1. PHOTO VOLTAIC GENERATORS
As name indicates
PHOTO = light
VOLTAIC = volts
PHOTVOLTAICS IS A METHOD of generating
electrical power by converting solar
radiation into direct
current electricity using semiconductors that exhibit
the Photovoltaic effect.
2. WHAT IS PHOTO VOLTAIC EFFECT?
Photovoltaic effect is the basis of photo voltaic
power generation.
The photovoltaic effect is the creation
of voltage or electric current in a material upon
exposure to light.
4. WHAT IS PHOTO VOLTAIC EFFECT?
•
When the sunlight or any other light is
incident upon a material surface, the
electrons present in the valence
band absorb energy and, being excited,
jump to the conduction band and become
free. These highly excited electrons jump
into a different material (electrodes). This
generates an electromotive force, and
thus some of the light energy is converted
into electric energy which means energy is
generated in this way.
5. FABRICATION OF SOLAR/PHOTOVOLTAIC CELL
In
1883, first photo voltaic cell was made by
Charles Fritts, who coated
the semiconductor selenium with an
extremely thin layer of gold to form the
junctions.
It was only 1% efficient.
To understand the fabrication of solar cells
we need to understand some basics,……….
7. FABRICATION OF SOLAR CELLS
The first practical photovoltaic cell was developed
in 1954 at Bell Laboratories .They used a diffused
silicon p–n junction that reached 6% efficiency,
compared to the selenium cells.
Most practical solar cells are silicon based ,
because it is cheap and abundant material.
8. STEPS OF FABRICATION
First step is refining silicon
Silicon dioxide (SiO2) is the most abundant mineral
in the earth's crust.
The manufacture of the hyper pure silicon for
photovoltaics starts with locating a source of silicon
dioxide in the form of sand.
The silica is reduced (oxygen removed) through a
reaction with carbon in the form of coal, charcoal
and heating to 1500-2000 °C in an electrode arc
furnace.
9. STEPS OF FABRICATION
oSilicon di oxide + Carbon = Silicon + Carbon di oxide
oThe resulting silicon is 98% pure. It contains Fe, Al, and
B , to remove these traces , further purification is
done ,
Powdered Si is reacted with anhydrous HCl
at 300 C to form SiHCl3
10. STEPS OF FABRICATION
•During this reaction impurities such as Fe, Al, and B react
to form their halides (e.g. FeCl3, AlCl3, and BCl3).
•The SiHCl3 has a low boiling point of 31.8 C and
distillation is used to purify the SiHCl3 from the
impurity halides.
•Finally, the pure SiHCl3 is reacted with hydrogen at 1100 C
for ~200 – 300 hours to produce a very pure form of silicon.
11. STEPS OF FABRICATION
Above reaction takes place inside large vacuum
chambers and the silicon is deposited onto thin
polysilicon rods (small grain size silicon) to produce
high-purity polysilicon rods of diameter 150-200mm.
Silicon used for solar cells can be single crystalline,
multi crystalline, polycrystalline or amorphous. The
key difference between these materials is degree to
which the semiconductor has a regular, perfectly
ordered crystal structure.
12. STEPS OF FABRICATION
AFTER GETTING THE REQUIRED SILICON
FROM ABOVE MENTIONED CHEMICAL
PROCEDURE , different methods of solar cells
fabrication are applied , each method involves
doping of silicon to make p-n junction , and
required processes to make a furnished solar cell.
13. METHODS OF FABRICATION
1) SCREEN PRINTED SOLAR CELL
FABRICATION TECHNOLOGY
Screen-printed solar cells were first developed in
the 1970's. Most mature solar cell fabrication
technology. The key advantage of screen-printing is
the relative simplicity of the process.
It involves cutting a wafer of 10*10 square cm
,0.5mm thick , this wafer is then p-type doped with
born to add up holes .
29. BURIED CONTACT FABRICATION TECHNOLOGY
The buried contact solar cell is a high efficiency
commercial solar cell technology based on a plated
metal contact inside a laser-formed groove.
Buried contact solar cell to have performance up to
25% better than commercial screen-printed solar
cells.
Shading losses are 2 to 3%.
without having a wide strip of metal on the top
surface as in last case, and a large metal height-towidth aspect ratio increases the efficiency of cell.
30. RECENT FABRICATION RESEARCHES
To further increase efficiencies of solar cells , it is
found useful to modify the structures of solar cells
to maximize the life of cells as well as to increase
their power rating .
Some new structures are shown next……
32. USE OF SOLAR CELLS FOR SPACE VEHICLES
Invention of solar cells for practical scales and their
implementation for power generation in space
vehicles has modified and eased the space
research work.
Solar panels are shaped and fixed on the body of
space vehicle .
Sine sun rays need no any medium to flow , these
rays are available in space and are utilized by solar
cells for power requirements of space vehicles.
So in space vehicles , D.C batteries are only used
for power storage , and they are not the only source
of power generation , as solar cells are installed
33. USE OF SOLAR CELLS IN SPACE FOR EARTH
The solar energy available in space is literally
billions of times greater than we use today.
Americans are working on to gathers energy from
sunlight in space and transmits it wirelessly to Earth
i.e. SPACED BASED SOLAR POWER PROJECT
Space solar power is by far the largest potential
energy source available.
A lot of work is to be done in this context.
