Racking issue, need some opinions.

cdherman
cdherman Solar Expert Posts: 32 ✭✭
in General Solar Power Topics #1
My system (I pretty much chose the parts, but hired a local company to install so they had to deal with the utility co inspectors) has Ironrdige rails and Kyocera 210 panels.

The installers have been great to work with, fine folks, but clearly also a bit in the learning phases.

On the day they were going to start putting up the racks, I warned them that the installation sheet that came with the panels did not specify the allowable range where the racks could be. I had planned to talk to Kyocera directly about it, but after I hired them, I figured it was their job. It was a package job -- I was not obligated to provide any technical assistance.

Anyhow, you can probably guess what happened. They placed the racks pretty far apart and then had a little "wander as they installed the panels. At the end, the panels were clamped right on the corners.

When they and I finally found the recomendations from Kyocera (a separate document, which is stupid from Kyocera's end) it turns out the clamps are quite a bit too close to the corners of the panels (portrait view).

But strangely, the panels are allowed to be racked from the ends, and if racked in that manner, the clamps can be all the way to the corners.

Anyhow, here's my question for anyone with some experience:

1) How likely will Kyocera refuse to honor their warranty down the road, based solely on the racking error? I am not asking for you to garantee it, just your opinion.

2) My roof is at 26 degrees, and sheds snow well, so I am less worried about snow load. But it can be windy in Kansas City. Maybe I am just overly worried. I could make the guys take the panels down and re-position the rails. Lot of work for them.... Am I being overly compulsive?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Racking issue, need some opinions.

    Most (many?) permits require a PE (licensed professional engineer) to sign of on structure building permits... If a PE was involved--they should answer the question.

    From a strength point of view, the panels are strongest when mounted in portrait and the rails are 1/4 the panel height in from top and bottom (or the whole panel+rack rotated 90 degrees).

    My fear is that if you have them move the rails (probably the right thing to do)--is you will now have a bunch more holes in your roof. :cry:

    If the installer purchased the panels and rails--make them do it right (per the design documents and/or PE direction). If you purchased the panels--It will be up to use to get warranty service--and it may be difficult if the panels snapped in a windstorm if they check the installation (Kyocera has been pretty good about warranty returns when the had a bad batch of panels many years ago).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • cdherman
    cdherman Solar Expert Posts: 32 ✭✭
    #3
    Re: Racking issue, need some opinions.

    Thanks for the reply.

    As for a "professional engineer" the only thing that the building inspector required a building engineer for was the snow and wind load calcs. The installer is an electrical engineer (the head of the company at least).

    As for extra holes in the roof -- well they put down stainless threaded lags ino the structure. If they just leave those existing bolts in the wrong locations, the holes will remain sealed. Its a metal roof, and the lags pierce on the ridges. The "wrong place lags" will be under the panels and not even visible.

    This all happened because I could not find a decent electrical engineer that would work with me to help with plans and permitting. All the companies with any interest in solar wanted to do the whole job. Had I done the mechanical and structural stuff myself, I would have not made this mistake.

    Oh-- 1/4 way down from the ends is not the "perfect" location either. Its more like 20, 60, 20 at least on the panels that I have looked at.
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #4
    Re: Racking issue, need some opinions.
    cdherman wrote: »
    Oh-- 1/4 way down from the ends is not the "perfect" location either. Its more like 20, 60, 20 at least on the panels that I have looked at.
    Was going to mention that - you've done your homework.

    Sounds like you already know what you want done - have them move the rails as necessary - otherwise they are not guaranteed to meet the loading requirements unless you can have an engineer run the calcs.
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  • pbartko
    pbartko Solar Expert Posts: 37 ✭✭
    #5
    Re: Racking issue, need some opinions.

