Photovoltaic Cells:
Solar Cells
EBB 424
Dr. Sabar D. Hutagalung
USM
Efficiency
 Efficiency = Fraction of incident light energy converted to electrical
energy.
 Efficiency is the most important characteristic because it allows the
device to be assessed economically in comparison to other energy
devices.
 For a given solar spectrum, the efficiency depends on:

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Semiconductor material
Device structure
Ambient conditions (temperature)
High radiation damage
Sun spectrum
 Efficiency alone is not enough, the cost of the cell is also important
and the life time.
I-V characteristics & Efficiency
in dark (diode)
under illumination
Typical I-V characteristic of solar cells
I-V characteristics & Efficiency
As the intensity
increases, the shortcircuit current ISC
increases linearly,
but the open circuit
voltage VOC increases
sublinearly.
The I-V characteristics of a solar cell with varying
illumination as a parameter.
I-V characteristics & Efficiency
I-V characteristics & Efficiency
(II)
(I)
(III)
(IV)
The I-Va characteristic of a solar cell.
The maximum power is obtained at Pm = ImVm
I-V characteristics & Efficiency
I-V characteristics & Efficiency
I-V characteristics & Efficiency
The I-V characteristics of a solar cell with varying illumination
I-V characteristics & Efficiency
Calculation, η
Consider a solar cell driving a 30Ω resistive load. The cell has area = 1
cm x 1 cm and is illuminated with light of intensity = 600Wm-2 and has I-V
characteristic as shown below.
0.425V
14.2mA
Q: What are the current and voltage in the circuit?
A: I’ = 14.2mA , V’ = 0.425V
Q: Calculate the power delivered to the load (Pout)
A: Area under the I’, V’ rectangular = P
P= 14.2 x 10-3A x 0.425V = 6.035mW
Calculation, η
Q: Calculate the input sun-light power
A: Pin = (light intensity x surface area)
Pin = 600Wm-2 x (0.01m)2 = 0.06W
Q: Calculate the efficiency of the device
A:
η = 100x (Pout/Pin)
Pin = 0.06W
Pout = 6.035mW
η = 10.06%
Q: State why the efficiency is very small?
Solar Spectrum
Conversion Efficiency
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The most efficient PV modules usually
employ single-crystal Si cells, with
efficiencies up to 15%.
Poly-crystalline cells are less expensive to
manufacture but yield module efficiencies of
about 11%.
Thin-film cells are less expensive still, but
give efficiencies to about 8% and suffer
greater losses from deterioration.
Solar Photovoltaic Plants
How PV Cells Work
Photovoltaic cells, modules, panels and
arrays
Diagram of a photovoltaic cell
Major photovoltaic system components.
Problem

Suppose that a particular family house in a sunny
geographic location consumes a daily average electrical
power of 1500 W supply by an 50 m2 are of solar panel. The
average solar intensity incident per day is about 6 kWh m-2.
What is the efficiency of solar cell?
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Solution

Total sunlight energy per day:
= intensity x area
= 6 kWh m-2 x 50 m2
= 300 kWh

Solar cell output = 1.5 kW x 24 h = 36 kWh

Efficiency = Output/Total energy light
= 36 kWh/300 kWh
= 12 %
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Solar Cells