Mounting solar panels above ac shrouds

[sushidog]

I am in the process of installing 2 solar systems on my Class A MH. The first is a small 12v system and in a couple years I will be installing a bigger 48v system. I plan on using large high voltage panels and racking them slightly above my AC shrouds from front to rear utilizing almost my entire roof. The reason I plan to go high is that I have no choice. I have 2 roof AC units, 3 covered vents, a new style disk shaped over the air TV antenna and a shower skylight, a fridge vent, air horns and a radio antenna on my roof. My current height is 11' 9" and I plan to keep it under 12 ft.

Now to my question, has anyone done this before and if so, how have they done it? I am considering using 2" furniture grade (UV protected, guaranteed for 15 years of direct sun exposure) plastic pipe to build a simple rack to mount my panels right down the center of the RV, about 13" off the roof. The panels would all be perpendicular to the length of the RV. Has anyone used this material before in this application?

Thanks for your replies!

Chip

[Lou Schneider]

Sounds to me like this is an excellent way to let the panels get airborne.  Think about carrying a piece of plywood in the same manner.

You'll get a lot more air (thus potential lift) under something 13" above the roof than something mounted an inch or so above it.

[k4rs]

While my install was not as large as yours,  I built a similar rack for my fifth wheel.  I used 2 inch square aluminum designed for pool enclosures.  I never had an issue for the 12 years I owned that rig.  Unfortunately I don't recall taking any photos.

Safe Travels...

[sushidog]

Thanks for the replies. A few years ago I saw a bus with a round metal rack up top about a foot or so off the roof, with about 1/2 of the roof covered in solar panels, so I know it can be done. I couldn't see the details of how he did it but it looked like it was all welded together. I first was thinking of building a rack out of aluminum angle. I was at Slab City about 2 weeks ago and spoke with Solar Mike, who does a lot of RV solar installations. He told me that he recently mounted 4 large panels, similar to the ones I'm looking at, about a foot off the roof of a motorhome using aluminum angle racking which was heavily cross-braced. They make rectangular aluminum rails for mounting panels, but they are typically used in fixed installations. Two inch square aluminum sounds much more sturdy. I sure don't want them blowing off the roof or causing undue handling issues in cross winds and such, so I was seeing if anyone else has racked  2,500 watts or more of solar on their roof and exactly how they accomplished it safely.

Where there's a will, there's a way. I could block off the front with a piece of plywood or plastic at a 45 degree angle to prevent wind getting under and lifting the panels while going down the road. This might actually help in the MPG department too as the roof has lots of things jutting out like  to disturb the airflow and cause drag. A smooth wind deflector might just be the ticket. I could even drop the front of the leading panel at an angle so as to bring it within an inch or so off the roof to deflect the wind over the other 7 panels.  Now you've got me thinking - perhaps a dangerous thing. 

Chip

 

 

[sushidog]

I just did a little trig and the angle of the 40" wide solar panel will only be at 17.5 degrees, a gentle slope indeed. It might also improve solar efficiency slightly if the rv is pointed south. It certainly wouldn't hinger it even at a random angle to the sun, cause you never know which way you might have to orient your rig. I could even mount both the first 2 panels on the same gentle angle of 8.63 degrees to ease the airflow over the others, leaving the other 6 panels for the 48v system flat at 13" off the roof. Decisions, decisions.....

Chip

 

[sushidog]

I just completed phase 1 of my 2 part solar project today. I purchased 2 - 310 watt Canadian Solar panels from N. Arizona Wind and Solar and instead of mounting them on top of the roof I decided to mount them on the passenger' side of the MH, about 6 inches behind the awning and at the same height so when both are flipped up the awning will not shade it. I mounted these 39" x 66" panels sideways one above the other so they take up 78 " when flat against the wall, over the bedroom window. As a bonus they provide a nice solar awning shading the bedroom window when extended. I just got finished installing them and wiring them up so I'm dusty, tired and bleeding from numerous wounds from all the sharp aluminum edges. I'll take some pics over the next couple days, as I'm on the move in the morning (my 14 day limit is up here at the Coconino National Forest by Flagstaff) so I had to complete the job relatively quickly. 

I decided on a side mount for 2 reasons. First so I could angle them into the sun to gain a little extra power, but mainly to free up my entire roof for the second phase of my system. I can fit 9 of these panels up there for phase 2, mounted flat and racked above the ac units with the first two sloping at a gentle 9 degrees, to ease the wind over the rest when I'm traveling down the road. the side mount makes it easier to clean too, so I'm apt to clean them more often.

I used 4 rails of 1" square aluminum tubing attached to 2 large gate hinges up top to pivot the 2 panels in phase 1. I also added a 1 1/2" aluminum angle brace at the bottom to prevent twisting when erecting them and taking them down. I used heavy 2 gate latches with sliding pins to secure them in place when traveling. The only thing I still need to do is add a pair of gas springs to help me lift them. I am looking at these: https://www.autozone.com/collision-body-parts-and-hardware/universal-lift-support/mighty-lift-lift-support/334504_0_0 They will make it a little easier lifting them and holding them in the precise position while my DW slides in the support bolts and wingnuts. The panels weigh 40 lbs each. With the 4 aluminum bars and mounting hardware I'm looking at about 90 lbs total weight for the module. Of course with one end pivoting,  I'm only lifting 45 lbs when near horizontal, which I am doing with a pole. Still I'm getting older and it won't be long when the pole itself might be a struggle for me to lift. Gotta think of the future, you know. 

