Cabin Solar during Winter

[Daddy Tanuki]

Looks like you have come into the hard truth about using LiFe in an area that gets winter.

It just does not make sense to use Li batteries in those types of conditions. Insulation will slow down the heat transfer but it will not stop it.

As far as the Trojan T 105s, those are a deep discharge, low current style battery. They are very good, but designed for use with things like fans, lights, the DC power needed for a fuel heater, etc. They are not really designed for use with the power demands of an inverter.

For an inverter, you will want a marine style battery, which is a sort of hybrid between a deep discharge and a starter battery. They are designed to keep up with the serious power draw of an inverter. Examples of this are Lifeline GPL series and Vmax tanks, there are a few more - will try to think of them.

Rough numbers design around the concept of 1 battery per 500 watts of inverter capacity as far as ability to delivery power minimum. You can add more capacity as needed for total needs, but it takes that to keep up with the inverter.

Nothing wrong with SOKs for the correct application - but your cabin is completely the wrong application for them.

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A 24 volt system will be more tolerant of cold weather conditions than a 12 volt system as it is less sensitive to voltage sag from the cold.

Poly panels tend to be better at collecting sunlight in over cast conditions - at least in my testing of some solarland ones with a bogart controller.

yes and no... with your requirements, take them home each week. you can charge them at home put them in the cabin while there, and still charge. that or build a battery heater.

 

[HarryN]

yes and no... with your requirements, take them home each week. you can charge them at home put them in the cabin while there, and still charge. that or build a battery heater.

Where will the power come from to run this battery heater? Certainly not from solar under these conditions.

That is the main challenge in vans parked in fairly cold areas. The ones with Li battery based systems will eventually get cold enough inside to not be able to turn on the diesel or gas heater, even if there is plenty of solar power to keep up.

There are a lot of views about what is an ideal approach. My personal view is that once you make the decision to use a Li battery in an application, you have also committed to keeping it at 40 F or more.

The BMS is there to make up for an occasional exposure to cold weather and prevent an accident ( similar to a breaker ) , not something that should be part of a design that is regularly exercised. Electronics will all fail at some point, even when NASA does it. Even they have to add decay based heaters to their systems to keep them warm.

This view is obviously not shared by everyone.

I like LiFe batteries as much as the next person, but I also routinely use good quality AGMs very successfully. It is a matter of design and component selection.

An AGM battery, intended for use with inverters, will have with it published data sheet info with discharge curves under various loads. It is just a matter of selecting the right operating point.

 

[RV8R]

Where will the power come from to run this battery heater? Certainly not from solar under these conditions.

That is the main challenge in vans parked in fairly cold areas. The ones with Li battery based systems will eventually get cold enough inside to not be able to turn on the diesel or gas heater, even if there is plenty of solar power to keep up.

There are a lot of views about what is an ideal approach. My personal view is that once you make the decision to use a Li battery in an application, you have also committed to keeping it at 40 F or more.

The BMS is there to make up for an occasional exposure to cold weather and prevent an accident ( similar to a breaker ) , not something that should be part of a design that is regularly exercised. Electronics will all fail at some point, even when NASA does it. Even they have to add decay based heaters to their systems to keep them warm.

This view is obviously not shared by everyone.

I like LiFe batteries as much as the next person, but I also routinely use good quality AGMs very successfully. It is a matter of design and component selection.

An AGM battery, intended for use with inverters, will have with it published data sheet info with discharge curves under various loads. It is just a matter of selecting the right operating point.

100% Harry !!

I have a Cabin in Canada & have a small bank of decent AGMs mostly charged up by solar & when that won’t do it a gas generator.

It gets colder than -20C sometimes over the winter. I shut the system down & take the battery bank home over the worst of the winter.

 

[Scoutmaster]

Thanks for sharing your experience.

It’s been a bumpy 2 years, but I’m still learning and my situation is sort of unique.

I’ve never gone without power thanks to the generator. I have plenty of wood and propane for heat. I also have propane lights so I have plenty of options. I do like having the battery power for lights/tv but I think year round power from batteries and solar panels is unlikely and cost prohibitive.

I’m curious when I set up the lead acid batteries and run both setups I probably will be able to get 2-3 days without to much trouble. I rarely stay more than 2 nights at a time. I just spent the weekend and only ran the generator for coffee and microwave…maybe 20 minutes total all weekend. I was able to run lights/tv charge my eBike without to much trouble.
I don’t think I can keep them warm enough in the winter or get enough sun to dream of a full winter without issues.

 

[Daddy Tanuki]

Where will the power come from to run this battery heater? Certainly not from solar under these conditions.

Two points: If the battereis are in the cabin, and the owner is running his wood stove the batteries will be fine temp wise.

