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Hey all, I am considering mounting a solar panel under my roof cage as I use it a lot for gazebos etc. I want the solar for my fridge as I drive 10 mins to and from work so battery’s don’t get a great deal of charge from driving.

I know everyone talks about shading etc, but I am seeing more and more people with them fixed underneath. My question is how many people on here have done this and how do you find it works, even people who just store them under the roof cage, do you still get a reasonable amount of charge out of them?
 

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I use an 80w panel under a mesh roof of rack. I haven’t tested it. But I don’t think it’s that great. As it can’t keep up with my fridge at this time of year. Waiting for my battery monitor to turn up so. I can measure it.

I have mine mounted on slide rails. When extended. It just keeps up with my fridge at the moment. As long as we get some sunny days.
In summer when the car gets stinking hot. It can’t keep up. And I have to top up with my 240v charger if my car sits for more than 2 days.
My 200w panel I had on top of the rack had no issue hot or cold.


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It's amazing how little shading it takes to knock the guts out of solar panel output....
 

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There is a thread don't know how to link it here but if you search it's under the title of Solar under roof. If you look at pages 2 and 3 Overboard made a great slide for his panel and wock78 tested his panel under his roof rack and got a 35% reduction in solar output.
 

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GUII ZD30DI Wgn
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Is this it?
 

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I would recommend at least a 120watt panel to charge a 100 ah battery
That will put out 6.6 amps max in peak sunlight.
Usually between 11 am and 4 pm



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I concur with the above statements - it only takes a small amount of shade on a panel to dramatically reduce its output. Its not a good idea. You could put it on a slide so that it could extend when stopped. That would help a lot.
 

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I concur with the above statements - it only takes a small amount of shade on a panel to dramatically reduce its output. Its not a good idea. You could put it on a slide so that it could extend when stopped. That would help a lot.
I don't have a panel on my car but I have 16 panels on my roof and the slightest bit of shading has instant and noticeable effect on the meter.
 

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I don't have a panel on my car but I have 16 panels on my roof and the slightest bit of shading has instant and noticeable effect on the meter.
I am reluctant to quote any numbers Ross, as I cannot remember, but I do know it is bad. One of the reasons I stuck with a portable panel, was that it can be positioned easily to minimise this problem.
 

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Here’s mine. The top 200w panel is off.
But the one on the slide was a foldable 160w panel that I split in to 2 x 80w panels.
Only have one on a slide at the moment and it can’t keep up with a 40lt drawer fridge (being used as a daily driver. So little use). The plan is to have the other half extend over the windscreen.

Oh and in Victoria at the moment. Flat panels do bugger all. By about 3pm. My 200w panel needed to be about 70degrees angle. For it to read 19volts.





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I was going to mention flat panels vs being on an angle but you beat me to it
But yes flat panels are less effective and the most efficient is 45 degrees and chase the sun.
I’ve seen with my panel loose half it’s out put when a cloud goes over
Loss of full sun and shade make a hell of a difference


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I was going to mention flat panels vs being on an angle but you beat me to it
But yes flat panels are less effective and the most efficient is 45 degrees and chase the sun.
I’ve seen with my panel loose half it’s out put when a cloud goes over
Loss of full sun and shade make a hell of a difference


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Sorry.

Looking forward to my cheap battery monitor to turn up so I can see what it does to my setup.
I am hoping it gives enough detail I can see what it’s doing. And I will play with it and get some examples.


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Is it one of these



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No but I do have one of those. Its one of these from Aliexpress.
Read a couple of online reviews and they look alright.
Also means I don’t have to put Anderson plugs on everything. Which would just make my engine bay more messy.




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That’s looks alright !
Does it come with a shunt?


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Yes. I think I selected the 100amp shunt. As that will be ample for my use. As most I will have running at once will be fridge, travel buddy and maybe charging some phones or torches.
So all that wouldn’t be over 30amp. And my charger is only good for 20amp.


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Discussion Starter #17
Cheers for all the info guys, I would make slide out if I could but due to lights under my roof cage I got no where it could come out, I know I’ll get bugger all out of one but surely something will be better than nothing, so at this stage I’ll probably give one a go, cheers again
 

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Cheers for all the info guys, I would make slide out if I could but due to lights under my roof cage I got no where it could come out, I know I’ll get bugger all out of one but surely something will be better than nothing, so at this stage I’ll probably give one a go, cheers again
I have been thinking that for my front rails. As I want a bogan light bar.
If I get the better rails. I actually see no issues with mounting the light bar to the rail. So it slides out with the panel.


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I was going to mention flat panels vs being on an angle but you beat me to it
But yes flat panels are less effective and the most efficient is 45 degrees and chase the sun.
I’ve seen with my panel loose half it’s out put when a cloud goes over
Loss of full sun and shade make a hell of a difference


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That's exactly why my set up has always been 2 folded 80 watt panels with simply 2 short tent poles as the support on a longish cable. Move them everywhere and angle them to whatever works and just adjusted them every few hours when at camp or when I walk past.
 
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My understanding is that each cell in the panel is in series, so shading one blocks a big chunk of output. I’ve experimented with mine and found that shading just a corner with a bill sized envelope from the mail box dropped amps feeding battery by between half and two thirds. Quite a lot.

I have two 100 a/h AGMs and one meazley 80w eBay panel, with a good quality MPPT controller. I forgot to turn off fridge last time I flew to work, a 40 litre Engel, and it all ran the whole time (nearly three weeks) with the lowest battery voltage (early morning before sun on panels) in that whole time being a whisker under 12.4v, without car started once.

Have to be happy with that, Especially being early winter, so includes cloudy days.

I think people put too much importance on having a billion watts of solar capacity but that’s not much use if you only have enough battery capacity so that one cloudy day leaves you in a bit of bother with insufficient excess battery capacity. This is especially the case if you have two fridges, particularly if one is used as a freezer. With only one battery, a thousand watts of solar won’t help I your battery is at a damaging low level by 6am, you need to go from say 4pm to 9am with just the battery. I like having the option to run stereo and subwoofer if it’s a boys weekend, and use my oven (6amps) to heat party pies or something and never worry about batteries.

Also, a good multistage MPPT will charge the batteries to the same level as a DCDC, so you can still use a cheap volt sensing dual battery separator and maintain battery end life.

My panel was $90, VictronConnect 15amp MPPT $150, and two AGMS which are now 5 years old and pass a load test before each trip with flying colours. I also use a dual sense redarc SBI so when rear batteries have a charge level of 13.2, it closes and trickle charges the optima starting battery too, so basically an 80w panel keeps three batteries fully charged as well as running a fridge indefinitely.

If I were to run two fridges I’d need more solar capacity, but that would compromise roof space, so I have an Anderson plug on the roof to temporarily add another panel if I need to.

It’s a modest system but works well for me, doesn’t have to cost an arm and a leg if you use the right combination 👍
 
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