Back up battery for solar power

[guitmusic11]

Say you have to power a simple motor with a solar panel, but that panel does not always supply the necessary power. What is the simplest circuit that could combine a DC motor, Solar panel and battery backup to ensure that the motor will continue running even when the solar panel cannot supply power?

 

[Baluncore]

Assume that the PV array converts more total energy than the motor requires over the year. The battery will need sufficient capacity to supply the motor overnight in mid-winter and cloud. The motor and controls will need to operate efficiently at the battery voltage available, or a converter will be required.

A battery of chemical cells operates at a chemically determined voltage. The battery will therefore need a voltage regulator to prevent the PV array from overcharging the battery.

The minimum circuit is therefore a voltage regulator. There are many minimum solutions determined by the “short circuit current” and “open circuit voltage” of the PV panel and the power requirements of the motor.

 

[sophiecentaur]

I would make the point that, as you are spending money on a solar array and battery, why would you want to use the simplest circuit? In many circumstances, you could actually save money (smaller panel or smaller battery) by using an intelligent charger. You wouldn't need to design it yourself; there are many designs (and off the shelf units) which will do it for you.
Of course, there is nothing essentially wrong with the brute force and ignorance approach - unless the economics make it too costly.