Solar Roof Design Spanning 2 Cans?

[yinzer]

Hi all! First post here, so here's the obligatory "thank you!' to everyone who is proving amazing research and support!

Diving right in, I have two 20' containers that I'm building into a garage/barn. They are off grid, so I'm trying to design a roof to span about 15 to 20' between them with solar in mind. The cans will be resting on concrete piers at the corners, and mounted to embedded steel plates. I have a few competing constraints that make this a bit of a challenge:

1. Snow load: I'm in the Colorado rockies at about 8500' elevation, and our ground snow loads are 140psf.
2. Solar panel load: I want to run panels on the southern slope of the roof.
3. Span height: the cans are 8.5' tall, and I'd like to be able to park a DOT-limit camper (13.5') under the span. So I either need a scissor-style truss, or a +5' loft on the cans

I have two questions. First, when designing the roof with solar in mind, are there any design tips that will cut costs, simplify the build, or improve the roof, given that I know we'll be mounting panels? Regarding a roof on a conex can, any tip/tricks when dealing with the corner supports and levering the fact that it's a steel body? Most roofs just want to go all-wood since that's what they typically work with. I don't have any panels picked out yet -- with everything changing so fast, I'll make that decision when I'm ready for it

Second, any thoughts on the overall roof design? I'm worried about only using the outside edges of the can to support the roof because that could create a massive torque on the anchor along the outside edges, resulting on a lot of twisting force and stressing the anchors. So a simple scissor truss is not idea. I'm thinking of building a lean-to style roof on each can, but with the inner supports designed to be load-bearing. That way, they can support a straight 20' truss for the center span with a steeper pitch, so that the snow distributes more evenly onto the cans.

Thanks!

 

[svetz]

Welcome to the forums! Hope you keep us appraised of your project!

...our ground snow loads are 140psf...

You can generally just add another rail for excessive snow or wind loads, for example, I have 3 rails instead of the usual two as I'm in an HVHZ. If you write the manufacturer they can send you an engineer's report for your permits.

... when designing the roof with solar in mind, are there any design tips that will cut costs, simplify the build, or improve the roof, given that I know we'll be mounting panels?

The proper tilt for your location is important, as is knowing what season you'll want the most energy (e.g., if you use the most power in summer for AC you'll tilt for summer). The caveats against that are if you have a good net-metering agreement (then go for max annual power), or if it's stormy in a particular season and you need to cover those power needs.

Second, any thoughts on the overall roof design? I'm worried about only using the outside edges of the can to support the roof because that could create a massive torque on the anchor along the outside edges, Wind forces on the outside edges and corners are magnified, you should stay away from them if possible.

 

[Hedges]

Typical roofs slope in two directions. If your containers are oriented East-West, then a shed roof to the South would make all area usable instead of just half.
To get clearance for RV, a roof joist from South edge of one container, to a 5' high support on North edge of same container (8' away), would need a 15' high support at South edge of second container (assuming 16' apart.)
Some additional truss work coming off North edge of second container would help support it. OK, not entirely a "Shed" roof, but 24' of coverage faces South and only 8' of it faces North.

I like to have some panels facing SE and some facing SW, to reduce peak production and flatten it out over the day. A bit more difficult to fully populate a roof with two slopes to accomplish that; I use separate ground mounts.

How many watts of panels do you want?
My proposal of 20x24 (projected to the ground) which is 20 x 28 area for panels gives 560 sf or 52 square meters.
One "sun" is 1000W/m^2 and good panels are 20% efficient, 200W/m^2 (cheap ones are 120 W/m^2).
The array is good for 10kW, maybe $3500 worth of panels ($0.35/W). Cheap less efficient panels can be had for $0.15/W, would fit 6kW of panels costing $900.