Modular Roof-mount Solar Complete

Rather than add to my previous similarly-worded post, I thought I'd start a new one.

Its done and it works. I have a 110W solar panel that is securely mounted to the roof of the 560. It won't fly off at 70 miles/hr and thieves can't take it without doing a lot of damage to it or the trailer. It can charge a portable lithium battery while travelling down the road (but not the trailer battery), and it can re-charge or top up the trailer battery while stationary and disconnected from the TV in camp. The custom aluminum frame does double-duty in that it secures the solar panel to the roof, and provides a variable angle stand for the panel on the ground, at a distance from the trailer, hopefully in full sun.

The starting point is the HDPE mounting strips that I secured to the forward section of the 560 roof using 3M VHB tape # 4952. HDPE is a 'slippery' plastic and does not adhere using trad adhesive methods. The 4952 is specifically engineered for slippery (or low surface energy) plastics. It and its 3M tape cousins have lots of applications in the automotive and construction industries where a tape fastener is required. I augmented its already considerable holding power by using a paint-on 3M tape primer which assists in the bonding. I used 100 sq inches of tape which by my calculations results in 8000 lbs of both tensile and shear strength. Its not coming off. Unexpectedly. If in the future I need to remove it, for say a new panel, its possible through the use of mechanical means and adhesive solvents, but it won't scar or damage the aluminum skin of the 560. The tape has a considerable thickness (you can see it below) which conforms to voids and irregularities in the two bonded material surfaces. It also has the ability to handle widely variable expansion coefficients between different types of materials; in this case HDPE and aluminum.



The HDPE is solid and 1" thick. This allowed me to recess flanged nuts into it with a Forstner bit:



Pic shows the bottom surface of the frame and the HDPE that mates with the trailer skin; the two brass screws are to prevent the flanged nut from freely turning in the hole.

The frame is custom-welded 1/8" aluminum angle of varying widths, for the most part, and was designed around the 110W panel. 1/16th aluminum, though cheaper, doesn't have the rigidity necessary for this design and size, and is difficult to weld as you just end up melting it into nothing. The close placement of the panel grommets (which correspond with my 4 hold-down points for the frame) dictated the frame design and the overlapping corner welds. The bolt holes go through two layers of aluminum (1/4" thick total), whereas a standard mitre joint would be a single 1/8th" layer of aluminum, and the strength of mitre weld would have been severely compromised by the placement of the bolt hole.




The top side of the frame (1 1/4" wide) goes only to the very edge of the solar cells as any infringement on the area of the solar cells can severely compromise the efficiency of the panel. Because the solar panel electrical connections box sits proud of the panel I had to accommodate the bump, but this also allowed me to create a recess for cord storage for road travel.



The frame is secured to the HDPE strips using 4 high security stainless bolts that use a Hex-pin config. These require a special (yet obtainable) hex driver bit. You can't spin them out with a vice grip, and they would frustrate a casual theft of opportunity, but are by no means undefeatable, especially by someone with the same driver bit. Mounting the frame without the solar panel installed requires some washers to take up the space normally inhabited by the panel and the grommet. Otherwise you could be forcing the end of the bolt entirely through the nut and possibly into the trailer skin.



Part of the modular capability of the system is being able to place the panel away from the trailer in the sun to optimize the angle and get away from any shadows that may fall on the trailer (the shadow of your hand alone can cut the panel's electrical output in half). I have a 25' extension cord with MC4 connectors. The frame is "reversible", in a sense, and two hinged legs provide support at an infinite number of angles, from 25 deg to 45 deg. This corresponds with the optimal angles needed to come close to maximum panel efficiency at latitudes from the Mexican border to Northern Alberta during normal travel times of the year. Short pan head bolts with lock-nuts tightened down provide enough friction at the pivot to place the legs in any position without fear that it will kick out on you.


I used velcro tape (blue rectangle below) to keeps the legs closed and prevents flopping when travelling at speed.



As you can see in the photo above I placed two 5/8" metal studs in the ends of the middle HDPE strips; these provide an extra lock-down capacity for the frame, without requiring any extra hardware that I have to manipulate. The frame simply mounts at the front, by lining up the two studs, seating them, and then the back of the frame drops down over everything; the four corners are then secured with the 4 bolts.

Correctly mounting everything on the top and having precise placement of the plastic strips (so that all your drilled holes grommets and nuts line up) meant assembling everything off the trailer using carpet tape to keep everything in place. And then dropping the entire assembly into position and pressing down on the 3M tape. The tape requires some pressure to "set" it; it achieves 100% adhesion over 72 hours of curing.

The panel can now be plugged into the galley (routed between the weather gasket and locked galley hatch if necessary) to charge either our portable Lithium, or the trailer battery. This allows us to charge either battery while we are away from the parked trailer, and not have to worry about theft of the panel. The blue oval device mounted on the back wall of the galley is a super simple, yet effective Eco Energy Sunsport 6 charge controller that doesn't draw any energy on its own or allow any "backflow" of power from the battery when the panel isn't generating anything. Very efficient and easy to read what it is doing with a single LED. It is hard-wired to the trailer battery with a 15A safety fuse inbetween. The coax plug-in beside the charge controller is a port used for heated motorcycle gear, and as such, is adequately rated for the amperage that the panel is producing.



