diy solar

diy solar

Unattended, frozen environment battery recommendations

wiseacre said:
Knowing a fairly accurate estimate of wattage needed/used (both max load and daily total) is required to plan out any system

My heated battery box (4 x 2 x 2 ft) is not ideal because the seed starting heating pad I use is on 24/7 but it does keep the box above 45F with -12F outside. Colder temps on the way but I'm confident the heat pad will suffice. I'd have better efficiency if I bothered to tape the foam board seams :)
My setup works for me but other/better heating pad solutions can be found on the forum

Extended unattended use combined with extended no sun days calls for a fairly large battery bank to keep things warm and running.
On the plus side, you'll have some nice capacity for when you are there.

Add my heating pad load (21w) and my inverter idle draw (25w) and I'm using 1100w per day.
with my 9600Wh battery bank (two - 24v, 200Ah batteries) I can go 8 days of no sun and keep the batteries warm.
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I built an insulated battery box for my 8S 230Ah battery (details here), and have been running lots of tests with it here in Denver until I take it up to our cabin this spring. So far it looks like if the temperature stays at or around 20°F, I can keep the battery between 50°F and 60°F with about 3.5-4.5Ah per day. I don't expect this to go with no sun for very long, but if I only let the battery get down to 50% (115Ah) it seems like I could keep the batteries warm for 25 days or more.
 
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posegate said:
I see there are 24v, 200Ah batteries for around $1100 (SOK) to $1500 (EG4) each. Now I get messed up on the math. If I use two of them, am I getting 24v at 400Ah or 48v at 200Ah? Which is better?
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It's handy to remember "watts are watts"
also:
series connections the amps add up
parallel connections the voltage adds up

take (2) 24v, 200Ah batteries
series connected they become a 48v, 200Ah bank
parallel connected and they become a 24v, 400Ah bank

now this is where "watts are watts" comes into the picture
Ah x voltage = Wh

48v x 200Ah = 9600Wh
24v x 400Ah = 9600Wh
 
Horsefly said:
I built an insulated battery box for my 8S 230Ah battery (details here), and have been running lots of tests with it here in Denver until I take it up to our cabin this spring. So far it looks like if the temperature stays at or around 20°F, I can keep the battery between 50°F and 60°F with about 3.5-4.5Ah per day. I don't expect this to go with no sun for very long, but if I only let the battery get down to 50% (115Ah) it seems like I could keep the batteries warm for 25 days or more.
Click to expand...
and a very fine box it is. (I've been watching)
good you posted a link to it for the OP to see.

Mine was slapped together with materials on hand because by the time I got my cells and built the battery the cold had already arrived.
Since I'm always present and have a "grid assist" system using an ATS I'm fine as is
 
posegate said:
I see there are 24v, 200Ah batteries for around $1100 (SOK) to $1500 (EG4) each. Now I get messed up on the math. If I use two of them, am I getting 24v at 400Ah or 48v at 200Ah? Which is better?
Click to expand...
That SOK link is for a 24V 100Ah battery, not 200Ah.

If you use 2 24V 100Ah batteries then you get 48V 100Ah if in series or you get 24V 200Ah if in parallel.
 
Maybe lithium titanate is an option? It can cope with low and high temperatures, lasts a lifetime but heavy and more expensive. I think Will did a video on them, but there are also others.
 
Why not just flip the battery breakers to off when depart the cabin? As others mention the issue is charging and discharging at low temps. Just make sure they are at least 50 percent state of charge before you leave since they self discharge a little bit and flip the breakers off on however many batteries you have. (Sounds like you need just 1 and a single aio like a 6kw growatts).

If you need power all the time for some reason - say you want a remote webcam or something - then this should be a separate system using a 12v heated lithium iron phosphate battery or lead acid. Battleborne makes them. Probably with it's own separate solar panel and charge controller.
 
I am in the same situation…. Probably colder…

Flooded batteries can be discharged to 50% of their capacity, true…. But you get a lot less capacity from your batteries when you are near 0 Celcius. 50% of a lot less is really a lot less ( this is why I am getting rid of my 430 Ah 24V flooded batteries and installing LFP batteries instead).

The 2 options I am looking at are:
- Installing a propane heater in the basement to keep the place (and the batteries) at 5 degrees when unattended.
- Buying self heated batteries. These things use power from your panels to heat up your batteries and when they reach the operating temperature, they start charging. Some power loss while heating but not a big deal while the place is unattended.

…. I will probably go for both options.

Oh. A little trick concerning water pipes. I installed a small air compressor on the line to clean all water from pipes, water heater and taps. I takes me 10 minutes get rid of all the water. :)
 
If you can get propane service (500gal tank, on "keep-full" service), then it would be possible to have a thermostat-controlled propane heater in your "battery room". We use a number of these inexpensive heaters in various critical areas to keep temps at 50 degrees F. ... utility shed, crawlspace, etc.

