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Jordan University of Science and Technology Department of applied Physics

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Jordan University of Science and Technology Department of applied Physics Solar cells [Operation principles and testing] Advisor: Dr. Adnan Shariah – PowerPoint PPT presentation

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Title: Jordan University of Science and Technology Department of applied Physics


1
Jordan University of Science and
TechnologyDepartment of applied Physics
  • Solar cells
  • Operation principles and testing

Advisor Dr. Adnan Shariah
Ghassan Mohammad Masadeh
2
Table of content
Introduction
Semiconductors
p-n junction
Solar cell system work
Performance of solar cells
Silicon solar cells
I-V Characteristic of solar cells

Testing and result
3
Introduction
  • Solar cells are devices in Which sun light
    releases electric charges so they can move freely
    in a semiconductor and ultimately flow through an
    electric load, such as a light bulb or a motor .
  • The phenomenon of producing voltages and
    currents in this way is known as the photovoltaic
    effect (PV e ffect).

4
The PV effect was discovered in 1839 by French
physicist Becquerel. It remained in the
laboratory until 1954. When Bell laboratories
produced the first silicon solar cell.
5
Solar cells are already being used in
terrestrial applications where they are
economically competitive with alternative
sources. Examples are powering communications
equipment ,pumps, and refrigerators located far
from existing power lines .
The first of the economic forces the rising
price of conventional sources particularly those
employing fossil fuels. continues automatically,
in part because the resource is limited.
6
The second reducing the cost of electricity
from solar cell system is the subject of world
wide research and development efforts today.
To increase the economic attractiveness of the
solar cell option
  • - increase cell efficiencies
  • - reduce cost of producing cells modules.
  • - devise new cell or system designs for lower
    total cost per unit power out put.

7
Semiconductors
Semiconductors are crystals that in their pure
state are resistive, but when the proper
impurities are added this process is called
doping in trace amounts often measured in parts
per billion, display much lower resistance along
with other interesting and useful properties.
Depending on the selection of impurities added,
semiconductor materials of two electrically
different types
n-type and p-type.
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p-n junction
The basic structure formed by the intimate
contact of p-type and n-type semiconductors
n-type semiconductor A semiconductor type in
which the density of holes in the valence band is
exceeded by the density of electrons in the
conduction band.
P-type semiconductor
A semiconductor type in which the density of
electrons in the conduction band is exceeded by
the density of holes in the valence band.
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The solar cell system work
12
The most important physical phenomena employed
in all solar cells are very similar to the
classical p-n junction. When light is by the
junction the energy of the absorbed photons is
transferred to the electron and hole both free to
move. These particles diffuse through the
semiconductor and ultimately encounter an energy
barrier that permits charged particles of one
sign to pass but reflects those of the other
sign.
The charge carriers in the junction region
create a potential gradient, get accelerated
under the electric field and circulate as the
current through an external circuit.
13
The current from the cell may pass directly
through the load or it may be changed first by
the power, conditioning equipment from those
provided by the cell, other subsystems that may
also be used include energy storage devices such
as batteries and concentrating lenses or mirror
that focus the sunlight onto a smaller to and
hence less costly semiconductor cell.
14
Performance of solar cells
An important feature of solar cells is that
the voltage of the cell does not depend on its
size, and remains fairly constant with changing
light intensity. However, the current in a device
is almost directly proportional to light
intensity and size.
15
Figure below shows example I / V curves for a
single cell as a function of light input
16
A solar cell's power output can be
characterized by two numbers a maximum Open
Circuit Voltage Voc measured at zero output
current and a short circuit current Isc
  • Where
  • Voc k T/ q ln (IL /I o)1
  • And
  • I I o exp.(qv/kT)-1 - I L
  • I L q AG (L e W L h )

And the power can be computed via this
equation P I V
17
As you might then expect, a combination of
less than maximum current and voltage can be
found that maximize the power produced. This
condition is called "maximum power point
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the single crystal silicon cell
Silicon has some special chemical properties,
especially in its crystalline form. An atom of
silicon has 14 electrons, arranged in three
different shells. The outer shell, however, is
only half full, having only four electrons. A
silicon atom will always look for ways to fill up
its last shell. To do this, it will share
electrons with four of its neighbor silicon
atoms. except that in this case, each atom has
four hands joined to four neighbors. That's what
forms the crystalline structure, and that
structure turns out to be important to this type
of PV cell.
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A solar cell has silicon with impurities other
atoms mixed in with the silicon atoms, changing
the way things work a bit. We usually think of
impurities as something undesirable, but in our
case, our cell would not work without them. These
impurities are actually put there on purpose.
Consider silicon with an atom of phosphorous here
and there, maybe one for every million silicon
atoms. It still bonds with its silicon neighbor
atoms, but in a sense, the phosphorous has one
electron that doesn't have anyone to hold hands
with. It doesn't form part of a bond, but there
is a positive proton in the phosphorous nucleus
holding it in place.
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This diagram shows a typical crystalline silicon
solar cell
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In solar cells applications this characteristic
is usually drawn inverted about the voltage axis.
The cell generates no power in short-circuit or
open-circuit. The cell delivers maximum power P
max when operating at a point on the
characteristic where the product IV is maximum.
This is shown graphically below where the
position of the maximum power point represents
the largest area of the rectangle shown.
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Testing and result
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  • THANK YOU
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