Hi DW493,
Great question!
The colder months of each year can be unfavourable to households with solar systems unfortunately. Not only will solar output diminish due to the changes in weather conditions (increased cloud coverage etc), but residential households also generally consume more power during the colder months due to the use of heating appliances etc. For this reason, bills do quite often jump up around this time of year.
If you've since seen your solar system return to the level of productivity observed at the start of this year, then it sounds like you're on your way to a lower bill next quarter!
Cheers,
Jayden