Seasonal Off grid in cold climate

[Kathadin]

My wife and I have built our 600 SF off grid cabin in Northern Maine and are looking for input on setting up and selecting replacement batteries.

We only go up on a few weekends a month and the place is unheated during that time. The solar system and batteries are in an unheated shed.

Here's our current setup:

4) Canadian Solar 255W panels on our shed roof at a 30 degree angle, facing due south with no shadows as we are in the middle of a field
Outback Power FM80 SCC
Outback Power VFX 3524 3500W inverter
2) 12 V 200AH AGM batteries in series, these are at least 6 years old
Honda 1000 W generator

My issue is fairly short battery capacity I'm guessing due to the age of the batteries and the lack of insulation/heat as they are in our shed there.

We recently moved these from another off grid location that was only used in the summer with very minimal loads so we never had to think much about the setup. It fired up and ran fine with the default Outback Power settings so I didn't mess with anything.

So after doing my load calculations we came in at 1000Wh/day, I'd like to build in some extra capacity and round that up to 1250. Our biggest load is a pellet stove and several LED lights. The stove and fridge are both propane. We can also run the cabin off the Honda generator to let the batteries charge during the day and swap over to inverter at night to allow the pellet stove to cycle during the night. On the last trip the batteries kicked off during the night when the stove was running and filled the place with smoke.

After reading this forum and watching Will's YouTube channel, I think my first step is to build an insulated battery box and install a few RV heaters to keep things toasty.

My next step is to replace the batteries and this is where I need help. Since this site is very cold in the winter, do I stay with the AGM or is now the time to make the jump to LiFePO4?

I don't mind spending the money to get what is best but as a rookie I don't want to make the wrong decision.

Thanks for the great forum!

James

 

[MichaelK]

Assuming you get about 85% of nameplate in terms of real-world production, and your battery is going to be bulk charging at ~26V, what you can reasonably expect out of your array is [ (255W X 4panels)/26V ] X 85% = 33.3 amps of charging current.

A lead-acid battery likes charging at ~ 1/8th of C, so the best battery size for 33.3A would be 33.3 X 8X= 266Ah. That happens to be really close to Trojan's T-105 golf-cart battery, a standard flooded lead-acid battery that I myself have used in the past. At 250Ah, that's 6000Wh total, or 3.0kWh at 50% withdraw.

If you want to go with a larger capacity battery, look at Trojan's L-16 size. 33A is a bit low for something in the 400Ah range, but if you could get two more of those Canadian Solar panels, that would be perfect.

I've never been a fan of AGM batteries. I've gotten excellent results with traditional lead-acid, but you need to buy a gallon of distilled water from the store for topping them off occasionally. It's best to check every single time you are there, but you are likely to need to add water only every three months or so.

 

[Kathadin]

Thanks for the reply, I can easily add more panels as needed. I have several more of the same panels available from a friend.

I'm wondering if it might be smart to mount them vertically on the south side of the shed so I wouldn't have to worry about snow covering the panels between trips?

 

[DPC]

Honda 1000 W generator

Great little units but you have to go out and start them and shut them down.....
Pay more to get more feature from modern RV units of you like...

This wee little fellow cost me 40 bucks at a yard sale. ( based on the colour I would say made before 64 )
Cast iron K91EP engine, 1.5RM21 1.5 kw generator, saturated field, exciter cranked, remote start stop with all the right safeties two stage battery charger.
True hard wire remote and the excellent EL-8 electro-mechanical controller Sisson electric choke.
Nothing here you cant fix yourself and because of the design all you need to do is change brushes and as needed and engine maintenance.
It will burn more fuel than the Honda but you can start and stop it as needed from inside so your not wasting fuel
Engine parts are dirt cheap but its a K series and you won't need them....

Just fog it up and let it sit as long as you want, it will require no excersise, but you should add an electric fuel valve and rotate your fuel once a year ( I use ethanol free gas )

The Onan LK is a good unit too but bigger burns more fuel.
Look for a spec N because it has the oil pump but the earlier splash units are very reliable.
You get this stuff cheap now because its heavy and no one in a shop will work on it anymore.
A savy owner will get something like this and it will last a lifetime with minimum care.

The penalty, cast iron is really heavy and you will burn more fuel if you just leave them run as apposed to more modern stuff.
A new inverter generator with a remote start stop is superior in every way.
Trouble is they walk off your property when your not there and they require a lot more care and attention to maintenance and storage

 

[Kathadin]

Hi DPC, Thanks for the info and photo's, I'll keep an eye out for a large generator but for now I'll stick with the little Honda. It has an external fuel tank and runs on a gallon a day and I can't hear it running.

I'm hoping to keep things as simple as I can and start with correctly sizing and updating the battery bank.

 

[Supervstech]

Changing to LFP would require they never get charged when it’s below 0C/32F so heated batteries, or a well insulated heated enclosure would be needed.
The advantage is the cells don’t need specific charging parameters they can trickle charge when you aren’t home, and be available when needed. They will survive longer, discharge lower, and they make better use of the solar you have.

