Instructables

how big a solar panel do i need to charge a 12 volt battery?

I have a camper with 12 volt lights and want to recharge my battery after use using a solar panel

Super_Dave4 years ago
Adding to Jeff-O's response, panels in the 30W and under range are considered battery tenders and are customarily used to keep a RV battery topped off while being stored.
Hmmm, good to know!  In that case yeah, go for something in the 100-150W range.
Super_Dave4 years ago
Companies that sell solar panels for RV use have a draw survey that tells them how much of the battery you use in a day.  That along with the amp hours available in your battery bank will determine what size you need.  As a fellow camper, I suggest something in the 100W to 140W for boondocking longer than 3 - 4 days at a time.
jeff-o4 years ago
I recommend looking for a 30W, 12V solar panel.  These can usually be found at some hardware stores (like Canadian Tire in Canada), auto parts stores, RV stores, and online.  It should cost about $100-$150.  You'll also need a charge controller, which will likely be available from the same place you got your solar panel.  It should be rated for at least the same power as your panel, but I suggest getting double in case you want to add a second solar panel later on.
Well, for a start, you'll need a panel with a voltage output > 12V ! Then you need to find out how much you lose running the lights, and how fast you need to recharge the battery.

Steve
.  Yep. What steveastrouk said. You could charge the battery with a panel just a few inch2 in size ... but it might take a week-and-a-half of strong sunlight to do it.
.  You'll probably want a PV panel that is rated to put out 24V or more (you can regulate it down to the 13-15V you need) or more at x(1) amps, to make sure you can charge on cloudy days.

(1)x will depend on how fast you want to charge the battery.