How close to the edge of the roof can panels be?

cdherman · August 2009

Nice forum here. Having trouble finding answers to a couple remaining ?? I have. Perhaps someone can help.

I have a 45x30 Morton shed. The roof measures about 47x18 on one side (the south facing one, obviously). I am aiming for about 8kw grid-tie

I am thinking of useing the Kyocera 205 panels, as they are a) reasonably priced currently and b) "short" at 59 inches

I think I can get three rows top to bottom onto the 18' roof. I have to start about 15 inches down from the ridgeline (there is a little cupola that I'd rather not remove.)

By the time I leave a gap between the tops of the panels for ventilation, I'll have about 15 inches at the bottom before I get to the gutter.

Side to side, I am figureing 1 inch gaps between the panels, which gives me 43'4" for 13 panels. That would give me about 16" set back from the sides as well.

Ironridge XRS rails are my likey choice, as they allow me to span the full distance from truss to truss (9'). I went to ironridge site and looked at their tech specs.

I believe my wind exposure would be rated as a "C" class. Though perhaps just a "B" In the Roof zone 3 (at the corners) there would be attachments.

Anyhow, obviously, pretty techical questions, but perhaps there are some common sense answers:

How close is it OK to put panels to the edges of a roof? It can get windy here in Kansas City......

niel · August 2009

Re: How close to the edge of the roof can panels be?

if you wish and the mounts allow they can hang past the house if need be. many pole mounts are wide open to the wind and the pvs stay put so i don't see too much of a problem here.

icarus · August 2009

Re: How close to the edge of the roof can panels be?

You do need enough roof to work on the system, around the top and or bottom, and the ends. Ideal between rows as well I would think, but I don't think people provide a work space that way. What happens if a panel in the middle row fails?

Tony

halfcrazy · August 2009

Re: How close to the edge of the roof can panels be?

On a grid tied system i would say you don't need to leave any space. If a panel in the middle fails you will be dismantling the array any way to find the bad panel. What you have planned sounds like a winner to me.

BB. · August 2009

Re: How close to the edge of the roof can panels be?

You may get some snow in the winter--so clearing snow and possible ice dams can be an issue too (unheated building?).

I live near San Francisco--what do I know about snow... :roll:

-Bill

niel · August 2009

Re: How close to the edge of the roof can panels be?

BB. wrote: »

You may get some snow in the winter--so clearing snow and possible ice dams can be an issue too (unheated building?).

I live near San Francisco--what do I know about snow... :roll:

-Bill

bb is right as this could be a factor, but that is something you may need to be the judge of.

bb,
as far as what you know of snow (even from what you've heard) is,
1> it's a four letter word.
2> it's cold.
3> it makes some of us miserable in winter to shovel it with slick conditions appearing at times that can cause accidents.
4> it blocks light from getting to the pvs for some time causing low production of power when it's needed most.
5> it can weigh allot when enough falls.
6> it hurts when you are hit with it when it is compacted into a ball.
:roll: anyone else care to join in?

:p

icarus · August 2009

Re: How close to the edge of the roof can panels be?

Ya mean this stuff?

T.

Ralph Day · August 2009

Re: How close to the edge of the roof can panels be?

How long ago was that picture taken Tony? Some of our American cousins might think it was June.;)

Ralph

icarus · August 2009

Re: How close to the edge of the roof can panels be?

Yesterday afternoon!

No seriously, sometime in April. Don't laugh, I've seen snow on the July long weekend. The question is it the last or the first?

Tony

Cariboocoot · August 2009

Re: How close to the edge of the roof can panels be?

From a structural POV the panel mounts should be within the supported structure area of the roof: i.e. not fastened down to any over-hang. On many roofs these over-hangs are supported by 'flying rafters' which have no real support under them. So keep the panels 'within the walls' as it were.

cdherman · August 2009

Re: How close to the edge of the roof can panels be?

Wow, you fellas give a hearty welcome of the most useful kind! Thanks for the excellent responses thus far.

All the fastening points of the racks will be directly to the supporting trusses. Morton pole buildings are a truss and perlon sustem. 45 feet divided into 9' bays with poles going down every 9'. There are large (2x8) trusses every 9' and then 2x4 cross pieces (perlons) that hold the metal roofing which runs peak to eve. There is no sheathing..

I am encouraged that there are no general "RULES" that say you cannot come closer than so and so close to the edges.

I would certainly have never thought of fastening to the rim or "flying rafter" of the building. That would be a definite recipe for disaster, at least based on common sense. When I re-roof a structure, I get nervous just working out there over an unsupported rafter (and not because I am afraid of hieghts).

I had not thought of the need for access to service the system. Am I going to have to dissassemble the array often? What's my chances? It will be VERY well grounded and pretty much zero debris. Is this a reason to buy one brand of panels over another?

The roof is 26.6 degree. Not quite latitude here (39) but steep enough to make walk around on it tricky. I was hopeing to not go up there for a good long while after I get it all done......

Well, again, thanks for the great advice so far.....

Cariboocoot · August 2009

Re: How close to the edge of the roof can panels be?

Most panel servicing consists of keeping them clean, whether of dirt or snow, and in some instances adjusting the angle periodically to stay relatively parallel with the sun: http://www.macslab.com/optsolar.html

My roof here is 37.5 and I go up there twice a year. Haven't fallen off yet!

mike95490 · August 2009

Re: How close to the edge of the roof can panels be?

22 sharp panels, in a pure grid-tie system, 1 bad panel after 6 months, spotted visually and replaced. Had walk isles around panels, to wash them on a 2nd story roof.

If you can get to the opposite pitch and wash them from the ridge, that would work.

icarus · August 2009

Re: How close to the edge of the roof can panels be?

As a follow up to a previous picture.

This is a picture of the entire slab of snow oozing off a standing seam steel roof. Bitter cold, building heat melting a small amount of snow on top of the snow, causing it to refreeze into the classic ice dam. This particular building has the entire winters worth of snow on the roof. The building was un-heated until sometime in March. There is often enough strength in the ice to hold the entire snow "bridge" ooze all the way to the ground, leaving a tunnel!

Often the entire slab will slide, with dangerous mass when it lands, but once again, snow and ice is pretty powerful (and cool) stuff! Because the entire mass can slide as one, it can under the right circumstances take all kinds of stuff with it, solar panels, stove pipes, antenna mounts etc.

Tony

PS This wasn't taken yesterday,, a few days ago! LOL

How close to the edge of the roof can panels be?

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