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Panels for 7x14 Trailer

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Kemp Outside

New Member
Joined
Jul 20, 2023
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16
Location
Lithia FL
Hey all, first post here. I’m designing my first solar 12 volt system for a 7x14 cargo trailer that has been converted into a camper. I have been watching a lot of Will’s videos on all things solar and I am trying to decide which panels to buy. I am going to use the Renogy 50 amp DC to DC with MPPT. I have room for 4 100 watt solar panels on the roof.

Some of the videos I saw are 4 years old so I am not sure what the current front runners are when it comes to panels. A couple of Will’s videos suggested poly panels produced more power than mono panels but it seems it is harder to find poly panels today. Have things changed since those videos? What’s the best 100 watt panel for the money today?
 
Supervstech said:
Why not use 200+ watt panels?
Higher wattage panels are a better buy, and frequently easier to setup.
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I may be wrong but I thought it had to do with the limitations on my controller. Will’s website recommended staying below 400 watts. Should I use 2 200 watt panels instead?
 
Kemp Outside said:
I may be wrong but I thought it had to do with the limitations on my controller. Will’s website recommended staying below 400 watts. Should I use 2 200 watt panels instead?
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Depends on what you are charging and how much power you want.
 
My plan is to have a 206AH SOK battery but may step that up to 2 of those eventually. Trailer will have LED lights and charging ports for mobile devices, a couple of fans, etc. the biggest item will be a 12 volt fridge that draws 50 watts. Also planning an inverter for small items that need 120 volts (laptop, extra monitors, etc.) Trailer will have DC to DC from the tow vehicle and a 60 amp converter for charging the batteries when on shore power or generator (3500 watt Predator). I’m not planning to rely on the solar but want it to extend times between recharging.
 
Not pushing it, but I went the 'other way'.

I built my trailer around an MPP 3048LV (48v battery / 3000w) as it handles AC input (campsite power or generator) + solar panels and outputs 120v. It has internal UPS, all seamless between battery and external AC - easy to manage. Not pushing MPP Solar specifically, just the idea of an all-in-one.

For 12v subsystem, I went with a 120v -> 12vdc @ 80a transformer for the 12v subsystem for MaxxFan, water pump, power tongue jack, leds, heatpads for water tank, safety break battery top-off, etc. They make 120v -> 12vdc at a wide range of amps - 20a, 40a, etc - easy to find something to suit you're needs.

We find that 120v @ 3000w is doable but a little light for Mini-Split, Fridge, K-Cup, Microwave , Hotplate, Hot water, TV/Computers/Starlink etc when all is on at the same time - it's amazing!.

MPP Solar makes a 24v (MPP 2424LV) all-in-one at 2400w 120v level as the next step down. https://www.ebay.com/itm/164987205373

There's even such a thing as a 12v 600w all-in-one - https://www.eco-worthy.com/products...r-inverter-30a-controller-for-off-grid-system - but probably not as full featured as MPP Solar or it's equivalent.

Again, nothing wrong with you're plans, just wanted to share that it's not the only way to think about 12vdc vs 120vac combo. :)
 
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OffGridInTheCity said:
Not pushing it, but I went the 'other way'.

I built my trailer around an MPP 3048LV (48v battery / 3000w) as it handles AC input (campsite power or generator) + solar panels and outputs 120v. Then I did a 120v -> 12vdc @ 80a for the 12v subsystem for MaxxFan, water pump, power tongue jack, leds, heatpads for water tank, safety break battery top-off, etc. We find that 120v @ 3000w is doable but even a little light for Mini-Split, Fridge, K-Cup, Microwave , Hotplate, Hot water, TV/Computers/Starlink etc.

MPP makes a 24v all-in-one at 2400w 120v level as the next step down. There may even be a 12v @ 1000w 120v level.

Again, not pushing this idea (or MPP Solar) and nothing wrong with you're plans, just wanted to share that it's not the only way to think about it :)
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If I ever do another build, I’ll probably go this route. I bought this trailer half completed with the 120v AC already installed. The guy who built it never planned to be away from shore power. I don't want to mess with the existing electrical so I’m adding a 12v system for off grid use.
 
Just in case you don’t know yet, that Renogy 50A dcdc MPPT is limited to a mere 25v solar input. A real solar charge controller like the Renogy Rover 30A or 40A can accept up to 100v

So you’re limited to 100W panels in parallel to stay under 25V. And if you intend to use it in cold weather, be sure to use a solar temperature calculator to make sure your 100W panels won’t produce more than 24v, or you will fry the MPPT. You can’t use 200W panels because they’re more than 25V. If you’re set on the idea of having a DC-DC charger, then get a dedicated device. I would recommend the Victron ones over Renogy’s.

