Do it
Measure the maximum voltage generated by the solar panel and compare it to the voltage required to run the electric motor.
So, our solar panel does not start the electric motor under room conditions. Why?
The physicist's way of dealing with the matter is to study the physical quantities that are important in the given context. In the case of electrical equipment, as the electric motor undoubtedly is, the voltage and current should be measured in the first place.
We're dealing with tension here. We measure the voltage at the terminals of both the solar panel and the battery. In addition, let's check if the electric motor still spins at low voltage. Then we try to analyze the results.
Voltage is measured with a voltmeter. The voltmeter is connected to the rail with the conductor at the ends of which the voltage is to be measured .