The maps show
the geographical distribution of the solar radiation
incident on the earth's surface each year. Depending
on the shape of the sun's apparent path (solar ecliptic),
the amount of radiation decreases towards the polar
regions. The maximum values occur slightly south
or north of the equator; their location is also
determined by the incidence and type of cloud cover.
On the land area worldwide, this results in a solar
radiation of at least 200,000,000 TWh per year.
(For comparison: 9 billion people, each requiring
2,000 watts, would have a total annual energy demand
of 160,000 TWh).
http://www.energie-atlas.ch/so-100.htm
