Mounting solar panels on a roof.

diyfrank · July 26, 2012, 09:56:14 PM

I'm getting ready to install my electrical on my cabin and to simplify things, my plan was to build a 12 x 8 shed on skids with a shed roof and use it to store tools such.
The main function is a place for the generators, battery's, inverter and solar panels. My thoughts was to build it with the correct pitch for the panels which I'm uncertain just what that is. 45 degrees or a bit less I suppose. Is there a good way or a best way to mount the panels to a roof? I'm not too concerned with an adjustable mount as the winters won't have any activity.

There is four 200 watt panels that measure approximate 3' x 5' 6" each giving me a area of roughly 6' x 11'

MountainDon · July 26, 2012, 10:39:49 PM

For starters the modules should not lay flat on the roof. There should be an air space behind the module, or between the module and the roofing. This is because the modules get hot when the sun shines on them. The hotter they get the less their output. Modules flat on the roof will be hotter than if they are raised / air spaced. So don't sweat the angle of the roof, make it whatever you like the looks of or whatever is comfortable to walk/work on. Then make or purchase a sturdy frame and mount.

If you will have metal roofing you also need a special GFCI for the modules according to NEC. Each module also needs a proper ground. Because the modules use aluminum frames there are special ground connectors available that will cut through the aluminum oxide. The oxidized surface does not conduct as well as the aluminum underneath.

Also do a lightning arrestor.

Info on module angles

July 27, 2012, 03:47:10 AM

If you are going to use metal roofing, I would suggest a product called "unistrut" or "superstrut". You can get this item from your local electrical supply house or Lowe's. You can "stack" these to get the desired air gap above the roof for air circulation.
Also, I used these for my solar panel install, http://www.te.com/aboutus/news/prodinnov.aspx?id=1764

These clamps are made for aluminum frame solar panels,
Good luck,

diyfrank · July 27, 2012, 04:59:37 PM

Quote from: MountainDon on July 26, 2012, 10:39:49 PM
For starters the modules should not lay flat on the roof. There should be an air space behind the module, or between the module and the roofing. This is because the modules get hot when the sun shines on them. The hotter they get the less their output. Modules flat on the roof will be hotter than if they are raised / air spaced. So don't sweat the angle of the roof, make it whatever you like the looks of or whatever is comfortable to walk/work on. Then make or purchase a sturdy frame and mount.

If you will have metal roofing you also need a special GFCI for the modules according to NEC. Each module also needs a proper ground. Because the modules use aluminum frames there are special ground connectors available that will cut through the aluminum oxide. The oxidized surface does not conduct as well as the aluminum underneath.

Also do a lightning arrestor.

Info on module angles

My first thoughts were to use either 2x4 or 4x4 on the roof to mount to and leave a gap for circulation. Am I right in thinking a minimum of 2" and 4" being plenty?
I don't see a need for a metal roof being the panels will more or less be the roof. I will use some sort of water proofing to keep water out of the shed.
I have some roofing that is in a 3' wide roll I planned on using just for water control.

When you say special ground connectors are you referring to the type Tickhill posted above?

Dose a lighting arrestor need to be any special type for the panels. I picked up a bunch of arrestors from a farm supply that when out of business a few years back, they are for fences.

MountainDon · July 27, 2012, 05:07:15 PM

Correct on the type of ground connectors that Tickhill posted. There are a few brands made for the job. It's also a good idea to make the ground circuit in such a manner that if one panel has to be removed from the array, the removal does not break the ground path. Easy to do with those and a continuous length of ground wire.

As for lightning arrestor, I don't know what the fences use. Here's a link to a typical DC type used on PV systems. There are different ones for DC and AC. http://www.affordable-solar.com/store/lightning-arrestors/delta-lightning-arrestor-la602dc

July 27, 2012, 05:11:42 PM

1-4 inches is probably okay. Be sure the lower and upper areas allow free movement of the air. Personally I like the freedom of air movement with pole mounts. But that is just me.

diyfrank · September 03, 2012, 09:50:16 PM

Iv'e been working on this shed and have a few questions.

Can I stain this so I don't have to side it. I like the look of the wood.

I have 2 2x4's nail togather to make a 3"x3.5" post, One on each corner with 2 more in between for a total of 4 to support a 12' wall.
I plan on placing a knee brace at each post top and bottom. Does this sound like enough to hold up. I think the snown load for the cabin was 40 lb.

For rafters would it be better to double up and place over the posts or just space on 24" center.

hpinson · September 03, 2012, 10:09:09 PM

What is your latitude? There are tables that state the optimal panel angle and orientation, based on where you are, and if you want to get fancy, time of year.

diyfrank · September 04, 2012, 07:15:52 AM

I'm going to fix them to the average between summer and fall so I won't have to adjust through the summer. I lined up 2 sticks at noon to find the angle for the shed using the shadow.

September 04, 2012, 09:45:38 AM

This will give you the angle for your area.

http://www.macslab.com/optsolar.html

40# snow load is quite high, and if they're covered in snow they won't work anyway !

I would do a proper roof designed to support the snow load, and cover with a finished roof,snow melts and refreezes and gets in everywhere.

Mount the panels to a suitable adjustable frame - set at 45dg ish for winter so they shed snow and function and lower for summer

Remember to concider the frame mounting when you set out the rafters

diyfrank · September 04, 2012, 09:10:52 PM

I fix the picture link so they load with the page.

The panel angle has been determined. Winter will never be in use so I'm not taking the winter months into consideration, only spring and fall with a little use in the summer. I'm going to use the average between fall and summer to see if it gives me the best over all fixed setting.

I do have some questions I could use some input on before finishing the shed.

I'll load a picture of what I was referring to on the stain and the rafters will probably be 2x10
doubled up and set over the posts. I'm also wondering a bit whether to add a 2x4 to the posts to make them 4.5" x 3.5" if needed to help handle the potential load.

MountainDon · September 04, 2012, 09:17:53 PM

Quote from: UK4X4 on September 04, 2012, 09:45:38 AM

Remember to consider the frame mounting when you set out the rafters

Yes, don't create point loads where the weight of the snow on the PV modules will be transferred to an area of OSB located midway between two rafters. One reason I like my pole mount.

diyfrank · September 04, 2012, 09:39:53 PM

The Rafters should then be located directly over the posts as the roof will be the framing for the panels. The panels will require an 8x12 surface taking the entire roof area.

I should add the shed is being built out of 2x6 t&g, floor walls and roof. Rafters 2x10 doubled up =3x10 4 total over a 12' x8' area.
Does this sound built up to the task of supporting the panels in a 40 lb snow load. I was guessing it will be more then able but I haven't done any calculations, just thinking its a solid chunk of wood.

The pictures of what I thought the look should be when finish if I can find what was used .