If not a well insulated battery box in the cabin will use very little power enough to run the cabin overnight and then charge up again in the AM with the genset. This allows for the genset to be run for a short period of time to juice the lifepo bateries up to 85~90 percent then limp along with whatever solar is avail.

Or reverse it and charge them for an hour in the evening prior to gong to bed and by the am they should still be good until what little solar he gets can power the house.

mix and match as needed. And as before take them home when not using the cabin, no need to warm them up or anything get home and then charge to full right before coming back to the cabin.
the OP is using a small set of 12vdc 100 aH batteries correct? these could be thrown in the trunk and taken home.

 

[Daddy Tanuki]

so i looked up the SOK batteries... they have a metal case for gods sake... slap 4 of the 25 watt heating pads wired in series (two on bottom, one on each long side) and then build a box out of the blue 2" xps foam to sit the battery in it will use very little power and wired in series with a 12 volt temp controller from amazon set on a 8ºc ~ 12ºc on at 8, off at 12 so they won't get too hot... the metal casing will help spread the heat.

(note when charging from the genset set the temp to turn on and off at higher temps to warm the battery up to say 25ºc while the genset is running and then back to the 8-12 routine when genset is off.)

so heater is figured out.. next is charging..

Treat them as if you do not have solar and fully charge them in the early AM with your genset while running your coffee pot and toaster oven... that way you have your genset running and taking care of multiple items keeping the genset up closer to 50~70% at its most efficient power generation curve. once full shut off genset and use the panels to grab what you can, as by now the sun is higher in the sky allowing you to get some power.

as before take batteries home with you at end of trip. lave the XPS boxes behind just glue the sides together but use packing tape for the top, make holes on the side for the cables to go through, open "lid" remove SOK battery place in trunk and go home.

 

[12VoltInstalls]

Insulation will slow down the heat transfer but it will not stop it.

Quite true in my experience.

As far as the Trojan T 105s, those are a deep discharge, low current style battery. They are very good, but designed for use with things like fans, lights, the DC power needed for a fuel heater, etc. They are not really designed for use with the power demands of an inverter.

Umm, what? Plenty of people use them. They will outlast marine batteries. I used marine batteries for years and was happy with them.

A 24 volt system will be more tolerant of cold weather conditions than a 12 volt system as it is less sensitive to voltage sag from the cold.

Umm. No

 

[HarryN]

Thanks for sharing your experience.

It’s been a bumpy 2 years, but I’m still learning and my situation is sort of unique.

I’ve never gone without power thanks to the generator. I have plenty of wood and propane for heat. I also have propane lights so I have plenty of options. I do like having the battery power for lights/tv but I think year round power from batteries and solar panels is unlikely and cost prohibitive.

I’m curious when I set up the lead acid batteries and run both setups I probably will be able to get 2-3 days without to much trouble. I rarely stay more than 2 nights at a time. I just spent the weekend and only ran the generator for coffee and microwave…maybe 20 minutes total all weekend. I was able to run lights/tv charge my eBike without to much trouble.
I don’t think I can keep them warm enough in the winter or get enough sun to dream of a full winter without issues.

That makes total sense.

In the winter you won't need to heat them, so you can just have the solar trickle charge them as available when you are not there. When you arrive, then the battery bank will be topped off under most conditions.

Often there is at least one location on the side of the house that tends to stay clear of snow and get a few hours of sunlight in the winter. Consider to mount a panel in this location - yes vertical - it just needs to be a place that self clears most of the time.

One common way to run an AGM based power system is to run the generator for an hour during breakfast or shortly after to help with the bulk stage charging. Then let the sun do the finish stages of charging.

The operating voltage of cold AGM batteries is lower than room temperature ones, and this results in lower chemical activity inside of the battery as well (lower current delivery capability ). For this reason it can be difficult to stay within the low voltage range of some "nominal 12 volt" devices and to feed the inverter with enough power.

24 volt systems are somewhat less prone to this problem for 2 reasons:
- Generally the input voltage range of 24 volt appliances / inverters is wider than for 12 volt versions. (not always, but often )
- You can use a good quality DC - DC converter to take in the reduced output of the 24 volt battery pack to make a stable, regulated 13 volts. I do it all of the time for van owners.

As far as charging the batteries, just make sure that your chargers have temperature compensation built in and set for your particular battery.

 

[Daddy Tanuki]

Often there is at least one location on the side of the house that tends to stay clear of snow and get a few hours of sunlight in the winter. Consider to mount a panel in this location - yes vertical - it just needs to be a place that self clears most of the time.

same for all chemistries, get the power however you can.

