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Car Roof Solar

nakman

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So I seem to have this conversation at least once per week. Let me summarize a few key points for you to ponder...

A hard mounted panel on top of a roof of typical rig like ours is great for keeping the battery(ies) float charged between uses. Like if you have an extra rig that sits outside a lot, great idea. If you want to park at the airport for 2 weeks and come back to a happy battery, great.

If your intent is to run a fridge indefinitely, this might not work as well as you think. Basically fridges and solar panels want different things in life... direct sun is best for one, while shade is best for the other. I have run this personally in several vehicles so will share my experiences.

Working setup 1: 60 in the shade. In the 60 this past summer at Overland Expo Mtn. the 60 was parked for 3 full days without the truck being started. I had a 120watt panel hooked up to a PWM charge controller, the battery was anywhere from 12.2-13.0 depending on time of day, in fact there were times the battery being charged by solar, which was also running the Iceco fridge, was so happy that the ACR switched on to charge the other battery for a while. Windows/hatch were open pretty much the whole time, one side of the truck was shaded by an awning most of the day, and the roof was further insulated by a RTT. So almost no direct sun going into the truck, and the inside of the truck stayed pretty close to ambient temp, mid 90's. Even though the panel was portable, I didn't bother optimizing its angle to the sun but rather just flopped it on top of the awning and left it there. Could have run the fridge all summer long in these conditions, here's a pic:

IMG_4840.jpg


Working setup 2: Class C Motorhome. We had a class C (sold it) but I installed 2 100 watt panels to the top of it, MPPT charge controller to the 2nd battery. And that setup kept a Dometic fridge running literally the entire summer of 2020. My son and his friend feeding off the sponsored supplies of Arnold Palmers and Gatorades, occasionally charging the portable power station that fed AC power to the TV and Nintendo. Big benefit here is the added airspace inside the RV, and the insulation, even when it's 100F outside it never feels that hot inside the RV, even with the windows closed... so a little more like a house than a car. Here's a pic:

IMG_4432.jpg


Failed Setup 1: GX470 under rack mount. I mounted a 100 watt panel underneath a roof rack, mainly to protect the panel and so I could strap other junk on top of it. But I also tried several times to let the thing just run the fridge in the driveway. It lasted longer than no panel, but at some point the inside of the car would get too hot and the fridge would error out and over-temp condition. Did this with both the ACO fridges and the Dometic... happened more often with the ACO's. Even with the 3rd row windows cracked, it's just too hot inside the car in the hot sun, and not enough airflow... the fridge is on pretty much constantly and at some point either runs out of juice or just gets too hot. Here's a pic:
IMG_2558.jpg




If you have a portable power supply, like a Goal Zero, Jackery, etc. and can measure inbound wattage from your panel, use that to do a little test of your setup. You will likely be shocked just how drastically you reduce wattage simply by running your hand in front of the panel, putting an object in front of it, or changing its angle to the sun. The most I have ever seen from a 100w panel is about 89 watts, and that was literally in the driveway doing my best to optimize conditions... point being don't do any math on recovery rate of your battery thinking you're going to actually get 100 watts from a 100 watt panel, you will just be disappointed. I'll further say that quality of the panel, the controller, and even the battery doesn't matter as much as quality of running conditions- a clean onubstructed panel is going to out-produce a dirty fancy panel tucked behind a branch any day. And I'd also say the actual fridge doesn't matter much either- put an ARB Zero in a closed hot car against an Iceco in a shaded car and I'll put my money on, and beer into, the fridge that costs less than half as much.

You can't offest lack of ventilation by increasing solar power generation. You can prolong the battle, but at some point the electronics hit their limit, think of how we preach mechanical sympathy relative to gearing. That's why when asked which setup to do, I so often recommend a portable panel that can be placed in the sun, optimized for angle, while the car can stay in the shade with the windows down. Do this instead of, or in addition to, a hard mounted panel, but don't just do the hard mount panel.

Two other points I'll make about car-top solar. Solar is terrible at night, it just doesn't work. It's slightly more useful when it's cloudy or raining, kinda useless in the snow too. And it doesn't work when you're driving- the alternator wins that race to who gets to charge the battery. So solar only really comes into play for a couple hours late in the day, presuming you're driving every day and you stop to setup camp. Or maybe that odd lag day where you choose to do a hike or something. But if it's a road trip, or overland adventure, you're really not using your car-top solar panel that much.
 
Last edited:

Shuksan

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Joined
Nov 1, 2017
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Denver
So I seem to have this conversation at least once per week. Let me summarize a few key points for you to ponder...

A hard mounted panel on top of a roof of typical rig like ours is great for keeping the battery(ies) float charged between uses. Like if you have an extra rig that sits outside a lot, great idea. If you want to park at the airport for 2 weeks and come back to a happy battery, great.

If your intent is to run a fridge indefinitely, this might not work as well as you think. Basically fridges and solar panels want different things in life... direct sun is best for one, while shade is best for the other. I have run this personally in several vehicles so will share my experiences.

