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I recently set up my own off grid solar system in a tiny cabin that I designed and had built. I used the Solar Controller+Inverter Combos recommended on this s

by zoba 5y ago

I recently set up my own off grid solar system in a tiny cabin that I designed and had built. I used the Solar Controller+Inverter Combos recommended on this site (Growatt) but ultimately switched to ones by Renogy. The Growatt one I purchased has a wifi adapter and app - wifi requirement was a deal breaker when remote. The renogy one has a Bluetooth adapter and app, plus feels better designed (though actually I think the internals are all pretty similar). There are a couple surprise gotchas I didn’t know: 1) These Controller+Inverter combo units require a battery to turn on. This means: if your battery runs completely out of charge, you have to get electricity from somewhere to charge your battery a bit before the Controller+Inverter will turn on and charge your battery again. I was pretty annoyed at how not “off grid” this felt. 2) Temperatures below freezing are bad for batteries. I purchased a Renogy 48v smart battery with self heating. Unfortunately less sun in winter means less energy, and heat production is energy intensive. I’m not at the cabin 100% of the time so I have to take the battery with me when I leave to avoid spoiling/freezing it. Still not sure how I’ll ultimately get around this.

redtexture 5y ago
Insulated Root celler equivalent location for the battery.
jf 5y ago
Could you dig a hole for your batteries and store them below the frost line?
- Syonyk 5y ago
  The problem with holes in the ground for storage of things like batteries is that... they're holes in the ground. The ground, as a general guideline, actively dislikes holes in it and strives to fill them in whatever way possible. Liquid rolling in, soil creep, debris blowing past and building up, it doesn't matter - given a long enough time, a hole in the ground won't exist anymore. You can build a hole that will hold up to this sort of stuff for a while, but that tends to be expensive - underground concrete work is neither cheap nor easy, and given the number of people injured in trench collapses who do it for a living, a serious underground hole isn't a good DIY project either. That just leaves the maintenance, which also sucks for a hole in the ground. Anything you have to do on the batteries is easier with them on or above the ground, instead of underground in a hole. For lithium, it's fairly low maintenance but you may have to replace some BMS boards every now and then, manually check balance, etc, and for lead it's water every few months, unless you go with sealed, which are "maintenance free," but also "maintenance and status check impossible," so you really just set them and run them to failure - you can't monitor condition like you can with flooded. It's the sort of solution that, technically, would work - it just ends up being radically more expensive and a hassle than it's remotely worth. Think "Spending $5000 to save $20/yr" sort of thing. You see the same trend with things like the complex solar trackers that were common in the 80s and early 90s. With the cost of panels, optimizing every bit of power from them was critical, so spending an awful lot of money on support infrastructure to optimize $10/W panel production made quite a bit of practical and financial sense. Today, with panels at $0.50/W, very few people bother with trackers anymore (for off grid installs). Most things you could improve with a tracker, you can improve with less effort and less money by just hanging more panels. Bonus: With more panels, you get more production on cloudy days when panel orientation doesn't matter (because the sky is more or less evenly lit). I've got south facing, east facing, and west facing panels on my office, of two different brands, all fed into a single MPPT charge controller input (I do have some blocking diodes to prevent backfeeding a shaded string, though). It's not nearly as "efficient" as some other options, but it's a whole lot cheaper, and gives me more power on the low cloud days that are the rough ones. The rest of the year, I have so much power out there that I'm demand limited, not supply limited (actually, inverter limited - if I added some 48VDC loads, I could use another 5kWh/day easily).
