Yes, but they produce less
Panels produce energy whenever they receive light, winter included. The difference from summer is large: the days are shorter, the sun is lower, the sky is overcast more often, and snow can cover the surface. That is why winter output is usually only a fraction of summer output.
Cold is not the enemy of panels
Panels are more efficient at low temperatures than in great heat. The problem in winter is not the cold, but the lack of light. On a clear, cold day a panel can produce well, provided it is not covered.
Snow and tilt
At steeper tilts, snow slides off more easily. At shallow tilts or on flat roofs, it can stay for longer. Climbing onto the roof or using hard tools to clear the panels is not recommended: the risk of injury and of damage is real. If something does need to be done, it is safer to use suitable equipment or to have it done by qualified people.
How winter is taken into account in sizing
A system is sized on annual consumption and its profile, not on the weakest month. In winter, part of the consumption will still come from the grid or from other sources. If you want to understand how much is actually covered, keep track of your monthly consumption and discuss it as part of energy consulting.
For areas with harsher winters, for example in Suceava County or in the mountain towns and villages of Bacău County, we also take into account the snow load on the mounting structure.