The problem with solar which you are already experiencing, is the amount of usable sun-light already.
You are likely down to 6 hours solar charging, and 18 hours of coping. Then the BIG IF comes in. Do you have a cloudy day, or cold clear day with sun?
Here in Minnesota we have had mostly cloudy days since middle of October, and colder than normal weather. The skies have cleared the last five days but temperatures have been staying below 32F (day and night).
I think you are already seeing what I was worrying about when we all were discussing, during the summer, the coming experiment for this winter season.
Mark B.