the motor is designed to be always turning in order to generate the pulses for commutation
If you want to power an Arduino with solar energy, study this great tutorial: https://www.gammon.com.au/forum/?id=12821
The problem with that is, it's not simply power coming from solar cells,
Any "magic" that you add is going to reduce the available power. Otherwise we would have perpetual motion and free electricity.If you want to power an Arduino with a solar cell then use the solar cell to charge a battery and power the Arduino from the battery.
The problem with that is, it's not simply power coming from solar cells, the same wire coming from the solar panels are used to create an electromagnetic field used to push the motors.
Not a problem. That is how all electric motors work.
Best to use separate PV cells to charge a battery. Great bargains here