Which screws for solar panels, and which configuration?

[DuneElliot]

EPDM and (I think) plywood roof on 27ft fifth wheel. I will be installing 4 100W panels shortly. I have all the parts except the connectors and screws.

I have read several discussions where people had problems with well-nuts on wood roofs (they kept loosening) so will stick with screws. However, what kind are best? I was thinking that probably a 1" coarse thread wood screw of a wider diameter would be sufficient but I'd like to get some feedback from others.

Also, I know I have 3 options for connecting them: series, parallel and series/parallel. I was leaning towards S/P but I want to be sure that I can run that kind of set-up to a 40A MPPT charge controller.

 

[Trebor English]

I have seen nuts and bolts with fender washers on the inside so nothing can pull through.  It won't look pretty on your ceiling.  

Which panels and charge controller do you have?  That will determine which combinations you can have.

 

[DuneElliot]

I have the Renogy 100W Eclipse solar panels (18.35 output) with their Commander 40 MPPT charge controller.

I don't want to put holes all the way through my ceiling, especially as it is around 2" thick, so just looking for the best screws

 

[jonsun]

I used 1/2" well-nuts with loctite and sealer...been on there about 5 years

 

[Trebor English]

That controller can take 150 volts input so you could wire 4 panels in series.  That would get charging going earlier in the morning and minimize loss due to cable resistance.  With the bypass diodes there will still be charging when shadows block several 1/2 panel areas as long as 2 complete 1/2 panel areas get full sun.

 

[Gary68]

size 8 or bigger stainless self tapping,but i would use an adhesive,sikaflex 221 too,i would also add a little pacer in the rear so while going down the road the wind pushed down on the panels,1/8th-1/4"would be enough

 

[CautionToTheWind]

Here is a CRVL thread: https://vanlivingforum.com/Thread-W...olar-panel-to-a-van-Roof?pid=137894#pid137894

Some people have used EternaBond (no holes): https://www.amazon.com/EternaBond-R...8&reviewerType=avp_only_reviews&sortBy=recent

 

[highdesertranger]

I don't like screwing into plywood. I recommend screwing into that wood on the edge. where the roof meets the wall. here's how I like to do it,

https://vanlivingforum.com/Thread-installing-solar-on-a-RV

highdesertranger

 

[jonsun]

you had trouble finding aluminum bolts? I got whole junk drawers full. Try motorcycle body bolt kits if you ever need them again.

https://www.amazon.com/Aluminum-Spe...94193&sr=1-16&keywords=aluminum+fairing+bolts

 

[tx2sturgis]

Buy a really small but strong magnet from harbor freight or home depot, autozone, places like that, and drag it around the roof to see if you can find the horizontal metal roof bows.

If they used aluminum, such as on the 'lite' trailers, this wont work.

If you do find some metal ribs, you can run self-drilling screws in those and they will NEVER turn loose.

 

[DuneElliot]

I have Eternabond for the wires...but it will not be adequate for the panels, not on an EPDM roof.

I don't get how the motorcycle body bolt kits would help on an insulated RV roof.

HDR, I like what you did but my panels aren't that big and I can't go across the roof. They are going down each side of a vent. I have the panel mounts.

 

[GotSmart]

3M VHB tape.  

No holes, no problems.

 

[tx2sturgis]

A little more info about the roof construction:


http://www.theadamssfamily.com/CG/construction.htm


And yes, please dont use tape for the panels on the rubber roof....the rubber gets soft and spongy in the heat of the sun.

 

[tx2sturgis]

Here is a typical application chart for the VHB type of tapes...'low adhesion' is a concern.

Lets cross those off the list for a rubber roof and not lose those panels.

 

[tx2sturgis]

Here is a small screen grab from the 2007 brochure for your Springdale.

Its very generic but it shows wood trusses. So a magnet will not work, unless you can find a pattern of screws (under the coating) that fasten the roof deck to the trusses.

You might be able to use a stud finder, the 'knuckle test', or simple measuring to find out where they are positioned under the roof material.

 

[Spaceman Spiff]

i would also add a little pacer in the rear so while going down the road the wind pushed down on the panels,1/8th-1/4"would be enough

I did that with my solar panels (1" higher in back = 3º tilt).  It doesn't have much effect.  The rain pools in front when parked but it doesn't have the cleaning action I had hoped.  As to downforce: my panels are 1" above the roof in front, 10" behind the front of the camper and 7" above and 20" behind the windshield.  The airstream is pushed up over the panels (as indicated by lots of bugs on the front of the camper but the front of the panels are bug free).  The air under the airstream would be turbulent so no idea of from what direction the wind is exerting force on the panels.

 -- Spiff

 

[tx2sturgis]

 The air under the airstream would be turbulent so no idea of from what direction the wind is exerting force on the panels.

 

Generally speaking, there is positive 'lift' on the panels above a certain road speed, due to the low pressure between the roof and the airflow above.

That's why partially opened roof vents make so much rattling noise when you start driving.

 

[Spaceman Spiff]

I would think not.  Airflow under the panel is constrained by the roof, so very little pressure gradient (if any) between bottom and top surface of panel, if the airflow is indeed going over the panel.

The rattling you hear in roof vents is due to turbulence: air currents constantly changing.  A dominant lifting force would stabilize the vent cover (i.e. damp and minimize motion).

 -- Spiff

 

[tx2sturgis]

The rattling you hear in roof vents is due to turbulence: air currents constantly changing.  A dominant lifting force would stabilize the vent cover (i.e. damp and minimize motion).

 

Conversely, if there was a dominant uninterrupted blast of air over the roof that is close to the roof, then the vent cover would be forced down against the lifting bar, and again, make no noise.

The airflow passing over the roof is turbulent, I agree, its not perfectly clean, it has some vortices that add to the buffeting.

But there IS a low pressure zone up there that's trying to lift the vent cover or solar panel, (due to the higher pressure underneath) same thing that happens with an airplane wing.

Notice the bus (which has a similar profile to a motorhome) in the top half of this wind tunnel testing.

Blue, in the side view, is the area of low pressure:

[video=youtube]

 

[Weight]

During a mounting system test, I had 4 renogy 100w panels mounted to the roof of my B250 van. We road fast, slow, bumpy, dusty, and off road. There were no problems with the panels or mounting system. Not even wind noise. The panels had 2 inches free board between them and the roof.