S OLAR R ADIATION

R ADIATION Sun is a sphere of hot gaseous matter with a diameter of 1.39*10^9m. Due to its temperature, sun emits energy in the form of electromagnetic waves, which is called radiation energy. The energy from the sun is X-ffered to the earth in the form of photons (Small packet of energy) moving at the speed of 3*10^8 m/s. When Photon energy- absorption (metal)- Heat energy When Photon energy- absorption (Plant)- (Photon energy combine with O 2 )Chemical energy

C ONT …. The heat energy received on the earth through photons is responsible foe earth’s temperature The amount of solar radiation reaching different parts of the world is not the same It varies from location to location and season to season its knowledge is important for designing and estimating the output from solar energy system.

S OLAR SPECTRUM Solar spectrum consists of a broad range of electromagnetic waves. The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.

C ONT … EMR consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light

C ONT … Sun Emits energy between 0.15 to 120 Micrometers 99% of the solar energy is received in the wavelength range between 0.15 to 4.0 mm The radiation in this range consists of ultraviolet radiation, visible radiation (which is seen by human) and infrared radiation. NameRange of wavelength (mm) Energy carried(%) UVR0.15 to VR0.38 to IR0.72 to Others > 4.01

E XTRATERRESTRIAL RADIATION The extraterrestrial radiation refers to the amount of radiation falling on earth, outside its atmosphere. The extraterrestrial solar radiation received by the earth is essentially constant. The solar constant, a measure of flux, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU) (roughly the mean distance from the Sun to the Earth). Solar constant is taken as 1367 W/m 2.

S OLAR CONSTANT.. Extraterrestrial radiation

C ONT …

Solar irradiance is solar power per unit area.

The inverse square law states that irradiance is reduced in proportion to the inverse square of the distance from the source.

Solar irradiation equals the total solar irradiance over time.

R ADIATION ON THE EARTH SURFACE Air mass is a representation of the amount of atmosphere radiation that must pass through to reach Earth’s surface.

Extraterrestrial radiation

Distance travelled by sun rays to reach earth’s surface or Air Mass Solar radiation flux reaching the surface (W/m 2 ) AM0 (Extraterrestrial)1376 AM1(Sun at overhead position)1105 AM1.5 (Sun at about 48 o from overhead position) 1000 AM 2 (Sun at about 60 o from overhead position) 894

Solar radiation entering Earth’s atmosphere consists of direct, diffuse, and albedo radiation.