Dealing with -30° F Winters.

[hankcurt]

OK. I guess the thing to do is build an insulated box, put a heating pad in the bottom, set an old lead acid battery on top for thermal mass, and use a recording thermometer to track box and ambient temperature over the winter. Then I'd have some data on how much heat solar makes during the day, and how much it'll cool off overnight.

There are insulated boxes, and then there are INSULATED boxes. The answer to your question is calculable if you know the combined square footage of surface area of all sides of your box, the temperature difference you want to maintain, and the R-value of your insulation. This assumes you have no thermal bridges in the insulation and no air leaks.

For instance, if you build a box that is 2 ft wide, 2ft high and 3 ft long (which would be enough space for a 15kwh LiFePO4 battery), it would have a total surface area of 32 sq. ft. If you want it to be 60°F inside when it is -30°F outside, and the box has R-15 walls, the loss of heat would be 192 BTU per hour. There are 3.41 BTU/hr per watt, so the power required to keep it warm would be 56 watts. To maintain that over a day would require about 1.3 kwh of energy. Better insulation, a smaller box, or a reduced temperature difference all will reduce the power required.

The heat loss calculator is available on this web page.

 

[cs1234]

Probably not. Ran into loads of buried boulders while digging the outhouse hole.

Sounds like you've already got a hole then!

 

[Hedges]

Warmed by compost!
... and there's methane available too.

If Microsoft tried a data center sunk in the sea for cooling, maybe that can be an inspiration.

 

[constantspeed]

Yes. The webcam, which includes 3 cameras, a router, a 600W sine wave inverter, and a 12v timer runs 365 days a year.

Hoel Pond WebCams!

When unattended in winter, how much power is needed to run these items? Even with a good pure sine wave inverter, there is a loss of efficiency in conversion, and in idle consumption. I am guessing it doesn't consume anything near 600 watts when unattended. Would there be a way to eliminate the inverter and go with only 12v DC? Or maybe use a smaller pure sine wave inverter for unattended use (300w?)---something that uses less power, and gives you a little better overall yield and duration from the solar you can collect.

 

[Daddy Tanuki]

Thanks guys. The place is so hard to get to in the winter (snow shoes), no thief would risk it.
I've thought about an insulated box and heater. Problems there are roof top solar panels can be buried in snow for a month or more. I have a couple more vertical panels hanging off the front porch but with the sun low in the southern sky, I don't know how much heat that would generate. Same thing for self-heating batteries. How long will they stay warm before power is depleted?
I was hoping there would be some kind of "Aha!" solution but I guess not. I just replaced my four 12-year-old Walmart Maxx marine batteries with new ones. While I got 12 years out of them, the last two years were on fumes. I'm generally not a big power user though the K-cup machine gets used once a day. I just replaced the plug-in Hoover vacuum with a rechargeable Dyson clone. The webcams, router & laptop don't use much power. I'll look into those other types of lead-acid batteries. If I were to get a set of four 100AH Weize LiFePo batteries, what would be the best way to switch them in and out of the system with the lead-acid batteries? Need to switch solar panels and load.

Thanks again for the advice.

if you got 12 years out of a SLA battery then thats what I would go with. most folks don't get that much from unsealed lead acid and while DIY LiFePo4 packs are the rage at the moment none of us have a real clue as to how long they will hold up in such cold conditions. I built a heater pad and insulated box for mine but the coldest it gets where i am at is maybe 0°f...not -40 and i am basically at my cabin every weekend through the winter so I can at least regularly check them.

I would stick with the batteries you used before, maybe up the bank size a bit for those long times with no or low sun and go with what you know! Good luck.

 

[Adarondax]

When unattended in winter, how much power is needed to run these items? Even with a good pure sine wave inverter, there is a loss of efficiency in conversion, and in idle consumption. I am guessing it doesn't consume anything near 600 watts when unattended. Would there be a way to eliminate the inverter and go with only 12v DC? Or maybe use a smaller pure sine wave inverter for unattended use (300w?)---something that uses less power, and gives you a little better overall yield and duration from the solar you can collect.

The cameras are native 12 volts. The router is not. My choice of routers is limited because I need one that can act as a client bridge and cover the approx 2000' wifi distance to my ISP. But even with that said, before I consider pinching watts for a heated battery box, I need to know if my situation is even close to making something like that work. I'd need to set up a recording thermometer, heated battery box with dummy battery, and collect data over a 'test' winter. I'm not sure it's worth the trouble.

