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Topic ClosedSolar wiring, chase through to roof?

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Direct Link To This Post Topic: Solar wiring, chase through to roof?
    Posted: 21 Jul 2019 at 12:47pm
No significant difference unless the glass module has an open air gap under it. About maybe 20-30 F if it is stood off 3-4 inches or on an open rack. But the difference isn’t tied to the ambient temp, it’s tied to how much sun is falling on the modules.
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Direct Link To This Post Posted: 21 Jul 2019 at 12:57pm
Originally posted by podwerkz

Ah, you miss the point, grasshoppah...
I will figure this out, make a video of it, upload it to youtube and make MILLIONS of dollars in micro-payments.
THEN I can buy that fifth wheel r-pod in the year 3535....
Tongue


He he, there are a whole bunch of companies mostly in Europe who are working on solar module recycling. It’s an EU requirement. Instead of posting it on YouTube, patent it in Germany and sell it to one of those companies for a million Euros. Why wait till 3535, get your pile now😁.
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Direct Link To This Post Posted: 21 Jul 2019 at 2:51pm
Just for grins, I went out and measured the surface temps of two panels, side by side in full sunlight, with an IR gun.

Ambient air temps, about 96. Panels exposed for about an hour.

The flexible panel was directly on a surface, the glass panel has some limited airflow under it, but that airflow is also quite warm.

The flexible panel read about 155 degrees, the glass panel read about 140. Plus or minus a couple of degrees depending on where the sensor was pointed. And yes, I know that IR guns register the first surface temp, NOT the underlying cell temps, but we can infer that the temperature differentials are relevant.

Because flexible panels rarely have much airflow under them, they get pretty hot. And if you use them as portable panels, with some airflow behind them, they eventually fail due to the constant flexing. 

I think one or two seasons with a flexible panel is about all they can be expected to provide, and this is why they usually have just a one year warranty.


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Direct Link To This Post Posted: 21 Jul 2019 at 4:41pm
The temp difference between the cells and the top surface is pretty negligible, and both glass and Tefzel have an emissivity close to 1 so IR temps are pretty accurate.

The 15 degree difference sounds about right if you weren't getting ambient air temp behind the glass module (IOW, it wasn't a fully open rack mount). The rule of thumb is with 4 inches or more air space you get about 25 degrees hotter for a surface mount than for an open rack mount at 1 full sun (1000w/m2) irradiance and still air. If there's any wind both the difference and the actual temps are of course lower. Less than 4 inches and the stand off module will heat up until the difference drops to zero when there is no airflow under the module. 

Even then though, the roof temp will be less with the glass module because there is an insulating air gap. That's important both to keep from damaging the roof and keeping it cooler inside the trailer. 

Tefzel "flexible" modules are generally considered to be a 5 year product tops. Glass modules are a 30 plus year product. Urethane potted modules around 10 years, but they're expensive. 
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Direct Link To This Post Posted: 22 Jul 2019 at 9:23am
Interesting discussion. I have read of some flex failures, but also some accounts that were 10 years old and still working.

Aerodynamically I would not want a front facing leading edge panel mounted with a gap under it. No problem with one up on the flat surface, or the rear, so my second panel might be conventional.

I'll keep a log of the flex panels performance and update that after every trip.
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Direct Link To This Post Posted: 22 Jul 2019 at 10:09am
I plan to place a module across the front but will build a little fairing for it if I do. After removing the a/c and the TV antenna I expect to end up no worse off aerodynamically than I am now, maybe better. 

In solar reliability testing there are a standard set of accelerated life tests that are loosely correlated with years in the field. Those are done on any new design to certify it and also to establish an initial warranty period. The "flexible" modules would generally only last about 1/4 or 1/5 as long in these tests as glass modules.

But there are big variations in the real world environments that these products face. Hot sunny desert climates and warm humid coastal climates are the hardest, with different failure mechanisms for each.  And its certainly possible for them to last longer especially if you'e in a benign climate or in your case if your trailer is under cover most of the time. YMMV. 


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Direct Link To This Post Posted: 22 Jul 2019 at 4:33pm
OG, fyi a 4x4 hollow white plastic fence post makes a good fairing/spoiler. On my truck camper I split one down the middle and used the two sections of the "V" to block air from getting under the over the cab bunk....worked perfectly.
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Direct Link To This Post Posted: 22 Jul 2019 at 9:14pm
Originally posted by offgrid

Roger that. its not like it won't work, its more a matter of longevity. Since you're now planning to use fasteners, you might want to minimize the adhesive to make it easier to replace down the road if need be. 

The 179 has a big space behind the a/c, I plan on using that for a 350-ish watt module. 

OG, I was thinking of a similar setup for my 179. I was planning a first phase where I install a Victron MPPT controller and one portable panel that I would plug into the Zamp connector after i rewired it to the controller. Do you think the Zamp wire would be sufficient for a 100 watt panel?  I’m aware I have to reverse the polarity. 

I plan to install a second rigid panel on the roof at a later date. I was hopeful that I could run the wire down the rear wall of the head. I’ve removed the sink so I have good access. Have you considered how you would line up the mounting points with the frame?
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Direct Link To This Post Posted: 22 Jul 2019 at 10:08pm
Sure the Zamp wire conductors should be fine for a single 100 watt module, those have a short circuit current rating of about 6A. I'd suggest adding a 15A fuse at the battery, and reversing the polarity at the connector not at the battery, to keep the wire color coding consistent. If you plan on adding a long wire run from the Zamp connector to the portable module you probably want to go with 10 gauge wire for that to keep the voltage losses down.

My plan is to buy a 72 cell large format module the same length as the rPod is wide, there are many alternatives to choose from. Plus, they are the lowest cost modules you can get on a per watt basis, you can often get them on CL or Ebay really inexpensively left over from a large solar project.  Then I would mount it using vertical aluminum plates on each end to the upper trailer wall edges rather than to the roof. The upper walls are a continuous 1 inch aluminum square tube so the mounting plates can be attached anywhere. I would use self tapping screws into both the end frames of the module and the upper wall tubes. The screws can go all the way through both walls of the aluminum square tubes and the tips would be concealed within the roof. That should be a very strong connection as the screws would be in shear rather than tension, and there would be no holes in the roof itself. 

I'm planning to remove the TV antenna and use that hole as the wire chase, I don't use the antenna anyway. 

One thing though, MPPT controllers depend on the solar module voltage being above the battery charge voltage, they are actually a step down dc/dc converter. Also, you can't connect both a 100 watt 12V module and a 350-ish watt 35-ish volt module to the same MPPT input simultaneously. So, I'd suggest getting a separate small PWM charge controller for the 100W module. Or get two 350W-ish modules and keep one portable and put one on the roof, then run both modules into the MPPT controller in parallel.  They're big things to lug around though, about 39 inches wide and 77 inches long and weigh about 50 lbs. 
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