Too much solar?

[29chico]

I just bought a used Wells Cargo 6x10 extended height cargo trailer.  I'm in the process of designing a solar system for it.  The local solar distributor has the Solar World mono 285 watt modules for $270.  So no shipping cost.

I'm thinking of putting three of the above mentioned modules on the roof of my trailer.  They are 66x39 inches and will be a pretty much perfect fit front to back on the roof of the trailer and will be 3 inches short of the sidewalls side to side.  They weigh 39 pounds each and the four factory load bars that I have ordered will support a total of 200 pounds.

Yes, I will have to use a MPPT controller as these modules are designed to be used in grid tie applications.  I probably will go with the Morningstar MPPT controller.

Yes, 855 watts is a bit much. However I also really like the idea of having the whole roof covered with panels and an air gap between the trailer and the roof helping to keep the trailer cool in hot weather.  I figure that a shaded air gap above the roof will be way more effective at keeping the trailer cool inside than any amount of insulation installed under the roof and still thin enough to not make me crouch as I am tall.

I'm guessing that the modules and the all aluminum racking will weigh a bit over 150 pounds total.  Is that too much weight up too high?  All of the other heavy items will be carried as low as possible.  The top of the trailer roof is 8 feet 2 inches high without any racks.

 

[highdesertranger]

I would say you will be ok. do you have shocks on the trailer? that would help if you have any sway/roll when cornering. highdesertranger

 

[29chico]

I would say you will be ok.  do you have shocks on the trailer?  that would help if you have any sway/roll when cornering.  highdesertranger

No shocks or sway bar to reduce cornering induced roll.  The axle is a #10 Dexter Torflex 3500 pound rated unit with electric drum brakes.

 

[SternWake]

I wouldn't stress the weight on top, especially if you are aware of it and store heavier objects inside down lower.

 

[jimindenver]

Sounds good to me. You can run a small A/C with that kind of power.

What are you looking at as a bank and a MPPT controller? I compared Morningstar, Outback and Midnight for my 750w. I really wanted the Midnight as the newest and the free wiz bang but went with the Morningstar because it didn't have a fan and was smaller. Now that I have had it running full blast running the A/C all day, I can tell you that it could use a fan when converting 105v down to 12v. (switching to parallel will help)

 

[IGBT]

I have a similar setup with four 270 watt grid tie panels and a Midnite Classic 150 MPPT controller.

So 1080 watts.   I can tell you right now it is awesome.   Cloudy, overcast, raining?  No problem, I am still getting 200 watts!   It is only 8am with the sun peaking up and I am getting 175 watts.

I used aluminum angle to make homemade mounts and have not had any issues.

 

[Almost There]

The only caution I have about your proposed layout is that you haven't left any room for a roof vent.

While the panels will give you some relief from direct radiant heat, there will be heat build up under the panels which will 'drift' through the trailer roof so with no interior insulation, it's still going to heat up in the trailer.

That and while you will have enough power to run a/c there's no room to put one with a roof completely covered in solar.

If you aren't planning on a/c (and it would have to be a window a/c at this point), then maybe you have excess solar and can cut down on it by one panel to allow room for a roof vent with fan. IMO, that would do you more good with less expense than the 3 solar panels.

 

[IGBT]

You can insulate the roof with cheap polyiso 2" rigid foam from Home Depot.  Space the panels an inch or two off the roof so there is some air beneath them which will also act to impede heat transfer to the inside of the trailer.

You can mount a window unit A/C totally inside the trailer as we did with our camper.  A little bit of sheet metal aluminum will allow you to create side ducts so the A/C still is able to draw in cool air and expel hot air both from the side of the trailer.   Probably window units at $100 are cheaper than rooftop A/C.

Here is the original mock up idea I tested:

 

[jimindenver]

We just hang ours out the window in the rare times it is needed. The energy star rated units are more in price but worth it for their low draw.

 

[29chico]

The only caution I have about your proposed layout is that you haven't left any room for a roof vent.

While the panels will give you some relief from direct radiant heat, there will be heat build up under the panels which will 'drift' through the trailer roof so with no interior insulation, it's still going to heat up in the trailer.

That and while you will have enough power to run a/c there's no room to put one with a roof completely covered in solar.

If you aren't planning on a/c (and it would have to be a window a/c at this point), then maybe you have excess solar and can cut down on it by one panel to allow room for a roof vent with fan. IMO, that would do you more good with less expense than the 3 solar panels.

Almost There:

The top of the factory ladder bars that are ordered are about 4-5" above the top of the roof. That and I will be running 4 lightweight 1" square aluminum extrusions for and aft perpendicular to the ladder bars for the solar modules to mount to.  So that is 5-6 inches above the roof to the bottom of the panels.  Add at least an inch more up to the actual bottom of the solar laminate gives me 6-7 inches as the existing vent will be pretty much in the middle of the center panel. The existing cheesy square roof vent fits pretty close to the roof of the trailer.  Also, while the existing vent is in a standard 14" square opening, the dome that pivots up is only 10" sq.  This makes me think that I will be able to get a reasonable tilt angle with the existing vent dome.  If not, I'll yank the existing vent and go with a couple of low profile marine vents in it's place.  No matter what vent I go with I will  have powered ventilation via brushless high efficiency fans.

