PHYS 1110
Lecture 15
Professor Stephen Thornton
October 25, 2012
Reading Quiz
Which of the following statements is not true?
A)
B)
C)
D)
The pn-junction diode is the basis of an LED.
The pn-junction diode is the basis of solar cells.
I have never seen an LED.
LEDs can be practically any color including
red, green, or blue.
E) Solar cells are essentially an LED operated in
reverse.
Reading Quiz
Which of the following statements is not true?
A)
B)
C)
D)
The pn-junction diode is the basis of an LED.
The pn-junction diode is the basis of solar cells.
I have never seen an LED.
LED can be practically any color including
red, green, or blue.
E) Solar cells are essentially an LED operated in
reverse.
Quiz next Tuesday, October 30 on
Ch. 5 Thermodynamics
Ch. 6 Fossil Fuels
Ch. 7 Hydropower only
You may bring in one regular sheet of
paper with anything written on it that
you wish. Quiz will start at 10:20 am.
Figure 7-49 Energy bands for a semiconductor
like silicon. Electrons are in the filled (valence)
band, but not the unfilled (conduction) band.
Electrons are forbidden to be in the energy gap.
Conduction band
Energy
Valence band
We add impurities to semiconductors to
make them better conductors. Add
arsenic to have one extra electron (ntype) and boron to have an extra hole (ptype). They become much better
conductors of electricity. Holes are like
free electrons with plus charge.
pn-Junction
Figure 7-50 p-type and n-type semiconductors are placed
side by side. The black dots are electrons, and the white
dots are holes. The electrons pass over the junction.
pn-Junction Diode
Figure 7-51 The electrons from the n side
drift over the junction to fill the holes in
the p side leaving a neutral depletion zone.
Figure 7-52 A forward-biased diode causes
electrical current to easily flow.
Figure 7-53 A pn-junction diode that is
reversed bias prevents electrical current
from passing through the diode.
Figure 7-54 When an excited atom in an LED
has an electron jump from the conduction band
back to the valence band, it releases energy in the
form of an emitted photon of visible light.
E = hf
Figure 7-55 Schematic process of a solar cell.
An incoming photo of light passes its energy
to an electron allowing it to jump to the
conduction band.
e
Electrical power output
=
Power of incident light
P = VI
Figure 7-56 A solar cell collects sunlight
and produces electricity to operate a motor
just like a battery does.
Figure 7-57 A diagram of a solar cell.
Figure 7-58 The Shockley-Queisser limit
for the theoretical maximum efficiency of a
single solar cell is about 30%. This can be
exceeded for multilayer solar cells.
Figure 7-59 The spectrum intensity of
solar radiation at the top of Earth’s atmosphere
and at sea level. Note that ultraviolet, visible,
and infrared regions are indicated.
Figure 7-60 The voltage – current
characteristics of a silicon solar cell as
a function of the solar luminosity.
Quiz
Which of the following statements is not
true?
A)
B)
C)
D)
E)
Electrons can be in valence bands.
Electrons cannot be in energy gaps.
Electrons can be in conduction bands.
Holes are normally in the conduction band.
Holes are normally in the valence band.
Quiz
Which of the following statements is not
true?
A) Electrons can be in valence bands.
B) Electrons cannot be in energy gaps.
C) Electrons can be in conduction bands.
D) Holes are normally in the conduction
band.
E) Holes are normally in the valence band.
Figure 7-61 A technician
installing solar panels on
a rooftop.
Figure 7-62 A self contained solar system for a
residence or other building usually has a charge
controller, battery, and inverter.
Figure 7-63 A five-solar PV
panel system that can supply
electricity to the grid.
There are many large PV power stations in the United
States and the World. The largest is a 200 MW plant in
China named Golmud Solar Park. It produces 317 GWh
of energy annually and has a capacity factor of 18%. The
second largest, and the largest until 2011, is the Sarnia PV
Power Plant in Canada, which has 97 MW nominal power,
production of 120 GWh, and a capacity factor of 17%.
The largest United States plant is the Copper Mountain
Solar Park (in Nevada) with a nominal power of 48 MW,
production of 100 GWh, and capacity of 24%. There are a
large number of PV power plants planned or under
construction. These include a 2000 MW plant in China,
1000 MW plant in Serbia, and several 500-750 MW plants
in the United States.
