7
Figure 2.2 Earth’s rotation
Figure 2.3 Revolution and rotation
Solar Irradiation: Sunlight and the Solar Constant
:
The sun delivers energy by means of electromagnetic radiation. There is
solar fusion that results from the intense temperature and pressure at the core of
the sun. Protons are converted into helium atoms at 600 million tons per second.
Because the output of the process has
lower energy than the protons, which
began, fusion gives rise to lots of energy in form of gamma rays that are absorbed
by particles in the sun and re-emitted. From The law of Stefan and Boltzmann
can estimate the total power of the sun P = 4πr
2
σϵT
4
W ………..…….2.1.
T is the temperature that is about 5800K, r is the radius of the sun which
is 695800 km and σ is the Boltzmann constant which is 1.3806488 × 10
-23
m
2
kg
s
-2
K
-1
. The emissivity of the surface is denoted by ϵ. Because of Einstein’s
famous law E=mc2 about millions of tons of matter are converted to energy each
second. The solar energy that is irradiated to the earth is 5.1024 Joules per year
this is 10000 times the present worldwide energy consumption per year.
Solar radiation from the sun is received in three ways: direct, diffuse and
reflected, Direct radiation: is also referred to as beam radiation and is the solar
radiation, which travels on a straight line from the sun to the surface of the earth
[5].