The World Meteorological Organization (WMO)
defines “Sunshine” as direct irradiance from
the sun measured on the ground of at least 120
Direct Sunlight gives about 93 lux of
illumination per watt of electromagnetic power.
Bright sunlight provides illumination of approx.
100,000 lux/Sq.m at Earth’s surface.
Sun’s surface temperature, T = 6000k.
About sun’s total radiated energy,
Ultraviolet region(λ<0.40μm) - 8.73%.
Visible region (o.40μm<λ<0.70μm) – 38.15%.
Infrared region (λ>0.70μm) – 53.12%.
Earth’s inner core is a solid made of iron and
2/3 of earth is covered with water rest 1/3 is
It reflects 1/3 of the sunlight received.
Earth is inclined about its axis at an angle of
The earth’s atmosphere absorbs the UV &
infrared radiation and allows only radiation
having λ between 0.29μm and 2.3μm (Short
Radiation of λ>2.3μm is not allowed.
Photovoltaic (PV device) – A device used to
convert SWR into direct current(dc) electricity.
Solar still – used for desalination for saline
Sunshine recorder – Pyranometer Or
Solar radiation reaching earth is classified into
two components : Beam & Diffuse radiation.
Beam radiation(Iь) – Direct Sunlight.
Diffuse radiation (Id) – solar radiation scattered
by aerosols, dust and molecules.
Total radiation (It) – (Iь+Id) also known as global
Pyrheliometer – broadband instrument that
measures the direct component of solar
radiation at normal incidence. It is sensitive to
λ’s in the band from 0.284μm to 0.3μm.
Sensor - Thermopile.
Pyranometer – is a type of actinometer used
to measure solar irradiance. It is designed to
measure solar radiation flux density (in
w/m²) from a view of 180º.
Silicon solar cells have the property that the
light current (approx. equal to Isc at normal
radiation) is a linear function of the incident
solar radiation. But their spectral response is
Where, θz = is Zenith angle,
α = solar altitude (is Zero at sunrise &
α + θz = 90º.
γsun = solar Azimuth angle.
Solar declination – the angle that sun’s rays
makes with the equatorial plane.
Where, n = no. of days of the year (1≤n≤365).
Its maximum value is 23.45º on 21 December &
the minimum value is –23.45º on 21June.