I'm building a solar power system for my Radio Control Airplane club. We were given three 24 volt 240 watt solar panels, controller, and some cables.
The panels will have to have two 12 volt batteries in series unless I can drop the 24 volts to 12 volts.

I don't want the hassle of tapping between the batteries to get a second pair of 12 volt wires, so converting the 24 volt output of the panels to 12 volts would be the ideal solution.

I can build or buy a converter; which ever is available.

 

The basis of a converter that reduces 24v to 12v could be two MOSFET totem poles switching, 180° apart, between 0v and 24v, each into its own filter. Using two that way tends to cancel ripple.

 

24VDC to 12VDC converters are readily available on Amazon, so they are certainly available, and not particularly expensive. The question is do you want to build one or buy one?