The earth receives more energy from the Sun in just one hour than the world’s population uses in a whole year. The total solar energy flux intercepted by the earth on any particular day is 4.2 X 1018 Watthours or 1.5 X 1022 Joules (or 6.26 X 1020 Joules per hour ). This is equivalent to burning 360 billion tons of oil ( toe ) per day or 15 Billion toe per hour. In fact the world’s total energy consumption of all forms in the year 2000 was only 4.24 X 1020 Joules. In year 2005 it was 10,537 Mtoe (Source BP Statistical Review of World Energy 2006)
Sunlight comes in many colours, combining low-energy infrared photons (1.1 eV) with high-energy ultraviolet photons (3.5 eV) and all the visible-light photons between.
The graph below shows the spectrum of the solar energy impinging on a plane, directly facing the sun, outside the Earth’s atmosphere at the Earth’s mean distance from the Sun. The area under the curve represents the total energy in the spectrum. Known as the “Solar Constant” G0, it is equal to 1367 Watts per square metre (W/m2).
The radiant energy falling within the visible spectrum is about 43% of the total with about 52% in the infra red region and 5% in the ultra violet region.
The graph below shows the energy at sea level.
Direct energy is the energy received directly from the sun.
Global energy includes energy diffused, scattered or reflected from clouds and energy re-radiated by the earth itself.
