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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 n

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.
- rklaehn 5y ago
  I agree that the difference between winter and summer is very large, like night and day. But, 2kWh or even less should be plenty to keep a well insulated battery compartment from freezing. On very cold and clear winter days you are going to get more than that, and on cloudy days it is usually not that cold.
rklaehn 5y ago
An old deep freeze is probably not sufficient, but packing them into a thick layer of insulation should be fine for the winter. The insulation would have to completely enclose them though, including the bottom. Maybe best to have them sit on a thick layer of insulation on the bottom, and a box that can be removed during the summer months so the batteries don't overheat. Another a bit weird idea would be to somehow put them next to a compost heap, which produces low temperature heat for a long time (years) including during the winter.

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.
rklaehn 5y ago
I agree that the difference between winter and summer is very large, like night and day. But, 2kWh or even less should be plenty to keep a well insulated battery compartment from freezing. On very cold and clear winter days you are going to get more than that, and on cloudy days it is usually not that cold.

rklaehn 5y ago

An old deep freeze is probably not sufficient, but packing them into a thick layer of insulation should be fine for the winter. The insulation would have to completely enclose them though, including the bottom. Maybe best to have them sit on a thick layer of insulation on the bottom, and a box that can be removed during the summer months so the batteries don't overheat. Another a bit weird idea would be to somehow put them next to a compost heap, which produces low temperature heat for a long time (years) including during the winter.