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If you track your usage and solar production, you will probably find it is . . . just winter.
A friend of mine got solar about same time as us, Nov / Dec last year, and he was just away for nearly 3 months overseas, returning to find his 6kw system is not even keeping up with his very low usage in his home with 2 people.
You may be using more power for certain things in the home in winter, but solar production is pretty much about 10% as beneficial in winter as it is in peak summer.
I intend to change a few things to improve production / reduce power use in the home, and then reconsider if mid to longer term I will get a battery to carry us through.