  - zdragnar 5y ago
    I think you are way overselling the difficulty of digging a hole in the ground. Go to any grave yard- full of sealed coffins, all below the frost line. Get a plastic storage box, drill holes for cables and seal them with caulk. Put inside a treated lumber box for extra crushing resistance. Run cables through metal conduits to avoid mice and moles chewing on them. Rent a backhoe, and you are done in half an afternoon. All of that said, I dont know that I would actually go that far- you avoid the battery freezing, but then you get to worry about it cooking. For an off-grid cabin that isn't constantly heated in winter, it isn't the worst idea.
    - deleted 5y ago
      [deleted]
  - 35mm 5y ago
    Agreed. It depends what you’re optimising for: $ per kWp or sq M per kWp. Most people off grid have plenty of space but care about efficiency in terms of cost.
  - rebuilder 5y ago
    I dug a hole in the ground to act as a makeshift cellar. About 1 meter cubed, dug it with a shovel, poured gravel as a floor with a French drain sunk in it, lined the walls with breezeblock, made a lid of plywood and foam insulation board. Erected a kind of tent on top to keep the rain out. No issues so far, two years in. It’s not terribly cool in the hottest days of summer and does require a small heater if I want to keep it above freezing through winter, but in terms of being difficult or expensive to build, not at all.
  - Scoundreller 5y ago
    > actually, inverter limited - if I added some 48VDC loads I know it’s only lighting as a load, but I’ve heard standard LED light bulbs will happily run as low as 36VDC, as they chop the voltage down to that level anyway. It makes me wonder how many “120VAC” devices with switch mode power supplies could be plugged into 48VDC without any thought at all. And not just electronics like a laptop or non-plasma flatscreen, but everything is moving in this direction: Like… what’s my Variable Frequency Drive “inverter” refrigerator motor voltage really running at? In theory it should happily run off 120VDC at least. Don’t do that, but somewhere under 110VDC should work fine. And it’s inherently soft start and easier on one’s low voltage wiring than an on/off duty cycle fridge. Of course I recommend none of this officially.
- jacquesm 5y ago
  What I did in Canada was to dig a bunker into the side of a hill near the house. That solved both the frost and any fluid issues in one go. It was a bit of work though to get that all done.
Syonyk 5y ago
> Still not sure how I’ll ultimately get around this. If it's portable, your option works well. For year round off grid use, there's something to be said for sealed lead acid, or flooded lead acid - they don't care about being cycled while cold (capacity is down and the voltage sags a good bit), and as long as they don't get too deeply discharged, they don't freeze. A single panel, facing south, absolutely vertical, will shed snow and if you have no other loads, is usually enough to offset controller loads and self discharge over time to keep the batteries fully charged (and therefore not freezing) over winter. There's no way you'll generate enough heat on electricity to keep a battery bank (or cabin) warm in the winter most places. I've got 5kW of panel on my office, and still can't manage that for a small, well insulated shed.
- chana_masala 5y ago
  Thanks for your post. I'm reading through some of your blog posts now - really great!
- devwastaken 5y ago
  Hypothetically, for the lithium batteries, what if you made a big stainless steel vacuum wall insulated enclosure? Or just a metal box with r-60 value of foam around it? The amount of heat needing to be generated can then be calculated based on the average temp over a longer period of time, and those batteries I don't imagine have to be "warm" exactly.
  - diamondlovesyou 5y ago
    What about summer? Those batteries also need to stay cool...
    - londons_explore 5y ago
      A $2 circulation pump and an outdoor radiator... It's good practice to snake a water pipe around every lithium cell anyway in big packs, because otherwise one bad cell can self-heat to the point of catching fire, even while other nearby cells are cold. The flowing water means the bad cell can't get to the point of fire.
