Solar Cell

Jeet Bhattacharjee, Int. PhD - 24483

August 2024

1 OBJECTIVE
The objective of this project is to study some properties of a solar cell. The studies are
been done in the following steps,

1. Determination of intensity of light at different distances.

2. Measurement of open circuited voltage and short circuited current for 4 different
position of light source.

3. Observation of I-V characteristics for 4 different positions of the light source.

4. Observation of I-V characteristics with different external conditions;

• different ranges of temperature (with blower),

• solar battery covered by glass plate.

5. Calculation of power and plot power-resistance. Calculation of Rmax .

6. Calculation of Fill factor in each case.

2 APPARATUS
The apparatus needed for this experiment are given below;

1. Light Source (a lamp).

2. Thermopile (to measure intensity in terms of voltage).

3. Solar Cell

4. Plug-in board

5. Bridging Wires

6. 2 Multimeters (used as ammeter and voltmeter)

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 7. Potentiometer

8. Blower (a dryer)

9. Glass Plate

3 THEORY
A solar cell or [1] photovoltaic cell (PV cell) is an electronic device that converts the energy of
light directly into electricity by means of the photovoltaic effect. It is a form of photoelectric
cell, a device whose electrical characteristics (such as current, voltage, or resistance) vary
when it is exposed to light. Individual solar cell devices are often the electrical building
blocks of photovoltaic modules, known colloquially as ”solar panels”. Almost all commercial
PV cells consist of crystalline silicon, with a market share of 95%. Cadmium telluride thin-
film solar cells account for the remainder. The common single-junction silicon solar cell can
produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts.

3.1 Construction of Solar Cell

A solar cell is a junction diode [2]. The construction of a solar cell varies from that of
a standard p-n junction diode. First, a thin layer of p-type semiconductor is allowed to
contact a thick n-type semiconductor. Then, on the p-type semiconductor, a few finer
electrodes are applied.
These fine electrodes do not cause any obstruction in the pathway of the light to reach
the thin p-n junction. A current collecting electrode is also placed at the bottom of the
n-type layer.
In addition, manufacturers can also encapsulate the assembly using thin glass to help
prevent mechanical shocks in the solar cell. The encapsulated solar cells can be placed in
an aluminium frame with a Tedlar back sheet.

3.2 Working of Solar Cell

When light reaches the p-n junction between the p and n-type semiconductors, photons
easily enter through a thin p-type layer.
The photons provide energy to the p-n [2] junction, creating electron-hole pairs. This
light disrupts the thermal equilibrium condition of the junction, encouraging the free elec-
trons to move to the n-type side of the junction.
The holes move to the junction’s p-type side in a similar pattern. As a result, free
electrons on the n-type side fail to move past the junction due to a potential barrier.
The same barrier potential of the junction blocks the newly-created holes, causing an
increased concentration of electrons on one side (at the n-type junction) and holes on the
other side. This process allows the p-n junction to operate as a battery cell.

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 Figure 1: Working Principle of Solar Cell

Source: https://www.solarsquare.in/blog/solar-cell-construction/

3.3 Concept of Short Circuit Current and Open Circuit Voltage

The I-V characteristics of a solar cell are shown in Fig. 3. When the circuit is shorted,
we get the short circuit current (Ishort ). On the other hand, for open circuit, we get open
circuit voltage (Vopen ). The ratio of these two, gives the value of internal resistance of the
circuit;

Vopen
Ri =
Ishort
For different irradiance, we get different I-V characteristics. For smaller distance (d)
from the source (i.e. higher irradiance ϕ) we get greater value of Ishort .

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 Figure 2: Solar Cell I-V characteristics

Source: https://www.alternative-energy-tutorials.com/photovoltaics

3.4 Expected I-V characteristics in Normal and Perturbed Conditions

The perturbed conditions used are : under a different temperature and with glass absorber.
For different temperature, as the irradiance remains unchanged, we should expect same
value of Ishort . But for greater temperature, thermal energy would contribute to the forward
current. This results in decay of magnitude of current at a lower voltage.
For using a glass absorber in front of the solar cell, all the factors remain same except
the irradiance. The glass absorber reflects and absorbs some light and the intensity falling
on the solar cell decreases. This causes a significant decrease of Ishort .

4 Procedure
1. At first a calibration data (distance and intensity) was taken by using thermofile.
Thermofile determines intensity and gives output in volts. The I - V curve is shown
below. From this calibration, the whole experiment can be analysed in terms of
intensity or irradiance just by performing the experiment for different distances.

