Can you charge a 24V system with a single 12V solar panel?

Is it possible to use 1 solar panel to charge 2 12volt batteries connected in series (24 volt) via 2 seperate 12 volt charge controllers, one linked to each battery? - Richard

Unfortunately, no.

The negative solar and negative battery terminal on most charge controllers are connected together internally - it's only for convenience that they provide you with two seperate terminals to connect the wire.

If you were to try putting two controllers in series, you would be joining the positive battery terminal of the first charge controller to the negative battery terminal of the second. If you then attach the negative solar panel lead to both solar negative terminals you have the following situation:

1) positive battery terminal of first controller is connected to negative battery terminal of second...
2) ... which is connected internally to the negative solar terminal
3) ... which is connected to the negative solar panel lead
4) ... which is connected to the negative solar terminal of the first charge controller
5) ... which is connected internally to the negative battery terminal

In short, you've connected the battery positive to the battery negative. That's called a short circuit, which is a cause of wires melting, fire, grieving next of kin etc etc.

If you must try it, I'd recommend making your will first. I can't see any reason why you couldn't put two 12V controllers in series with seperate solar panels, though don't take my word for it. However, it's more usual to simply wire two 12V panels in series to a single 24V controller. See our handy 24V solar panel wiring diagram.