 

[John Frum]

Perhaps go old school? Any chance you can dig a hole below the frost line? ?

And above the water table.

 

[Adarondax]

Digging holes can be difficult. The glaciers dropped a bunch of boulders a few years ago.

 

[Adarondax]

if you got 12 years out of a SLA battery then thats what I would go with. most folks don't get that much from unsealed lead acid and while DIY LiFePo4 packs are the rage at the moment none of us have a real clue as to how long they will hold up in such cold conditions. I built a heater pad and insulated box for mine but the coldest it gets where i am at is maybe 0°f...not -40 and i am basically at my cabin every weekend through the winter so I can at least regularly check them.

I would stick with the batteries you used before, maybe up the bank size a bit for those long times with no or low sun and go with what you know! Good luck.

Good advice. If it ain't broke, don't fix it. Thanks!

 

[On_The_Road]

Probably a horrible idea - but you don't have to dig a very deep hole to stay above freezing. You could fashion a system that is buried. Or buried but uses a few feet of xps foam for the covering.

 

[Northernchateau]

Let me throw my 2 cents in as I have bitter cold Upstate NY weather experience.
I own run northernchateau.com, gotsnowcams.com, I live on the Tug Hill Plateau and have 4 solar powered webcam running.
I built and installed the 2 solar powered web cam units you see below 6 years ago which are still up and running on snowmobile trails.
The units consists of a 175 watt panel, Renogy Rover 20a MPPT solar charger, TP Link router running a Verizon air card, a Microseven webcam, low voltage cutoff and 2 Walmart 12v deep cycle batteries one in each of the white coolers on the bottom.
Our option for batteries in environment we deal with is LTO lithium–titanate battery. I thought switching but the lead acid deep cycles have worked just fine and I can not justify the cost.
The only issues I have had are, having to go clean them after we get days of snow and even with the cooler vented you MUST use dielectric grease on any exposed metal/wire. After the 1st year in service I found the dielectric grease trick as the fumes in the cooler will eat wire and terminals like a pacman.
Oh as far as the other 2 solar units, one is 2 100w Renogy panels again on a 20a Renogy Rover charging 2 large 12v bus batteries in an unheated cabin. The last unit is on a friend of mines place which has been running for 8 years, uses to be 6 100w panels charging AGM cells and I don;t remember the solar controller.

 

[Charleswgibbs]

What about using a silicate salt battery?

Bolt Ultra 150Ah 12V Advanced Silicate-Salt Battery | Deep Cycle Solar - ShopSolar.com

Bolt Ultra 150Ah 12V Advanced Silicate-Salt Battery | Deep Cycle Solar Battery + FREE Lifetime Customer Support Welcome to the future of renewable battery technology. Originally developed for the military, Silicate-Salt batteries blow lead acid batteries out of the water. Wether you are in...

shopsolarkits.com

 

[Northernchateau]

What about using a silicate salt battery?

Bolt Ultra 150Ah 12V Advanced Silicate-Salt Battery | Deep Cycle Solar - ShopSolar.com

Bolt Ultra 150Ah 12V Advanced Silicate-Salt Battery | Deep Cycle Solar Battery + FREE Lifetime Customer Support Welcome to the future of renewable battery technology. Originally developed for the military, Silicate-Salt batteries blow lead acid batteries out of the water. Wether you are in...

shopsolarkits.com

It doesn't look like that product is available and I get nervous when there is no cost and they have a payment plan.
Also for me, if we get snow for days I have a spare pair of charged batteries ready to go and I will snowmobile in and swap the low voltage ones out. Those batteries weigh 98 lbs which means I will need some help as I will not be carrying that thru 3 feet of snow....

 

[chrisski]

I vote to
1) Continue to use lead acid

Or

2) take the lithium home over the winter

You have a good plan with the thermal mass idea and gathering data over a winter. I’m just not sure I’d feel confident in a single winter to build any insulated box to protect a battery. You mentioned panels can be covered for up to a month.

 

[NC_hydro]

Edison Batteries maybe?

 

[curiouscarbon]

if you want to learn about the insulated heated box approach, please feel free to check out @Horsefly's build here https://diysolarforum.com/threads/horseflys-cabin-solar-lifepo4-upgrade.27472/

there are pictures of the box build in progress. they have also posted graphs of the temperature swings

hope this helps and good luck with this project