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The SI unit of irradiance is watts per square metre (W/m 2 = Wm −2). The unit of insolation often used in the solar power industry is kilowatt hours per square metre (kWh/m 2). [11] The langley is an alternative unit of insolation. One langley is one thermochemical calorie per square centimetre or 41,840 J/m 2. [12]
The angular diameter of the Earth as seen from the Sun is approximately 1/11,700 radians (about 18 arcseconds), meaning the solid angle of the Earth as seen from the Sun is approximately 1/175,000,000 of a steradian. Thus the Sun emits about 2.2 billion times the amount of radiation that is caught by Earth, in other words about 3.846×10 26 watts.
The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,368 W/m 2 (watts per square meter) at a distance of one astronomical unit (AU) from the Sun (that is, at or near Earth's orbit). [99]
Multiplying the figure of 1,050 watts per square meter by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98,000 lux (lumens per square meter) on a perpendicular surface at sea level. The illumination of a horizontal surface will be considerably less than this if the Sun is not very high in the sky.
Positive EEI thus defines the overall rate of planetary heating and is typically expressed as watts per square meter (W/m 2). During 2005 to 2019 the Earth's energy imbalance averaged about 460 TW or globally 0.90 ± 0.15 W per m 2 .
astro: power per square meter potentially received by Earth at the peak of the Sun's red giant phase 2.0 × 10 6 W tech: peak power output of GE's standard wind turbine 2.4 × 10 6 W tech: peak power output of a Princess Coronation class steam locomotive (approx 3.3K EDHP on test) (1937) 2.5 × 10 6 W biomed: peak power output of a blue whale ...
The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 122 PW·year = 3,850,000 exajoules (EJ) per year. [12] In 2002 (2019), this was more energy in one hour (one hour and 25 minutes) than the world used in one year. [13] [14] Photosynthesis captures approximately 3,000 EJ per year in biomass. [15]
Pd (Watts/meter 2) = E × H (Volts/meter × Amperes/meter)where Pd = the power density, E = the RMS electric field strength in volts per meter, H = the RMS magnetic field strength in amperes per meter. [6] The above equation yields units of W/m 2. In the USA the units of mW/cm 2, are more often used when making surveys.