Planned Mount on 6x6 treated posts - comments?

Hey all,

Planning an install at our family cabin, looking for recommendations, comments or suggestions on our plan to date. This is just a plan so far, none of the mounting supplies have been purchased.

Due to logistical reasons, a roof mount on our cabin isn't going to cut it and as such we needed to figure out an alternative. We have found the best patch of ground, south facing -- clear of shading for the peak hours of the day from 10am - 4pm. To protect the panels, primarily against theft we've decided to get them off the ground. Fully understand that a determined bad guy can and will get them, but figured that if a thief needs to pull out a ladder, it less likely they will swipe the panels as we present less of an easy opportunity.

We've looked at a few different options from a steel pole to utility poles and have landed on a pair of pressure treated 6x6 posts in 16' length as the best option. Our area gets very little freezing, some snow but loads of rain in the winter months (Southern Vancouver Island). The treated posts appear to be the lowest cost, and are likely the easiest option to work with given the remote nature of the cabin and available tools.

Plan is to place two posts approximately 3' apart. Base of the posts would be down a minimum of 4', sitting on a bed of packed gravel (for drainage), and then cemented within a sonotube. Sonotube would stick up about 6" above grade to ensure proper drainage and no earth around the base of the post. I will then install a cross brace between the two posts at the top, and a second approximately 3' down.

To mount the 3 panels (each 56" x 28" = 10sqft & 25.5lbs), I have built a rectangular braced frame out of treated 2x4's. I have screwed the aluminum standoffs directly to this frame using Stainless Steel hardware. I will also place a plastic shim between the aluminum standoff and the frame to prevent corrosion from the pressure treated chemical compounds. In order to angle the frame/panels, I had the idea of using Heavy Duty gate hinges that would affix to the top of the frame and screw into the top brace. I would then use a pair of support "legs" at the bottom of the frame to adjust the angle (which gives me the option to increase/decrease the panel angle seasonally if I choose). I plan to install a guy-wire opposite the load, and ether side of the posts for increased stability. If you can picture it, the frame and posts form a giant #4 if viewed from their side.

I was concerned about wind loading on the structure. The panels would not be exposed to significant wind in their location -- they are protected by the cabin, and surrounding forest, but I wanted to understand the risks. I was able to find that the strength of a 6x6 post ranges from 1000-1200 PSI (wet to dry). I've also calculated that a wind speed of 50mph would place a load of approximately 400lbs on the panels/frame (total area of 30sqft) so it appears that the structure should have plenty of strength.

Anyhow, I'm not an engineer. I think my plan is pretty solid, but would appreciate any feedback or concerns on something I might be missing here as I only want to do this one time :-)
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Comments

  • mike95490mike95490 Solar Expert Posts: 8,822 ✭✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    i'd use stainless, instead of a plastic corrosion protector. Stainless is good for 30 years, plastic may last 5 years, then crumble. (even protected from light)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Is it a nice spot to build a storage shed to keep the charge controller, batteries, inverter, and back-up generator?
  • Solar GuppySolar Guppy Solar Expert Posts: 1,963 ✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    PT lumber will warp like pretzels and twist anything attached to them. If I read your post correctly, your mounting the panels on 2x4's which could twist and shatter the panels glass
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    don't forget that wood deteriorates in time too and insects could speed that up as well. pvs have 20-25yr warranties on them so the mount should be of the same life expectancy.
  • PhotowhitPhotowhit Solar Expert Posts: 5,223 ✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Wow, I'm surprised people are so discouraging, the 25 year old panels I picked up had aluminum rails it connected directly to, but a PT wooded back mount/standing frame that was fine.

    My 4yr old PT free standing mount is fine for my 8 Evergreen panels, though I do have the panels mounted 2 each to 2 pieces of wood and hung from the top to avoid stressing the panels across, we get 50-60mph straight line winds here and this give the panels and the 2 pieces of wood they are directly mounted to a tiny bit of play to avoid torquing the panels across the glass.

    I can do a mock up in Photoshop if work stays slow.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    There are numerous different types of pressure treated wood. They range from interior grade to extreme marine use. If you pick the right type it is good for 25+ years. It is not known for warping or insect damage, guys; it wouldn't be much good if it were. It is designed to be used in wet conditions from damp basements up to marine applications. If you've experienced problems with PT then it's almost a certainty that the wrong grade of lumber was used.

    I've used it for ground contact foundation work and it has never failed. No rot, no insects, no warping. UC4A or above should have no trouble.

    I just figure if you need to build something to hold the panels and you need some place to put the equipment you might as well build the shed.
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Thanks for the feedback guys. We are fortunate here in BC that we have probably the best and widest choice of quality lumber around!

    Cariboocoot - all the electronics will be installed in the basement of the cabin. It's dry, secure, well ventilated, warmer and a much safer location to install the gear. Like your idea of building a shed, but we've already got 2 of them and really don't want a 3rd. When we're not there, we like to have all expensive gear hidden away. We've built a hidden room at the cabin and find it's the best place to store generators, engines, tools etc. Bad guys have entered the cabin before and have yet to discover this room.