Chip

 

Edited July 2, 2019 by sushidog

[Lou Schneider]

14 hours ago, sushidog said:

 I am looking at these: https://www.autozone.com/collision-body-parts-and-hardware/universal-lift-support/mighty-lift-lift-support/334504_0_0 They will make it a little easier lifting them and holding them in the precise position while my DW slides in the support bolts and wingnuts. The panels weigh 40 lbs each. With the 4 aluminum bars and mounting hardware I'm looking at about 90 lbs total weight for the module.

How about using an electric linear actuator instead?  Run some wiring down to a switch and it will raise and lower the panels without needing assistance from a pole.

If you wire it so the motor leads are shorted while it is stopped it will have dynamic braking to hold the panels in position.

Here's one example found with a quick Google search.  This has a shorter stroke but more lifting capacity than the gas lift so it's just a matter of changing the geometry of the mounting points to get the proper lift on the panels.  Reasonable price, too.

https://www.walmart.com/ip/Heavy-Duty-Linear-Actuator-6-Inch-Stroke-12-Volt-DC-225-Pound-Max-Lift/408252473?

Edited July 2, 2019 by Lou Schneider

[sushidog]

Thanks for the suggestion of a linear actuator, Lou.

I would have to choose another model though, as with only a 6 inch stroke my pivot point would need to be about 6 inches from the pivot. The force needed to lift a 78" long panel assy that weighs about 90 lbs total, at the center of gravity (39" from the pivot) is 90 lbs. Six inches from the hinge, the force on the actuator would be about 585 lbs. Since the actuators only lift 225 each (450 lbs of total force) they aren't quite powerful enough to do the job. Besides, I'm not too keen about applying 585 lbs of force (292.5 lbs on each side) directly on the end of the upper solar panel, as I'm sure it would break the glass from excessive force.  By moving the pivot point closer to the center, the force is greatly diminished. Ideally, I'd like the lift attachment as close to the center of the panels (the center of gravity) as possible. If I could lift there, where the panel frames meet and the strength is doubled as not only is this a stronger lift point, but I'll only need 2 - 45 lb gas springs to lift the module. If I use the gas springs in my link with only 15.4" of lift, I'll have to settle with a mounting point about 15" from the hinge pivot point. At this point it would require about 234 lbs of force to lift the module. The pair of 80 lb gas springs would provide about 160 lbs of lift (68% of the force required) leaving me to lift 32% of the module's 45 lbs downward force at vertical at the end of the panel,  or  14.2 lbs - a much more acceptable weight to lift over my head, even for an old fart like me.

Besides, how can I be sure the linear actuator motors stay in sync and lift evenly on both sides. I'm afraid if one actuator motor spins a little faster than the other, or one side has a little more drag or binds, that it would twist the panel and the force could pop the glass. If there is a few lbs of lift difference in the gas springs that develops over time, I doubt that it would exert enough force to damage anything.

Also I can get a pair of those gas springs for only $64 while a pair of linear actuators that could do the job, like these:  https://www.amazon.com/Stroke-Linear-Actuator-Pounds-Maximum/dp/B00OGQQCDI  would cost about $200 with mounting hardware and switch. I really like the idea of the module lifting itself, if I could only guarantee the actuators remain in sync while lifting and won't break anything. Reading the Q and As on the link, they don't recommend using them in tandem as a slight difference in speed is possible, justifying my fear of a broken panel.

Chip

 

 

 

[Friz]

What will be your new height? May be a problem with some underpasses. 

[sushidog]

I am 11'9" now. This will add about 2 - 2 1/2" so I will still be under 12 ft.

Here's a couple photos of my recent side mounted solar installation.

Chip

 

[$ Spot]

Best awning ever!

[Fro]

Earlier in the year a friend and I built and mounted  frames for the panels on our rigs.  We used 3/16 x 2 " aluminum angle stock and 1/8 flat stock for the upright cross braces.  Total cost was 200 bucks for each build.  The frames are 30 ft long by 35 in wide and all the struts/braces/mounts were fitted to avoid the a/c units, vents, etc. In addition, we utilized residential solar mounting rails, bolted to the top of the frame and the panels then affixed to the rails.There is less than an inch clearance from the panel to the top of the highest a/c unit.    I was concerned with the wing/lift effect so I set my son on the issue.  He is an mechanical engineer and his buddies are aeronautical engineers/pilots. (They are USAF test pilots)  Their opinion was no additional support was needed and a potential for lift at horizontal plane was  zero.  My friend chose to mount his panels perpendicular to the roof.  I followed him from Yuma to Tuscon and there was no movement in the panels that I could detect.  Mine are mounted parallel to the roof and there has been no shifting either.  My buddy affixed mounting brackets in place using gorilla glue and screws, then installed a new roof over them.  They are never coming off..  I used 3M High bond tape.  Don't recall the specs off hand but shear factor was something like 1100 lbs/sq in and tensile strength was in the area of 700 lbs/sq in.  My total mounting brackets total 144 sq/in.  If I hit a bridge I will probably peel my roof off before losing the rack.

[sushidog]

Thanks for the props, $ Spot and the great information, Fro. This kind of real world experience is exactly what I was looking for. I'm sure it will help others here as well. Are you using 66" x 39" format panels, or some other size?

Details, details, please.  

How much wattage do you have up there?

What is your voltage going into your charge controller and what size, battery type and battery bank voltage do you have?

Inquiring minds want to know! Pictures help.

Chip