Multiple pole mounts

peteoldman
peteoldman Registered Users Posts: 5 ✭✭
in Solar Beginners Corner #1
has anyone used concrete pillars instead of steel pipe? We get a lot of wind and I am worried about pipes rusting off. Any experience with this would be appriaciated
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Multiple pole mounts

    You probably will need some engineering help with that... Concrete is very weak in tension/bending. You will either need to oversize the diameter or look at pre/post stressing the concrete (using steel rod or cable that you tighten to place the post in compression to make it stronger against bending forces).

    Solar panels can exert a lot of sideways force in high winds.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: Multiple pole mounts

    Trust the engineers. Steel pipes of various sizes and schedules are rated for the number of sq ft of panel they can support in high winds. If you are worried about rust, you can buy steel pipes that are galvanized.

    Whatever you do... don't fill a steel pipe with concrete! Concrete in steel is great for a lally column, but a pole for solar panels needs to flex. If you put concrete in it, it will snap off where it emerges from its foundation.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,023 ✭✭✭✭
    #4
    Re: Multiple pole mounts

    "
    Whatever you do... don't fill a steel pipe with concrete! Concrete in steel is great for a lally column, but a pole for solar panels needs to flex. If you put concrete in it, it will snap off where it emerges from its foundation.
    --vtMaps "

    Really? I heard that with flex you end up with a tube full of gravel eventually. The only steel tubes I've seen snap off were wind turbine poles without any guying and lots of flexing until...crash. Metal fatigue will cause failure. Maybe the concrete in tube limits where flexing can happen and concentrates that action to a limited area resulting in failure at the foundation emerging point.

    Ralph
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
    Re: Multiple pole mounts
    Ralph Day wrote: »
    "Really? I heard that with flex you end up with a tube full of gravel eventually. The only steel tubes I've seen snap off were wind turbine poles without any guying and lots of flexing until...crash. Metal fatigue will cause failure. Maybe the concrete in tube limits where flexing can happen and concentrates that action to a limited area resulting in failure at the foundation emerging point.

    If the pole snaps because of too much flexing, the system wasn't designed properly. Trust the engineers! The manufacturers of top of pole mounts publish specifications indicating what size and schedule of pole will hold a certain number of panels.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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