Wood shed, solar panel roof

The panels go on the roof. Most panels will work well as stationary since the angle change from 90 degrees up to about 30 degrees makes little difference. Point them at the half way point and enjoy.

Solar panels for what? how big a system?
I would like to build a system that would tend to a battery pack that I could hook up to an inverter that will power a sub panel in my house incase the power goes out, I would like to power my well pump, boiler for hot water, refrigerator, a light or two (led already) and my wood stove blower.
When not using the battery pack for the house I would still excersize the batteries by using the same setup to power the shed the panels will be installed on.
I believe what I'm planning on doing is considered a closed system since there is no interconnect to the supply utility. Can this be done, absolutely, I can get the batteries for nothing (heavy duty deep cycle that power forklifts) The big money portion would be the panels, converter, wire, and sub panel.

In northern Michigan you are probably close to 45º latitude so if you have a 45º tilt from horizontal you should be at peak insolation at summer solstice but will be close enough to be useful all year. A 12 in 12 roof slope should have no trouble at all shedding very heavy snow.

Think about the sun's arc during a sunny day. It starts on the eastern horizon, continues higher until solar noon and then drops toward the western horizon. In the north/south direction it is pretty close to a constant angle but you will only be close to peak for an hour or two under ideal conditions unless you set up an expensive tracking system.

Oldman47 said:

Think about the sun's arc during a sunny day. It starts on the eastern horizon, continues higher until solar noon and then drops toward the western horizon. In the north/south direction it is pretty close to a constant angle but you will only be close to peak for an hour or two under ideal conditions unless you set up an expensive tracking system.

Click to expand...

The charts comparing no tracking, continuous tracking, and several iterations of "tracking" that involve changed the angle of your panels is specific times of year are all readily available. They demonstrate that there is a very clear, and non-negligible advantage of changing the angle of the panels to match the season. The more times you change the angle the less "gain" you get each time. IE, full tracking will provide 100% of the available power, no tracking will provide 30-70% depending on the season. Changing the angle just twice a year will get you 70%, 4 times a year will get you 80%, 8 times will get 85% etc. (those numbers aren't the true numbers, I'm only using them to demonstrate the diminishing returns of changing the angle more times).

All of that being said, as the cost of solar panels has decreased over the years the gains/returns of tracking or adjustable mounts have diminished. In many cases (at least for smaller, home setups that don't have complex control strategies) it's more cost effective to just buy a few extra panels to cover the periods of lower output and just let the extra energy "be wasted" during periods of peak output. The advantages of buying a few extra panels and rigid mounting them is that #1 you save in complexity, #2 you don't have to worry about building a "moving" roof strong enough to handle the loads etc, #3 You don't have to actually move the roof, #4 You don't have to worry about where you stack the wood to avoid having the roof hit it when it gets raised/lowered, #5 you get more "under-roof" area for your wood-shed at only a very slight increase in cost.

Things to keep in mind: the back side of most solar panels is a thin, weather proof coating that is damaged very easily. If that coating is damaged your panel will degrade rapidly. Having a moving roof above wood (sharp, jagged edges) is not a great idea. What happens if wind storm causes it to collapse and fall? The damage to the panels could be pretty extensive. What happens if something happens while you're in the process of changing the angle? It could damage the panels... IMHO you can build a MUCH more sturdy roof by building it rigid.

I have a couple of adjustable angle arrays, one is pole mount, one is wall mount. I am right around 45 latitude. I adjust my panels 4 times a year at 30 degrees in winter to 60 degrees in summer with 45 spring and fall. I notice some difference when I make the seasonal changes. I usually have to change to winter angle early as 45 degree pitch really does collect snow compared to 30 degrees, I do loose a bit of production. I also end up delaying the spring angle change a bit to avoid late season snow. I don't really lose production in the spring as there is snow on the ground which acts as a reflector that offset the slightly lower angle. Folks in snowy regions that need power in the winter hand the panels vertical so that snow cant build up and the snow reflectance makes up for the low angle. Contrary to popular belief snow can and will build up at 30 degrees. Generally the next sunny day it will slide down but on occasions it may stay a couple of days. My roof mounted array is close to 66 degrees from vertical year round and unless I shovel the lower edge of the roof and about a foot up the panels the snow stays in place for days and when it does come down its dangerous to anyone under it.

