If God had wanted us to have nearly unlimited clean energy, He would have placed a fusion reactor into the sky.
(europe.pub)
1W of installed capacity would yield 24Wh of energy at 100% in 1 day at capacity. (1W * 24h = 24h)
Hence, you are getting an average of 6Wh / 24Wh * 100% = 25% capacity. Your winter numbers end up being 4-12% and summer 25-50% of capacity.
Wh/Wi/h is your capacity factor.