Teacher guides

Solar cell test

In this experiment, it is the student's task to measure how much power and voltage a solar cell can generate. This assignment is intended to demonstrate how to test solar cells and how to find out how much power they produce.

You can print the teacher guide without teacher hints or with teacher hints.

How to test and use one or more solar cells?

Figure 1. Test setup.

What you need

One polymer solar cell (two for the last part of the experiment)
Light bulbs with different power ratings (1 - 6W)
Voltmeter
Ampmeter
Lightsource (floodlight lamp or the sun)

Background

The sun's light contains energy that can be converted into electricity in a solar cell. In these experiments we will look at how we can use the energy from the solar cell and how we can utilize more solar cells.

Experiment 1

Figure 2. Diagram with solar cell and ampmeter.

Place the solar cell under the sun or a lamp. Measure the current with the ampmeter. Then remove the solar cell from the sun or turn off the lamp and measure the power again.
What is the difference between the two measurements?
When the light is on, you will measure the largest current. The current you have now measured is called the short circuit current of the solar cell. It is the maximum current that the solar cell can produce. Note the short circuit current.

Figure 3. Diagram with solar cell and voltmeter.

Now measure the voltage of the solar cell under illumination using a voltmeter. This is the voltage of the unloaded circuit and is the maximum voltage that the solar cell can achieve. Note this voltage. When the solar cell is used to run an electrical circuit, charge a battery, or similar it will be under resistive load. Therefore, you will see that the current and voltage are lower than the two numbers we have just measured.

The two values we measure at present are the current and the voltage that the solar cell provides. At present, it will be inviting to proceed to calculate the effect that the solar cell produces ($ P = I \cdot V $, power = current times voltage). However, it will not be the right current and voltage that we use in the calculation. The reason is that in our experiments the solar cell does not see any electrical resistance and therefore the two numbers are misleading. Actually, the produced power will be zero in both these cases. Experiment 2 is about how we can measure the power the solar cell produces by introducing an electrical resistance.

The virtual instruments emulate the experiment. It is possible to switch between measurement of current and voltage by clicking on the multimeter. The illumination can be turned on or off by clicking the solar cell.

Experiment 2

Figure 4. Solar cell with lamp and ampmeter and voltmeter.

Now try to connect one of the incandescent bulbs to the solar cell. First measure the current with the ampmeter through the incandescent bulb. Then measure the voltage. Compare these numbers with the short-circuit current and the open circuit voltage from the unloaded circuit from task 1.

The current and voltage you are measuring now corresponds to a produced power. In experiment 1, the produced power was 0 in both cases. Now try to calculate the power with the incandescent bulb (Power = Voltage x Power) and note the power as well as current and voltage.
Repeat the attempt for all the different bulbs you have available and note the effect the solar cell delivers for each.
Does the solar cell give the same powerfor each incandescent bulb?

If the bulbs provide different resistance in the circuit it is expected that the solar cell will produce different power. The basic reason is that the solar cell has the maximum power that can be produced. The way you find this maximum is to measure an IV curve for the solar cell.

Experiment 3

Try connecting the two solar cells in parallel and repeat the experiment with the incandescent bulbs. Then do the same with two solar cells in series.
Is it the same incandescent bulb that gives the best effect when the cells are connected in series and in parallel?

Since the IV curve of the coupled solar cells is different, it is expected that it is no longer the same incandescent bulb that produces the highest power. This is explained more in depth in other experiments. In this context, the attempt is intended to illustrate that exploiting the power of a solar cell is complicated. There is a difference as to whether the electronics that exploit the effect of the solar cell can optimize the utilization of the maximum power of the solar cell or not. In solar cell installations it is the inverter that handles this.

Concluding questions

How do we best utilize the energy that the solar cell produces?

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