Planning new install - 5 degree metal roof aimed north, need advice

[littleharbor]

Would not a reverse tilt in snow country be a big snow trap?

[solarix]

Panels mounted at less than 15 degrees of tilt get dirty and stay dirty. Your 5 degree roof should be treated as a flat roof and put tilt racks on a 10ft spacing. We use 20 degree tilt here at 34 deg latitude, but you'll want more tilt up north and maybe a lot of tilt to deal with snow.

[J.P.M.]

1.) You mention some things you'll need to address, but how do you plan to deal with them ?

2.) If the roof was designed for a large solar array, why was it built facing north ?

3.) As a first approx. to address the row pitch vs. tilt vs. shading for tools that don't allow north facing roofs/support surfaces, use a horizontal roof and a (5 + 5) = 10 deg. tilt angle for the rows for a 5 deg. southerly tilt.

(Note to Ampster: This is an example of why the distinction between flat and horizontal might be useful to help avoid confusion)

4.) As a 1st est., an approximate fact of life: Before losses to snow cover and greater fouling, annual production out of any array with rows in a sawtooth pattern on horizontal surfaces such as a roof will be about the same as an array covering the whole roof with no gaps that has a horizontal orientation parallel to the roof. The same approx. actually applies to sawtooth arrays on surfaces of most any angle.

5.) More 1st approx. stuff: Your optimum tilt (from the horizontal - not the roof) will be ~ 40 deg., maybe a bit less. Using #4 above, set the row pitch for no self shading from the array with the panels at a 40 deg. tilt (from the horizontal - not from the roof). Or, better yet, use PVWatts and get an optimum tilt and azimuth and then set the row pitch for either minimum shading or most cost effective row pitch - the two are probably not the same - using a shading tool of your choice.

6.)The optimum tilt will minimize the array size and maybe save a few bucks in material. The 40 deg. or so tilt will mean a beefier support structure, a fair amount of engineering and quite possibly a roof/structure that you might find inadequate to the task with respect to applied/imposed loads from wind forces.

7.) A lower tilt will mean more array area required to meet whatever duty you're designing for and if a low enough tilt to get the wind loads low enough for the supports and building to handle, you may not have enough array production to meet the duty you've designed for

8.) Whatever you do, and if you plan on getting a reasonable amount of production out of the array during snow season, I'd suggest you get some advice from folks like Bruce here with respect to living with an array in snow country and ignore what he writes at your peril - at least with respect to designing arrays for snow.

9.) If you haven't done so already, I'd suggest you download a slightly dated version of "Solar Power Your Home for Dummies", or get a revised (newer) version for ~ 20 bucks at bookstores or Amazon and then get familiar with PVWatts. If you had done those two things first, your plans might well have been different. As it looks to me (only), from what you've written so far, you'll have a less than fit for purpose design. Maybe it can be salvaged with some education.

10.) If it was me (and it ain't) and I still lived in snow country (I don't), if I considered doing PV at all in snow country, particularly of that size, I'd first reconsider doing it, and then, if I continued, I'd first consider mounting panels on the south wall of the building in adjustable leanto fashion and consider summer shading from eaves/gutters and use about 3-5 ft. of ground clearance for snow and then maybe mount a row or two of panels sawtooth fashion on the roof with the same 3-5 ft. elevation clearance for snow. I'd then see how it goes and then perhaps consider adding rows as you see fit until you meet your required duty or you run out of roof.

Good luck.

Welcome to the neighborhood.

[snowmonster]

Based on PVwatts, it doesn't look that bad to me even with a 5 degrees north sloped roof. I figure 5 years tops to break even. Power outages in my area aren't common and I'm fine with an occasional day of being closed. We've had 2 days of that in the past 14 years. An appropriately sized battery bank would be cost prohibitive. The dimensions provided did account for a 3-4' setback for firefighter access. I'm in Indiana with potentially bad net metering laws going forward. I'm looking to cover expenses but do not depend on reimbursement for overproduction.

[Mike90250]

Does the power harvest projection pencil out? How many years to break even ? And you understand there would be no power from the array in case of a Grid Outage?

Will array setback rules apply in your case (3 foot walkways for firefighter access) Do you have pre-apprval from the utility for a project over 10KW ? Will that turn you into a commercial power producer with resulting low selling rates ?

[snowmonster]

Do you have space for a pole mount or a ground mount ?

Unfortunately no. It's actually office space and we maximized the footprint. I guess pole mount is theoretically possible but I'm looking at a 20kW+ system and that would be crazy. The roof is the only option and something is better than nothing in my mind.

[Mike90250]

Do you have space for a pole mount or a ground mount ?

[snowmonster]

First post. Have enjoyed the reading so far here.

I've got new construction with a standing seam metal roof that I want to put solar on. It was designed to support a solar array 45' deep x 42' wide. My latitude is 40.4259 in Indiana. The key problem here is that the roof here has a 5 degree slope to the north and I do have to worry about snow in the winter.

I could post all the details of electric bills and system size, etc. But is my best option to simply install more panels on a fixed/flat roof mount and simply deal with less production? I know I would have to worry about dirt/etc and it would be more difficult to deal with if a panel in the middle goes out. Or am I better of slightly tilting (5 degrees using 10 degree tilt legs) the panels in the opposite direction (toward the south) and deal with shading from neighboring rows and snowbanking in the winter? I've looked at the row spacing calculators and they don't take into account the fact that each row farther north is lower than the previous because of the roof level. It seems like shadowing is a major issue with this as the tilt legs get taller.

PVwatts isn't really that bad for a 5 degree roof aimed north so I'm guessing I'm best off with a flat roof mount and more panels? I know it would be massively better with a 25 degree southern facing array but that's not realistic for this application.

Thanks in advance!