Download Solar cell

Solar Energy System
Presented by
Prof. Dr. M. Ruhul Amin Bhuiyan
22/02/2017
Department of Electrical and Electronic Engineering, Manisa Celal
Bayar University, TURKEY
Sunlight:
Sunlight is composed of photons,
of electromagnetic radiation or energy.
which
are
simply
small
bundles
Photon:
A photon is defined as a discrete bundle (or quantum) of electromagnetic (or
light) energy. Photons are always in motion, have a constant speed of light to all
observers. c = 2.998 x 108 m/s.
Basic Properties of Photons:
 Move at a constant velocity, c = 2.9979 x 108 m/s in free space.
 Have zero mass and rest energy.
 Carry energy and momentum, which are also related to the frequency and
wavelength of the electromagnetic wave.
 Can be destroyed/created when radiation is absorbed/emitted.
 Can have particle-like interactions (i.e. collisions) with electrons and other
particles.
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Solar cell:
A solar cell or photovoltaic cell is an electrical device that converts the
energy of light directly into electricity by the photovoltaic effect.
The operation of a photovoltaic (PV) cell requires three basic attributes:
 The absorption of light, generating either electron-hole pairs or excitons.
 The separation of charge carriers of opposite types.
 The separate extraction of those carriers to an external circuit.
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Photovoltaic effect:
The photovoltaic effect is a process that generates voltage or
electric current in a photovoltaic cell when it is exposed to sunlight.
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Solar cell materials:
Photovoltaic solar cells are thin silicon disks. The basic component of a solar cell is
pure silicon, which is not pure in its natural state. Pure silicon is derived from such
silicon dioxide. The resulting pure silicon is then doped with phosphorous and boron
to produce an excess of electrons and a deficiency of electrons respectively to make a
semiconductor capable of conducting electricity. The silicon disks are shiny and
require an anti-reflective coating, usually titanium dioxide.
 Purifying the silicon,
 Making single crystal silicon,
 Making silicon wafers,
 Doping,
 Placing electrical contacts,
 The anti-reflective coating, and
 Encapsulating the cell.
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Solar cell production:
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Thin Films Solar Cell
I-III-VI2 semiconductors
CuInSe2
Cu : Ag : Au
In : Ga :Al : Ti
Se : Te : S
CuInSe2
CuxAg1-xInSe2
CuInxGa1-xSe2
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Solar cell connection:
Required for Voltage : Series connection
Required for Current : Parallel connection
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Solar cell functions:
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Equivalent circuit of a solar cell:
Equivalent Circuit
The schematic symbol
of a solar cell
An ideal solar cell may be modeled by a current source in parallel with
a diode; in practice no solar cell is ideal, so a shunt resistance and a
series resistance component are added to the model.
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Characteristic equation:
From the equivalent circuit it is evident that the current produced by the solar cell is equal
to that produced by the current source, minus that which flows through the diode, minus
that which flows through the shunt resistor:
I = IL − ID − ISH
where
I = output current (amperes)
IL = photo generated current (amperes)
ID = diode current (amperes)
ISH = shunt current (amperes).
The current through these elements is governed by the voltage across them:
Vj = V + IRS
where
Vj = voltage across both diode and resistor RSH (volts)
V = voltage across the output terminals (volts)
I = output current (amperes)
RS = series resistance (Ω).
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By the Shockley diode equation, the current diverted through the diode is:
where
I0 = reverse saturation current (amperes)
n = diode ideality factor (1 for an ideal diode)
q = elementary charge
k = Boltzmann's constant
T = absolute temperature
By Ohm's law, the current diverted through the shunt resistor is:
where
RSH = shunt resistance (Ω).
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Substituting these into the first equation produces the characteristic equation of a
solar cell, which relates solar cell parameters to the output current and voltage:
Open circuit voltage and short circuit current:
When the cell is operated at open circuit, I = 0 and the voltage across the output terminals is
defined as the open-circuit voltage. Assuming the shunt resistance is high enough to neglect the
final term of the characteristic equation, the open-circuit voltage VOC is:
Similarly, when the cell is operated at short circuit, V = 0 and the current I through the
terminals is defined as the short-circuit current. It can be shown that for a high-quality solar cell
(low RS and I0, and high RSH) the short-circuit current ISC is:
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Graphically presentation:
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Solar cell and panel I-V characteristic curves:
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Fill factor, FF of a solar cell:
The FF is defined as the ratio of the maximum power from the solar cell to the
product of Voc and Isc.
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Efficiency of a solar cell:
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Solar or PV System:
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Thanks to all