Saturday, February 28, 2009

World Energy Council

The energy delivered by the sun is both intermittent and changes during the day and with the seasons. When this power density is averaged over the surface of the earth's sphere, it is reduced by a factor of 4. A further reduction by a factor of 2 is due to losses in passing through the earth's atmosphere. Thus, the annual average horizontal surface irradiance is approximately 170 W/m2. When 170 W/m2 is integrated over 1 year, the resulting 5.4 GJ that is incident on 1 m2 at ground level is approximately the energy that can be extracted from one barrel of oil, 200 kg of coal, or 140 m3 of natural gas.
World Energy Council
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