Solar Radiation. Characteristics of the Sun. The sun has layers The middle is called the core – it is 27,000,000 degrees! The outer layer is the chromosphere The layer under the chromosphere is the photosphere, where light and other forms of energy are released
90% of the energy is generated in the region between 0 and 0.23R which contains 40% of the sun’s mass.
The sun generates an approximate energy of about
(1 x 10 ^(1 8 )kWh/a).
The amount of energy in the sunlight reaching the Earth's surface is equivalent to around 10,000 times the world's energy requirementsand only0.01 per cent of this energy would cover mankind's total energy needs.
It first interacts with the atmosphere and then reaches
to the earth’s surface and the amount of energy reaching the atmosphere is known as solar constant.
EQ = 1367W/m2
47% of this energy ( as an average) reaches the earth’s surface and 57% is absorbed by the atmosphere.
Sunlight on the Earth’s surface comprises from:1)Direct Radiation radiation from the sun that reaches the earth without scattering
2)Diffuse Radiation: radiation that is scattered by the atmosphere and clouds
It represents how much atmosphere the solar radiation
has to pass through before reaching the Earth’s surface.
AM = 1/ Cos Өz
Air Mass (AM) equals 1.0 when the sun is directly overhead
at sea level.
At high altitudes or in a very clear days, Peak Sun may be more than 1000 W/m^2 but it is a practical value for most locations.
Winter Solstice is at minimum solar declination (-23.5º) and occurs around December 21st
Days are significantly shorter than nights.
occur when the solar declination is zero. Spring equinox is around March 21st and the fall equinox occurs around September 21st –Sun is at Zenith at solar noon on the equator.
Around the equinoxes the daily [rate of] change is at maximum as oppose to change of declination during the solstices when it is at its minimum.