About solar energy

The world generated 2TW of electrical power on average in 2005 [1].  Each (unobstructed, clear) square meter of the earth’s surface is illuminated by around 1.4 kW of solar energy [2].  Replacing the world’s electrical generation with solar sources would then require at least 2TW / (1.4 kW/m^2) = 1.4 billion sq. m = 1400 sq. km (equivalent to a square 37km on a side) worth of ideally efficient solar panels with unobstructed solar light.

With realistic panel efficiency and atmospheric effects like clouds are taken into effect, this can still suggest a rough order of magnitude estimate.  A 50% efficient solar panel in a desert would need to be about the size of Rhode Island to supply enough power for the entire 2005 world.

As always, if my data or my calculations contain errors, please bring them to my attention

[1] http://www.eia.doe.gov/emeu/international/electricitygeneration.html
[2] http://hypertextbook.com/facts/1998/ManicaPiputbundit.shtml