One common way to run an AGM based power system is to run the generator for an hour during breakfast or shortly after to help with the bulk stage charging. Then let the sun do the finish stages of charging.

mentioned that earlier it is the same for all chemistries this would allow you to run a heater on the SOK's that would use probably honestly less than 30% of their capacity just to self heat, maybe less if your insulation regime is stricter than mine.

The operating voltage of cold AGM batteries is lower than room temperature ones, and this results in lower chemical activity inside of the battery as well (lower current delivery capability ). For this reason it can be difficult to stay within the low voltage range of some "nominal 12 volt" devices and to feed the inverter with enough power.

24 volt systems are somewhat less prone to this problem for 2 reasons:
- Generally the input voltage range of 24 volt appliances / inverters is wider than for 12 volt versions. (not always, but often )
- You can use a good quality DC - DC converter to take in the reduced output of the 24 volt battery pack to make a stable, regulated 13 volts. I do it all of the time for van owners.

not true. 12/24/48, sag in cold weather is sag in cold weather, and adding a power eating device like a dc-dc converter is probably a heavier draw on your batteries than using heating pads.

 

[HarryN]

same for all chemistries, get the power however you can.


mentioned that earlier it is the same for all chemistries this would allow you to run a heater on the SOK's that would use probably honestly less than 30% of their capacity just to self heat, maybe less if your insulation regime is stricter than mine.


not true. 12/24/48, sag in cold weather is sag in cold weather, and adding a power eating device like a dc-dc converter is probably a heavier draw on your batteries than using heating pads.

I think the difference in our perceptions has more to do with the occasional nature of his cabin use and what voltage the loads will be.

My perception is that the use case is more like 2 each, long weekends per month vs continuous use, and mostly 120 vac loads but I could be wrong.

The Li batteries would need to be heated even if he is not there and I am just estimating - would need at least 25 watts x 24 hrs/ day to keep warm.

Since he is not there ~ 24 days / month, then this might not be all that efficient of use of power - at least in my mind.

If the loads are mostly 24 VDC and 120 vac, with an occasional 12 volt load - the DC - DC setup can make a lot of sense. Very good quality ones have very small idle / standby power. I use them in vans. I need to go through my notes but it was very small - a few watts at most and could be turned off when not in use.

In a situation where the bulk of the loads are 12 volt (which is not something I really ever work on ) then you are right - 12 volt packs make the most sense - especially if they are LiFe.

Quite a few people were bringing their vans into my shop with 12 volt AGM and flooded cheap batteries and the voltage sag was just too much to run their diesel heaters and refrigerators. People still have this problem with some solar generators on the market.

 

[12VoltInstalls]

people were bringing their vans into my shop with 12 volt AGM and flooded cheap batteries and the voltage sag was just too much

Neither of those should cause sag. Maybe loaded capacity availability, but sag only really happens at higher amperage.
FWIW I ran walmartha flooded marine successfully for years including a 120V electric fridge and coffeemaker. I’m not special, either.

 

[Scoutmaster]

I appreciate all the info. My situation hopefully can help a few others in their quest.
When I first started playing around I thought this would be plug-n-play. After a few years of messing around in the woods I’m humbled by the project. Having a cabin nestled against a mountain with massive trees and the potential for epic snowfall makes this a moving target for what works one day doesn’t work the next. Just getting the cabin weather tight and out of dirt so it stops rotting has been consuming of time and money. I still have some minor structural issues which have made me reluctant to move on any permanent installation of anything. It’s all tacked together with tape and bubble gum.
I think I’ll be able to add a shed later this year or next year to house the batteries and wiring/generator and maybe put some panels on the roof and side walls.

Over the next 3-4 weeks I’m going to hook up the 6v batteries and test them out. It’s one big experiment……They were basically free so 6x6v batteries with my 2x100ah lithium in a switch is going to double my previous battery bank…even if the 6v are crap they’ll still run my lights and tv for a day or 2 I hope…. I only run 100-300 watts total at a time for probably 24-36 hours over a long weekend. 3-4 hours in the AM 6-8hours in the PM. There are 3-4 sets of string lights from Costco and a TV with misc charging.

 

[RV8R]

Yup it is weird how Solar charging is so weather dependent ?. We are currently in our cabin & the last couple of days have been crappy sun days.

Our 12vdc loads; Fridge, Propex Propane Heater, Water Pump, LED Lights, USB Chargers ( phones & tablets etc ), Composting Toilet Fan.

Even on a mostly cloudy day we were able to get out AGMs back up to 100% yesterday. Here is a look ( note when we are away 80Wh to 90Wh is used by the Composting Toilet );

 

[Daddy Tanuki]

thank god I followed my own path to solar and do not have your problems.