As for poly vs mono, I saw Will do a video where the poly produced slightly more watts than the mono panels. But poly panels tend to be larger for the same wattage, so keep that in mind.
 
SolarArchitect said:
Looks good. How are those rails/struts/channels attached to the trailer? Would you do it differently now?
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The feet of the L-Brackets for the rails were bolted thru the roof into the cross (metal) beams under the roof + sealed with standard butyl tape and Lap Sealant - https://www.amazon.com/Dicor-501LSW...t-10-3-Fluid_Ounces/dp/B000BRF7QE/ref=sr_1_10 - on top of the bolt heads/L-Bracket feet.

Did this while the interior wood was taken out in prep for insulation which exposed the metal frame - was not too hard. Just drilled up from underneath. The rails are mounted to the L-Brackets and panels to the rails. About 5,000miles nearing 3 years and no issues.

Doing it differently....
- I would add some amount of Panel tilt so the water won't pool due to being flat with metal frame edges keeping water from running of. This leads to evaporation / dirt scum that reduces PV a bit.
- Also, I would have done 2" (R10) or 3" (R15) of insulation knowing what I know now instead of only 1" (R5) to reduce power needed for heat/cool. The silver radiant reflection coated foam panels (more expensive) didn't seem to add much. I suspect it's mostly the raw RX value that does the heavy lifting. We like winter camping!
 
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I would use a different solar charge controller with more flexibility.

As far as poly vs mono - I have some test stands at my shop that I use for my own personal comparison and my "data" is not at all perfect or documented well enough to hold up to scientific review. It is good enough that it solved some problems with customers in coastal conditions like mine do.

Keep in mind that when there is plenty of sunlight - really anything works well enough. What matters for my mobile customers is in the winter, it is overcast a lot, the days are shorter, and the sun angles are lower - so the tougher conditions are what I am focused on here. Not really "perfect optimization of the "best" sunlight conditions.

So I test for things like finding wide acceptance angles (to maximize the amount of time the sun light is gathered) and how well they worked through heavy overcast and the smoke from our annual forest fire smoke.

The panels shown are solarland - both are 26 x 58 inch.

The poly ones are 140 watt and the monos I think are 160s.

No question - the poly ones have a wider acceptance angle - and so far every time that companies come out with these super high efficiency panels, it seems like this acceptance angle keeps getting more narrow. That is bad for mobile users.

Under really bright sunlight conditions - the monos produced more power - but not that much more.

Under really terrible sunlight conditions - the poly produced more power - but not that much more.

The key really is to have the array wired so that the controller turning on as early in the morning as possible.

Controllers need the panel voltage to hit a minimum number to turn on. For a controller like a bogart engineering PWM controller - that number is very low - so even though PWM controllers are not as optimal under every condition, they are great for panels wired with a Vmp < 25 volts and a 12 volt setup.

If your panels are wired so that the Vmp is > 30 volts and 12 volts then probably get something like a victron controller.

A really great setup for your trailer actually would be a 24 volt battery pack, bogart controller and your panels wired with a Vmp 30 - 40 volts.

I will see if I can find some photos.
 

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Here is a possible idea for your trailer electrical system. I built this late last year for a friend's trailer.

He has a small work bench in it so I put a "drip plate" board over the electronics and outlet. That way when he drops tools and parts - they won't fall on the electrical items and outlet plugs.

It is mostly under the fold down seat but part of it is sticks out. He added the battery hold down area himself.

In this case, it is in fact what I suggested - a 24 volt system and he has just one 12 volt item so there is a small DC converter for that feeding a 12 volt fuse block ( the left one )

I use battle borns for this area because they will continue to work (discharge) at a lower temperature than the SOKs and I am also a fan of cylindrical cells for mobile applications.
 

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featherlite said:
Are you aware of any issues with charging a LIFPO4 battery with a PWM controller?
FYI, I am a big fan of using Bogart products to charge lead acid batteries.
Click to expand...

Not a problem - I build 24 volt setups using bogart and battle born all of the time. Downstream of the controller I can't see the pulse with the meters that I own. Perhaps with a high resolution scope you can.

Look at the scale involved. For instance in that minimalist build for the trailer it is 2 x 100 amp-hrs battery pack. The internal cells themselves could easily absorb 2000 watts charging pulses, the BMS rating limits it to ~ 1 000 watt charging continuous. (mfg spec)

The Bogart SC 2030 self limits to ~ ( 28 volts ) x ( 30 amps ) ~ 750 watts, no matter how many panels.
 
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Watts Happening said:
Thanks! It’s a High Country Cargo trailer
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Would you mind telling us a bit more about how you mounted those panels?

It looks like perhaps there is an angle aluminum piece in back bolted or screwed into the back of the rear panels.

I am having difficulty visualizing how you got them up there and attached.

I looked back through quite a few of your older posts and could not find the info.

Thanks Harry
 
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