I have about 4 KW of solar… I have thought about making an air storage system using a compressor to a large tank… I have more energy than my batteries can hold so have been using it to heat water, but compressed air not as efficent as a battery, the tanks do last far longer than batteries.
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I still have main problem with solar offgrid - missmatch between need and production. I know it’s specific to latitude. Anywhere between tropics I consider solar as feasible solution. North of 50’ I have serious doubts of fully off-grid based on solar.
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I totally agree. You would need to adjust your mix to match the reality on the ground. Heat recovery tech or biomass heating etc.
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I agree 100% with you KamilK.
The now many reported results here in North American now say an effective PV solar as a true homestead 80%+ of the year around: the line is probably more at 40 degrees latitude.
Of course many; too many here, install for bragging rights; or a political statement; and/or highly subsidized financial incentives.
The moods here are now swing to eliminate the all-must-pay-for; forced Subsidies Incentives.
Home PV solar has matured enough now to no longer where it is actually needs Incentives.
Not just my opinion now. The majority opinion.
Steve Unruh
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One way to handle lower solar output in the winter is minimize power usage/needs during that period. A “combined heat and power” system using a gasifier generator fills in gaps for electricity and provides sorely needed heat during cold winters.
Most places get colder (vs desired room temperatures) than they get hotter. This is especially true in Northern latitudes. This is a tricky part for heat pumps in heating mode, especially air source heat pumps. Their efficiency drops with temperature and the coldest days are going to be short ones for solar*. Some areas are also cloudy during those periods as well. Basically, you need a backup system and it might as well use that “waste” heat to good purpose.
Ground loop heat pumps present an interesting option. You might push heat into the field in the late summer, early fall with passively heated water or pump more heat in with excess power. This hot field would be harvested in the winter when efficiency is critical. basically, just aim for the field to run hotter than it would be naturally… 75F vs the 60F that would be typical of ground loop soil temps in Northern areas. That would better balance summer and winter loads vs power produced.
If you’ve got the $$$, two fields makes this concept very easy- one hot field and one cold field, have at it… but fields are expensive and never quite big enough. The two-field idea is more an ambition of resources than cleverness.
*I know there are some air source heat pumps intended for cold climates that maintain efficiency to low temperatures. They are more expensive and relatively new. Ground source is always going to have advantages where the loops are possible.
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I don’t even know if that is true, if you get condensation in the tank, they do eventually rust out. The compressor will wear out before the tank.
The LiFe batteries last what 20-30 years. Sodium batteries are starting to creep onto the market and handle low temperatures better and in theory will end up cheaper.
there was a big push in Australia for distributed battery storage. however 4kw of solar is only like 10 panels nowadays.
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Ground source heat pumps use a lot of electric to run the compressor, pump and then the blower fan. The one at my parents has a 50a breaker on it for the motor startups. It is the larger issue of backup power. You can’t just plug in a 5kw genset and get the heat working.
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I understand your enthusiasm, Anthony. But these backups and redundancies make overall system more complex, expensive and vulnerable.
I always think about off-grid as of system with least possible need for the commodity provided by the grid. Going off-grid in electricity means for me to make your house habitable almost without electricity at all or at least capable to run on interuptible source which is provided by most affordable and simple system.
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@Sean, startup power is indeed an issue. If you have a solar array and battery then you’d start the heat pump on the inverter and use the genset to top up batteries. A 4-ton ground source heat pump uses 4-6kwatts to start but “only” 1.5-2kwatts running. Pumps and fans add to that.
A kilowatt hour of resistive heat is only 3400 BTU, so 2kw is 6800… Meanwhile a 4 ton heat pump is 48000 in BTUs… Heat pumps are pretty amazing if you have the watts. Theoretically a heat pump could be turned by an engine directly, though no residential units support that to my knowledge. A car AC or truck chiller unit would take a driven pulley. You’d need to adapt for heating. Some folks on Ecorenovator have done that on regular ACs.
@Kamil, I hear you. I grew up with a wood stove for heat. The setup I put forward has complexity and cost. You will still need backup, I agree. But when the system is working, it is an “on-grid” lifestyle and that has appeal.
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Even without solar, you still need either a really large generator, or inverters and batteries and a smaller generator. It is different then say running a propane furnace where you just need electric to run the fan and a few of the safety features.
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How much could you do vs how much do you need to do…
I live in my box, knowing and understanding what I need, what i can… Everybody’s box might be different in needs and capability’s…
However, in my dreams, I live and do things outside my little box…
I still dream of that white V10 Wayne showed me in 2018…( pictures)
Do I need it in my box ? Or do I want it …
Good thing is, seeing other’s idea’s and study … ( How the *** did they pulled that off )
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I like to think in two different modes of thought for being off grid.
One, what is the most stable thing we can get in today’s world? For me that is a mini split for heating / cooling, proven reliable…
Two, how would I keep cool in the 1800’s? or in another way of looking at it how would I keep cool if I had to go camping? that might involve a battery and a fan and jumping in a swimming hole to keep cool.
So, the mini split for today, when the power goes out the swimming hole.
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Everyone’s resources and goals are different. There is no one “best way”, and it is great to have a forum like this to share our individual strategies, successes and setbacks.
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Mart,
You would go out to a frozen pond, in coldest mid-Winter, with a horse and sleigh, and saws, and helpers. You would cut ice blocks from the pond or still water area. Then you would take them back to a sturdy building and stack the blocks surrounding them with the sawdust you made from working wood for building and heating. Then, you would hope you did a proper job, and there was still ice left in the heat of Summer. Go sit in the icehouse and drink cold drinks while remembering the hard work and planning done last Winter. 
If you live in a warm climate, swim in the pond. I suppose a Swamp Cooler would work in a warm / dry climate. 
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I visited a man who had a water powered saw mill up in Michigan, he used that mill to cut the blocks of ice for just that reason…
Today another friend of mine fills up buckets of water and lets them freeze and put them in an Amish made igloo.
Swamp coolers do work in humid Florida, but not inside the home, they are used in mini green houses where the air is pushed right on outside, but the incoming air is cooler than what is in the greenhouse and the tomatoes love the humidity.
In doing my sand battery tests, I have wondered if it is easier to store heat, or is it easier to store cold…
I was watching a guy in Michigan build a dome home, for temp support for the roof he filled the structure with packed snow from off his lake… He had to bring in a fan to melt the snow in the summer as it was storing the cold way longer than he thought…
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