Despite the rapid growth of solar PV power
since the late 1990s, solar power accounts for less than 1% of
the United States electrical use. Germany has by far the largest
use of solar power, partly due to feed-in tariffs that guarantee
that utility companies will purchase the solar power at a high,
fixed price. The United States also has had large incentives
along with many states, especially California, but electricity
still remains relatively cheap in the US, and solar power
produced electricity is still more than twice as expensive as
hydro, coal, oil, and nuclear power. In 2010 Germany had 29
MW of the world’s 40 MW of PV peak power. Spain, Japan,
and Italy were next with 3-4 MW each. The United States was
fifth with only 2.5 MW of installed PV capacity. Curiously, the
Czech Republic has almost as much per capita capacity (186
W/capita) as Germany (212 W/capita). Spain is third at 83
W/person, less than half as much as Germany and the Czech
Republic. The United States has only 8 W/capita.
Chinese solar cell manufacturers have captured most of the world’s market in
recent years with the help of lavish government subsidies of low loan rates,
cheap or free government owned land, and large economies of scale. China
has the top four manufacturers and 7 of the top 10. Taiwan has the other
three. No European or United States manufacturers are in the top ten.
Regarding the top ten companies producing solar modules, eight are Chinese,
one is German, and one (Sunpower) is US. One of the companies in 2009
with the largest PV capacities capability (420 MW) and production capacity
(200 MW) is a Chinese company named Canadian Solar! The Chinese
manufacturing growth has been phenomenal. It had half the global market in
2010, and its share continues to grow. Its three largest solar power companies
announced huge growths in early 2011. The United States has complained
about unfair trade practices and won a preliminary ruling against China in
2011. Three American companies filed for bankruptcy in August 2011:
Solyndra of California, Evergreen Solar of Massachusetts, and SpectraWatt of
New York. The case of Solyndra has been frequently mentioned in the media
because of a $527 million loan from the federal government that appears to
be completely lost. The price of solar panels plunged more than 40% during
2011, and the huge Chinese capacity flooded the market.
Building-integrated
photovoltaics
(BIPV)
Figure 7-64 The CIS
tower in Manchester,
England was retrofitted
with 7,000 PV blue panels
in 2005 to replace mosaic
tiles that had a tendency
to come loose.
Generations of Solar Cells
First generation solar cells are primarily the large, monocrystal silicon
PV cells that continue to dominate the market. Despite high
manufacturing costs, these cells, consisting of silicon wafers, have higher
efficiency and account for more than 80% of the market. First
generation cells are also made from polycrystalline silicon and
amorphous silicon.
Second generation cells, also called thin-film PV cells, are
considerably cheaper than pure silicon cells but have lower efficiencies.
Besides cost they have a huge advantage in their flexibility. This allows
them to be rolled out onto surfaces like roofs. The films are lightweight
and visually pleasing. Second generation cells may dominate the
residential market as new, higher-efficiency thin-film cells are produced.
But the monocrystal silicon wafers have become cheaper and continue to
dominate the market, although it is expected that the second generation
materials will overtake the first generation panels in the next few years.
Third generation cells are at the cutting edge of technology. These
are still in the research phase and do not require pn-junction diodes.
There is a wide range of possibilities including polymers,
nanocystals, and dye-sensitive solar cells. It is hoped that these new
cells will overcome the Shockley-Queisser limit of 31-41%
efficiency for single bandgap solar cells. The efficiencies can be
improved by stacking very thin cells with different bandgaps on top
of each other – called the tandem cell or multi-junction approach.
Gallium arsenide (GaAs) cells with three layers currently hold the
experimental record of 41.6% efficiency.
First generation cells currently have the highest efficiencies,
while second generation cells are cheaper with acceptable
efficiencies. It is expected that third generation cells will eventually
succeed, but no one knows when that will happen.
Figure 7-65 A neighborhood with
solar panels on every house. Is this
the reality of the future?
Figure 7-66 Location of the
Mojave and Sonoran deserts in
California, Nevada, Utah,
Arizona and Mexico cover
376,000 km2.
Calculate how much power
can be produced. Use an
existing solar farm as model.