    Back to my proposed design -- agree that I will have to watch the frame mounts and make sure I brace and secure it well. Anyone else see any other structural concerns or does it look sound?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Couple of possibly obvious caveats about using PT. First is to coat all the cuts and holes with end-cut preservative. The second is to not place aluminium directly against the wood. With a bit of moisture it will react with the copper-based preservative and end up eating away the aluminium mounts.

    Otherwise the 2x4 frame might be a bit weak. You can not expect any rigidity from the panels themselves. Given the width of nearly 8' and length of 5' two by sixes might be better. Hard to envision it in words and there's no easy way to draw here. Remember triangles are your friends and try to balance the weight load equally in both directions. Think "trestles".
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    now for the obvious question, just how far away are you mounting the pvs? longer distances = greater voltage drops and thus the need for either larger diameter wire or higher voltages. higher voltages are for mppt controllers with down-converting capability.
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Wire-run from the panels will be roughly 80ft to the controller. Plan is to use #2AWG direct bury cable. I've priced that out at about $300.

    Schematic something like this:

    3xpanels in parallel - switch - 80ft #2AWG - switch - 300A fuse - controller - 300A fuse - switch - battery - switch - 300A fuse - inverter - AC panel

    Monitors: TriStar TSM-2, Trimetric

    Other: Temp monitor, battery sense wires
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    I would use Unistrut instead of wood for a DIY panel mounting system.
    http://www.flickr.com/photos/nsaspook/4694617830/in/set-72157622934371746/
    http://www.unistrutohio.com/pdf/unistrut-catalog-16.pdf

    It lightweight and will last as long as the PV panels.
    http://www.unistrut.com/
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    ok. well do you wish for me to calculate your voltage drops or would you like to do it? see the link in my signature.

    to properly get all possible needed info you might need the vmp and imp of the pvs, what controller you will be using (saying if mppt too), and give the distance from cc to batteries as this voltage drop is important. almost forgot the intended battery system voltage desired.

    btw, instead of another shed then why not a picnic area with a roof?:cool:
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Thanks for the link.

    Panels are 3 x CTI 125W, 12V, 7A - with supplied short runs 6ft of 12AWG to combiner box, and then 80ft of 2AWG to controller.

    CC is a TriStar-45 PWM

    Cable run from TriStar to batteries is about 6ft of 2AWG.

    Batteries are 4 x Trojan T105s.

    From Batteries to Inverter (Go Power 2000W) is 6ft of 2/0AWG cable.

    If I'm calculating this correctly, it looks as though my loss is 2.92% from array to battery. Your spreadsheet shows a similar measurement to the owners manual for the CC (it also says to use #2AWG for 3% loss) and other web links I've found say the same.
  • mike95490mike95490 Solar Expert Posts: 8,822 ✭✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    PV & copper wires, prime target if you are away and have to resort to a hidden room.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?
    nsaspook wrote: »
    I would use Unistrut instead of wood for a DIY panel mounting system.
    http://www.flickr.com/photos/nsaspook/4694617830/in/set-72157622934371746/
    http://www.unistrutohio.com/pdf/unistrut-catalog-16.pdf

    It lightweight and will last as long as the PV panels.
    http://www.unistrut.com/

    Thanks NSASpook. I've seen your Unistrut recommendations in other posts. I've tried to find a local supplier so I can check the stuff out but have been unable to find one in Victoria BC. My concern is that it's relatively easy to put a ladder on a 6x6 to install or maintain panels, but I thought that a ladder on Unistrut would be unsafe (and we don't have scaffolding or a bucket truck available). How do you address getting up higher on it?
  • solar_davesolar_dave Solar Expert Posts: 2,366 ✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?
    TenMile wrote: »
    Thanks NSASpook. I've seen your Unistrut recommendations in other posts. I've tried to find a local supplier so I can check the stuff out but have been unable to find one in Victoria BC. My concern is that it's relatively easy to put a ladder on a 6x6 to install or maintain panels, but I thought that a ladder on Unistrut would be unsafe (and we don't have scaffolding or a bucket truck available). How do you address getting up higher on it?

    I think both Home Depot and Lowes carry unistrut in the elctrical departments.
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    I will take another look in my local HD. I found them on the US Home Depot website, but it doesn't appear that the Cdn Home Depot's carry the Unistrut products.

    Any of the Canadian dudes know where to see the stuff and purchase it?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?
    TenMile wrote: »
    I will take another look in my local HD. I found them on the US Home Depot website, but it doesn't appear that the Cdn Home Depot's carry the Unistrut products.

    Any of the Canadian dudes know where to see the stuff and purchase it?

