mount panels on top of a 40 ft container

[geekwithoutacause]

I once had a new (recent) graduate M.E. (EIT) designing a set of lifting lugs to be welded to the wall of a pressure vessel. The vessel was a low pressure design and the wall thickness was 7 ga. (~ 0.187" thickness). The engineer did a good design on the lug, using the correct vessel dry weight and also did a thorough and acceptable design on the welds, all fit for purpose with correct weld procedures and PQR's (procedure qualification record) for the material and service requirements. Unfortunately, he neglected what the weight of the lift would do to the vessel wall. The lug would have separated from the vessel wall in any way the rigging could have been done. Fortunately, as happens in any well run engineering outfit of any size, everyone was always checking everyone else's work before it got to a fabricator.

To the OP: Know the design loads on the welds (probably wind loadings) as well as how and in what form those loads will be transferred to what the weldment is attached to.

Example : A seriously bodacious lifting lug attached by serious welding to the roof of a 5,000 lbm vehicle will lift and leave the car behind.

Attach the panels to something more substantial than an or under reinforced roof.

Excellent points, thank you. What you are basically saying is that it would have to be connected to the edges of container which is where the beef is ?

[J.P.M.]

Excellent points, thank you. What you are basically saying is that it would have to be connected to the edges of container which is where the beef is ?

You're welcome. I'm not saying use the edges or that welding is a good idea at all. What I am saying is that if you weld, use your head and make sure you think about what you are doing.

I'd also add, that if it was me, I probably wouldn't be welding anything to the roof of a shipping container. Nuts and bolts are easier on the roof than welding. Done correctly, it can also be pretty leak tight. It's also more easily modified if/when you get more informed and aware of what a good PV design entails.

[Mike90250]

I would not rely on panel frames as the mount. The proper rails and clamps are a much better way and retain the warranty.

[geekwithoutacause]

You're welcome. I'm not saying use the edges or that welding is a good idea at all. What I am saying is that if you weld, use your head and make sure you think about what you are doing.

I'd also add, that if it was me, I probably wouldn't be welding anything to the roof of a shipping container. Nuts and bolts are easier on the roof than welding. Done correctly, it can also be pretty leak tight. It's also more easily modified if/when you get more informed and aware of what a good PV design entails.

I took another look and I could use nuts and bolts thru the edges. The edges are thick square tubing steel. Will hold it. probably run a frame across the roof left to right and build from there.

[geekwithoutacause]

I would not rely on panel frames as the mount. The proper rails and clamps are a much better way and retain the warranty.

yeah, it didn't seem like a good plan. Getting some good rails.

[bcroe]

Show us what you develop. The winter vertical position should have the snow sliding straight
off the panel to the ground, if it hits the top of the container you will be clearing snow from there.
Bruce Roe

[geekwithoutacause]

Here's another idea I've had. What if I build a frame that goes down both sides of the container and underneath it (and on top of course). That won't go anywhere.

[J.P.M.]

Here's another idea I've had. What if I build a frame that goes down both sides of the container and underneath it (and on top of course). That won't go anywhere.

There are lots of options for securing what amounts to a sail on a structure that imparts occasional and variable loads to that structure. However, there's a lot more to wind design of a structure or assembly than the design of a simple anchorage.

I'd guess 15 ea. 350 W. panels will have an area of something like about 25 m^2 ( ~ 270 ft.^2). Strapping each end of any racking to a shipping container might not be sufficient when the wind induced deflection of things like support rails is considered. And that's before any consideration of wind induced vibration which can be a real problem. Lots more.

Consider this: In a 100 MPH wind event, such an array may well see, very roughly, ~~ 6,000 to 8,000 lbf or more of wind induced loading on an array, and that's before any increases from vibrational effects. Even split between 2 containers, depending on panels elevations and container anchorage, the wind force induced moments might even overturn one or both containers.

Point is, there's more to wind design than you may know about at this time.

Take a wider view of what happens when wind (and other external loadings) interacts with an array, it's supports including all the structural components and connections, and whatever structure the supports are attached to, and then the anchorage of that structure to the earth. Old timers sometimes call that process "taking the loads out" - basically checking and accounting for all the induced load combinations for each member and connection in an application or design.

[geekwithoutacause]

The empty container weighs 8400lbs. There is at least another 2000 lbs of material inside. I could even wieght it down with bricks if needed.
If I mount the panels at a fixed angle for my area (I think that's around 25 degrees), don't you think the sail affect would be much smaller. ?

[J.P.M.]

The empty container weighs 8400lbs. There is at least another 2000 lbs of material inside. I could even wieght it down with bricks if needed.
If I mount the panels at a fixed angle for my area (I think that's around 25 degrees), don't you think the sail affect would be much smaller. ?

What you write pretty much convinces me you're out of your depth and knowledge base with respect to what's required for a safe wind design.

