Engineered stamped pergola system for 10-12Kw DC grid tie Charlotte, NC. 5 years since last post! :)

rollandelliott
rollandelliott Solar Expert Posts: 834 ✭✭
in Grid Tie and Grid Interactive Systems #1
I used to visit this site almost daily, my first post since being away for about 5 years. 
The stars have aligned for getting a 10-12KW grid tie system installed in my NC home. Duke Energy is offering up to $6000 rebate for residential installs. Federal Tax Credit can be applied, and my HOA actually approved a pergola for my backyard (probably because no one can see it anyways).

I can't put the solar panels on my homes roof facing about 220 degrees from 0 degree north, so I have to build a pergola about 11' tall in my back yard, if the panels were on ground they would get too much shade.  I looked at PV watts and flat roof solar racking solutions from unirac R-5. with a 5 degree tilt to each panel and minimum panel spacing. Pergola will be huge about 20x36 feet for the roof. Assuming a couple of feet of overhang the posts will probably be 16' apart.   I need to pull a building permit and can make the pergola out of PTwood, steel or aluminum. Leaning towards steel because its cheaper. PT wood longer than 16' is pretty expensive anyways. 

I'm guessing the city permit will want stamped engineering drawings for such a big pergola. Anyone know of a company that has drawings for a project already so I do not have to reinvent the wheel?

Thanks!
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #2
    a lot of things have changed in 5 years. Schlettler racking looks like it's out of business? Jetion Solar panels in Charlotte, NC, which I used for my last project is also out of business and OMG solar panels are so cheap. lol.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,974 ✭✭✭✭✭✭
    #3
    I think you are far better off not using the roof. I will ask my solar consult group and get back in a day or two. One question first, your power panel can handle 12KW? If not you can have the utility modify the drop?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #4
    I have an external 200amp breaker box that was installed about 10 years ago. Home originally only had a  125amp breaker box, which is now a subpanel. I remember asking about this about 7 years ago, need to go and read my old posts. If I need to upgrade to a 400a panel it would be fairly easy. I do remember the last solar install was not an issue for a 10kw dc array.
    http://www.cncsolar.com/solar-pergola-solutions.html
    I called above company but they told me engineer is too busy to make plans, but they could possibly sell me old plans that I can get stamped by a local engineer. 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,684 admin
    #5
    Have you checked with your utility directly about the size of your GT solar system? They may want their engineer(s) to check the local distribution and see if all is OK (too much solar on a local distribution is not good for them either).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #6
    I will be submitting a request for an interconnect agreement which requires a solar panel wiring schematic. I assume duke power will let me know if it is an issue at that time. I would be fine with a smaller 9kw system if needed. Just trying to maximize the rebate of up to10kw AC, which means about a 12kw DC system after losses.  NC law allows HOA's to restrict solar panels to areas where they are not seen along public areas. Basically you can't install them on the front area of your home or roof if the hoa says so 
    this has resulted in few solar installs because back yards are not good locations on tiny 1/4 acre lots and most homes tend to face southward.
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    edited June 2019 #7
    https://www.structureworksfab.com/contact/
    found this online company that does custom pergola drawings. Always nice to find a company that specializes in exactly what you want done. I'll see what they quote. (edited to add they will only do drawings if you buy the pergola kit from them which is too expensive)
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #8
    https://pergoladepot.com/product/big-kahuna-solar-pergola-kits/
    another company that does custom pergolas for solar, but the kit price of $6000 for a 20x20 seems high, good thing it qualifies for 30% fed tax credit. 
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #9
    Called several GC yesterday and emailed a few Structural engineering firms. One Engineer quoted $1000 and another $2500. Does this seem reasonable? I might put a bid on upwork.com, but I think the engineer has to be licensed in North Carolina right? Or does it not matter where the engineer is located for a permit. Probably should call the charlotte permit office. 
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #10
    I'd check, but local AHJ likely wants local NC stamp.  For structural stuff, it makes some sense as soil conditions etc are pretty local.

    $1000 sound about right to me.  The $2500 guy may not really want to do smaller jobs (especially if dealing directly with owner), so quotes them high?  OTOH, if there's more to it than I think (eg. complicated wind analysis), maybe not.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #11
    posted the job on upwork.com and got quotes from $300 to over $1000. Problem is none of them have a North Carolina License and I can't find a local engineer who would rubber stamp the plans for a reasonable amount. 
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #12
    In fairness, the local guy still needs to check the numbers etc.  The stamp says he has, and there would be significant reputational risk if they didn't and the plans had issues.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #13
    Checking the numbers is easy. Less than 1 hrs work and only company to reply back wants $750 to do so. High demand, and very low supply means high price.

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #14
    1 hrs work is not equal to 1 hrs work plus liability for work product. 

    Frankly, people who work for fixed wages with no liability for loss often have little understanding of the risks taken by those who work on a gig basis, and/or who end up working for negative wages at times. 

    If checking numbers is so easy, why aren't you setting up a business to do so as we speak?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #15
    Because as a former engineer I found sitting down at a desk all day pretty boring and unsatisfying.  I work for myself now and know about doing projects and loosing money.   It's high school level math. $750 to rubber stamp an already proven design is a rip off IMHO.
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