International as well as American Energy Associations expect that
the combination of PV and CSP may produce as much as 25% of
the world’s electricity needs by 2050. This is not an unreasonable
estimate based on expected technology and conservation efforts. It
has been estimated that an area of 26,000 km2 is needed to supply
all the electricity required by the United States. Is this large? It is
only a square about 100 miles on each side. The Mojave Desert in
California, Nevada, Utah, and Arizona covers 65,000 km2 so only
40% of it would be needed. There have been proposals to cover
nearly 40 square miles of the Mojave Desert with solar projects that
would produce 3500 MW. The Sonoran Desert is even larger
(311,000 km2) than the Mojave and runs down into Mexico (see
Figure 7-66) into Sonora, Baja California, and Baja California Sur.
There is ample desert area for solar power facilities, and there are
already numerous solar plants in the Mojave Desert.
Two solar projects in the Mojave Desert:
Mojave Solar Project; 280 MW, 1785 acres, 0.157
MW/acre. 2013
Ivanpah Solar Power Facility; 392 MW, 3500 acres,
0.112 MW/acre. 2013.
Use average of 0.13 MW/acre.
1 km 2 = 247.1 acres
376,000 km 2 = 376,000 (247.1 acres)
= 9.3 ´ 107 acres
0.13 MW/acre ´ (9.3 ´ 107 acres)
= 1.2 ´ 107 MW = 12 TW
Global power need is 15 TW
12 TW x (7 h/day) x (365 days/y)
= 31,000 TWh
Global energy usage in 2008 was
132,000 TWh
Discuss differences in calculation
(electricity vs. energy, MW/acre, ever
optimistic)
In the late 1970s President Jimmy Carter and Congress
passed renewable energy incentives. To show his
commitment, President Carter installed solar panels on the
White House for a solar hot water system. When Ronald
Reagan became President, he helped removed federal solar
incentives and after only two years after their installation,
he even removed the solar panels Carter had installed. Oil
was king again. But President George W. Bush, without
fanfare, installed solar thermal systems on the presidential
spa and on a maintenance shed. President Barrack Obama
promised to put the solar panels back on the White House
roof and publicly stated in 2010 that they would be
installed by spring 2011. By October 2012 the solar
panels have yet to be installed.
There were no solar projects on public land when
Obama took office. Now there are 17.
Solar installations continue to skyrocket in the USA in
2012. Much of this is a result of the federal stimulus for
jobs.
In September 2012 the US had 5700 MW of installed
solar capacity. It is almost doubling each year.
These are new installations.
Concentrating Solar Power (CSP and CPV):
Cogentrix’s 30-MWac CPV Alamosa Solar came on-line.
Construction progressed at the BrightSource Ivanpah
Project, with 92 percent of pylon installation complete at
Unit 1 at the end of June.
Two CSP projects, the 100-megawatt Quartzsite Project
and the 100-MW Moapa Solar Energy Center, were
expedited under President Obama’s “We Can’t Wait”
initiative.
As of the end of Q2 there is a cumulative of 546 MW
concentrating solar capacity operating in the U.S.
Photovoltaics (PV):
PV installations totaled 742 MW in Q2 2012, up 45 % over Q1
2012 and 116% over Q2 2011.
The residential market remained relatively flat in Q2, while the
non-residential market shrank 33% on a quarterly basis.
Q2 2012 was the largest quarter ever for utility PV installations,
as more than 20 projects were completed, totaling 447 MW.
There is now a cumulative 5,161 MW of PV capacity spread
amongst nearly 248,000 individual systems operating in the U.S.
as of the end of Q2.
GTM Research forecasts that 3.2 GW of PV will be installed in
the U.S. in 2012, up 71% over 2011.
Quiz
Which of the following countries could more
easily use solar energy?
A)
B)
C)
D)
E)
United States
Sweden
Rwanda
Germany
Canada
Quiz
Which of the following countries could more
easily use solar energy?
A)
B)
C)
D)
E)
United States 400 latitude
Sweden 700 latitude
Rwanda 20 latitude
Germany 600 latitude
Canada 600 latitude
Quiz
Which one of the following US Presidents
was or is least supportive of renewable
energy?
A)
B)
C)
D)
Jimmy Carter
Ronald Reagan
George W. Bush
Barrack Obama
Quiz
Which one of the following US Presidents
was or is least supportive of renewable
energy?
A)
B)
C)
D)
Jimmy Carter
Ronald Reagan
George W. Bush
Barrack Obama