 

[JAS]

Changing to LFP would require they never get charged when it’s below 0C/32F so heated batteries, or a well insulated heated enclosure would be needed.
The advantage is the cells don’t need specific charging parameters they can trickle charge when you aren’t home, and be available when needed. They will survive longer, discharge lower, and they make better use of the solar you have.

Are you saying it's OK to leave charging connected for months at a time w/ LFP? I've been disconnecting my solar and letting my battery sit usually somewhere around 70% charged...

 

[MisterSandals]

After reading this forum and watching Will's YouTube channel, I think my first step is to build an insulated battery box and install a few RV heaters to keep things toasty.

Have you considered installing your batteries below ground where it does not freeze? This would open the possibility of using lithium.

 

[Kathadin]

Have you considered installing your batteries below ground where it does not freeze? This would open the possibility of using lithium.

I could do that in the spring, the frost line is about 3-4 feet here.
Do you feel that's a better option then a self heating battery inside an insulated battery box? I'm sure your option is fool proof which might be better for a rookie like myself.

I'm pretty good running a shovel,,,

 

[PreppenWolf]

When you say 30degrees, do you mean from verticle or horizontal?

Can you dig a root cellar? Or just a big hole down in the shed, insert something like a big Rubbermaid trashcan or an old cylindrical plastic water tank from a junk yard? Then put batteries in the bottom, then layer foam on top. The Earth will keep the batteries warm for you. No power needed.

 

[MisterSandals]

I'm sure your option is fool proof which might be better for a rookie like myself.

There are things that can go wrong, like flooding.

I have not tried it so am not aware of tested ways of doing this.

A few related discussions here:

Search results for query: bury batteries

diysolarforum.com

Search results for query: underground batteries

diysolarforum.com

 

[Kathadin]

When you say 30degrees, do you mean from verticle or horizontal?

Can you dig a root cellar? Or just a big hole down in the shed, insert something like a big Rubbermaid trashcan or an old cylindrical plastic water tank from a junk yard? Then put batteries in the bottom, then layer foam on top. The Earth will keep the batteries warm for you. No power needed.

The panels are 30 degrees from horizontal, I think the best angle for my latitude would be around 45 if i understand it correctly.

I can mount a second set off the side of the shed but would have to take into account snow sliding off the roof and panels.

 

[PreppenWolf]

Something like these below. Typically they are 30-36" in diameter. You seal any side/bottom ports and cut the top off. Dig a hole bigger than the tank diameter at least 6". Place the tank in the hole touching the ground. Add sand if necessary to level the bottom and ensure full contact. Fill around the tank with packing peanuts. Top with pieces of foam board. Place batteries in the bottom of tank, cover with solid foam board cut snug to fit.

 

[PreppenWolf]

The panels are 30 degrees from horizontal, I think the best angle for my latitude would be around 45 if i understand it correctly.

I can mount a second set off the side of the shed but would have to take into account snow sliding off the roof and panels.

Best angle for winter is at least 67 degrees from horizontal. I'm in S NH and my panel ideal winter angle is 65deg. Snow clears from my panels most days left alone which should be fine for your applications.


Shedding during snowfall at 65deg

 

[Kathadin]

Best angle for winter is at least 67 degrees from horizontal. I'm in S NH and my panel ideal winter angle is 65deg. Snow clears from my panels most days left alone which should be fine for your applications.


Shedding during snowfall at 65deg

Thanks for the pictures and the correct angle. I can install the next 6 panels at that angle in the spring. That will max out my SCC at 2500 watts, which should be plenty once I get my batteries situated.

 

[MichaelK]

Thanks for the pictures and the correct angle. I can install the next 4 panels at that angle in the spring. That will max out my SCC at 2000 watts, which should be plenty once I get my batteries situated.

Your best option is to make an array frame that's adjustable. I can set my arrays at the summer angle, the winter angle, or anything in-between. Door hinges work well for this. In winter the snow just slides off.

 

[PreppenWolf]

The legs on my stand fold to allow for 25deg in the summer. A compromise of the size they are when folded. 15deg would have been better, but I'm not worried about production in the peak summer months.

 

[12VoltInstalls]

next step is to replace the batteries and this is where I need help. Since this site is very cold in the winter, do I stay with the AGM or is now the time to make the jump to LiFePO4

Well the above fla suggestions are good ones- not an agm fan. Never heard anyone praise them for longevity if’n they actually get cycled.
The LiFePo option. I am not opposed to LiFePo but those honkin’ big lead acid batteries are your best option for your circumstances imho.

The panels are 30 degrees from horizontal, I think the best angle for my latitude would be around 45 if i understand it correctly.

45 maybe in summer. Winter is probs 55 or 60*
I run mine vertically.
In southern New Hampshire they’ll probably shed ok but where I’m at in Vermont? Doesn’t work out a lot of the time in my experience.

wondering if it might be smart to mount them vertically on the south side of the shed so I wouldn't have to worry about snow covering the panels between trips

Absolutely in my opinion.