    I recently installed panels on our roof here in Maryland. I had to make a decision on where to mount the rails just as you do. The Evergreen panels I installed are rated for 40 lb/sqft load at the corners, which meets local building codes. However, after going through the brutal winter we just had (over 5 feet of snow from back to back storms) I decided to go for the maximum load of 60 lb/sqft (20-60-20% spacing). We saw many roof collapses due to the storms even though they met building codes. I even talked to a local solar installer who was working with several clients to file warranty claims with panel manufacturers, over broken panels.

    It may be another 100 years before we get another winter like the last one but I'd rather not take the chance with such a large investment.

    Pete B
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  • cdherman
    cdherman Solar Expert Posts: 32 ✭✭
    #6
    Re: Racking issue, need some opinions.
    pbartko wrote: »
    I recently installed panels on our roof here in Maryland. I had to make a decision on where to mount the rails just as you do. The Evergreen panels I installed are rated for 40 lb/sqft load at the corners, which meets local building codes. However, after going through the brutal winter we just had (over 5 feet of snow from back to back storms) I decided to go for the maximum load of 60 lb/sqft (20-60-20% spacing). We saw many roof collapses due to the storms even though they met building codes. I even talked to a local solar installer who was working with several clients to file warranty claims with panel manufacturers, over broken panels.

    It may be another 100 years before we get another winter like the last one but I'd rather not take the chance with such a large investment.

    Pete B

    So, I threw out the 20 60 20 as a personal guess. I wound NOT want anyone useing that as science. But Pete used that # as well. Pete, drees -- where did you get those numbers?? Is there some science to that? I came up with it based on a lot of years putting up shelving (same principle), as well as looking at spec sheets for various panels.

    But it stands to reason that a given panel's maximum load carrying capacity would be obtained at a certain location. There might even be some physics principle that governs those locatation in a general sense. Hmmmm...

    Anyone?????
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #7
    Re: Racking issue, need some opinions.
    cdherman wrote: »
    But it stands to reason that a given panel's maximum load carrying capacity would be obtained at a certain location. There might even be some physics principle that governs those locatation in a general sense.
    Yes, physics applies here.

    The reason why a panel (or shelf) has a higher load rating closer to 20-60-20 has a higher load rating than 25-50-25 is because the panel provides additional strength in the middle span because you end up spreading the load over both rails.

    The optimum spacing will ultimately depending on how stiff the panel is - how much it resists flexing.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: Racking issue, need some opinions.

    If you go 25% in from each end, you have a balanced overhang of sq.foot of panels and the panel is all equally far (maximum span) from the mounts.

    If you included the side frame and resistance to bending moment at the center of the panel, then you should be able to move out to the 20% (or whatever is the exact distance) to obtain maximum resistance to bending moments/static loads. (imagine the strength difference if the middle of the solar panel span had a hinge instead of a solid web from end to end).

    Here is Unirac's Code compliant installation manual (PDF download 26 pages).

    -Bill

    PS: Remember that materials, to resist bending, must actually bend. If you have ever stood on a highway bridge when heavy trucks go by--you can feel the bridge flex as the vehicles go by.

    In the case of solar panels, both the aluminum rails and the tempered glass have to flex to "resist" a load. Obviously, the ability of tempered glass to flex (bend) is a lot less than that of aluminum--so their are limits to how much load the aluminum can actually assume before it flexes so much, that the tempered glass panel itself fails.

    Also, there may be an issue with how much the glass bends too... Bending develops shear forces in the material itself (tearing or imagine placing your hands together and trying to slide them apart--that is shear force on the face of your hands). In the case of a solar panel, there are shear forces between the face of the solar cell and the glass itself--you will want to keep bending (actual movement) to a minimum to prevent failure of the very thin and brittle solar cells themselves.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • pbartko
    pbartko Solar Expert Posts: 37 ✭✭
    #9
    Re: Racking issue, need some opinions.

    drees & BB are correct. It is the boundary conditions at the ends vs. the middle which give the 20-60-20 solution the highest load rating. This also is stated as the maximum load carrying mounting points in Evergreen's installation instructions.

    Pete B
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