Without a lot more information it's impossible to say.

My whole bottom line is that you are beyond your knowledge base for the information you need for a safe, fit for purpose design.

Get informed or get some knowledgeable advice from a professional of the type you'll probably have to pay for that's beyond the scope of a semi public forum such as this.

Or, take your chances.

The usual response when I make comments such as that is something like: "Nobody does that and things don't seem to be sailing around in the wind. You're full of crap."

Yea, probably. But I've got a lot of company in the cesspit - mostly other engineers.

Either way, Whether you agree or not, what you don't know can hurt you.

BTW: Any local building codes or permits you need to conform to or obtain ?

[geekwithoutacause]

What you write pretty much convinces me you're out of your depth and knowledge base with respect to what's required for a safe wind design.

Without a lot more information it's impossible to say.

My whole bottom line is that you are beyond your knowledge base for the information you need for a safe, fit for purpose design.

Get informed or get some knowledgeable advice from a professional of the type you'll probably have to pay for that's beyond the scope of a semi public forum such as this.

Or, take your chances.

The usual response when I make comments such as that is something like: "Nobody does that and things don't seem to be sailing around in the wind. You're full of crap."

Yea, probably. But I've got a lot of company in the cesspit - mostly other engineers.

Either way, Whether you agree or not, what you don't know can hurt you.

BTW: Any local building codes or permits you need to conform to or obtain ?

No, I am not saying you are full of crap. I hear what you are saying about this and I know that there are factors here beyond my knowledge. I knew there was more to it than simply hanging these panels on top, hence my research on here. I appreciate your insight and warnings.

[littleharbor]

Whatever you end up doing structurally, it cant hurt to build some sort of wind block to reduce the amount of uplift under your array.
PS wire management was dealt with after this photo was taken.

Solar array at the Rock House 1.JPG

[geekwithoutacause]

Whatever you end up doing structurally, it cant hurt to build some sort of wind block to reduce the amount of uplift under your array.
PS wire management was dealt with after this photo was taken.

Solar array at the Rock House 1.JPG

Good idea, thanks

[J.P.M.]

Whatever you end up doing structurally, it cant hurt to build some sort of wind block to reduce the amount of uplift under your array.
PS wire management was dealt with after this photo was taken.

Solar array at the Rock House 1.JPG

Doesn't necessarily help. May, and in my engineering judgement, probably will make things worse under any given wind vector scenario, but not in ways you'll detect structurally any time soon depending on how large any factors of safety for the structural components might calc. out. under any given wind vector.

A few points:

1.) Marginally effective against the northerly components of wind vectors but transfers some of that loading to the southmost roof contact points through the panel frames which then shows up as an additional/different variable/occasional compressive load on the roof.
2.) What about the ends ? I'd suggest most winds have vector components besides those normal to the back of the array.
3.) What about any additional flow induced vibration the added surfaces will excite ? Gust factor loading can also be enhanced by additional planar surfaces that act, in effect like baffles when close to other planar surfaces.
4.) What does the probable impairment of the under panel wind flow do with respect to panel temps. ?
5.) That plywood or CDX can add a tension load to the panel frames and the structure for wind vector components from the south.

In the end, that vertical surface at the back of the array results in just as much or more wind stagnation energy that still needs to be dissipated against the array and its attachments. More surface = more energy to dissipate. That's where the wind loading comes from. Besides probably adding more wind catching surface to an array assembly, adding more surfaces does little more than change the magnitude, direction and distribution of the wind (and other) forces impinging on an array/assembly. Only the magnitude, quite possibly the direction, and the distribution of the resulting forces has changed. Adding more planar surfaces only makes the analysis more complicated, but the forces on some components and attachments may actually increase or change from tensile to compressive.

And, for all the complexity added to the analysis, and all the added mat., labor and expense added to the project, the array will probably run hotter.

Another example of KISS not being applied.

On the good side, it looks like you can remove the wood rather easily.

Take what you want of the above. Scrap the rest.

[littleharbor]

Take what you want of the above. Scrap the rest.

Not being an engineer, a lot of the above is Greek to me. I'm sure some of what you mention has some validity but my practical mind tells me that the strong northerly winds and the uplift created on this 9' x 23' air scoop are considerably mitigated by adding this feature. I added it for a couple reasons, one being to lessen uplift but also so I, and others don't have to look at the underside of the array. I love the look of a nice big array of solar panels but not from that angle, which from the front of the garage is all you could see.

The fence, as I call it is dog eared cedar with close to 1" spacing now that the Baja air has dried it out. There is plenty of airflow though and around it and the array runs considerably cooler than an array mounted mere inches above a tile or asphalt roof.

jeep (2).jpg There are 3 additional modules added to this array before the dog eared fence was added. So as I was saying, aesthetically speaking, it needed to be done.