2. Then 2 different solar cells (those were disconnected initially), were connected using
a wire.

3. After that, the circuit was shorted and Ishort was measured at different distances
(500mm, 600mm, 700mm and 800mm here)

4. Then the circuit was disconnected and the open circuit voltage Vopen was measured
for the above distances.

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 5. Then the data was taken for some finite resistance (using potentiometer) connected
in the circuit for the above distances.

6. After that for 600mm distance, the solar cell was heated using a blower and then the
data was taken for different resistances.

7. Then, a glass plate was introduced in front of the solar cell (at 600mm distance) and
the data was taken.

8. For all the cases, the power-resistance plots are done also.

By using the data taken during the experiment, resistances, error in resistances and fill
factors are calculated.

5 Observations
To observe the behaviour of solar cell we need to check the I-V characteristics in different
values of intensity. For varying the intensity, the distance from light source can be var-
ied. The calibration (voltage and distance) needed for this experiment is done by using
thermopile. The calibration data (inverse squared distance d12 and voltage V ) are plotted.

Thermophile
distance (in mm) Voltage (in mV) 1/d2
300 31.3 1.11E-05
400 20.6 6.25E-06
500 14 4.00E-06
600 9.9 2.78E-06
700 7.4 2.04E-06
800 5.3 1.56E-06
900 4.2 1.23E-06
1000 3.3 1.00E-06

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5.0.1 Table for I-V characteristics (Normal Conditions)

d = 500 mm
V in Volts I in mA R (in ohm) Power (in mW)
1.63 57.6 28.2986111 93.888
1.94 46.7 41.5417559 90.598
2 37.8 52.9100529 75.6
2.04 27.8 73.381295 56.712
2.05 24.2 84.7107438 49.61
2.06 20.9 98.5645933 43.054
2.07 17.9 115.642458 37.053
2.07 15 138 31.05
2.07 13.3 155.639098 27.531
2.07 12.1 171.07438 25.047
2.06 10.9 188.990826 22.454
2.07 9.6 215.625 19.872
2.07 9.2 225 19.044

d = 600 mm
V in Volts I in mA R (in ohm) Power (in mW)
1.38 52.4 26.33587786 72.312
1.8 46.5 38.70967742 83.7
1.94 32.7 59.32721713 63.438
1.98 26.8 73.88059701 53.064
2 21.4 93.45794393 42.8
2.02 18.1 111.6022099 36.562
2.03 15.8 128.4810127 32.074
2.03 13.5 150.3703704 27.405
2.03 12 169.1666667 24.36
2.03 10.8 187.962963 21.924
2.04 10.2 200 20.808
2.04 9.4 217.0212766 19.176
2.04 8.8 231.8181818 17.952

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 d = 700 mm
V in Volts I in mA R (in ohm) Power (in mW)
1.15 51.2 22.4609375 58.88
1.79 41.3 43.34140436 73.927
1.89 31.7 59.6214511 59.913
1.94 25.2 76.98412698 48.888
1.97 21.2 92.9245283 41.764
1.98 18.6 106.4516129 36.828
1.99 15.7 126.7515924 31.243
2 13.5 148.1481481 27
2.01 12 167.5 24.12
2.01 10.7 187.8504673 21.507
2.02 9.9 204.040404 19.998
2.02 9.1 221.978022 18.382
2.02 8.7 232.183908 17.574

d = 800 mm
V in Volts I in mA R (in ohm) Power (in mW)
1.26 43.9 28.7015945 55.314
1.52 42.5 35.7647059 64.6
1.72 38.5 44.6753247 66.22
1.78 34.5 51.5942029 61.41
1.84 30.3 60.7260726 55.752
1.88 25.8 72.8682171 48.504
1.91 23.4 81.6239316 44.694
1.93 20.3 95.0738916 39.179
1.94 18.5 104.864865 35.89
1.95 17.4 112.068966 33.93
1.94 16 121.25 31.04
1.95 15 130 29.25
1.96 13.9 141.007194 27.244

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5.0.2 Plots

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Figure 3: Voltage vs d2
plot

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Figure 4: I-V characteristics for various distances

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5.0.3 Table for I-V characteristics (Perturbed Conditions)

Using Blower , d = 600 mm

V in Volts I in mA R (in ohm) Power (in mW)
1.27 49.2 25.8130081 62.484
1.75 42.5 41.1764706 74.375
1.85 30.1 61.461794 55.685
1.85 24.7 74.8987854 45.695
1.88 20.1 93.5323383 37.788
1.89 16.8 112.5 31.752
1.89 15.3 123.529412 28.917
1.89 13.8 136.956522 26.082
1.89 12.5 151.2 23.625
1.88 10.9 172.477064 20.492
1.89 9.6 196.875 18.144
1.9 8.9 213.483146 16.91
1.9 8.2 231.707317 15.58