Working setup 1: 60 in the shade. In the 60 this past summer at Overland Expo Mtn. the 60 was parked for 3 full days without the truck being started. I had a 120watt panel hooked up to a PWM charge controller, the battery was anywhere from 12.2-13.0 depending on time of day, in fact there were times the battery being charged by solar, which was also running the Iceco fridge, was so happy that the ACR switched on to charge the other battery for a while. Windows/hatch were open pretty much the whole time, one side of the truck was shaded by an awning most of the day, and the roof was further insulated by a RTT. So almost no direct sun going into the truck, and the inside of the truck stayed pretty close to ambient temp, mid 90's. Even though the panel was portable, I didn't bother optimizing its angle to the sun but rather just flopped it on top of the awning and left it there. Could have run the fridge all summer long in these conditions, here's a pic:

View attachment 99677

Working setup 2: Class C Motorhome. We had a class C (sold it) but I installed 2 100 watt panels to the top of it, MPPT charge controller to the 2nd battery. And that setup kept a Dometic fridge running literally the entire summer of 2020. My son and his friend feeding off the sponsored supplies of Arnold Palmers and Gatorades, occasionally charging the portable power station that fed AC power to the TV and Nintendo. Big benefit here is the added airspace inside the RV, and the insulation, even when it's 100F outside it never feels that hot inside the RV, even with the windows closed... so a little more like a house than a car. Here's a pic:

View attachment 99678

Failed Setup 1: GX470 under rack mount. I mounted a 100 watt panel underneath a roof rack, mainly to protect the panel and so I could strap other junk on top of it. But I also tried several times to let the thing just run the fridge in the driveway. It lasted longer than no panel, but at some point the inside of the car would get too hot and the fridge would error out and over-temp condition. Did this with both the ACO fridges and the Dometic... happened more often with the ACO's. Even with the 3rd row windows cracked, it's just too hot inside the car in the hot sun, and not enough airflow... the fridge is on pretty much constantly and at some point either runs out of juice or just gets too hot. Here's a pic:
View attachment 99679



If you have a portable power supply, like a Goal Zero, Jackery, etc. and can measure inbound wattage from your panel, use that to do a little test of your setup. You will likely be shocked just how drastically you reduce wattage simply by running your hand in front of the panel, putting an object in front of it, or changing its angle to the sun. The most I have ever seen from a 100w panel is about 89 watts, and that was literally in the driveway doing my best to optimize conditions... point being don't do any math on recovery rate of your battery thinking you're going to actually get 100 watts from a 100 watt panel, you will just be disappointed. I'll further say that quality of the panel, the controller, and even the battery doesn't matter as much as quality of running conditions- a clean onubstructed panel is going to out-produce a dirty fancy panel tucked behind a branch any day. And I'd also say the actual fridge doesn't matter much either- put an ARB Zero in a closed hot car against an Iceco in a shaded car and I'll put my money on, and beer into, the fridge that costs less than half as much.

You can't offest lack of ventilation by increasing solar power generation. You can prolong the battle, but at some point the electronics hit their limit, think of how we preach mechanical sympathy relative to gearing. That's why when asked which setup to do, I so often recommend a portable panel that can be placed in the sun, optimized for angle, while the car can stay in the shade with the windows down. Do this instead of, or in addition to, a hard mounted panel, but don't just do the hard mount panel.

Two other points I'll make about car-top solar. Solar is terrible at night, it just doesn't work. It's slightly more useful when it's cloudy or raining, kinda useless in the snow too. And it doesn't work when you're driving- the alternator wins that race to who gets to charge the battery. So solar only really comes into play for a couple hours late in the day, presuming you're driving every day and you stop to setup camp. Or maybe that odd lag day where you choose to do a hike or something. But if it's a road trip, or overland adventure, you're really not using your car-top solar panel that much.
I recently replaced my somewhat expensive group 31 AGM battery with a slightly less expensive group 29. Of course the 31 failed at ~40 months with a 36 month warranty. I did put it on a charger somewhat frequently to try and keep it in good shape. Since I live so close to my work, the land cruiser can sometimes go 3-5 days without being driven. So I have considered a 50/100 W panel on my roof to basically be a permanent battery tender. This should keep my battery in better long term shape right?
 

AimCOTaco

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Yep, my 100 is usually outside sitting for a week or so at a time and my solar maintains the batteries nicely. Its helped my current set of AGMs last (60 months on optimas) longer and was one of the major reasons I added solar.
 

nakman

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So these past couple of weeks I have added flexible solar to both the Tundra and GX. In the GX, I replaced a rack-mounted rigid solar panel that was on top of my roof rack, while in the Tundra all I had was a flexible panel, so now it's got something on all the time.

