltaic Power Generation Photoelectric
Effect, P and N type Layers, Band Gap Solar Cell
Manufacture Types of Solar Cells Solar
Vehicles Photovoltaic Systems
2
Energy in the News
3
Contribution of Solar to U.S. Power
Growth rate of solar is 15 per year, when will
it reach 0.15 of total Power supply?
4
Change in Cost of Solar Cells
Solar power Already competitive For peak
power Production In New York area. Why??
Present price 3.50 per peak watt-needs to go to
1.50 per Peak cost of generation of 12 cents
per kilowatt hour, then Economically competitive
for typical power production.
5
Photoelectric Effect
Light hits a metal plate In an evacuated tube,
Result is the emission of Electrons. The
electrons Have kinetic energy. Circuit
diagram-shows that There is an electrical
potential Generated, therefore, a Possible
electrical current. Solar cells use the
Photoelectric effect in Semi-conductors.
6
Quantum Nature of Light
Light behaves like a wave and like a particle.
Particle Nature of light demonstrated by
photoelectric effect. If energy of light is not
enough, no photoelectric effect. (No electrons
knocked out of outer shell of electrons in An
element) Conversion of light energy into
electrical energy is quantized That is discrete.
(these amounts of energy are called photons,
their energy Is measured in electron volts (eV).
) Energy of a photon of light h f where h is
Plancks constant And f is frequency.
7
Solar Radiation vs Photon Energy
Available energy From sunlight, has A certain
range of Photon energies (measured in
eV) Materials In solar cells
exhibit Photoelectric effect Have certain
energies In their electron shells These match
energies Of incoming photons Of light.
8
Materials in Solar Cells Band Gap
Band gap energy in incoming photon needed to
produce Photoelectric effect (knock electrons out
of outer shell) Two tradeoffs higher band gap
more electrical energy per photon Photons with
not enough energy no photoelectric effect What
do photons with not enough energy do to the solar
cell?
9
Inside a Solar Cell
Solar Cells at least 3 layers P-type
semiconductor With electron holes (positive
charge) N-type semiconductor With extra
electrons (negative charge) Active layer In
between generates Electric field
10
Blowup of 3 layer Solar Cell
Top N-type semi-conductor Middle junction or
active layer Bottom P-type semi-conductor
11
Incoming Photons Possibilities
Photons enter solar cell. Some absorbed by
P-layer,free Electrons for circuit. Some pass
through, reflected off bottom of cell. Some meet
up with holes, recombine within cell. Ultimate
result conduction of electricity.
12
Photoelectric Effect
Incoming photons hit Electrons in valence
band. If enough energy, knock them Up to the
conduction band. Incoming photon, knocks
electron Out, makes a hole region Of positive
charge.
13
Within a Solar Cell
Holes float upwards in n region Electrons move
downwards in P region. Recombine in the active
layer.
14
Introducing Boron
Boron has a 3 charge, Silicon has 4
charge. Bluesilicon Redboron Doping silicon
with boron Makes P-type semi-conductor. Why?
15
Introducing Phosphorus
Silicon 4 charge Phosphorus 5 charge Doping
with phosphorus Get extra electrons N-type
semi-conductor
16
Picture of a Solar Cell
17
Layers in a Solar Cell
18
Common Types of Solar Cells
Single crystal silicon up to 23
efficiency Amorphous silicon 5 to 10 efficiency
(40 of marketcheapest) Polycrystalline silicon
gt 10 efficiency GaAs cells 25
efficiency Stacked cells higher
efficiencies Highest so far stacked GaAsGaSb
34 efficiency Stacked silicon 28
efficiency Polycrystalline silicon 18
19
Single Crystal Silicon
Single crystal silicon solar cells Refined from
sand (SiO2) Reduced at 900 deg C, Heated to 1500
C (Czochralski process) To produce silica for
growing Crystals. Crystals sawed up into
wafers. Wafers polished and coated. Assembled
into solar cells. Expensive to make because of
high T Czochralski process
20
Amorphous Silicon Cell
Top contact tin oxide at base of glass SiO2
protects the tin oxide. P-type layer Amorphous
silicon (undoped) N-type layer Bottom contact
Aluminum
21
Multi-junction Amorphous Silicon Cell
Multiple layers increase number of photons Whose
band gaps are matched. (Each part of Cell tailed
to part of visible spectrum). Silicon alloy
with carbon increases band gap Better response
to blue light. Silicon alloy with germanium
decreases band Gap better response to red
light.
22
Amorphous Silicon
Absorbs solar radiation 40 times more
efficiently Than single crystal silicon A one
micron thick film Absorbs 90 of usable
solar Energy.
23
Current Voltageof Solar Cell
Maximum power point- Open circuitcell not
connected Short circuitno resistance Sometimes
add resistance to Circuit to increase cell
Efficiency.
24
Solar Cells Connections
Connect in series Increases voltage Connect
in parallel Increases current
25
Residential Photovoltaic System
26
Stand Alone Solar System
27
Solar SystemGrid Connected
28
Solar Powered Car Sunraycer
29
Solar PlaneSun Seeker
Plane flew 4060 km across the United
States Ultralight plane piloted by designer Eric
Raymond Power from amorphous silicon cells.
Cells charge A Ni-Cd battery that runs an
electric motor. Motor turns a propeller for take
off. Plane is a glider during flight.
30
Mirage Solar Car
31
Solar Oven
Reflects 97 Of solar energy
32
Solar Power Plant in the Desert
33
Solar Trivia
Sunniest city in the U.S.A. Yuma, Arizona Gets
90 of potential sunlight Cloudiest city in the
U.S.A. Quillayute, Washington (241 cloudy days
per year) Time it takes for sunshine falling on
the U.S. to equal Energy in all fossil fuel
consumed by the U.S. in one Year 40
minutes Estimated area of land needed to meet US
energy needs From photovoltaic cells 58,360
square miles Land area of Georgia 58,060 square
miles