The sun is often behind a cloud. If this is the case again, the supercapacitors could be charged in a different way.

This can be done - either with a power supply unit, batteries or a battery bank.

It is important to note the voltage at the terminals of the current source used - our two supercapacitors connected in series could be applied with a voltage of up to approx. 6V. The power source must also withstand a fairly high current - if the capacitors are empty, then connecting them to the power source essentially means a short circuit for the power source.

Also, the voltage of the current source should not be less than about 4 V - such a voltage is needed for our electric motor to start working properly, and it is not possible to get a higher voltage from the capacitors than was applied to it during charging.

The easiest way to arrange charging is with batteries - their significant internal resistance prevents the current from getting too high, and the output voltage is, for example, a perfectly suitable 4.5 V when three 1.5 V batteries are connected in series.

We have a test kit battery with an output voltage of 7-8V. This is pretty much at or above the limit for capacitors. The more fundamental problem is that this battery also has short circuit protection and if you connect the battery to the capacitors it will activate and the voltage will be lost from the battery terminals until it is briefly removed from the circuit.

For example, a light bulb or a potentiometer can be used to limit the current. But you can also use the load used in the experiment anyway - the electric motor.

Below is the electrical diagram used for such charging.