Another Roof or Ground mount / which one would you do question...

TxflyboyTxflyboy Registered Users Posts: 15
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I have the land to put my panels either on the roof or ground. 5KW / 24 panels / 215w 3X5 evergreen panel


If you will, please list your pro's and con's to each type of installation, and which one you would want if you had the choice. :confused:




My particular situation is the home will have a new galvalume roof. I'm not liking the thought of drilling holes in it.
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Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Another Roof or Ground mount / which one would you do question...

    Talk with your roofing contractor... Mine made a pretty good living repairing roofs after solar panel installs. So much so, they were looking into getting into the GT Solar business.

    Security of panels is a good reason for mounting them on the roof (using security hardware and even running an alarm loop through the frames can help). Also, you keep the panels up high (no fencing required to keep electrical wiring protected from kids, less problem from rocks thrown by lawn mowers, etc.).

    Mounting on ground is certainly easier to maintain (clean, check wiring). Out here--the commercial installs are making "carport" type installs (keep sun off cars).

    Where the panels will be installed based on battery/Main Service panel can be important. Some people have trees/buildings/etc. that force remote panel installations--Sending power over longer distances costs $$$ for copper, can affect reliability for Grid Tied power sensing (too much "voltage rise" can cause GT inverters to turn off for 5 minutes--Typically high line like 255 VAC + long wire runs from inverter to pole/pad transformer).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    i'm not sure if you get snow in your location, but a roof can be more difficult to clear off the pvs of snow and keep them clean in general in warmer months. usually this isn't a problem for minor snows as it soon melts in the sun.

    as bb said, safety and theft prevention is probably 2 of the major reasons for being on a roof, but sometimes the added height keeps the pvs illuminated longer without shadows too. areas on the ground would need a larger area to be clear of being able to have shadows cast to the pvs.
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    I think Bill got most of the considerations. Here's a few more: In favor of ground mount is that you can make seasonal adjustments in the angle. In snow country, its easier and safer to clean the snow off a ground mount.

    Among the ground mounts I prefer top of pole mounts because of the great flexibility in changing orientation. My only regret for my particular brand of top of pole mount is that I cannot get the panels all the way vertical, which is nice to do when there is snow on the ground... the sun's reflection off the snow makes up for the fact that the panels are aimed too low for optimal direct sun.

    Some folks would recommend top of pole mounts so that you could add a tracker if you wish. I think the economics are changing... its cheaper (or soon will be cheaper) to just add more panels.

    One more thing in favor of top of pole mounts... their orientation can easily be changed to bias them to the east or west. If I ever decide to enlarge my 940 watt array, I might put in a second pole and aim one southeast and the other southwest. The larger array would probably go to the southeast for bulk charge and the smaller array to the southwest for absorb charge. Also, if you find that during part of the year you have morning fog, or afternoon rains, or whatever, you can easily aim your array to the east or west.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • VicVic Solar Expert Posts: 3,113 ✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Hi tfb,

    The only thing that I might add, is, that roof mounts add a bit of lightning exposure to the structure. If this is a residence, this might not be good for you, if you are in lightning country.

    Blowing debris is a bit of a negative for ground mounts.

    The most recent project here, used roof mount on a dewlling due to shading issues, and security concerns of ground mounts. Would have loved to do (expensive) trackers, but this is a very windy location on a ridge top with trees, so roof mounting seemed best.

    Good Luck, .. great Avatar!. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Another Roof or Ground mount / which one would you do question...

    One other consideration (for some) is roof/high mounting allows the snow room to fall on the ground (with array set near vertical in winter).

    Of course, having an array on the roof in snow country brings its own problems--shedding snow on people, ice dams, snow behind array, etc... (I don't live in snow country--so it's all academic for me).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    I had a small roof-mounted array and now have a larger ground-mounted array and I much prefer the ground mounting. Besides the roofing/lightning issues mentioned above, I would emphasize what BB said about maintenance; I used to climb on my roof 2+ times a month to clean pollen, pine needles, bird droppings, etc from my panels, and my walking around up there was also added wear on my (shingle) roof. Now I just need a minute with a soft broom and a wet paper towel.

    You may find ground-mounting cheaper too. Assuming you can get them approved/permitted (if you need it), you can build DIY ground-mounts much more easily; I got the price down to under $0.30/watt with the same size Evergreens as you have building my own ground mounts. There's no way could I have done that on my roof. Even if you go with pre-made mounting systems, ground-mounting is usually less.
  • TxflyboyTxflyboy Registered Users Posts: 15
    Re: Another Roof or Ground mount / which one would you do question...

    Tough decision.

    Snow is not a factor where I live. And the sun angle and codes are not a factor. This is in the sticks out on the farm. I can do pretty much anything I want.

    I like the pole mount idea but I have many panels. Weedeating and maintenance around a pole seem's easier to my thinking. And maybe a little more theft proof.

