At the distance of the earth’s orbit from the sun, an average flux of 1,358 watts of solar energy fills every square meter of space above the earth’s atmosphere. At the earth’s surface, this solar flux is reduced to about 990 watts per square meter. The total amount of power received by the earth from the sun daily works out to about 18,000 terawatts while global energy demand today is only about 9 terawatts.