I don't plan on going with AC at this point.  I want to have plenty of power to get by even if bad weather sets in for several days.  On better charging days I should be able to cook with a microwave and run some power tools.  All the while staying cool with fans running and a nice air gap between the panels and trailer roof.  The roof will be insulated, just not a lot of thickness, so not to impair my headroom.

 

[29chico]

You can insulate the roof with cheap polyiso 2" rigid foam from Home Depot.  Space the panels an inch or two off the roof so there is some air beneath them which will also act to impede heat transfer to the inside of the trailer.

You can mount a window unit A/C totally inside the trailer as we did with our camper.  A little bit of sheet metal aluminum will allow you to create side ducts so the A/C still is able to draw in cool air and expel hot air both from the side of the trailer.   Probably window units at $100 are cheaper than rooftop A/C.

IGBT:

Nice solution to the AC mounting.  If I do decide to do the AC thing in the future I will refer to your above input.

 

[29chico]

Sounds good to me. You can run a small A/C with that kind of power.

What are you looking at as a bank and a MPPT controller? I compared Morningstar, Outback and Midnight for my 750w. I really wanted the Midnight as the newest and the free wiz bang but went with the Morningstar because it didn't have a fan and was smaller. Now that I have had it running full blast running the A/C all day, I can tell you that it could use a fan when converting 105v down to 12v. (switching to parallel will help)

I'm planning to go with the Tristar MPPT also.  It looks like I will be able to program the Tristar to properly deal with a 100AH LiFeMnpo4 GBS 12v battery pack.  I just don't yet know what the solar power reconnect voltage set point will be, or how to set it, as I will need shut off float and equalize entirely in MSview.  Hopefully Morningstar tech support will be able give me that answer tomorrow am.

I also have an industrial LiFePo4 40ah pack that I have been fiddling with for a while now.  I plan on the 40ah pack getting the brunt of my low current battery cycling.  It's max charge rate is only 15a.  I hope that I will be able to use the Tristar on Li packs as the supplied charger for the 40ah pack has only 10a of output and I could limit the Tristar's output to 15a in MSview.

Hmm, I was thinking of putting the three panels in series.  I looks like wiring them in parallel might be a better idea.

 

[29chico]

I have a similar setup with four 270 watt grid tie panels and a Midnite Classic 150 MPPT controller.

So 1080 watts.   I can tell you right now it is awesome.   Cloudy, overcast, raining?  No problem, I am still getting 200 watts!   It is only 8am with the sun peaking up and I am getting 175 watts.

I used aluminum angle to make homemade mounts and have not had any issues.

Nice system.

Per your 200w in poor charging conditions I should get about 158w with 855w of solar input.  Sweet!

 

[patrickp82]

I recently bought an rv & replacing the roof with EPDM from Amazon then installing my 6- 225 watt panels. I've got 4 - 225 watt panel's on 4 Walmart deep cycle 122 ah batts as a 12 vdc system then I have 2 more 225 watt panel's set up as a 24 vdc system with 2 122 ah Walmart batts for the $800 Engle fridgerator. 2 Renogy MPPT 1,000 watt controllers from Amazon for $209 each. All over kill I know but I wanted to use up all available roof space. I removed the vents & ac off the roof & re-decked it with wood just yesterday & by thursday I'll have it finished. Since my ceiling is 6'3", I placed 2 x 4s side ways 16" on center inside to take the extra roof weight bow away.
I'm gonna install 4 Reversible Fantastic Fans in the side walls with the vents pointing to the rear. I've seen them done this way before on other rvs with no problems. I did however take lots of pics once I figure out how to post them before & after.

 

[highdesertranger]

yeah Patrick let's see some pics. highdesertranger

 

[patrickp82]

Nice system.

Per your 200w in poor charging conditions I should get about 158w with 855w of solar input.  Sweet!

I like the way you did the led amber lighting to the solar panel frame.

 

[patrickp82]

I recently bought an rv & replacing the roof with EPDM from Amazon then installing my 6- 225 watt panels.  I've got 4 - 225 watt panel's on 4 Walmart deep cycle 122 ah batts as a 12  vdc system then I have 2 more 225 watt panel's set up as a 24 vdc system with 2 122 ah Walmart batts for the $800 Engle fridgerator.  2 Renogy MPPT 1,000 watt controllers from Amazon for $209 each.  All over kill I know but I wanted to use up all available roof space.  I removed the vents & ac off the roof & re-decked it with wood just yesterday & by thursday I'll have it finished.  Since my ceiling is 6'3",  I placed 2 x 4s side ways 16" on center inside to take the extra roof weight bow away.
I'm gonna install 4 Reversible Fantastic Fans in the side walls with the vents pointing to the rear.  I've seen them done this way before on other rvs with no problems.  I did however take lots of pics once I figure out how to post them before & after.

 

[ZoNiE]

X2 on lack of space for roof vent. You may want to reconsider that. I was thinking of hinging two panels so one folds over the other when traveling, and out and extended over the edge of the roof when camping...

 

[29chico]

X2 on lack of space for roof vent. You may want to reconsider that. I was thinking of hinging two panels so one folds over the other when traveling, and out and extended over the edge of the roof when camping...

You don't think that 6-7 inches vertical between the bottom of the solar laminate and the top of the trailer roof is inadequate to provide proper ventilation?

 

[highdesertranger]

well the more space the better. but you are limited if you want to drive on the road. so I will go out on a limb here and say yes 6-7 inches IS ADEQUATE. highdesertranger