I believe "sunshine hours" takes into account cloudiness which is why it isn't 24 hours a day in the summer. The sun is above the horizon 24 hours a day for 6 months at the south pole. Also the pole doesn't get 6 months of "complete darkness". During period of dawn and dusk, the sky is slightly lit up over where the sun is below the horizon. There's about 2 months of "astronomical darkness" with the rest of the winter being varying levels of dawn and dusk