csours 5y ago
#2 reminds me of this: http://www.todayifoundout.com/index.php/2016/04/cold-war-nuclear-chickens-defend-west-soviet-invasion/ http://www.todayifoundout.com/index.php/2016/04/cold-war-nuc...
poleguy 5y ago
Have you considered Lithium Titanate batteries? They can discharge at a temperature of -40C.
- Syonyk 5y ago
  Have you priced LTO? They're rather staggeringly expensive for their capacity. The cycle life is excellent, but they excel in very high C-rate applications (10C-20C), which is the opposite of what you need for off-grid systems. If an off grid system is getting anywhere near C/10 discharge rates, you're going to be in the dark awfully soon. It's old tech, it's boring, but it works fine... flooded lead acid. Don't fully discharge it in the winter, and they won't freeze. They'll cycle just fine in the cold. Well tested, proven, and unless you're full time living and heating an interior space that can be lithium-friendly, they're the right option. Disconnect all the loads and run them on float in the winter with a high, vertical, south facing panel (obviously swap that if you're in the southern hemisphere), and they'll do just fine.
  - madaxe_again 5y ago
    Yeah, lead wins hands down. This is a few years out of date now, but when speccing out my system I did a bit of analysis of battery types. We went with OPzS, and so far, so good. https://docs.google.com/spreadsheets/d/1w8vPBHkMyY5jvkxtK1QhUEg1VAhMDzOWHjJDCCN22Pg/edit https://docs.google.com/spreadsheets/d/1w8vPBHkMyY5jvkxtK1Qh...
    - jacquesm 5y ago
      Recycled Lithium Ion is much cheaper still, but more risky (and less maintenance). You'll have to do some pretty fanatic inbound QA to determine whether all your cells are safe to use. but if you do that and fuse your cells individually you should be able to make that work.
      - vincnetas 5y ago
        but still main problem is subzero temperatures. recycled lipo batteries do not become immune to this problem.
jandrese 5y ago
Could you insulate the batteries to reduce the heating demand? Instead of heating the entire cabin just heat the battery compartment, and only to the minimum necessary to keep them from being damaged (plus a margin for safety). Maybe even just toss them in an old discarded deep freeze? You could even have one battery in there that is disconnected from the rest of the system so it can be used to jump start the system if it ever gets fully discharged.
- Syonyk 5y ago
  You can insulate them to reduce heating demand, and it will help to an extent (undo that before summer to avoid cooking them), but for an unattended system, it's never going to work out very well. If the system is a year round cabin, the solution is easy enough - keep them in the heated space (which you'll have propane/kerosene/biomass heaters for), and it's not a real problem. But unattended stuff... you really just need to plan for something that can tolerate bitter cold without damage. Or to seriously overpanel the system, 10x+ what you need for summer use, and hope they produce something. I think most people underestimate just how much delta in production there can be on solar. My house array is grid tied, 16kW, a bit weird looking (mostly east-west panels, designed for post net metering). On a really good, cool, clear, windy spring day, I can produce about 105kWh out of the system from sunup to sundown. On a really bad, low, grey, winter day, that same system produces about 2kWh. It's literally a factor of 50 difference. And we can get several days of that in a row. I have a backup generator that I use for my office on weeks like that (separate, off-grid system). "Winter, electric heat on solar" is a fairly good filter for those who have read about solar or pondered it, and those who have a few years of it under their belt. The second group are the ones who've tried it, discovered just how horribly it doesn't work, and are trying to convince the first group that, no, really, insert well worn idea here really doesn't fix the problems with it. I guarantee if it were easy, people would be doing it. That you won't find any serious off grid system doing electric battery heating is because it doesn't work.
  - mcot2 5y ago
