Horizontal vs vertical panel installation

I am looking at adding another PV system on the house roof and when I layout the panels I am thinking of using, its looks like I have to mount them horizontally versus vertical due the size fo the space on the roof. To date I have only done vertical installations. I dont see any specific warnigns or recommedations against horizontal mounting but was curious if I am missing something? I would prefer vertical as it is two less seams on the slope to slow down snow sliding off but given the arrays relatively shallow angle for my latitude, I expect my winter production is going to be pretty poor due to snow buildup.

Comments

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Horizontal vs vertical panel installation

    If you have snow, it's best to lay them horizontally. Why? Because most panels are made up of two or more strings of cells that run lengthwise the panel. If the panel is mounted vertically, snow will slide down, covering the bottom part of each panel, blocking some cells from all strings in that panel, thus practically killing all output. If however they're mounted horizontally, when the snow slides down each panel, it will totally uncover the top string/s of that panel, allowing the panel to provide half power until the rest of the snow melts off, whenever that may be. Because of experience with snow cover years ago, that's how I mounted mine, and I'm NOT sorry for those very reasons!
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Horizontal vs vertical panel installation

    The reason vertical is so common is that mounting rails are easier to mount crossways to the roof framing and less rails are used when the PV modules are crossways to the rails - thus mounted in "portrait" orientation. Doesn't have to be though. Can mount the rails running up the roof, 48" on center to match the usual framing and then put the modules in landscape. However, modules being about 65" long, it will be hard to make a continuous row of them. Putting the rails horizontal and the modules in landscape will require about twice as much railing and mountings. Landscape mounting is best however in snowy conditions as the bypass diodes will be more effective as Wayne explained.
  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    Re: Horizontal vs vertical panel installation

    I have my panels mounted horizontally onto a frame where I can adjust the tilt angle seasonally. I have them set at 15 degrees off vertical in winter, and at lesser angles when the sun is higher. I find usually most of the snow will slide off, leaving just a bit that catches on the bottom lip. I give them a quick sweep after a snow fall, with a modified broom (regular broom that is inserted into a really long handle). Perhaps you could also use a roof rake (not a metal one I would think?), to pull snow off.
  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Horizontal vs vertical panel installation

    Good point on having the mounting line up with the roof rafters, I have access to under the deck so worse case is I install a bridge between the joists to pick up the mounts.

    The panels would be on a second floor roof with and 8/14 pitch. No good way to get a rake up there unless I use an extension ladder (I need to do that to rake the roof). I have a pole mount array set at 30 degrees in winter and even that will build up snow if the conditions are right. Most of the time as soon as sun come up the snow will slide off the pole mount.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Horizontal vs vertical panel installation

    I remember seeing a post here where the OP laid out his array racking from inside the attic and then using a jig, drilled through the joist to the outside to get alignment to be perfect on center.
  • Cheric_Energy1Cheric_Energy1 Registered Users Posts: 1
    In Africa we rarely see snow built up on a roof, but shorting the array with a low value resistance for an hour or so should warm the panels sufficiently to defrost the contact surface of the snow creating a fluid sheet between the two, as I've noticed they warm up when producing power? just a thought.....
  • animattanimatt Solar Expert Posts: 295 ✭✭✭
    Until that last post i had entirely forgot. At one point midnite solar was messing around with a snow melt mode for their classic controllers.  Not sure if that went anywhere.
  • JohannJohann Solar Expert Posts: 245 ✭✭✭
    edited September 2016 #9
    In Africa we rarely see snow built up on a roof, but shorting the array with a low value resistance for an hour or so should warm the panels sufficiently to defrost the contact surface of the snow creating a fluid sheet between the two, as I've noticed they warm up when producing power? just a thought.....
    But you have to make power in the first place before you can melt that snow, and with snow covering the panels the power output is very little or does not exist.
  • JohannJohann Solar Expert Posts: 245 ✭✭✭
    If you mount the panels horizontally, then you gonna mess that DC full sinus wave up and the power will go sideways and that could  cause problems.


    LOL, Just having fun.
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