SOLAR CELL ENERGY

Solar cells are used to generate energy using the sun, which is a renewable source of energy, in place of using non-eco friendly methods like burning fuel. The increasing use of Solar cell technology to produce energy gives a clear indication of the increasing awareness about the declining level of fossil fuels and their impact on the environment. Today, the electricity produced through solar technology is being used to power homes, cars and appliances. This has made solar technology to be one of the most important advances in technology in recent times

The development of the solar cell stems from the work of the French physicist Antoine-César Becquerel in 1839. Becquerel discovered the photovoltaic effect while experimenting with a solid electrode in an electrolyte solution; he observed that voltage developed when light fell upon the electrode. About 50 years later, Charles Fritts constructed the first true solar cells using junctions formed by coating the semiconductor selenium with an ultrathin, nearly transparent layer of gold. Fritts's devices were very inefficient, transforming less than 1 percent of the absorbed light into electrical energy.
By 1927 another metalÐsemiconductor-junction solar cell, in this case made of copper and the semiconductor copper oxide, had been demonstrated. By the 1930s both the selenium cell and the copper oxide cell were being employed in light-sensitive devices, such as photometers, for use in photography. These early solar cells, however, still had energy-conversion efficiencies of less than 1 percent. This impasse was finally overcome with the development of the silicon solar cell by Russell Ohl in 1941. In 1954, three other American researchers, G.L. Pearson, Daryl Chapin, and Calvin Fuller, demonstrated a silicon solar cell capable of a 6-percent energy-conversion efficiency when used in direct sunlight. By the late 1980s silicon cells, as well as those made of gallium arsenide, with efficiencies of more than 20 percent had been fabricated. In 1989 a concentrator solar cell, a type of device in which sunlight is concentrated onto the cell surface by means of lenses, achieved an efficiency of 37 percent due to the increased intensity of the collected energy. In general, solar cells of widely varying efficiencies and cost are now available.
Structure
Modern solar cells are based on semiconductor physics -- they are basically just P-N junction photodiodes with a very large light-sensitive area. The photovoltaic effect, which causes the cell to convert light directly into electrical energy, occurs in the three energy-conversion layers.

Two technologies that are currently used to harvest solar energy are the solar photovoltaic and solar thermal methods. Basically, solar photovoltaic technology (PV) involves the conversion of solar rays into electricity, which can then be fed into a grid or used separately to power lighting, heating and cooling systems as well as a wide range of appliances. Solar thermal technology, on the other hand, harnesses sunlight directly to produce solar power, which enables appliances such as solar cookers and water heaters to function without conventional electricity.

Worldwide production of PV cells increased 51% in 2007. Globally, SunPower panels are reported to be the most efficient solar PV panels on the market. The other major global producers are Kyocera, Sharp and Q – Cells. With rising oil prices and growing awareness of the need to adopt environment friendly energy sources, the market for photovoltaic technology is poised for healthy growth.

A fraction with its denominator as `100'
is called a percentage. Percentage means per
hundred.
So it is a fraction of the form
6
1 0 0
3 7
1 0 0
1 5 1
1 0 0
, and and these fractions
can be expressed as 6%, 37% and 151%
respectively.
In such a fraction, the numerator is called
rate percent.
To express x% as a fraction or a decimal,
divide x by 100.
If the price of an item increases by r%,
then the reduction in consumption, so that the
expenditure remains the same is
r
r
x


 

 
1 0 0
1 0 0%
If the price of the commodity decreases
by r%, the increase in consumption, so that
the expenditure remains the same is
r
r
x
1 0 0
1 0 0 %


 

 
If the value is first increased by x% and
then by y%, the final increase is
x y
   xy
 

 
100
%
If there is a decrease instead of increase, a
negative sign is attached to the corresponding
rate percent.
If the value of a number is first increased
by x% and later it is decreased by x% then net
change is always a decrease which is equal to
x2
100

 

 
%
If pass marks in an examination is x% and
if a student secures y marks and fails by z
marks, then the maximum mark
=
1 0 0 (y  z)
x
A candidate scores x% in an examination
fails by `a' marks while another candidate
who scores y% gets `b' marks more than
the minimum required for a pass, then the
maximum mark =
100 (a b)
y  x
If the length of a rectangle is increased
by x% and the breadth is decreased by y%,
then the area is increased or decreased by
(x  y  xy )%
1 0 0
according to the (+) ve or
(-) ve sign obtained.
If the present population is P which increases
R% annually, then
(i) the population after n years
= P 100 R n
100
 
 

 
(ii) the population n years ago
=
n
100 R
100 P 





If the present value of a machine is P
which depreciates at R% per annum, then
(i) the value of the machine after n years
= P 100 R n
100
 
 

 
(ii) the value of the machine n years ago
=
P
R
n 100
100 

 

 

BASIC ENGLISH

THE PRESENT TENSE
1. The Present Simple
Used for a habitual or repeated action, that is,
for something that we do always, every day,
often, usually, etc.
Example: He plays football on Sundays.
a. Used for a general truth or a fact, that is, for
something that is true.
Example: Night follows day.
b. Used for something or an action happening
now.
Example: See how she walks.
c. Used instead of the future tense.
Example: He arrives tomorrow.
d. Used instead of the past tense, to make some
thing look more real.
Example: The tiger comes; it catches the boy.
e. Used instead of the present perfect tense.
Example: We hear that the king is dead.
f. Used to introduce a quotation, that is, to repeat
words spoken or written by someone else.
Example: Shakespeare says: “Neither a bor
rower nor a lender be.”
2. The Present Continuous Tense
Used to show that something is still happening,
that is, an action is still going on at the
time of speaking. It shows that the action is
not yet complete.
Example: He is writing a letter.
a. Used instead of the future tense. We usually
say the time when this future action will take
place
Example: He is going to Japan next week.
b. Used to use the phrase ‘is going’ which
means ‘about to’.
Example: It is going to rain.
c. Used to show an action which happens many
times. We often use ‘always’ with this expression.
Example: He is always getting into trouble.
3. The Present Perfect Tense
Used to show an action which has just been
completed or a past action when the time is
not mentioned. The action may be a recent one
or it may be one which happened a long time
ago.