## Solar cell efficiency

In this experiment, the efficiency of the solar cell is measured and calculated. The load characteristic of the solar cell is examined and is used as a basis for the calculation.

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

## Calculate the solar cell efficiency

How do you calculate a solar cell's efficiency? Figure 1. The experimental setup.

### What you need

• 1 solar cell (e.g.: OPV School Set)
• Wires with banana plugs and crocodile clamps
• Voltmeter
• Ampmeter
• Light source (projector lamp or the sun)

### Background

To describe the efficiency of a solar cell, it is not enough to measure what voltage and current it produces without load. When measuring the voltage with a voltmeter directly over the solar cell contacts, you measure VOC, which is the voltage of the unloaded circuit. In other words, this voltage is the maximum voltage the solar cell is capable of delivering. At a higher load, the voltage will drop until the load is infinitely high. The situation reached by infinite load is a short circuit of the system and is precisely the state you measure when you connect an ammeter to the solar cell to measure the current. The short circuit current measured in this context is called ISC and is the maximum current that the solar cell can deliver. Since P = IV (the power is equal to current times voltage) we can calculate the power in both situations. At VOC we have a voltage, but the current is zero, so the power is also zero. If you know ISC there is a current, but the voltage is now 0, so the power is again 0.

To find the point where the solar cell produces the maximum power, we therefore need to expose the solar cell to many different loads and measure current and voltage. We can then find the maximum power as the product of power and voltage. The experiment below is about finding the maximum power by connecting a variable resistor to the solar cell, recording current and voltage and repeating this for many resistor settings.

### Experiment 1 Figure 2. Diagram for the circuit with solar cell, voltmeter, ammeter, and variable resistor.

Arrange the solar cells and components as shown in the diagram in Figure 2. Start by setting the resistance to the minimum value. Then record current and voltage. Change the resistor value a little bit and note again current and voltage. Repeat until the output voltage is very small or 0. A plot of current and voltage is called an IV curve and is a widely used way of characterizing a solar cell.

Multiply current and voltage for all values and find the maximum power.

The experiment can be completed using the following virtual instrument. Use the instrument by changing the value of the resistor and read the current and voltage as described above.

### Experiment 2 - Calculate the efficiency of the solar cell

To calculate the efficiency of the solar cell, it is necessary to know how much power the solar cell receives and how much power it produces. From Experiment 1 we know the power the solar cell produces. If the light source used was the sun on a cloudless day, the incoming power is approx. 1000 W / m2. To calculate the efficiency of the solar cell, you must use: Efficiency = Pout / Pin. To calculate Pin (the input power) use the area of the solar cell. You can measure the module area with a ruler. Then calculate the efficiency.

### Related shop items

DIY Solar Lamp kit
1x solar tape bidirectional
3x connector cables
1x 105mAh Li battery
1x DIY Solar Lamp board
School set (32 solar cells)
infinityPV School set contains 32 OPV modules ready for use.
DIY Solar Lamp board
DIY Solar Lamp board allows the safe charging of a small Li battery from solar cells.The board includes JST connectors, internal switch and white LED.
CalCell reference device
The CalCell reference device for calibration of your solar simulator.

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