Mount Strength

[KBWaldron]

This is going to seem an odd question. I am planning a method of mounting my panels to my RV roof, but am unable to find some information I need.
When driving, or even in high winds, the air rushing over the roof will create a force trying to lift the panels off the roof (I’m thinking of the flat mounted situation). Does anyone know the strength of lift that can be generated?
Thanks in advance,

 

[Craig]

I do not know. However I have been driving trucks with ladder racks on them my whole life. Sometimes these racks can make a pretty good squeel of air noise if they are at an improper distance from the cab. Because of this I have asked anybody I have ever met who had solar mounted to top of van or bus or trailer, if the panels make wind noise and without exception they all say no. So my point here is I do not think the force is that large at all.
Sorry I know its not an answer but just a thought. I think if panel does not extend over the arc of top front of cab that wind influence would be minimal. Or I always figured if I mounted panels to roof I would add a spoiler to help with aerodynamics anyhow.

 

[eddie1261]

This is going to seem an odd question. I am planning a method of mounting my panels to my RV roof, but am unable to find some information I need.
When driving, or even in high winds, the air rushing over the roof will create a force trying to lift the panels off the roof (I’m thinking of the flat mounted situation). Does anyone know the strength of lift that can be generated?
Thanks in advance,

You are int eh right place to learn. Will us the guru, and many people here have a lot of experience with this topic. I knew zero about it until I started watching Will's videos and bought his book. It is a simple to follow, accurate and concise guide to solar power.

My thought it this. Mine is mounted to a roof rack, 5 inches above the roof at the front and back, 3 inches at the center. (The roof of my time trailer is curved.) Air rushing across that flat surface should not create lift. If you think about a plane, the plane develops life when the flaps are down and the slats are extended, That creates low pressure above the wing and high pressure below it. When the plane is at altitude, those are retraces and the wing is essentially flat. At that point there is no lift. In my case, just to be safe, I am also going to have an aluminum air dam made to keep the 65 mph wind from getting under the panel. You really don't have a lot of aerodynamic life created form the sides, only from the front. Also in my case, my car deflects most of that wind. When I towed that trailer from Florida to Ohio it towed like it wasn't there. To the point where a few times I looked down and saw I was going 84.

Many people here have used, trust and believe in the VB tape. I wanted my panel bolted, and that curved roof made the decision for me, as I couldn't tape a panel to a curved roof. That was why I ordered the roof racks to begin with.

 

[Deleted member 783]

The squared off nature of a solar panel is not conducive to lift, unlike a curved surface.

 

[murphylawe]

The 'Force' you are describing is the Bernoulli Effect and this is what provides lift for aircraft. It requires a curved wing, which changes the distance wind must travel. A longer distance on top and a shorter distance on the bottom, which create a low pressure differential on the top of the wing which translates to lift.

Wind will occasionally move flat objects, but it really requires the pressure differential to generate the force necessary to 'Rip' something off.

 

[KBWaldron]

Actually the Bernoulli effect doesn't require a curved wing. A flat surface will generate lift if the angle of attack is correct. That's why the cheap balsa wood gliders of my youth would fly despite having a flat wing.
As soon as their is a positive angle of attach the wind going over the top generates turbulence behind the leading edge which effectively acts as a curved surface, lengthening the distance.
At any rate I've changed my design and this is no longer an issue for me.
Thanks everyone for the feedback.

 

[jasonhc73]

My Mission solar panels are rated at 90 mph. The chances of 90 mph wind doing anything to them is also depending on what the angle the wind is to the panel.

Being installed on the roof of anything going down the road, the concern really is the drag they induce, and the reduced fuel economy. If the worry is about them getting blown off from the wind speed of driving, that is more of a mount point issue than anything else. You can get a tarp to cover everything when traveling and triple secure with straps, much like flatbed trucking.

Triple secure?

1. It's bolted to the roof already
2. It has the tarp keep the wind effects at bay,
3. The straps retaining the tarp are securing everything again to the hardpoints.

Keep the panels parallel to the roof, don't try to NASCAR or Formula 1 these for lifting or downforce!

 

[Deleted member 783]

If I were going to put panels on the roof of a vehicle, the first thing I would install is an air deflector over the cab. That solves the issue and will increase fuel economy.

 

[HRTKD]

While planning the install of my Mission Solar 320 watt panels on the roof of my RV, I discovered there are no roof supports (truss) near the built-in mounting points on front end of the panel. I have the typical Z brackets.

What is the common approach when a solid base isn't available? Do I drill new mounting holes in the panel? The new holes would be about 6" forward or rearward of the holes provided by the manufacturer. My preference would be to put the holes 6" forward. But if I do that, I'm thinking that another Z bracket halfway between the two might be necessary to support the middle of the panel.

I considered mounting the panels with unistrut. But the expense of doing that would be much more than the Z brackets.

 

[namesgolden]

I considered mounting the panels with unistrut.

I'm considering the same with my 37' motorhome, I already have a bunch of unistrut

buy 10 sticks at home depot's website, get a $20 off $200 coupon from ebay for $2, make up the rest of the cost with fasteners.

I currently have 65x39" 60cell panels, but may want to upgrade later. it makes more sense to have a reusable universal mounting method to me.

 

[HRTKD]

I decided I needed to control my costs, so I'm going to drill new mounting holes in the panels and use the Z brackets that I already have.

If I did a strut type mount, it would have to be aluminum. Steel strut is readily available locally, but it's just too heavy. There are lots of solar panel mounting brackets, but they all seem to work with that brand's flavor of strut. A set of brackets that worked with standard (aluminum) strut would have been ideal.

 

[namesgolden]

steel strut is readily available locally, but it's just too heavy.

I forget that's an issue for most people (I'm in a diesel pusher) -- I have seen someone on youtube put down aluminum angle 39" apart and rivet it to the panel frames.

 

[HRTKD]

I forget that's an issue for most people (I'm in a diesel pusher) -- I have seen someone on youtube put down aluminum angle 39" apart and rivet it to the panel frames.

I briefly considered that, but not a length of angle aluminum that covered the entire length of the panel. Doing that would seem to be counterproductive for allowing air movement under the panel from all directions.