    Maybe check out this page: http://www.unistrutbc.com/

    I'm on the phone and trying to post at the same time so I didn't look through it.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?
    TenMile wrote: »
    Thanks NSASpook. I've seen your Unistrut recommendations in other posts. I've tried to find a local supplier so I can check the stuff out but have been unable to find one in Victoria BC. My concern is that it's relatively easy to put a ladder on a 6x6 to install or maintain panels, but I thought that a ladder on Unistrut would be unsafe (and we don't have scaffolding or a bucket truck available). How do you address getting up higher on it?

    We have things that weigh tons on 1 5/8 41mm Unistrut frames. The whole thing wouldn't have to be strut just the actual panel frame mounts that can be made from half channel. A cheap source is a metal junk yard that takes construction leftovers.
    www.unistrut.us/DB/PDF1/Unistrut_App_Showcase.pdf
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Here is a rough sketch of a frame using UniStrut -- not done to scale. Thanks for the link to the UnistrutBC website -- looks like I can purchase from them directly.

    https://docs.google.com/drawings/edit?id=1nXmk78EhTo2Ui0q-MqMrZBDlBBydN8egC9MFTM8zHXE&hl=en&authkey=CPHxsvYL
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    That channel socket they have is slick. I'll have to mod a cheap deep one with a grinder to make something like it.

    http://www.unistrutbc.com/ChannelSocket.ubr
  • bobdogbobdog Solar Expert Posts: 191 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Can the panels (aluminum) be mounted directly to the Unistrut (metal???) without corrosion occurring? I need 2 pieces of that exact channel, but I've always thought that it had to be aluminum. I have an Iron ridge mount and they won't sell me just the channel. They want me to buy an entirely new mounting system when all I need is longer channel. Won't buy or recommend them again.
  • mike95490mike95490 Solar Expert Posts: 8,822 ✭✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Generally, unistrut is galvi steel. You need a dielectric washer, (SS) and use SS screws when mounting it, so only SS touches the aluminum frame.

    At least I think that is the way to do it.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • bobdogbobdog Solar Expert Posts: 191 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?
    mike90045 wrote: »
    Generally, unistrut is galvi steel. You need a dielectric washer, (SS) and use SS screws when mounting it, so only SS touches the aluminum frame.

    At least I think that is the way to do it.

    I'll make sure and pick up some SS washers and bolts/nuts. Thanks for the advice.
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    So all my Unistrut parts arrived the other day. I got it all assembled and the panels mounted. I came up with an improved design -- the mount looks like a roman numeral 2.

    Posts are also now in the ground. Rented a post-hole digger which was a waste of $$$. Ground was all glacial till and FULL of rock and gravel. Post hole digger didn't do anything but make a bunch of noise so I ended up digging the holes by hand.

    Unistrut makes heavy duty hinges for their hardware. I will take a length of the unistrut rail and bolt it across the top of my 6x6 posts. The top of my mount has the hinges installed and will then bolt to the cross-rail between the posts. The hinges allow me to adjust the angle of the 3 panels as required.

    I will post some photos when it's installed.
  • Ralph DayRalph Day Solar Expert Posts: 917 ✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    I know that slap forehead rental feeling. I rented a ditch-witch but the ground was really dry and hard, it just didn't work. Called someone with a backhoe instead. Messier, but it worked! $250 wasted in 45 minutes. Backhoe cost $85 for 1.5 hours. Should, woulda coulda.

    Ralph
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Finished Product

    Here it is -- all installed now.

    Found it was easier to assemble and wire the system on the ground and then hoist it up. One person to lift, and one person on each rope. At the top of the UniStrut frame, I used two large hinges that UniStrut make. Made it easy to attach the frame to the cross brace -- plus the hinges allow me to adjust the angle of the panels.

    IMG-20110507-00033.jpg

    Panels mounted on posts. Great day for first test -- was cool out -- about 57 degrees, and the panels output up to 23Amps (rated at 21Amps):

    IMG-20110508-00035.jpg

    Braces to adjust angle of the panels:

    IMG-20110508-00036.jpg
  • mike95490mike95490 Solar Expert Posts: 8,822 ✭✭✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?

    Nice, as long as the middle panel does not try to bend....
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Planned Mount on 6x6 treated posts - comments?
    mike90045 wrote: »
    Nice, as long as the middle panel does not try to bend....

    Looks like he's got a couple unistruts running vertical.
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: Planned Mount on 6x6 treated posts - comments?
    dwh wrote: »
    Looks like he's got a couple unistruts running vertical.

    That's correct -- frame behind the panels looks like the Roman Numeral II. The to braces that allow me to adjust the angle of the panels are also attached via UniStrut hinges as that provides some mounting flexibility.

    Here's a link to the drawing I did so that I could figure out the sizes of the UniStrut I needed.

    https://docs.google.com/drawings/d/1nXmk78EhTo2Ui0q-MqMrZBDlBBydN8egC9MFTM8zHXE/edit?hl=en&authkey=CPHxsvYL

    Panels don't flex or move.
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