I'm at 47°N and anecdotally, I did ~30-40 minutes walks in the midday sun this summer, with either face/hands/arms or additionally also legs exposed. At the end of summer I measured at 26mcg/l, which is barely above the "deficient" threshold of 20mcg/l and still well below the often recommended target of 50mcg/l. So I doubt that "face and hands alone" will give you "sufficient vitamin D for the whole year". Note that I was also taking 2000 IU per day in winter/spring, which I stopped taking in summer. Now after the bloodtest I've resumed the supplement for fall and upped it to 4000 IU + added Vitamin K2.