# Finding the internal resistance of a solar cell

Finding the internal resistance of a solar cell.

Aims: I intend to create an experiment which will measure the internal resistance of a solar cell. To do this I will create a circuit which will measure the current and voltage of the external circuit ‘the load’ which will enable me to calculate the internal resistance of the solar cell (fig.1). Internal resistance is the resistance within the cell, symbol ‘r’ as shown in fig.1 below.

Apparatus: The circuit I will create to measure the internal resistance will comprise of;         A solar cell

Variable resistor

(Multimeter)-        Ammeter

(Multimeter)-        Voltmeter

Fig.2 shows this setup.

Extra apparatus

I will use a permanent light source, this will be a lamp. I have also decided to use a tube of black card fixed around the head of the lamp that goes to the solar cell. This should stop most background light from affect any results.

Safety: There are safety implications when caring out this experiment. Before the experiment begins the experimental area must be clear. This involves making sure that there are no bags or coats left near experimental areas as accidents may occur. During the experiment the permanent light source may be on for long periods of time which will cause the bulb and its casing to heat up. This may cause burns and should therefore be avoided. The low voltages and currents used in the circuit pose no potential to shock or burn anyone who touches the circuit although it is advisable not to touch any apparatus for the purpose of preservation of consistency for the experiment.

Variables: During this experiment I have noticed that there will be conditions that are variable and conditions that are not variable. Considerations of these conditions must be made.

The conditions which must remain constant are the amount of light energy which the solar cell receives as this may affect the internal resistance of itself so must remain constant as to not affect the results. This can be solved by making sure a constant light source such as a lamp remains at a set distance from the solar cell.

The solar cell used must remain constant as different solar cells may have varying internal resistances. This can be solved just by making sure that during all tests the solar cell used is always the same one.

The wires must stay constant as variation of these wires may affect results of the experiment. This is not a problem as long as the same wires are used throughout the experiment.

The condition that will be being varied is the resistance of the variable resistor as the name suggest it will have its resistance varied as this is part of the experimental procedure. This is because as the resistance of the load changes the voltage and current of the circuit change but the internal resistance doesn’t so the precision of the experiment will be increased because of the ...