    The roof would be the most secure out of the way location, but I don't like the thought of drilling holes in my brand new metal roof. Thanks all for your replies.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Another Roof or Ground mount / which one would you do question...

    Pole mounting does have its own issues too... Deep hole with lots of concrete to make a stable structure. We have a few discussions here about them:

    Tips and tricks for pole mounts?


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    i can understand your concerns with the roof so maybe you can go with an elevated ground mount. it would be a bit more work than a standard ground mount, but would add some height and help keep it out of accidental encounters. the extra height may not stop a thief, but it would add another obstacle. i would go at least 6 to 7ft higher and would keep you from smacking your head off of it while staying within a reasonable height for a large step ladder.
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    Tough decision.
    If you are like me you will want a carport or shop or shed or whatever space for storage, in my case all of the above. The advantage of building a shed roof to mount the panels on is that you can get a twofer for not a lot more money.
  • TxflyboyTxflyboy Registered Users Posts: 15
    Re: Another Roof or Ground mount / which one would you do question...

    The roof would be so much simpler to install really.

    Less cable, less U/G ditching, less everything.

    And so much more out of the way. It's hard to decide. I hate punching holes in a new metal roof. Is there any bulletproof way to do this so it will never leak or cause problems?

    I should ask if there are superior fasteners for an array on a metal roof on wood deck?
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Homemade pole mounts and homemade trackers. House roof has million dollar shade trees I'd never cut.

    ry%3D400


    ry%3D400


    ry%3D400

    ry%3D400

    ry%3D400
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Another Roof or Ground mount / which one would you do question...

    Some rear views that TnAndy has posted before here:
    TnAndy wrote: »
    I went pole mount, simply because I wasn't willing to cut the trees that shade my roof, and are worth a LOT in terms of summer cooling.

    I stripped the trees off a hillside out from the house, and put my arrays there. Plus, putting them on poles allowed me to build tracking mounts.

    ry%3D480

    ry%3D480

    ry%3D480


    -Bill "we all want to see behind the curtain" B. :D
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Yeah, the two original ones, I made single axis.

    Got a little more creative with this last one, and made it dual axis. The North/South tilt is manually controlled via a linear actuator. I figure to adjust it about 4 times/year.
  • TxflyboyTxflyboy Registered Users Posts: 15
    Re: Another Roof or Ground mount / which one would you do question...

    Wow. That's quite an installation.

    Do tracker's increase efficiency enough to spend the $?

    And those footer's look huge. Mucho concrete. I have an 18" auger we could drill up to six feet deep. Would that not work full of concrete?
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    Txflyboy wrote: »
    Wow. That's quite an installation.

    Do tracker's increase efficiency enough to spend the $?

    And those footer's look huge. Mucho concrete. I have an 18" auger we could drill up to six feet deep. Would that not work full of concrete?

    My guess is not, especially if you have any wind.....but there's one sure way to find out ! :roll:

    I'm a "seat of the pants" engineer, and tend to over build things because I really hate doing it twice.

    The first two, I used a 6" sch40 pipe, and a 4'x4'x4' concrete footer. 10 x 175w panels on each.
    The third array, 10 x 245w, I used an 8" sch40 pipe, and went 5x5x5 on the footer.

    Are the trackers worth it ? Well, depends. I pick up a bit over 20% more kw/hrs with them, and when I put up the first 175w panels, they were $800/ea. The last 245w ( fall 2010 ) were down to $600, and now you can buy them for about $450. If you had to buy the trackers, I'd say no. But since I was building my racks and all, it wasn't much more trouble to add the tracking feature, as I have a pretty good shop and ability to do so.
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    And so much more out of the way. It's hard to decide. I hate punching holes in a new metal roof. Is there any bulletproof way to do this so it will never leak or cause problems?
    if your metal roof is of the standing seam variety, they make fasteners that clamp to the standing seams. I haven't used them and don't know how well they work. I guess I would a litle leary knowing the metal seam is taking all the wind load.
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    Txflyboy wrote: »
    And those footer's look huge. Mucho concrete. I have an 18" auger we could drill up to six feet deep. Would that not work full of concrete?
    Depends on soil type. Around here 24 inch diameter is the standard. check out:
    homepower.com/view/?file=HP108_pg28_Schwartz
    homepower.com/view/?file=HP109_pg82_Schwartz

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    mikeo wrote: »
    if your metal roof is of the standing seam variety, they make fasteners that clamp to the standing seams. I haven't used them and don't know how well they work. I guess I would a litle leary knowing the metal seam is taking all the wind load.

    I used them on this install.....and it gets a LOT of wind, being right on the crest of a ridge. They hold fine.

