Cabin in the woods, steep metal roof, snow country.

[Electric Personality]

Luckily, the cabin (upstate NY) is oriented north/south, but is in deeply wooded trees. It will be mostly three season. Just trying to sketch out a system for my friends that own it. The summer season will light up the western side of the roof for maybe 4 hours maybe a little more, but their load is fairly light. A 1 hp on demand water pump, a fairly efficient 7 cu. ft vissani fridge, led lighting, and the kicker, plumbed for a washer and (propane) dryer.
I know very little about mounting panels to a steel roof, I have some reading to do. My thoughts are, it would be great if I could angle the panels on the western face of the roof to the south, but, that would present a lot “fetch” for snow to build up. If the panels were mounted flat, I imagine that it would not be much of an issue, but less harvest. Guessing 4000 watts would fit up there easy. Maybe more, don’t have the actual dimensions yet.
Back of the napkin math, how big would you go in batteries and inverter?
Cabin is wired with a 240 panel, but no 240v appliances. Wood stove. They currently use a generator for everything.
Thinking a 48 volt system, probably an EG4 all in one, as big a battery as they can afford (min 100 ah? I would be happier with twice that, but they do have a generator) but still in learning mode.
Open to any and all ideas. Previous experience was getting my trailer off the generator habbit. Diy’d a battery for that, been working great for a few years, can even run the ac for a while.

 

[OffGridForGood]

Steep metal roof - how steep?
Depending on the roof metal profile, there are clips designed to fit on them for a secure and water tight seal. When they measure the roof area, get them to trace the roof profile onto a piece of cardboard so you can find the correct mounting clips.
If you go to PVWatts online and plug in the location, 1kW array, and set the tilt angle to the roof angle (East 90-degress then West 270-degrees) you can get the average monthly solar expected for each month, per kW of array. This should be reduced if you know there is shading issues. Add these up and divide by 30days per month to get an idea of daily PV energy available each month of the year. Typically PV watts will over estimate so cut the numbers down some percentage for sizing.

If you go to the resources section on this forum and plug in all the loads you listed, to the calculator it will give you an idea of the loads side (I assume there is no utility history information ie no grid was ever available at the cabin) so no other way to estimate loads easily.

If they never need 240 it may be best to work with a 120 only output inverter. The original MPP 6548 is 6500 watt output 120volt. *don't buy the one they call the high voltage unit use the original 250v PV input - search the forum if you want to know why) These seem to still be available from Watts247 at a super price.
To fully support 6500W at 48v = 135A ie two 100Ah server racks would be ideal starting point, add more as the gasoline savings start to add up...
Up-State NY, and
"The cabin is three season" it may be best to take the batteries with them for the winter, or leave them at 50% SOC and disconnected from the array for the winter. LFP can't be charged below freezing temps without damage.

 

[offgrid-curious]

This sounds somewhat similar to my cottage build in Quebec: https://diysolarforum.com/threads/off-grid-system-upgrade.71025/

In my case my cottage roof is facing east/west but is in a heavily treed area. I have a metal roof with a 12:12 pitch (45 degrees). I had originally wanted to use S5 mounts that wouldn't penetrate the roof, but it wasn't feasible with my roof profile. I ended up using Kinetic Solar Rhino mounts to attach to the roof and Kinetic Solar Rapid 1 rails to mount the panels. I have 12 Longi LR4-60HPB-350M panels for 4200 watts of PV total. Because of the trees and panel orientation I'm not able to actually capture 4.2kW, but I expected that going in. The most I've been able to capture so far has been just about 3kW, which is totally fine for me.

If it's a three season cabin, I assume your friends won't be there for an extended period of time - maybe 3-4 days max at a time? It sounds like you've already started to do a basic energy audit in your head. I was very conservative with mine and I'm using far less energy than I had budgeted. You may be able to start with just one 100AH server rack battery and expand later if need be. It's a lot easier to take away a 100AH battery for the winter than a 280AH one.

One thing I would keep in mind if using an AIO is the idle draw and noise, especially if the cabin is small.

 

[Madcodger]

mounting panels to a steel roof, I have some reading to do.

Check out S-5 mounts. Pretty much the standard. I used the the type designed for a corrugated metal roof on a shed system two yers ago and they've been great. Will use another of their designs on a standing seam metal in a few weeks.

it would be great if I could angle the panels on the western face of the roof to the south, but, that would present a lot “fetch” for snow to build up.

I wouldn't worry too much about the snow buildup. Keep tue wires and MC4 connectors mounted close up under the panels so snow/ice sliding under won't catch them, and if people will be there when it snows have long snow rake to clear the, a bit from the ground. Otherwise, don't worry about 'em.

Back of the napkin math, how big would you go in batteries and inverter?

I have a 3 KVA Victron 120V system and it has been fantastic. Would work for your situation, I suspect. I'd go 48V, 100AH battery to start, leave the generator in place just in case, and put a cutoff switch to prevent the battery from being charged in the cold. You can always add another battery in a few months or even a year or two later if needed, without too much of a problem. If they come up in winter, a couple of hours of warming it up and they can charge away. I would also strongly consider the EF4 6000XP as someone else mentioned (I have three on order right now).

 

[Electric Personality]

I love a collective mind, thanks everyone.
Quick question (I may have a LOT more in the future!), He uses open frame, non inverter generators. Will they be a problem with hybrid inverters?

 

[OffGridForGood]

I love a collective mind, thanks everyone.
Quick question (I may have a LOT more in the future!), He uses open frame, non inverter generators. Will they be a problem with hybrid inverters?

Chargeverter is the solution!
Although I noticed these can be pretty loud too btw.
(mine is in an electrical room in a workshop 60 feet from my home, so I'm not too worried about the Chargeverter fan noise, however I noticed they are nosier than the Inverters, so thought I should note that for ya)

 

[dopeassjackson]

I'm also "building"(really just taking my temporary system and making it permanent) offgrid system in central NY. One thing I can say is even If the cabin is 3 season put a few pannels vertical or have the ability to clean them off for winter use. All it takes is one ice or freezing rain storm and all your solar gain is 0v.

For a weekend seasonal cabin I dont think you need 4kw of solar. Think more batteries, the system will have 5 days to charge up before your back again. My system has been running its self through 2 NY winters with no input from me. I do shit the inverter off when I leave.

For major draws like the washer/dryer I may just expect to run it on a generator. Not much point in building a system off a use like that if your not living there.


My system is 700w solar, 6 gc2 batteries and a 1200w inverter. Epever 40A charge controller. It runs a 4.3cuft fridge, lights and the such just fine. I also have a 1kw inverter generator and 120v 12v/30a charger. The whole system including the generator and fridge cost less than $1300. It also only sees 2hrs of sun a day.

Now that my real cabin is built I'm going to be putting 1kw of solar on the top of my gambrel roof with provisions to put 1kw on the lower gambrel side for snow season.

I'm useing S5 versa brackets to attach to the roof. Then unistrut to the S5 brackets. I have exposed metal roof.

 

[Electric Personality]

Thoughts on this kit? Vendor?

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[OffGridForGood]

I have a 3000KVA Victron

are you sure?

 

[Madcodger]

are you sure?

Ha! I wish. Let me correct that... 3 KVA. I think that might have been on the first cup of coffee. Thanks - fixed it in the original post.