The two images use the same color scale. Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre (W/m 2) in SI units.
The amount of solar energy per unit area arriving on a surface at a particular angle is called irradiance which is measured in watts per square metre, W/m2, or kilowatts per square metre, kW/m2 where 1000 watts equals 1. 1.4 KW solar energy is received by the earth per square kilo meter.
Solar irradiation Irradiance is the power of solar radiation per unit area. In the international system of units, it is measured in (W/m 2 ). Solar irradiation is the quantity that measures the energy per unit area of incident solar radiation on a surface - the power received during a time (J/m 2 or Wh/m 2 ).
The average annual solar radiation arriving at the top of the Earth's atmosphere is about 1361 W/m 2. This represents the power per unit area of solar irradiance across the spherical surface surrounding the Sun with a radius equal to the distance to the Earth (1 AU).
If the extraterrestrial solar radiation is 1367 watts per square meter (the value when the Earth–Sun distance is 1 astronomical unit), then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1050 W/m2, but the total amount (direct and indirect from the atmosphere) hitting the ground is around ...
This represents the power per unit area of solar irradiance across the spherical surface surrounding the Sun with a radius equal to the distance to the Earth (1 AU). This means that the approximately circular disc of the Earth, as viewed from the Sun, receives a roughly stable 1361 W/m 2 at all times.