13 October 2009

Photovoltaic cell

Photovoltaic cell
The invention: Drawing their energy directly from the Sun, the
first photovoltaic cells powered instruments on early space vehicles
and held out hope for future uses of solar energy.
The people behind the invention:
Daryl M. Chapin (1906-1995), an American physicist
Calvin S. Fuller (1902-1994), an American chemist
Gerald L. Pearson (1905- ), an American physicist
Unlimited Energy Source
All the energy that the world has at its disposal ultimately comes
from the Sun. Some of this solar energy was trapped millions of years
ago in the form of vegetable and animal matter that became the coal,
oil, and natural gas that the world relies upon for energy. Some of this
fuel is used directly to heat homes and to power factories and gasoline
vehicles. Much of this fossil fuel, however, is burned to produce
the electricity on which modern society depends.
The amount of energy available from the Sun is difficult to imagine,
but some comparisons may be helpful. During each forty-hour
period, the Sun provides the earth with as much energy as the
earth’s total reserves of coal, oil, and natural gas. It has been estimated
that the amount of energy provided by the sun’s radiation
matches the earth’s reserves of nuclear fuel every forty days. The
annual solar radiation that falls on about twelve hundred square
miles of land in Arizona matched the world’s estimated total annual
energy requirement for 1960. Scientists have been searching for
many decades for inexpensive, efficient means of converting this
vast supply of solar radiation directly into electricity.
The Bell Solar Cell
Throughout its history, Bell Systems has needed to be able to
transmit, modulate, and amplify electrical signals. Until the 1930’s,
these tasks were accomplished by using insulators and metallic conductors. At that time, semiconductors, which have electrical properties
that are between those of insulators and those of conductors,
were developed. One of the most important semiconductor materials
is silicon, which is one of the most common elements on the
earth. Unfortunately, silicon is usually found in the form of compounds
such as sand or quartz, and it must be refined and purified
before it can be used in electrical circuits. This process required
much initial research, and very pure silicon was not available until
the early 1950’s.
Electric conduction in silicon is the result of the movement of
negative charges (electrons) or positive charges (holes). One way of
accomplishing this is by deliberately adding to the silicon phosphorus
or arsenic atoms, which have five outer electrons. This addition
creates a type of semiconductor that has excess negative charges (an
n-type semiconductor). Adding boron atoms, which have three
outer electrons, creates a semiconductor that has excess positive
charges (a p-type semiconductor). Calvin Fuller made an important
study of the formation of p-n junctions, which are the points at
which p-type and n-type semiconductors meet, by using the process
of diffusing impurity atoms—that is, adding atoms of materials that
would increase the level of positive or negative charges, as described
above. Fuller’s work stimulated interested in using the process
of impurity diffusion to create cells that would turn solar energy
into electricity. Fuller and Gerald Pearson made the first largearea
p-n junction by using the diffusion process. Daryl Chapin,
Fuller, and Pearson made a similar p-n junction very close to the
surface of a silicon crystal, which was then exposed to sunlight.
The cell was constructed by first making an ingot of arsenicdoped
silicon that was then cut into very thin slices. Then a very
thin layer of p-type silicon was formed over the surface of the n-type
wafer, providing a p-n junction close to the surface of the cell. Once
the cell cooled, the p-type layer was removed from the back of the
cell and lead wires were attached to the two surfaces. When light
was absorbed at the p-n junction, electron-hole pairs were produced,
and the electric field that was present at the junction forced
the electrons to the n side and the holes to the p side.
The recombination of the electrons and holes takes place after the
electrons have traveled through the external wires, where they do useful work. Chapin, Fuller, and Pearson announced in 1954 that
the resulting photovoltaic cell was the most efficient (6 percent)
means then available for converting sunlight into electricity.
The first experimental use of the silicon solar battery was in amplifiers
for electrical telephone signals in rural areas. An array of 432
silicon cells, capable of supplying 9 watts of power in bright sunlight,
was used to charge a nickel-cadmium storage battery. This, in
turn, powered the amplifier for the telephone signal. The electrical
energy derived from sunlight during the day was sufficient to keep
the storage battery charged for continuous operation. The system
was successfully tested for six months of continuous use in Americus,
Georgia, in 1956. Although it was a technical success, the silicon solar
cell was not ready to compete economically with conventional
means of producing electrical power.
One of the immediate applications of the solar cell was to supply
electrical energy for Telstar satellites. These cells are used extensively
on all satellites to generate power. The success of the U.S. satellite program prompted serious suggestions in 1965 for the use of
an orbiting power satellite. A large satellite could be placed into a
synchronous orbit of the earth. It would collect sunlight, convert it
to microwave radiation, and beam the energy to an Earth-based receiving
station. Many technical problems must be solved, however,
before this dream can become a reality.
Solar cells are used in small-scale applications such as power
sources for calculators. Large-scale applications are still not economically
competitive with more traditional means of generating
electric power. The development of the ThirdWorld countries, however,
may provide the incentive to search for less-expensive solar
cells that can be used, for example, to provide energy in remote villages.
As the standards of living in such areas improve, the need for
electric power will grow. Solar cells may be able to provide the necessary
energy while safeguarding the environment for future generations.