One thing to keep in mind is if its not easy to change the angle, most folks will lose interest and not do it if it becomes chore. Contrary to what you may think solar panels become and "appliance" at some point and get ignored, I usually do a quick inspection of my systems when I change the angles but the rest of the time I ignore them. My pole mount takes less than 5 minutes as its counterbalanced. My wall mount requires about 10 minutes with a hydraulic floor jack and a precut pole to jack up the bottom edge. I would probably leave it at 30 degrees but it acts a window awning over an angle bay window and it makes big difference in cooling my house if I have the angle bay completely shaded by the panel .

Given the low cost of panels, if you have the room there is a lot to be said to go with a fixed mount and use the savings to install more panels.

If you do go ground mount makes sure you design for deep snow. In Massachusetts there are numerous large solar farms that had issues last winter. They were designed for normal snow depth but not for the extra depth due to piling of snow that slid off array thus leading to arrays with the bottom row of panels covered with snow. These arrays are high voltage string arrays so one partially covered panel shuts down the array. Reportedly anyone who had equipment to remove snow between array rows had plenty of work. My pole mount was upgraded to larger panels at one point lowering the edge of the lower panel. I have to run my snowblower in front of it on occasion to keep snow from building up.

I see issues with designing a wood shed that has an adjustable roof as it adds a lot of loading and potential racking. Plus as the angle is changed the horizontal run of the roof changes.

Might take a few days but I will get some photos.

Just lending more weight.

Panels are weak. I'd never use them for a roof. They are mounted on my woodshed roof at about 2 inches or so off the roof. Installers said that with the cost of panels VS the cost of mounts and trackers.. it's just way easier and cheaper to add a few panels than anything else.

I've kept trimming trees (ok dropping!) as I see any panels get shaded. I'll post pics of roof an woodshed.

Here are the photos, kind of a foggy day. The pole mount in the first pole is set at 30 degrees as well as the wall mount. You can see the holes in the strut on the wall mount that correspond with the three settings. The bottom hole is "hurricane" mode it drops the panels down as close the window awning as possible. The solar hot water panels to the left on the roof are around 50 degrees to optimize hot water production in the spring and fall. The small PV panel attached to it runs the circulator pump for the gycol that runs to the storage tank. The house roof is 8/14 pitch (around 34 degrees). To adjust the pole mount I detach the lower wind braces that hook down to the concrete and then remove two stainless steel bolts on the higher brace. The pole is predrilled for three positions, the array is balanced at the pivot point on top of the pole so all I do is hold onto the array with one hand, move it to the angle I want and then use the other hand to thread the bolt in the threaded hole in the post. Definitely not something to do on windy day. I installed the entire pole and array myself with no help. If I were to do it again I would use double strut but this is actually an upgrade from a smaller array so I used what I had. I added the wind braces mostly for winter and only use one in the spring and fall.

It is quite noticeable that when the panel angle is set at 30 degrees that there isn't a lot of cover for firewood. As you can see in two of the photos I have one of my newer firewood stacks for 2017 with metal roofing on it. I do have a two cord wood shed out back with a shallow pitch roof along with 3 piles covered with steel or some old PVC signboard. With the minisplit visible in the house photo to the right, two cords is probably all I will need this winter as I have only run my boiler twice so far.

bfitz3 said:

I know that a ton of efficiency can be gained by raising the pitch in winter for three reasons....

Click to expand...

No.

Some efficiency can be gained. Until you have real numbers to tell you how much, it's all just jaw jacking.

How much of an issue is snow accumulation for you at the base of your post-panel? Also, what are the dimensions of the panel and the footings? I really like your awning set-up.

Snow build up is an issue in front of the pole mount. Its basic geometry. A certain depth of snow that normally would collect on a flat surface is concentrated on a lot smaller surface area when it slides down. If the snow does build up to the lower edge of the panel, then the snow just doesn't slide off anywhere near as quickly. I can get around 48 to 60 inches of snow on the ground some winters so to be truly maintenance free I would need the lower edge to be much higher but that means the pole needs to be higher and much bigger (technically it needs a higher section modulus) and the footing needs to be either deeper or heavier). The original panel array was set up for 4' clearance and rarely had enough snow build up to be an issue but the upgraded array has less and I do have to keep an eye on it. The footing is 2'by 2' by 6' deep. I will need to go out and measure the panels and get back to you.

I don't normally clear the snow. The panels shed snow about the same as a metal roof would.

BUT.. last year was very strange. 4 feet in a 10 day span, with no real warming.

In my excitement of the first year with panels, I went up and cleaned around the edges, then used the hose.. I got it clear.. but I should have just waited the couple more days for it to come off on it's own. I won't mess with it this year.

JP