The 8x16 insulated utility shed holding water tank, off-grid utilities (inverter/charger, LFP batteries), and other critical gear has a thermostat-controlled heater; light once at start of heating season, runs all winter long ... inside temps always at 50, outside at anything down to 20 below. No maintenance ...

We are onsite most of the time, but have left things running for a week or more, with no problems. A bit of remote monitoring gear, and you could keep an eye on things all (heating) season long.
 
This also sounds like a great place to have a few vertically mounted panels to power a battery heater or keep the battery topped up. Says someone who lives in a place with no frost line (chuckle). I don’t know how you folks survive up there.
 
Bluedog225 said:
This also sounds like a great place to have a few vertically mounted panels to power a battery heater or keep the battery topped up. Says someone who lives in a place with no frost line (chuckle). I don’t know how you folks survive up there.
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Buy a snowmobile and ride it on our deserts of snow…. You will never want to leave…

Vertical panels with a battery heater is a good idea as well…. I’ll have to consider it. Thanks
 
My cabin gets cold I use 16 6v golf cart battery’s from Costco .
My place sees 15/20 below0 for a few weeks every winter las weekend it was -7 3 nites in a row .
I drive in Friday nite power up and fire the stove .
Turn on the water
I have a 250 gallon tank in my utility room full of water the place is unheated but I’m insulation heavy
When it’s time to leave I have a compressor hooked up to the water system .
I turn on the compressed and open the water valves one at a time and blow out the lines .
I charge the battery’s with my inverter / charger off the generator to full .
Lead acid Battery’s (don’t ) discharge when they are cold , they can sit for months .
my trailer battery sit every winter and in April’s they are @ 100%
I use 10% of my battery power in the summer and 15 to 18 in the winter with no solar power
I just charge with the generator .
 
One other thing , my battery can be @ 10o but after a few days of charging the battery’s
stay @ 45 47o so I’m not really losing to much power to the cold ?
 
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The problem I have with those Winston cells is that it seems no one has ever validated the charge claim. In addition, in the datasheet you can find a discharge curve and you can see the drop in capacity when the temperature goes below 0C, with a substantial voltage drop which would cause most BMS to cause a low voltage disconnect. The datasheet then presents a charge curve at normal temperatures, but not a word on low temperature charging...

I always wanted to get one to test that aspect, but I've not had time. Is there an interest in this? If I'm not doing it just for myself I'm willing to get one and test.
 
upnorthandpersonal said:
The problem I have with those Winston cells is that it seems no one has ever validated the charge claim. In addition, in the datasheet you can find a discharge curve and you can see the drop in capacity when the temperature goes below 0C, with a substantial voltage drop which would cause most BMS to cause a low voltage disconnect. The datasheet then presents a charge curve at normal temperatures, but not a word on low temperature charging...

I always wanted to get one to test that aspect, but I've not had time. Is there an interest in this? If I'm not doing it just for myself I'm willing to get one and test.
Click to expand...
That's true. I suspect those cells are meant to survive and not get damaged by charging attempts at real low temp rather than really supply energy.
 
The top name lithium batteries mentioned are significantly higher $$/Wh of capacity than lead-acid. They also have significantly longer cycle life, for perhaps (previously?) the same lifetime cost per kWh.
Lithium does off various other advantages, but lead-acid and its AGM subtype do too.

If you aren't going to make use of the several thousand cycle life of lithium, I think you are would be paying extra for something you're not using.

AGM batteries are sealed maintenance free, with higher specific gravity than FLA which means more freeze resistant. Brands, price, and quality vary. What I'm using for grid backup (occasional cycling) in mild climate is SunXtender. Data sheet indicates 650 cycles to 70% DoD, and 10 year float life. An old set I have was mostly on the shelf (occasional recharge, not float) and at 12 years only delivers about 40% of label capacity before inverter disconnects. New set is always being floated, less than 2 years old so I can't report lifespan yet.

Sun Xtender Solar Batteries - Photovoltaic Battery

The Sun Xtender Battery line consists of specialty lead-acid solar, photovoltaic batteries, and renewable energy storage batteries manufactured by Concorde Battery Corporation.
sunxtender.com

I think this brand costs about 1/2 as much per kWh of capacity as a LiFePO4 brand like SoK (because those prices are dropping), so with around 1/5th the cycle life the comparison isn't as compelling as a couple years ago. But having a dumb battery without BMS is a KISS solution that addresses the environmental conditions issue.

Cost-wise and lifespan, FLA would be more competitive than AGM but a bit more work.

At the present time, supply chain affects availability of many sorts of batteries, which may force your selection.
 
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