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Location of solar panels on roof

Progress continues on the North Idaho ranch. I'm planning to install a 7 kW grid tie solar system that will have 2 rows of 11 or maybe 12 panels. My roof pitch is 7:12 and my orientation is 10 degrees east of true south with no obstructions. The roof overhangs 3 feet on the section that will have solar panels. I attached a crude depiction of the installation.
The contractors I'm considering to install are not in agreement on where to install panels. One is suggesting as low as possible so if snow slides off it will not tear the gutters off the house. The other says the middle of the roof is fine as snow if more likely to melt off than slide on my roof pitch. My research concludes that snow might slide on a 7:12 pitch.

Any knowledge or experience with this issue would be appreciated. If you know of a forum that might be a good resource I'd like to hear about that as well.

Thanks,

Steve

Steve Wolfe image 3.jpg347.53 KB
solar panels on roof.pdf68.21 KB
Asked by Steve Wolfe
Posted Jul 17, 2017 1:37 AM ET
Edited Jul 17, 2017 8:58 AM ET

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12 Answers

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1.

Steve,
- What type of roofing are you using?
- I'm having trouble understanding what is happening immediately to the left on the elevation. A change in roof pitch? Could you include an end elevation that shows it?

Answered by Malcolm Taylor
Posted Jul 17, 2017 4:53 AM ET

2.

Steve,
Firefighters prefer to see a margin of roofing around the entire perimeter of the PV array, so that in an emergency, a firefighter with an ax can maneuver on the roof. Such a band of roofing is required by code in some areas. You might want to check with your local fire department or building department.

I don't think the location of the PV array will increase or decrease the likelihood of snow ripping off your gutters. The most important thing to keep in mind when installing gutters is to keep all of the gutter (including the outer lip) below the plane of the roofing (reducing the chance that sliding ice will intersect some part of the gutter).

Remember that the sun is low in the sky in December. If you have distant trees to the south, you may be surprised to discover that the trees shade the lower part of your roof at Christmastime. That's why most PV installers prefer to mount PV modules high on the roof, not low on the roof.

Answered by Martin Holladay
Posted Jul 17, 2017 4:55 AM ET

3.

locating the panels too close to the roof edge increases the wind loading to the panels. Make sure the panel anchorage to the roof and to the rack is designed for the increased load.

Answered by Tim R
Posted Jul 17, 2017 10:50 AM ET

4.

Residential PV setback requirements starts on Page 19, but you should read the whole document. See 605.11.3.2 Residential systems for one- and two-family dwellings.
I should add that Code requires to add 6 psf dead load min. to roof framing, but I always require Truss Engineer to add 10 psf dead load to all trusses.

Solar IFC Setbacks 42208-1.jpg Solar IFC Setbacks 42208-2.jpg Beaver Brook Back 2.jpg
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Solar 2012 I-Codes.pdf 1.91 MB
Answered by Armando Cobo
Posted Jul 17, 2017 11:30 AM ET
Edited Jul 17, 2017 11:38 AM ET.

5.

I attached an elevation drawing. There is a change in elevation, the section to the west is higher by about 40 inches. I attached an overhead and south view photo as well. This was taken around 5:30 PM last week. The roof is composite shingle. There is a single roof vent on that section of roof which I had them install high on the roof.
I am "fortunate" to not have any trees too close on the south side so the only winter sun I'll have to deal with is my own tree and that should be pretty late afternoon.
If I do install a bit higher on the roof, I'm concerned that snow will slide off the panels and build up in a pile at the lower edge.
Thanks for the code info Armando.

200 OH view.jpg south view.jpg
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elevation solar design.pdf 1.04 MB
Answered by Steve Wolfe
Posted Jul 17, 2017 12:34 PM ET

6.

Yes there are code requirements, but your local jurisdiction may be noncommittal to them. A fire that is to the axe thru the roof stage is probably a total loss anyway. That being said, my neighbor has a 10/12 barn with shingle roof. The snow will slide off his solar panels but then get caught on the 3 ft. wide shingled area below, causing the panels to stop shedding snow. He's thinking of installing metal snow slides below. My 12/12 roof with panels close to eave does not have that problem.

Answered by Joel Cheely
Posted Jul 17, 2017 1:58 PM ET

7.

How about ground mounted array with passive solar tracking?

Answered by John Clark
Posted Jul 17, 2017 2:23 PM ET

8.

I use Sunpower327 panels which are 42"x61", so I need 30 panels for an 9.81kW system for the 5,000 sf house I've attached. I have plenty of room and no trees to content with, nor the overhang you have on the higher roof on the back, or tree. If you have the room, I would install the panels as far to the right edge code clearance (36") and do three or four rows of panels, so you can stay away from the shade, as much as you can.

Answered by Armando Cobo
Posted Jul 17, 2017 2:54 PM ET

9.

Joel,
Thanks for the pictures. Very cool drone shot!

Answered by Malcolm Taylor
Posted Jul 17, 2017 3:24 PM ET

10.

Joel thanks for confirming that snow would pile up at the bottom of panels if I install higher.
John, I like the idea of ground mount but that got vetoed by my wife.
Armando, did you mean to attach something to last post? I understand the logic of your location recommendation.
Malcolm, the pictures were taken with a DJI Mavic Pro I bought to document the house project, love it.

Answered by Steve Wolfe
Posted Jul 17, 2017 4:07 PM ET

11.

No attachment on post #8. I was explaining what I did on the last picture in comment #4 and making a suggestion to install your panels on your roof.

Answered by Armando Cobo
Posted Jul 17, 2017 4:42 PM ET

12.

Here is the finished product. System is grid tied 30 290 watt panels. Actually a bit over-sized for present needs, but I anticipate an EV or plug in hybrid in the future.

I'll post again after the first big snow as to whether or not my gutters got ripped off.

Idaho ranch panels.jpg
Answered by Steve Wolfe
Posted Sep 20, 2017 2:19 PM ET

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