Didn't have a lot of choices in where to run the resultant wiring. The back of the upper shelf is usually filled with things so the wiring really won't be much of a visual distraction.



I married the cable up with some other wiring that I had already run for the third centre brake light, (which has it own forum post if you're interested)



There are a number of benefits to this type of panel and particular install from what I can see, and which I hope we can realize:

1) The panel is elevated off the surface of the trailer and has a (somewhat) ventilated air-space beneath it. This should keep it cooler. Panels are more efficient at producing electricity at colder temps. Higher panel temps resulting from glued flush surface mounts have contributed to panel delamination and damage and given some flexible solar panels a bad name.
2) The flexible panel can be (with care) stowed under or on top of the mattress if you are not in a position to re-mount it on the trailer due to time or environmental conditions. Or if you don't want to leave it attached to the trailer while you're in a questionable area. Or if you're away from the trailer for an extended period... such as at trailheads on multi-night excursions. Can't really do that with a heavy standard glass solar panel
3) No perforations in the trailer skin, and with effort, the mounts can be removed and reconfigured for a different size of panel in the future.
4) The overall weight of the system including the HDPE (I think its about 15 lbs total) is negligible, as is the wind resistance. Its not an eyesore, and wouldn't really attract the attention of a thief, given its higher position.
5) Aluminum angle, though tricky to weld, is cheap, easily obtainable in the required dimensions, and can be cut and finished by those with the ability and tools to cut wood. You just may need to source a proficient welder, as I did. Assembly was assisted with a plywood jig made out of scraps that held all the pieces true, plumb and square during welding.

I haven't painted it yet... probably will go black. If left as is it will develop the standard motley grey aluminum oxidation and be not terribly attractive.

There's more technical data and methodologies I can share if you wish more than what is contained here.

Thanks for reading one of my exceedingly long dissertations, again.

Steve

 

Wow! It looks just perfect. And I bet it's working good also. I realized the need of solar panel very late and then it was important to remodel my roof for the perfect position and protective installation of solar panel. I searched out on internet solved my query from this site. And hired the professionals for the complicated work.

 

Hi Steve,
I like the way you thought out the installation of your system, and your attention to details. Avoiding skin penetrations is laudable, especially in the roof.
I am wondering how waterproof your wire entry under the hatch will prove to be over time however. It seems to me that when exposed to rain, especially while driving, some water will follow the wires path through the hatch's weather seal into the galley, and you may eventually end up with some water damage to your beautiful woodwork.
Having just installed a waterproof Zamp solar receptacle in the sidewall near the battery compartment, I can tell you that it isn't difficult (especially with your obvious skills), and using a little silicone or other waterproof caulk on the underlying hole in the wood before installing the receptacle should give you some added assurance of keeping the water out. With your system, having some kind of waterproof connector go through the sidewall in the back of the upper cubby would probably even work better since it would lessen the distance the leads would need to travel outside, and be convenient to your controller wiring too. Just some friendly, hopefully helpful observations.

Dustin

 

Great job!

 

Dustin: Sorry I didn't see this when you posted it.

Prior to starting this project I had considered some sort of port or receptacle in the outside wall of the trailer and routing it through the galley or cabin on the inside, but decided on the simple solution. Your concerns are well-noted. However, the single wire that goes over the hatch gasket isn't as large as it appears in the photo. And the hatch gasket itself is thick, pliable, and can easily accommodate the wire without compromising waterproofness.

I also don't anticipate using the solar charging with the hatch closed for the much of the time, or while on the road, although that scenario is possible, if I am able to figure out a way to secure the cable to the roofline for travel at speed.

Using the panel for charging while on the road is really a non-starter, insofar as the trailer battery itself is concerned. Because the trailer battery would be receiving a charge from both the car alternator and the solar charge controller at the same time, Cary has pointed out that these two simultaneous charging systems "won't play well together", with one going into float while the other is charging, and vice versa.

However, I would consider using the panel on the road to charge my support lithium back-up battery only. The reason for this would be that I absolutely need the lithium fully charged during that time. However the car is always charging both the trailer battery, and running the Dometic inside the car. Under these circumstances, my TV alternator may be pushed past its limits if I added the lithium to the list. I don't want to find that out. This will be primarily for stationary use. So if I had to close the hatch on the wire, it won't be at speed. And if its raining, there likely won't be enough sunlight to warrant the system being connected in the first place.

Originally I had thought about running it past the side door gasket. However, this is a different material, size, and pliability and wouldn't accommodate much more than the thickness of a piece of paper before it interfered with the proper closing of the door.

Thanks and take care.

Steve

 

........glad to hear it's working well for you!

 

Confessional: I didn't calculate the airfoil effect on the rear leg. (the front one is unaffected) At speed the wind really does catch it and the velcro failed, leaving the leg vertical in the air and putting a small crease in the top of trailer. It also pried up a corner of the HDPE mount, which I had to re-set. I now have a strap the circles both the frame and the leg so the wind can't grab it.

FYI for those inclined to replicate this project.

And for those worried about the 3M making a mess or being difficult to deal with... it peels off by hand very slowly leaving no marks on the aluminum. But I have zero doubts about it's holding power.