SOLAR

RADIATION

From:- Amitesh kumar

The World Meteorological Organization (WMO) defines “Sunshine” as direct irradiance from the sun measured on the ground of at least 120 w/m².

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 (DIA = 13000KM)

Earth’s inner core is a solid made of iron and nickel.

2/3 of earth is covered with water rest 1/3 is land.

It reflects 1/3 of the sunlight received. Earth is inclined about its axis at an

angle of 23.5º. The earth’s atmosphere absorbs the UV

& infrared radiation and allows only radiation having λ between 0.29μm and 2.3μm (Short wavelength radiation).

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 water.

Sunshine recorder – Pyranometer Or

Pyrheliometer. A Pyranometer

MEASUREMENT OF SOLAR RADIATION ON EARTH’S SURFACE

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 radiation. 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 not linear.

SUN- EARTH ANGLES

Where, θz = is Zenith angle,

α = solar altitude (is Zero at sunrise &

sunset), 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.