pHYSICS

BSPY205

Experiment 7

Aim of the Experiment

To plot the V-I Characteristics of the solar cell.

Principle

Working principle of a solar

A solar cell operates in somewhat the same manner as other junction photo detectors. A built-in depletion region is generated in that without an applied reverse bias and photons of adequate energy create hole-electrons pairs. In the solar cell, as shown in Fig. 1a, the pair must diffuse a considerable distance to reach the narrow depletion region to be drawn out as useful current.

Hence, there is a higher probability of recombination. The current generated by separated pairs increases the depletion region voltage (Photovoltaic effect). When a load is connected across the cell, the potential causes the photocurrent to flow through the load.

The e.m.f. generated by the photo-voltaic cell in the open circuit, i.e. when no current is drawn from it is denoted by VOC (V-open circuit). This is the maximum value of e.m.f.. When a high resistance is introduced in the external circuit a small current flows through it and the voltage decreases. The voltage goes on falling and the current goes on increasing as the resistance in the external circuit is reduced. When the resistance is reduced to zero the current rises to its maximum value known as saturation current and is denoted as ISC, the voltage becomes zero. A V-I characteristic of a photovoltaic cell is shown in Fig. 1b.

The product of open circuit voltage VOC and short circuit current ISC is known a ideal power

Ideal Power = V_OC × I_SC

The maximum useful power is the area of the largest rectangle that can be formed under the V-I curve. If Vm and Im are the values of voltage and current under this condition, then

Maximum useful power = V_m × I_m

The ratio of the maximum useful power to ideal power is called the fill factor

Fill factor = V_m × I_m/ V_OC × I_SC

Materials required

Solar cell mounted on the front panel in a metal box with connections brought out on terminals. Two meters mounted on the front panel to measure the solar cell voltage and current. Different types of load resistances selectable using band switch also provided on the front panel. Three single points and two interconnectable patch cords for connections. Wooden plank with half meter scale fitted on it and a lamp holder with 100 watt lamp.

Procedure

When experiment is performed with 100 Watt lamp:

1. Place the solar cell and the light source (100 watt lamp) opposite to each other on a wooden plank. Connect the circuit as shown by dotted lines (Fig. 2) through patch cords.

2. Select the voltmeter range to 2V, current meter range to 250µA and load resistance (RL) to

50Ω.

3. Switch ON the lamp to expose the light on Solar Cell.

4. Set the distance between solar cell and lamp in such a way that current meter shows 250 µA

deflections. Note down the observation of voltage and current in Table 1.

5. Vary the load resistance through band switch and note down the current and voltage readings

every time in Table 1.

6. Plot a graph between output voltage vs. output current by taking voltage along X-axis and

current along the Y-axis.

When experiment is performed in sunlight:

1. Connect the circuit as shown by dotted lines (Fig.) through patch cords.

2. Select the voltmeter range to 4V, current meter range to 2.5mA and load resistance (RL)

to 50Ω.

3. Expose the solar cell to sunlight

4. Note down the observation of voltage and current in Table 1.

5. Vary the load resistance through band switch and note down the current and voltage

readings every time in Table 1.

6. Plot a graph between output voltage vs. output current by taking current along X-axis and

voltage along the Y-axis. You should get a curve similar to shown in Fig. above

Observation Table

Voltmeter reading for open circuit, VOC = …. Volts

Milliammeter reading with zero resistance, ISC = . . . mA.

Calculation

From the Graph:

Value of Vm = … volts

Value of Im = … mA

Maximum useful power = Vm × Im mW

Ideal power VOC × IOC = … mW

Fill factor = V_m × I_m/ V_OC × I_SC

Result

Value of Vm = … volts

Value of Im = … mA

Maximum useful power =

Ideal power = … mW

Fill factor =

Reference Material

Thermal Physics, S. Garg, R. Bansal and C. Ghosh, 1993, Tata McGraw-Hill
Virtual Lab (https://vlab.amrita.edu/?sub=1&brch=194&sim=354&cnt=1)

Questions

1. What is the difference between solar cell and a photodiode?

2. What are the types of semiconductor materials used for solar cell?

3. What is Dark current?

4. What is the difference between solar photovoltaic and solar hot water system?

5. What is the response time of photo cell?

Developed by

Dr. Poonam Sharma,

Assistant Professor, Physics

Poonam.sharma1@gsfcuniversity.ac.in

Mr. Dhairya Patel

Teaching Assistant , Physics

dhairya.patel@gsfcuniversity.ac.in

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