Question s regarding mounting panels on a curved roof?

[J.P.M.]

If I had the engineering skills I probably would not need to ask the question.....,.

So, lacking necessary knowledge, I sought assistance from the smartest group of people that I could find.

Personal tip: NEVER drive behind a car with a mattress on the roof.

True story: I was driving on an expressway in Buffalo in the early '80's on the way to work. I was maybe 6 - 8 or so car lengths behind a full size dump truck carrying a load of dirt/etc. when the box on the truck suddenly started to rise. We were traveling at speed and things were pretty crowded on the road. My lucky day as I was about 5 car lengths from an exit so I scooted off and only had a few dirt/stone chips. I was driving my winter car at the time so a few more scratches/dents didn't matter. Most of the load was dirt but some small stones/pea size gravel etc. got spewed on the road before the driver realized WTF was happening. Fortunately there were no overpasses coming up. The TV news said driver unfamiliarity with the truck operation was the cause. Expessway was closed for several hours while probably 15 -20 yards of dirt etc. were removed over maybe 1/4 mile of roadway.

[foo1bar]

Here we go...

I think you could do a similar rails-down-the-length with unistrut or a more traditional solar-rail.

But I don't know how you'd calculate that the rails are fastened sufficiently.
Nor how to check that the fastening of the modules to the rails is going to hold up at highway speeds (with a headwind, and when going under overpasses.)
Possibly you could design it with IronRidge or something and use a windspeed well over 65mph.

[J.P.M.]

I think you could do a similar rails-down-the-length with unistrut or a more traditional solar-rail.

But I don't know how you'd calculate that the rails are fastened sufficiently.
Nor how to check that the fastening of the modules to the rails is going to hold up at highway speeds (with a headwind, and when going under overpasses.)
Possibly you could design it with IronRidge or something and use a windspeed well over 65mph.

I don't know if the DMV or state requirements would be considerations but my first observation/opinion is that the roof attachment will be the most problematic to design. Attaching panels to the usual building roof racking is probably an OK (but still checked) attachment, but I'd think a vehicle roof that's gage thickness sheet metal might be a challenge to make work.

I'd agree on your wind speed considerations and add that the NHSB has some information. I'm not now or ever was qualified for such vehicle wind design, but I'd probably consider several scenarios/conditions:1.) Some high ground wind speed, consider it a headwind, add the most likely max. vehicle speed to that wind speed for one condition. 2.)That condition however, because it may present a lower array area profile to the wind, might not be the most severe case. I'd might also consider (for example) the wind condition of max. vehicle speed and max wind velocity with the wind coming from a direction that is normal to the diagonal of the array, and then take the vector sum of those two resultant forces. There may be and probably are other conditions that might be considered depending on the judgement and experience of the designer and, of course, any jurisdictional requirements. But, I'd consider some ground speed and not simply vehicle induced wind forces.

[littleharbor]

The first thing I'd consider would be adding a foil at the leading edge to deflect all wind over the panels

[J.P.M.]

The first thing I'd consider would be adding a foil at the leading edge to deflect all wind over the panels

Yea probably, but then there are considerations of the effects on array operating temps. that would have. Not a deal killer, just another design consideration.

[PNW_Steve]

Thanks for all of the replies!

I am quite confident of the all steel structure that I am attaching to.

My biggest concern is making sure that the panels are adequately supported.

The method shown in the picture looks slick and economical on materials but I lack confidence that it is adequate for the 300 watt panels.

Thanks

[Ampster]

Yea probably, but then there are considerations of the effects on array operating temps. that would have. Not a deal killer, just another design consideration.

At 60 MPH I am not sure it would make them much hotter because you could design the foil to allow some air but deflect the uplift forces. The biggest heat issue will be when you are stationary. If you park in the shade that wont be much of an issue.

[SunEagle]

At 60 MPH I am not sure it would make them much hotter because you could design the foil to allow some air but deflect the uplift forces. The biggest heat issue will be when you are stationary. If you park in the shade that wont be much of an issue.

The problem with RV type solar panels is that most people like to park in the shade to keep their coach cooler. But for some reason the lack of direct sunlight seems to reduce the pv production output.

[J.P.M.]

At 60 MPH I am not sure it would make them much hotter because you could design the foil to allow some air but deflect the uplift forces. The biggest heat issue will be when you are stationary. If you park in the shade that wont be much of an issue.

And just how would you go about that ?

[Ampster]

And just how would you go about that ?

If you are referring to the foil it depends on the foil.and where it is mounted in relationship to the front of the bus. Right now it is a concept suggested by littleharbor. As far as specifics, I will leave that up to the OP to decide what works for him.The foil could be placed a few inches ahead of the panels or he could drill some holes in it.
If you are referring to parking in the shade it would depend on the time of day.

[Mike90250]

The first thing I'd consider would be adding a foil at the leading edge to deflect all wind over the panels

And at speed, the suction underneath will pull the panels onto the roof . Lots of tricky stuff happens after 40 mph. Thats when wind starts getting some real energy in it

[J.P.M.]

And at speed, the suction underneath will pull the panels onto the roof . Lots of tricky stuff happens after 40 mph. Thats when wind starts getting some real energy in it

Depending on deflector design orientation and intended purpose, I believe you may have the direction of the vertical forces reversed. I would think that for the simple example of still air and a 60 MPH vehicle velocity, and a flat deflector at some angle at the front of the roof of the vehicle with the deflector's leading edge at the vehicle roof and the trailing edge height ~ the same height as the panels (or a straight vertical bluff for that matter) and reducing the relative air velocity under the panels, that the relative air velocity would be greater above the array than below the array. If that's the deflector orientation and result, Bernoulli's Principle would tend to result in lower pressure for greater fluid velocity over the panels and so an upward force from higher pressure below the panels would be exerted on the panels/array and so cause the array to have an upward (tensile) force on the array supports. That's an oversimplification for description of the principle.

As you write, tricky (and I'd add unexpected) stuff can and will happen in the real world. If the deflector orientation were to be changed from what I described so that the relative magnitude of the flow velocity beneath the array was greater than above, the induced force on the array would be downward. But I can't see a downward force from the simple initial conditions I've specified and the deflector orientation as I initially specified. For most real world conditions, I might also be concerned about flow induced vibration of the relatively flimsy panel surfaces and the fatigue damage that might result, but that's just one of any number of tricky things you mention that might be addressed if a rigorous analysis to be done.

[Ampster]

The problem with RV type solar panels is that most people like to park in the shade to keep their coach cooler. But for some reason the lack of direct sunlight seems to reduce the pv production output.

Haha, that is the irony of putting solar panels on an RV.

[SunEagle]

Haha, that is the irony of putting solar panels on an RV.

For me at least. Some people like to boon dock where there aren't any trees. So using solar panels will help extend their batteries.

My wife (and I) prefer a grid tie power connection and parking in the shade with our RV. To each their own.

[PNW_Steve]

For me at least. Some people like to boon dock where there aren't any trees. So using solar panels will help extend their batteries.

My wife (and I) prefer a grid tie power connection and parking in the shade with our RV. To each their own.

Yeah... Not much shading problem in Yuma

We like to spend time in AZ and Sonora in the Winter.