    Adding on to this the energy usage of my multi-head heat pump system has been quite surprising when it drops below freezing. I have a Mitsubishi unit which is rated down to something like -15F however below 32F it uses enough energy to get pretty close with fossil fuels on price. It looks like I will have to add on to my 11.85kW solar system to be able to get the projected energy use throughout the year. Winter time will have a significant deficit and summer overproduction will make some of it back but not all. I am also investing in air sealing and additional insulation.
stephen_g 5y ago
Yeah, some people had problems with all-in-one battery systems in their homes that were AC coupled to their solar here in Australia over some weather disasters where there were prolonged outages for that reason. I’d quite like a battery system, I think I’d DIY (well, design the system but here you need a licensed electrician to wire up the AC/grid connect side) using Victron equipment. I have a 5 kW solar system already with a AC inverter which I can keep, so I would probably use a 5000KVA inverter-charger (Multiplus-II), but then I’d add another 1.5kW or so of solar that is directly DC coupled to the batteries and the DC side of the inverter-charger through a separate DC MPPT tracker. So the DC coupled solar would be enough to kick-start the system to get the AC side back on after a bit if the grid was out and the batteries were depleted overnight.
- jacquesm 5y ago
  Victron is top of the line stuff and will serve you well. On marine installations it's not rare at all to see their inverters outlast the hull.
deleted 5y ago
[deleted]
driverdan 5y ago
LiFePO4 batteries can be stored and used below freezing, they just shouldn't be charged. All you have to do is turn the system off when you're not there.
- Retric 5y ago
  In most areas keeping them underground can get around this, you can also use a backup heater and temperature probe before charging them.
irae 5y ago
You can dig a 2 meter deep hole and store the batteries there. It won't freeze during the winder if left turned off. If you plan to turn it on on the holes, you might need to plan for heat dissipation though.
sandworm101 5y ago
>> 1) These Controller+Inverter combo units require a battery to turn on Which is why you want to install disconnects between your battery bank and the electronics. In a worst-case scenario of total discharge you can then bypass the dead batteries, hook the control electronics up to car batteries if necessary (be careful about voltages) and perform some diagnostics or at least read the logs of what went wrong. But the controller+inverter should be running if supplied with voltage from solar/wind/generator regardless of how the batteries are doing.
- Syonyk 5y ago
  > But the controller+inverter should be running if supplied with voltage from solar/wind/generator regardless of how the batteries are doing. Most of them don't operate that way. They need the battery bank connected first, and run off the battery bank side, while controlling the panel side. Some may tolerate that sort of recovery from deep discharge, but it's not a safe bet, and some controllers are pretty clear that if you connect the input side before the batteries, you'll damage the controller. A dumb PWM controller stands a better chance of doing this, but something like an MPPT controller, unless it's explicitly designed to fail into a PWM configuration at low battery voltage, won't - they need power to drive the buck converter circuitry (the controlling ICs and oscillators and such) in order to get power out of the panels.
jmnicolas 5y ago
Have you considered a small backup generator? If it exists I would go with one that is propane powered. Propane goes to -50° before freezing so unless you live in Alaska, you have quite some margin here.
naikrovek 5y ago
> Temperatures below freezing are bad for batteries. bad for lithium batteries. even then, it is only bad if you charge or discharge them in freezing temps. lead-acid handle cold just fine.
willprowseiv 5y ago
You need to manually set the low voltage disconnect so that your batteries bms does not go into safety mode. then you won't have the first problem you stated. What you need is more insulation. I've tested that battery and the internal heaters work great, but you should put it somewhere where the heat that is created stays in the battery.

