Published on 10/18/2006

The term solar power is used to describe a number of methods of harnessing energy from the light of the Sun. It has been used in many traditional technologies for centuries and has come into widespread use where other power supplies are absent, such as in remote locations and in space.

solar energy

Energy from the Sun
Theoretical annual mean insolation, at the top of Earth’s atmosphere

and at the surface on a horizontal square meter .
Global solar energy resources. The colors in the map show the actual

local solar energy, averaged through the years of 1991-1993. The

scale is in watts per square meter.
The land area required to supply the current global primary energy

demand by solar energy using available technology is represented by

the dark disks.The rate at which solar radiation reaches a unit of area

in space in the region of the Earth’s orbit is 1,366 W/m , as measured

upon a surface normal (at a right angle) to the Sun. This number is

referred to as the<a href=http://www.energyhandbook.com> solar constant</a>.[1] The atmosphere reflects 6% and

absorbs 16% of incoming radiation resulting in a peak power at sea

level of 1,020 W/m . [2] [3] Average cloud cover reduces incoming

radiation by 20% through reflection and 16% through absorption.[4]

The image on the right shows the average solar power available on the

surface in W/m calculated from satellite cloud data averaged over

three years from 1991 to 1993 (24 hours a day). For example, in

North America the average power of the solar radiation lies

somewhere between 125 and 375 W/m , between 3 and 9 kWh/m

/day.