The main difference between winter and summer is that the time between sunrise and sunset is shortened, and solar lights are charged the same way no matter what time of year they are.
In winter, the sun is lower in the UK sky, which has two knock-on effects. On the one hand, sunlight provides more atmosphere for the sun's rays, and on the other hand, solar panels produce more energy when they are tilted at an angle of about 45%, rather than straight up.
Avoiding shade is especially important in winter, as extensive shade that may not be a factor in summer can make checking solar panel placement an important winter task.