by zoba 5y ago

redtexture 5y ago

Insulated Root celler equivalent location for the battery.

jf 5y ago

Could you dig a hole for your batteries and store them below the frost line?

Syonyk 5y ago
The problem with holes in the ground for storage of things like batteries is that... they're holes in the ground. The ground, as a general guideline, actively dislikes holes in it and strives to fill them in whatever way possible. Liquid rolling in, soil creep, debris blowing past and building up, it doesn't matter - given a long enough time, a hole in the ground won't exist anymore. You can build a hole that will hold up to this sort of stuff for a while, but that tends to be expensive - underground concrete work is neither cheap nor easy, and given the number of people injured in trench collapses who do it for a living, a serious underground hole isn't a good DIY project either. That just leaves the maintenance, which also sucks for a hole in the ground. Anything you have to do on the batteries is easier with them on or above the ground, instead of underground in a hole. For lithium, it's fairly low maintenance but you may have to replace some BMS boards every now and then, manually check balance, etc, and for lead it's water every few months, unless you go with sealed, which are "maintenance free," but also "maintenance and status check impossible," so you really just set them and run them to failure - you can't monitor condition like you can with flooded. It's the sort of solution that, technically, would work - it just ends up being radically more expensive and a hassle than it's remotely worth. Think "Spending $5000 to save $20/yr" sort of thing. You see the same trend with things like the complex solar trackers that were common in the 80s and early 90s. With the cost of panels, optimizing every bit of power from them was critical, so spending an awful lot of money on support infrastructure to optimize $10/W panel production made quite a bit of practical and financial sense. Today, with panels at $0.50/W, very few people bother with trackers anymore (for off grid installs). Most things you could improve with a tracker, you can improve with less effort and less money by just hanging more panels. Bonus: With more panels, you get more production on cloudy days when panel orientation doesn't matter (because the sky is more or less evenly lit). I've got south facing, east facing, and west facing panels on my office, of two different brands, all fed into a single MPPT charge controller input (I do have some blocking diodes to prevent backfeeding a shaded string, though). It's not nearly as "efficient" as some other options, but it's a whole lot cheaper, and gives me more power on the low cloud days that are the rough ones. The rest of the year, I have so much power out there that I'm demand limited, not supply limited (actually, inverter limited - if I added some 48VDC loads, I could use another 5kWh/day easily).
- zdragnar 5y ago
  I think you are way overselling the difficulty of digging a hole in the ground. Go to any grave yard- full of sealed coffins, all below the frost line. Get a plastic storage box, drill holes for cables and seal them with caulk. Put inside a treated lumber box for extra crushing resistance. Run cables through metal conduits to avoid mice and moles chewing on them. Rent a backhoe, and you are done in half an afternoon. All of that said, I dont know that I would actually go that far- you avoid the battery freezing, but then you get to worry about it cooking. For an off-grid cabin that isn't constantly heated in winter, it isn't the worst idea.
  - deleted 5y ago
    [deleted]
- 35mm 5y ago
  Agreed. It depends what you’re optimising for: $ per kWp or sq M per kWp. Most people off grid have plenty of space but care about efficiency in terms of cost.
- rebuilder 5y ago
  I dug a hole in the ground to act as a makeshift cellar. About 1 meter cubed, dug it with a shovel, poured gravel as a floor with a French drain sunk in it, lined the walls with breezeblock, made a lid of plywood and foam insulation board. Erected a kind of tent on top to keep the rain out. No issues so far, two years in. It’s not terribly cool in the hottest days of summer and does require a small heater if I want to keep it above freezing through winter, but in terms of being difficult or expensive to build, not at all.
- Scoundreller 5y ago
  > actually, inverter limited - if I added some 48VDC loads I know it’s only lighting as a load, but I’ve heard standard LED light bulbs will happily run as low as 36VDC, as they chop the voltage down to that level anyway. It makes me wonder how many “120VAC” devices with switch mode power supplies could be plugged into 48VDC without any thought at all. And not just electronics like a laptop or non-plasma flatscreen, but everything is moving in this direction: Like… what’s my Variable Frequency Drive “inverter” refrigerator motor voltage really running at? In theory it should happily run off 120VDC at least. Don’t do that, but somewhere under 110VDC should work fine. And it’s inherently soft start and easier on one’s low voltage wiring than an on/off duty cycle fridge. Of course I recommend none of this officially.
jacquesm 5y ago
What I did in Canada was to dig a bunker into the side of a hill near the house. That solved both the frost and any fluid issues in one go. It was a bit of work though to get that all done.

Syonyk 5y ago

> Still not sure how I’ll ultimately get around this. If it's portable, your option works well. For year round off grid use, there's something to be said for sealed lead acid, or flooded lead acid - they don't care about being cycled while cold (capacity is down and the voltage sags a good bit), and as long as they don't get too deeply discharged, they don't freeze. A single panel, facing south, absolutely vertical, will shed snow and if you have no other loads, is usually enough to offset controller loads and self discharge over time to keep the batteries fully charged (and therefore not freezing) over winter. There's no way you'll generate enough heat on electricity to keep a battery bank (or cabin) warm in the winter most places. I've got 5kW of panel on my office, and still can't manage that for a small, well insulated shed.

