5.1
•
•
•
•
5
Solar radiation
In this chapter we discuss the aspects of solar radiation, which are important for solar
energy. After defining the most important radiometric properties in Section 5.2, we discuss
blackbody radiation in Section 5.3 and the wave-particle duality in Section 5.4. Equipped
with this knowledge, we then investigate the different solar spectra in Section 5.5.
However, prior to these discussions we give a short introduction about the Sun.
The Sun
The Sun is the central star of our solar system. It consists mainly of hydrogen and helium.
Some basic facts are summarized in Table 5.1 and its structure is sketched in Figure 5.1.
The mass of the Sun is so large that it contributes 99.68% of the total mass of the solar
system. In the centre of the Sun the pressure–temperature conditions are such that nuclear
fusion can take place. In the major nuclear reaction, the proton–proton reaction, via a
number of steps, four protons react to produce:
1 helium core (two protons and two neutrons);
2 positrons (the anti-particles of electrons);
2 neutrinos;
electromagnetic radiation.
The positrons are annihilated with electrons, leading to additional radiation. The mass of
the helium core is 0.635% less than that of four protons; the energy difference is converted
into energy according to Einstein’s equation
Table 5.1: Some facts on the Sun.
Mean distance from the Earth
149,600,000 km (the astronomic unit, AU)
Diameter
1,392,000 km (109 × that of the Earth)
Volume
1,300,000 × that of the Earth
Mass
1.993 × 10 27 kg (332,000 × that of the Earth)
•
•
•
•
5
Solar radiation
In this chapter we discuss the aspects of solar radiation, which are important for solar
energy. After defining the most important radiometric properties in Section 5.2, we discuss
blackbody radiation in Section 5.3 and the wave-particle duality in Section 5.4. Equipped
with this knowledge, we then investigate the different solar spectra in Section 5.5.
However, prior to these discussions we give a short introduction about the Sun.
The Sun
The Sun is the central star of our solar system. It consists mainly of hydrogen and helium.
Some basic facts are summarized in Table 5.1 and its structure is sketched in Figure 5.1.
The mass of the Sun is so large that it contributes 99.68% of the total mass of the solar
system. In the centre of the Sun the pressure–temperature conditions are such that nuclear
fusion can take place. In the major nuclear reaction, the proton–proton reaction, via a
number of steps, four protons react to produce:
1 helium core (two protons and two neutrons);
2 positrons (the anti-particles of electrons);
2 neutrinos;
electromagnetic radiation.
The positrons are annihilated with electrons, leading to additional radiation. The mass of
the helium core is 0.635% less than that of four protons; the energy difference is converted
into energy according to Einstein’s equation
Table 5.1: Some facts on the Sun.
Mean distance from the Earth
149,600,000 km (the astronomic unit, AU)
Diameter
1,392,000 km (109 × that of the Earth)
Volume
1,300,000 × that of the Earth
Mass
1.993 × 10 27 kg (332,000 × that of the Earth)