I have a 24V solar panel, that I want to hook up to 2 x 12V batteries in series to give me 24 V. The panel is 15m away from the batteries- I'm not sure what size wire to use?

 

You should follow any applicable local electrical codes..
You didn't provide your location..

 

New Zealand

 

The size of the wire is not about voltage, it is about current. How much current will be flowing through the wires?

4 instance, 14 gauge wire is rated for 15 amps and 12 gauge wire is rated for 20 amps.

 

Another consideration is acceptable loss. I mean, maybe you'd lose 1V at maximum panel current with a cable you have, say 18 gauge. Is it worth the expense to buy 12 gauge to decrease the loss?

Note that you can also almost eliminate cable losses if your inverter is at the panel. Oh never mind, you said batteries.

 

Does the panel have integral reverse-current protection? If not you will need a diode for that.
A 24V panel is unable to fully charge 2 x 12V batteries in series. 12V is the nominal voltage of the battery; the charging voltage would need to be something like 13.8V-14V.

 

A 24V panel is unable to fully charge 2 x 12V batteries in series.

Excellent point. The panel might be rated as one appropriate for a 24V system, meaning it will be more like 29V, but it's more typical to quote the open circuit voltage. If that's the case, it'll be inadequate for 2 batteries in series. Depending how big it is, it might be better to charge the 2 batteries in parallel instead. With a charge controller, of course.

 

Thanks for your help guys. After reading your responses, and due to my lack of experience, I should have told you my solar panel is 190w, Vmp=36.05 v, Imp= 5.72 A, I am using a 10 amp 12/24 VDC PWM Solar controller.
I have 2 12v batteries hooked up in series, running a winch. Do you think that set-up will keep those batteries charged? I am thinking of using 6mm wire connecting the panel to the regulator which is beside the batteries, and the distance from the panel to the regulator is about 15m. Appreciate your advice.

 

6mm diameter is larger than 3 gauge American. That is so big I would have to look it up in a book. Easily enough to carry 10 or 12 amps with more than 5000 feet per ohm.

15 meters both ways is 30 meters. It will lose less than .18 volt when 10 amps flows.

 

The wire gauge is not critical! The 24v panel will make approx 5.7A, which can be carried safely with most standard type wire gauges.

The voltage drop probably doesn't matter, as a couple volts dropped will just mean the panel runs a couple of volts higher, there will be little to no effect on the current from having a couple volts dropped in the wiring.

 

Thank you for helping me with that, is there any consideration when hooking the 24 v regulator up to. Two 12 volt batteries that are wired in series rb and others I am happy about the wire size now thank you again

 

I am not sure if you have picked up the idea. In case you did not. You still need blocking diode.

 

...is there any consideration when hooking the 24 v regulator up to. Two 12 volt batteries that are wired in series...

That should be fine. as long as the controller is meant to charge batteries with your chemistry and nominal voltage. In other words if it is meant for 24V lead acid, and that's what you have, it'll be fine.

Anytime batteries are in series there is some risk that the beginnings of failure of one will accelerate the failure of the other. The only way around that is to monitor and charge them separately. Short of that, it helps to start with two batteries that are as similar as possible.

 

I have a 24V solar panel, that I want to hook up to 2 x 12V batteries in series to give me 24 V. The panel is 15m away from the batteries- I'm not sure what size wire to use?

Hello friend were you able to find the right way to do it.. I am applying similar series batteries so please help me..

 

Thank you for helping me with that, is there any consideration when hooking the 24 v regulator up to. Two 12 volt batteries that are wired in series rb and others I am happy about the wire size now thank you again

Wayneh already covered it well in post #13.

I would add that a "24v battery" is just a lead acid battery with 12 series cells, while a "12v battery" is a lead acid battery with 6 series cells.

If you plan to join two 12v batteries in series (to make a 24v battery) then they need to be very well matched. Ideally they should be the same make, model, size and both should be NEW and always charged and used together after connecting in series.