chana_masala 5y ago
Thanks for your post. I'm reading through some of your blog posts now - really great!
devwastaken 5y ago
Hypothetically, for the lithium batteries, what if you made a big stainless steel vacuum wall insulated enclosure? Or just a metal box with r-60 value of foam around it? The amount of heat needing to be generated can then be calculated based on the average temp over a longer period of time, and those batteries I don't imagine have to be "warm" exactly.
- diamondlovesyou 5y ago
  What about summer? Those batteries also need to stay cool...
  - londons_explore 5y ago
    A $2 circulation pump and an outdoor radiator... It's good practice to snake a water pipe around every lithium cell anyway in big packs, because otherwise one bad cell can self-heat to the point of catching fire, even while other nearby cells are cold. The flowing water means the bad cell can't get to the point of fire.

csours 5y ago

#2 reminds me of this: http://www.todayifoundout.com/index.php/2016/04/cold-war-nuclear-chickens-defend-west-soviet-invasion/ http://www.todayifoundout.com/index.php/2016/04/cold-war-nuc...

poleguy 5y ago

Have you considered Lithium Titanate batteries? They can discharge at a temperature of -40C.

Syonyk 5y ago
Have you priced LTO? They're rather staggeringly expensive for their capacity. The cycle life is excellent, but they excel in very high C-rate applications (10C-20C), which is the opposite of what you need for off-grid systems. If an off grid system is getting anywhere near C/10 discharge rates, you're going to be in the dark awfully soon. It's old tech, it's boring, but it works fine... flooded lead acid. Don't fully discharge it in the winter, and they won't freeze. They'll cycle just fine in the cold. Well tested, proven, and unless you're full time living and heating an interior space that can be lithium-friendly, they're the right option. Disconnect all the loads and run them on float in the winter with a high, vertical, south facing panel (obviously swap that if you're in the southern hemisphere), and they'll do just fine.
- madaxe_again 5y ago
  Yeah, lead wins hands down. This is a few years out of date now, but when speccing out my system I did a bit of analysis of battery types. We went with OPzS, and so far, so good. https://docs.google.com/spreadsheets/d/1w8vPBHkMyY5jvkxtK1QhUEg1VAhMDzOWHjJDCCN22Pg/edit https://docs.google.com/spreadsheets/d/1w8vPBHkMyY5jvkxtK1Qh...
  - jacquesm 5y ago
    Recycled Lithium Ion is much cheaper still, but more risky (and less maintenance). You'll have to do some pretty fanatic inbound QA to determine whether all your cells are safe to use. but if you do that and fuse your cells individually you should be able to make that work.
    - vincnetas 5y ago
      but still main problem is subzero temperatures. recycled lipo batteries do not become immune to this problem.

jandrese 5y ago

Could you insulate the batteries to reduce the heating demand? Instead of heating the entire cabin just heat the battery compartment, and only to the minimum necessary to keep them from being damaged (plus a margin for safety). Maybe even just toss them in an old discarded deep freeze? You could even have one battery in there that is disconnected from the rest of the system so it can be used to jump start the system if it ever gets fully discharged.

Syonyk 5y ago
You can insulate them to reduce heating demand, and it will help to an extent (undo that before summer to avoid cooking them), but for an unattended system, it's never going to work out very well. If the system is a year round cabin, the solution is easy enough - keep them in the heated space (which you'll have propane/kerosene/biomass heaters for), and it's not a real problem. But unattended stuff... you really just need to plan for something that can tolerate bitter cold without damage. Or to seriously overpanel the system, 10x+ what you need for summer use, and hope they produce something. I think most people underestimate just how much delta in production there can be on solar. My house array is grid tied, 16kW, a bit weird looking (mostly east-west panels, designed for post net metering). On a really good, cool, clear, windy spring day, I can produce about 105kWh out of the system from sunup to sundown. On a really bad, low, grey, winter day, that same system produces about 2kWh. It's literally a factor of 50 difference. And we can get several days of that in a row. I have a backup generator that I use for my office on weeks like that (separate, off-grid system). "Winter, electric heat on solar" is a fairly good filter for those who have read about solar or pondered it, and those who have a few years of it under their belt. The second group are the ones who've tried it, discovered just how horribly it doesn't work, and are trying to convince the first group that, no, really, insert well worn idea here really doesn't fix the problems with it. I guarantee if it were easy, people would be doing it. That you won't find any serious off grid system doing electric battery heating is because it doesn't work.
- mcot2 5y ago
  Adding on to this the energy usage of my multi-head heat pump system has been quite surprising when it drops below freezing. I have a Mitsubishi unit which is rated down to something like -15F however below 32F it uses enough energy to get pretty close with fossil fuels on price. It looks like I will have to add on to my 11.85kW solar system to be able to get the projected energy use throughout the year. Winter time will have a significant deficit and summer overproduction will make some of it back but not all. I am also investing in air sealing and additional insulation.

