There is no 'normal' amount of sleep.
The average amount of sleep for adults is 7 - 8 hours, but the range of nighttime sleep duration must be expanded to between 6 - 9 hours in order to include the large majority of people.
Do you find 8 hours of sleep making your effective, rested and happy during the day?

It's OK. But during the winter I feel like sleeping more. Like up to 9 or 10 hours. Is that also normal? Does it have something to do with the circadian rhythm of the seasons?

Circadian rhythm is mainly determined by our genes, but can be modulated by external factors, primarily daylight.

Do you find difficult to wake up in the morning?
Are you experiencing daytime sleepiness?

Yes, both of those. I am really groggy and sleepy in the morning and I get sleepy around 2-3 in the afternoon. Are there some dietary supplements that might help with this? Heard of ginseng, for example ...

Do you feel depressed and with lack of energy during winter? Are you craving for sweets?
Are you experiencing difficulty falling asleep?
In the afternoon, when our circadian rhythms generally are at a low point of the daily cycle, it's tougher to fight off the sleepies.
We are biologically programmed to be more sleepy and less alert in overnight hours and mid-afternoon, and those times in the 24-hour cycle are known as circadian dips.

You can try to use:Lecithin (a good source of choline that acts as a neurotransmitter and is important for brain function), Omega-3 essential fatty acids (fish oil and flaxseed oil are good sources), Vitamin B complex plus extra vitamin B6 (boost metabolism and are essential for increased energy levels and normal brain function).