Before pic of the GX...
IMG_2113.jpg


After pic of the GX...
IMG_2961.jpg


pic of the Tundra...
IMG_2994.jpg


Goals of the project were to:
- create a more stealth-like install... literally can't see the solar panel now unless you're looking down on the truck.
- capture back more of the roof rack for hauling stuff. I couldn't mount a ski box, haul plywood, or move other roof racks with that panel up there... and that was a problem.
- understand how much loss I'd experience with the rack shadow on the solar panel.

What I learned is that the loss of panel performance is totally livable, and way more offset by my positives of my other goals. And I can measure a greater performance difference with a solar panel by just changing its angle to the sun, way more than any performance loss found by placing it underneath a roof rack. Probably the greatest downside to any permanent mount panel is that it's almost never ideally aimed at the sun, so really never getting close to actual panel wattage.. but you knew that. but the big plus side to permanent mounted panels is that they're always there, doing at least something, with zero setup. you knew that also.

Anyway this was so much fun that I even made a video about it.. let me know what you think! 🍻

View: https://youtu.be/Bk8agLfFz4s
 

Corbet

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I keep going back and forth on a permanent mount as well for the 80. Roof is a hard sell for me as the RTT will pretty much completely block it. Hood mounted kits seem the most logical. But hard to swallow the $500 cost for only 90w that will probably only provide 50% in most conditions.

A number of kits are available. Looks like Slee stocks one. Quick Google search shows this as the most affordable. Not sure what variables exist between them but the pricing can sure vary. https://lensunsolar.com/products/to...QSrmDJxmVYuek5q7W8_5Iu_-ST9w4LNU5PiF4TljanbHs
 
Last edited:

nakman

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Yeah putting a tent over the top of a solar panel is generally the wrong direction.. if you have a hard shell tent you can do a flex panel on the top of the tent though, @AimCOTaco has this setup and has it dialed in pretty well. But it doesn't work on the old school flip-over tents with the soft cover obviously. So hood mount is your ticket, if you don't mind the appearance.

and yeah I'm a dealer for Lensolar if you want a kit... https://www.gamiviti.com/solar but like so many other companies it's just impossible to stay current on their sales, but happy to reach out to get a quote if you want.
 

wesintl

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I would love to have some slides built in under the rack for a hard panel to pull out from under the rack.
 

zgfiredude

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How did you "overcome" the humps in the roof skin (haven't watched the video) vs doing the hood mount? My rig can sit at times and just having this to keep the starter battery topped up seems like a decent idea.
 

Corbet

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How did you "overcome" the humps in the roof skin (haven't watched the video) vs doing the hood mount? My rig can sit at times and just having this to keep the starter battery topped up seems like a decent idea.
I've read reports of flexible panels coming off roofs due to "lift off". So I'm interested here also. Both my 80 and 250 are ribbed on the roof. Watching water on both hoods at speed lead me to believe that airflow there is pretty minimal.
 

nakman

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No way, you caught that! :bowdown:

for the ribs on the roof I did 2 things- first is I didn't use the tape on the top of them, so I kept the elevation lower, just put the tape in the valleys... on the Tundra I even did double layers of tape just so the panel didn't have to flex down that much. But the more important one I'm thinking is the added silicone all the way around the perimeter. In fact, I'm not even sure what that tape is really even doing tbh, the silicone is what's holding the thing down. I couldn't imagine doing this install with just the tape, even on the hood with no ribs.
 

nakman

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I would love to have some slides built in under the rack for a hard panel to pull out from under the rack.
I did that on the GX initially. The pic above is from after I abandoned the idea and just secured the panel under the rack with pipe clamps, you can still see the slides. Just didn't work that great- for one the needed slack in the wires had to be tied back somehow, so that was an added step. Otherwise the wires would flap all around when driving and start to wear out the paint, as well as be annoying. Also it didn't extend out that far, as I was using the panel under the rack to keep it flat, didn't have any kind of kick stand... so figure about 2/3 extended with the last 1/3 still under the rack to hold it up. And then I got a foldable panel and realized it was faster and easier to just set that up, rather than undo some slide thing then undo some wires only to expose a little over half the panel... anyway probably could have been done better, but just seemed like it created more issues than it really solved.
 

DouglasVB

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Wow those Lensun flexible panels are pretty reasonably priced (aside from the hood shaped ones). If I can ever settle on a camper shell, I'll be hitting you up @nakman
 

gungriffin

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I picked one of these up last month and I can confirm that it works really really well dealing with partial shading. I bought it specifically because of the partial shading performance. A pretty good option if you aren't looking for a flex panel.

The flex panel mounted to the roof is also a really great option Tim. I am surprised at how well it dealt with the shade blockage from the cross bars.

I also bought my panel for pretty much the same reason Tim did. I don't want to worry about draw on the battery when parked. You are much better to get an inexpensive DC/DC charger if you are after large amounts of charging. My DC/DC charger will charge up to about 50 amps when the engine is on. It can also be programed to charge at a lower amp draw if needed. It was about $260 and also serves as a solar charge controller.

 
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