Using Glass Absorber, d = 600 mm

V in Volts I in mA R (in ohm) Power (in mW)
0.86 45.3 18.9845475 38.958
1.68 39.4 42.6395939 66.192
1.79 31.5 56.8253968 56.385
1.86 24.4 76.2295082 45.384
1.88 21.1 89.0995261 39.668
1.9 17.5 108.571429 33.25
1.91 14.7 129.931973 28.077
1.92 13.1 146.564885 25.152
1.94 11.7 165.811966 22.698
1.94 10.6 183.018868 20.564
1.94 9.6 202.083333 18.624
1.95 8.9 219.101124 17.355
1.95 8.4 232.142857 16.38

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5.1 Plots

Figure 5: With various perturbed conditions

It can be observed that due to thermal heating, the saturation value of current remains
unchanged. The change occurs for lower values of current (i.e. higher values of resistance
or voltage).

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6 Fill Factor
The formula for fill factor (F) is,
Pmax
F =
Ishort Vopen

The values of Pmax are obtained from above

d (in mm) Ishort in mA Vshort in V Pmax in mW F

500 67 2.04 120.476 0.873
600 43.1 1.98 70.617 0.755
700 33.4 1.92 48.129 0.768
800 22.5 1.75 32.344 0.708

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6.0.1 Power Law plot

Figure 6: Power Law Plot

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7 Error Analysis
The internal resistance is given by

Vshort
Ri =
Iopen
From the power-resistance plot we can get the value of R (let, Rmax ) for maximum
power. Then the relative error (percentage) will be,

|Ri − Rmax |
∆R = ∗ 100
Ri
The error in internal resistance is calculated below,

d (in mm) Ishort in mA Vshort in V Ri in kΩ Rmax in kΩ ∆ R (%)

500 67 2.04 0.032 0.023 5.67
600 43.1 1.98 0.045 0.080 7.89
700 33.4 1.92 0.058 0.055 3.65
800 22.5 1.75 0.078 0.075 5.19

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8 Results and Discussions
Calibration
The lamp used during the experiment was not perpendicular to the solar cell surface (as
well as the aperture of the thermopile). This would cause errors in the calibration data
(Table 1). As the surroundings were not maintained properly, reflected lights were also
coming. These also would cause some errors.

Wire connections
For the whole experiment, the wire connection has been a sensitive issue. Minor loose con-
nections affected the readings. So that thing is to be maintained carefully.

I-V characteristics
For lower values of voltage (or resistance), we get constant current and near the value of
Vopen, we get constant voltage. Thus, for lower resistance we get constant-current source
and for higher resistance we get constant-voltage source. For higher distances, the constant
current region is much larger than the constant voltage region.

P-R characteristics
For lower resistance, the graph increases linearly . The reason for this is the relation
P = I 2 R (as for lower resistance we have constant current region). For higher resistance,
the power is inversely proportional to the resistance, i.e. the P = V 2 relation is followed
(as for higher resistance we have constant voltage region).

Changes in different temperature

The temperature effect (increase in temperature) can be observed in the plots (I-V charac-
teristics) and (P-R characteristics). In the I-V characteristics, a sudden decrease of current
can be observed. This is because of increase of forward current due to consumption of
thermal energy. The forward current causes decrease in the net value of the current. In
the P-R characteristics, the temperature effect can be interpreted by decreasing in Rmax
(because of thermal effect, internal resistance of a semiconductor decreases). Unfortunately
this effect is not obtained in fitting curves. The reason for this is the unfitting of data
points for perturbed conditions. This makes the fitted curves slightly incorrect. But by
observing the individual data points, we can get an approximate idea about value of Rmax .
Also, for using blower to heat the solar cell, the temperature doesn’t have some uniform
change (i.e. ID would also have some random changes). This causes abrupt changes in I-V
characteristics in the higher voltage region. Changes during the presence of glass absorber.
If the glass absorber is used, some part of the incident light gets reflected or absorbed.
This causes decrease in intensity or irradiance. For this intensity change, the nature of the
characteristics remains unchanged but the peak value of power (Pmax ) decreases (in P-R
characteristics. In the I-V characteristics, both Ishort and Vopen decreases.

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References
[1] https://en.wikipedia.org/wiki/Solar_cell

[2] https://www.solarsquare.in/blog/solar-cell-construction/

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