    S-5! clips ( and the mounting section above the clip shown )

    newPVKit-1.jpg

    ry%3D400
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    I used them on this install.....and it gets a LOT of wind, being right on the crest of a ridge. They hold fine.
    Were there any additional screws used under the standing seam where the panel brackets attach for extra strength? I suppose the stiffness of the standing seam may be enough if the metal roofing has a screw into the decking every 2 ft or so.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Mike,

    No, not that I know of. I didn't put the roof on, so I don't know the screw spacing.
  • TxflyboyTxflyboy Registered Users Posts: 15
    Re: Another Roof or Ground mount / which one would you do question...

    Thank you Thank you Thank you.

    We will be doing a standing seam galvalume roof.

    These fastener's are just the ticket. Love it. Now no holes in my new roof.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    Txflyboy wrote: »
    We will be doing a standing seam galvalume roof.

    Standing seam is the only metal roof I'd consider, solar or not.

    The standard "Century Rib" version you often see on barns/shed, and that a lot of folks around here use as well (because it's cheaper), uses exposed metal screws with rubber washers to fasten. It would seem to me the life of the roof is the life of that rubber washer, and when it finally cracks and dries out, the leaks would begin. Not a huge issue in a barn maybe, but in a house, a different story.

    Another thing to watch is the decking under the metal. I've seen a LOT of metal screws in the above type roof backing out from the expansion of the metal and the fact they only used a fairly thin ( like 7/16" ) OSB roof decking. I'd go a minimum of 3/4".
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    Another thing to watch is the decking under the metal. I've seen a LOT of metal screws in the above type roof backing out from the expansion of the metal and the fact they only used a fairly thin ( like 7/16" ) OSB roof decking. I'd go a minimum of 3/4".
    With either type of metal roof, it is important to use an underlay to stop moisture from sweating. I used two layers of 40# felt paper under my metal roof. This also made the roof very quite during a rain or hail storm from inside the house. I think there are special products for this now.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Yeah, we used Ice/Water shield underlayment on the buddy's roof in the pic.

    Normally only used on the first 3' or so of the roof as a preventative to ice dam problems, since the roof was fairly small, we did the whole roof in it. ( I framed the cabin to the point of "under roof". ) Thick, self repairing for roofing nail/screw punctures, self adhesive on the roof, needs only a few roofing nails to hold it in place as a temporary roof....really good stuff, but sort of expensive for a large roof.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    My local AHJ wants to see a screw every 8" beneath areas that have solar standing seam clamps when using 4 clamps per module. Either that or use lots of clamps (1 on every seam or about 8 per module) in order to spread out the load. If I'm not mistaken, the S5! clamp instructions suggests one on every seam that the module crosses. This gets a little pricey.
  • solarvicsolarvic Solar Expert Posts: 1,060 ✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...
    Txflyboy wrote: »
    Wow. That's quite an installation.

    Do tracker's increase efficiency enough to spend the $?

    And those footer's look huge. Mucho concrete. I have an 18" auger we could drill up to six feet deep. Would that not work full of concrete?
    It depends on the soil you have. I think 18 inch auger 6 foot deep holes would be plenty good. I have 2 large 8 panel racks that went thru a hurricane and they didn,t move. Mine are only 50 inch deep and about 18 " round. Have clay soil here in Pa. and once it gets hard holds like cement. :Dsolarvic:D
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Yeah...it depends on local conditions, for sure....and the amount of "sail" area you have. I just personally didn't want to find out the hard way, because working on that hillside is enough of a challenge already without wondering about the footer. An extra hundred bucks or so in concrete is cheap insurance, IMHO.

    Built a temporary deck under the last array to keep from falling off down the hill.

    ry%3D400


    ry%3D400
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Here's a "behind the curtain" look at my latest array. It's dual axis, powered in both, but only automatic in the east/west axis. Since this one tilts both ways, I decided to add a pair of "MonroeMatic" shocks in the North/South axis to add some stability and more points of support. The limit of tilt on this axis is the extension of the shocks. The 36" actuator (Venture Products, Ohio) is the E/W driver.....a 24" model in the back is the N/S.

    ry%3D400

    That's an S-5 clip installed on Unistrut, which is my racking, rather than a standing seam, but you get the idea.

    ry%3D400

    Box for tracker electronics, disconnect for 24v power supply, Midnite 6 circuit combiner box with Delta lightning arrestor.

    ry%3D400

    Same thing, but you can see the toggle switch on the side of the tracker box....simple on-off-on switch wired to jog the actuator up/down as the season requires.

    ry%3D400


    Side view showing N/S actuator. I put a Sharpie mark on the shock for Winter (full retract), Spring/Fall (mid point), Summer (full extension)......real scientific,huh ?.....ahahahaha

    ry%3D400
  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: Another Roof or Ground mount / which one would you do question...

    Another "Pro" for roof mounting:

    If you are in a hot climate, having an extra layer between the sun and your roof can help keep your cooling costs down. Many wineries have put solar on the roofs of their cellars or storage facilities to offset their cooling costs and found that their power needs decreased due to less thermal gain after the installation.

    I've also noticed a stark difference in the tempurature of attics and uninsulated garages too.
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