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Author Topic: 12v/24v Solar Panel Questions  (Read 1170 times)

12v/24v Solar Panel Questions
« on: October 07, 2014, 04:38:41 PM »
I've installed solar systems in two different RV's now and had quite successful outcomes...much thanks mostly to you folks for walking me thru it in years passed.

I am looking at the peel and stick kind of solar panels this year on our new RV instead of the typical glass framed bulky ones. I was just looking at the recipt for the units I purchased last night (and are already on the way) and they are listed as 24v peel and stick solar panels...will I have any problems using these with a battery bank of three 12v deep cycles? I don't know why this didn't catch my eye before my purchase. My instinct and limited knowledge tells me I am fine but I thought I should ask folks who know better. 

Gary RV_Wizard

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Re: 12v/24v Solar Panel Questions
« Reply #1 on: October 07, 2014, 04:56:26 PM »
You need to reduce the voltage that goes to the batteries - the output of a 24v panel (could be as much as 40v!) will damage then. This is usually done via the charge controller for the solar system. I'm told an MPPT type controller can do this, but I have no experience to judge that..
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Re: 12v/24v Solar Panel Questions
« Reply #2 on: October 07, 2014, 05:16:39 PM »
Oh - I was going thru a 20A mppt regardless. Do we think this is enough? Or should I use an mppt Controller with a higher amperage rating?

Two 144w 24v solar panels into three 12v deep cycles

PJ Stough

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Re: 12v/24v Solar Panel Questions
« Reply #3 on: October 07, 2014, 05:40:34 PM »
I dont believe a 20 amp controller is large enough.  288 watts/12 volts=24 amps

PJ Stough   Iowa
2005 Winnebago Voyage 38J

Kevin Means

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Re: 12v/24v Solar Panel Questions
« Reply #4 on: October 09, 2014, 03:01:59 AM »
Yes, 24 volt panels can be used with 12 volt batteries but, as Gary mentioned, you must use an MPPT controller to reduce their output voltage. It sounds like you've got that covered. 24 volt panels will also enable you to use a thinner gauge wire when installing them (Less line loss). However, a 24 volt panel will only produce about half the amps a similar watt-sized 12 volt panel will produce, and repleneshing the amps we've consumed from our battery-bank is our goal when using solar.

For example, Uni-solar makes 144 watt, 24 volt flexible panels and under ideal conditions, (which almost never exist), they have a rated output of about 4.5 amps at 33 volts. A typical 150 watt 12 volt panel has a rated output of about 8.5 amps at 18-20 volts. A good MPPT controller will be able to harvest some additional power from either panel by converting excess voltage to amps but exactly how much can only be determined by the quality of controller. Most MPPT controllers are designed to be most efficient wihen they have an input voltage of 39-41 volts.

2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ
RVI Brake 2, Minder TM-66 TPMS, 960 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California


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Re: 12v/24v Solar Panel Questions
« Reply #5 on: October 09, 2014, 08:10:45 AM »
2 144w panels would push my 20a MPPT controller but it would handle it. Make sure you understand about Voc of the panel and the Voc limit of the controller. My controller could only take them in parallel, another can take them in series.