stephen_g 5y ago

Yeah, some people had problems with all-in-one battery systems in their homes that were AC coupled to their solar here in Australia over some weather disasters where there were prolonged outages for that reason. I’d quite like a battery system, I think I’d DIY (well, design the system but here you need a licensed electrician to wire up the AC/grid connect side) using Victron equipment. I have a 5 kW solar system already with a AC inverter which I can keep, so I would probably use a 5000KVA inverter-charger (Multiplus-II), but then I’d add another 1.5kW or so of solar that is directly DC coupled to the batteries and the DC side of the inverter-charger through a separate DC MPPT tracker. So the DC coupled solar would be enough to kick-start the system to get the AC side back on after a bit if the grid was out and the batteries were depleted overnight.

jacquesm 5y ago
Victron is top of the line stuff and will serve you well. On marine installations it's not rare at all to see their inverters outlast the hull.

deleted 5y ago

[deleted]

driverdan 5y ago

LiFePO4 batteries can be stored and used below freezing, they just shouldn't be charged. All you have to do is turn the system off when you're not there.

Retric 5y ago
In most areas keeping them underground can get around this, you can also use a backup heater and temperature probe before charging them.

irae 5y ago

You can dig a 2 meter deep hole and store the batteries there. It won't freeze during the winder if left turned off. If you plan to turn it on on the holes, you might need to plan for heat dissipation though.

sandworm101 5y ago

>> 1) These Controller+Inverter combo units require a battery to turn on Which is why you want to install disconnects between your battery bank and the electronics. In a worst-case scenario of total discharge you can then bypass the dead batteries, hook the control electronics up to car batteries if necessary (be careful about voltages) and perform some diagnostics or at least read the logs of what went wrong. But the controller+inverter should be running if supplied with voltage from solar/wind/generator regardless of how the batteries are doing.

Syonyk 5y ago
> But the controller+inverter should be running if supplied with voltage from solar/wind/generator regardless of how the batteries are doing. Most of them don't operate that way. They need the battery bank connected first, and run off the battery bank side, while controlling the panel side. Some may tolerate that sort of recovery from deep discharge, but it's not a safe bet, and some controllers are pretty clear that if you connect the input side before the batteries, you'll damage the controller. A dumb PWM controller stands a better chance of doing this, but something like an MPPT controller, unless it's explicitly designed to fail into a PWM configuration at low battery voltage, won't - they need power to drive the buck converter circuitry (the controlling ICs and oscillators and such) in order to get power out of the panels.

jmnicolas 5y ago

Have you considered a small backup generator? If it exists I would go with one that is propane powered. Propane goes to -50° before freezing so unless you live in Alaska, you have quite some margin here.

naikrovek 5y ago

> Temperatures below freezing are bad for batteries. bad for lithium batteries. even then, it is only bad if you charge or discharge them in freezing temps. lead-acid handle cold just fine.

willprowseiv 5y ago

You need to manually set the low voltage disconnect so that your batteries bms does not go into safety mode. then you won't have the first problem you stated. What you need is more insulation. I've tested that battery and the internal heaters work great, but you should put it somewhere where the heat that is created stays in the battery.