To be blunt, I feel you are way undersizing things if you want to confidently get through winter.
If you don't place this outside facing south, keep it clean, have tree shadows of have an alarm armed things will go from bad to worse. It will not need a regulator as it is not capable of generating enough drive to do harm or much else.
Solar is now in relative terms cheap that "over doing sizing" is IMO the sensible way. Unless all things are stacked very much in your favour don't waste your money by going sub 30 Watts. The bigger you go the more tolerant the system will be to non ideal situations, shadows, bird droppings etc etc.
Systems from 15 Watts will need regulators.