Anonymous said...

DiLorenzo's finances was unclear yesterday, and he is bound to repeat itself.
And although she went halves with her mother, Linda Ann Weston, 51, cheap landlord insurance (http://2nd.divorcing.co.kr) who is believed to have
been made in the case, visit the Capital Gazette. Graphic X-rays of his skull show the three bullets
which remain in his head.

Anonymous said...

Great blog! Do you have any hints for aspiring writers? I'm planning to start my own blog soon but I'm a
little lost on everything. Would you recommend starting with
a free platform like Wordpress or go for a paid option? There are so many options out there that I'm completely confused ..
Any tips? Many thanks!

Also visit my weblog Inverter Fuji

Anonymous said...

Hey there I am so happy I found your blog page, I really found you by mistake,
while I was looking on Askjeeve for something else, Nonetheless I am
here now and would just like to say thank you for a tremendous post
and a all round thrilling blog (I also love the
theme/design), I don’t have time to go through it all at the minute
but I have bookmarked it and also added your RSS feeds, so when I have time I will
be back to read much more, Please do keep up the awesome b.

Here is my weblog :: buy cheap viagra online

Guo Guo said...

lacoste shirts
kate spade outlet
beats headphones
gucci outlet
louis vuitton
hollister pas cher
hollister canada
cheap snapbacks
louboutin shoes
iphone 6 case
ray ban sunglasses
longchamp handbags
ray ban
ralph lauren polo shirts
herve leger dresses
michael kors outlet
louis vuitton outlet
oakley sunglasses
tods outlet
abercrombie and fitch
kate spade outlet
tiffany jewelry
michael kors uk
toms shoes
coach outlet
ray ban sunglasses online
adidas outlet
tods shoes
swarovski jewelry
cheap jordans
louboutin shoes
mcm bags

林磊 said...

2016-5-12 leilei
coach outlet online
michael kors outlet
chaussure louboutin
lululemon outlet
toms outlet
coach outlet
cheap nike shoes
louboutin outlet
yeezy boost 350 black
versace sunglasses
sac longchamp pliage
cheap air max
micahel kors
michael kors bags
fitflops outlet
lacoste polo shirts
puma shoes
cheap jordans
fitflops sale
michael kors outlet clearance
adidas supercolor
adidas nmd
polo ralph lauren outlet
cheap ray-ban sunglasses
ray ban outlet
longchamp outlet
coach purses on sale
jordan shoes
cheap oakley sunglasses
nike tn pas cher
burberry handbags
louboutin pas cher
coach outlet
michael kors bags
nike cortez red
cheap oakley sunglasses
polo ralph lauren
ralph lauren outlet
air max

chenmeinv0 said...

oakley canada
cheap ugg boots
moncler coats
ugg boots
canada goose outlet
tory burch sale
cheap ray ban sunglasses
gucci belts
michael kors outlet online
oakley sunglasses

Pilule pour bander en pharmacie sans ordonnance said...

La dysfonction érectile (impuissance, panne d’érection ou troubles érectiles) est une incapacité d’obtenir et/ou de maintenir une érection, Les causes de la dysfonction érectile sont multiples et ont pour origine des facteurs organiques (troubles cardiovasculaires par exemple) ou psychologiques (stress, anxiété). Pour résoudre ce problèmes, les experts invitent les patients a faire recours aux Pilule pour bander en pharmacie sans ordonnance. Pour plus d’efficacité, lire attentivement la notice d'information et respecter la posologie du médicament tout en évitant le surdosage.

Meiqing Xu said...

sac longchamp pas cher
tommy hilfiger shoes
adidas yeezy
coach outlet online
adidas yeezy
true religion outlet
kate spade outlet
oakley sunglasses
pandora charms
coach canada