Has anyone permanently mounted a solar panel to the roof rack to help the batteries when not driving? My fridge/freezer lives in the back of the 4runner 24/7 and if I don't drive for a few days it reaches the cut off (around 11.1-11.5) and fridge starts warming. I have a 30watt panel and thinking about mounting it to the roof with some specialty bolts to make theft a little more challenging.

My idea is that during sunny hours when the car gets warm and the fridge is constantly on the solar will help offset the fridge and when its cold at night its not needed anyway.

I would think that part of your issue would be capacitance - in other words how will you hold the "power" that you generate during the day? Maybe an additional battery?

I say go for it. You can probably rig up a couple panels in series and make enough power to keep the fridge going. Have you thought about adding some additional insulation to the outside of the fridge to keep the temp under control? You can duct tape some foam insulation and then cover it with cardboard for some additional insulation. Also tinting your windows and blocking any direct sun from the fridge should help keep it cooler and let it go longer between cycles because it will stay cooler longer.

Well I have 2 yellow tops already, no more room for batteries. Im pretty sure I wont even need a charge controller since the fridge will constantly be turning on and sucking out some power. It would take allot more than a 30w panel to over charge 2 batteries with the fridge hooked up. Some day ill do the Chevy alternator mod for more charging on short drives.

I haven't insulated the fridge yet, I know I really need to get on that one. Im sure it would help stretch out the battery life a little more. good idea.

Sounds like a good idea. Honestly, a smaller battery such as a powersports battery would give you that extra discharge time. You could fit one of those in the small compartment in the rear of the 4runner. Strap it down and run it in series with the rest of your batteries.

Remember - running in parallel gives you the same amount of voltage or "pressure" which in this case is 12 volts DC but a longer discharge time. Running in series will give you twice the power but the same discharge time.

What are the power ratings on the fridge, im a bit curious as i want to calculate an estimated time for total discharge on three batteries.

As for insulating, may i suggest using some cheap home depot brand insulation board (contractor issue stuff) taped onto the top and sides followed by old carpeting. Dont use insulation board on the doors, just carpeting. Get some color to match your 4r's interior.

I use this method at work on our lab chillers. It cuts the compressor run time in half per hour.

The real question is how much amperage is the fridge using over a period of time?

Also how much amperage is your old alternator actually producing?

You maybe better of just doing this.

HO alternator/Dual Battery/Battery Separator/"Big 3 Upgrade - Tacoma World Forums

However for days at a time you are going to need more storage and as you propose, something to fill that storage.

Idk if It would matter if it was more insulated. It's like putting a cooler in the oven. If the op has enough sun to run a solar panel then it'll be enough to warm the inside of his runner like a green house and warm the fridge. Most fridges only keep the inside contents 40* cooler than the outside temp.unless you have a freezer model.

I think any outside source would help. How big is one panel? Can you fit more on your roof? Or atleast mirrors on the sides of the one to help catch sun light?

As far as the bigger alternator I have 2 red tops and wonder how the optimas would take to the stronger current going into them. When I tried to get one of my red tops recharged by autozone it wouldn't charge because they need a trickle charge instead of just shoveling as much into as you can like battery chargers do.. My concern is how much power is too much to actually charge the optimas?

I thought about that for my set up, but after I switched out my second battery for a Diehard Platinum, the problem went away. What Solar set up were you thinking of going with? controller?

I think its draws about 4 amps while running. Adding a third mini battery is only as good as the amp hours. While It would add some amp hours, a 30w solar panel will provide more amp hours in a day then a small battery will and is much lighter.

also that's only 4 amps while running, so you can almost avg. 2 amps per hour across a day. So roughly 48 amps in a day? runs allot in the day and very little at night.


a 12v - 30w panel is amp x volts = watts. so in full sun I should be getting arounds 2 amps in full sun

yea that's the alternator I would like to install cheap and works great



I think the stock alternator is like a 70amp ? and only 20 amps at idle where as the cs-144 chevy alternator that fits runs around $150 and charges 100amps at idle and 150amp at 2000rpm



I think the panel is only 12"x 36" so i could fit a could more but for now I just have the one sitting around. The larger alternator should be no problem as many cars have much larger alternators and optima battery handle it fine.

"Remember - running in parallel gives you the same amount of voltage or "pressure" which in this case is 12 volts DC but a longer discharge time. Running in series will give you twice the power but the same discharge time."

Don't put them in series.

Running them in series will give you 24 volts. This will damage your refrigerator unless it is designed for 24 volts.

The voltage from batteries adds when you put them in series and the current will be equivalent to the lowest ampacity battery.

When you put batteries of equal voltage in parallel the voltage remains the same but the current capacity adds. (Never put 2 different voltage batteries in parallel. I promise you won't like the results!!!)

I was not telling him to run in series...It was just a heads up to ensure that he did not run them in series. Im sure he understands that his fridge is currently running on 12 volts...he seems like he has a grasp on basic electrical power.

"Idk if It would matter if it was more insulated. It's like putting a cooler in the oven. If the op has enough sun to run a solar panel then it'll be enough to warm the inside of his runner like a green house and warm the fridge. Most fridges only keep the inside contents 40* cooler than the outside temp.unless you have a freezer model. "

Yes it does in fact matter. The idea is to SLOW the rise in temperature down. By using insulation you are essentially creating a temporary barrier that the tightly packed molecules must break through to reach the cooler temperatures of the fridge. In most cases heat moves toward the cold, so the goal here is to block our cold molecules off.

Slow the molecule transfer ------> Slow the rise in temperature in the fridge-----> Reduce the times in which your fridge is calling for the compressor-----> Less power used.

did you ever install any type of solar panel(s)?