Page 32 - Advances in Renewable Energies and Power Technologies

1. Introduction 5

FIGURE 1.1
The general photovoltaic system.

2. Battery storage: To be available at the absence of the solar radiation, the electric
energy produced by the array must be partly stored, normally using batteries.
So, the second main unit is the battery storage.
3. Power conditioning circuits: According to the nature of the load, the generated
electric power must be conditioned using DC/DC converters and DC/AC
inverters.
The PV array is composed of solar modules. Each module contains a matrix of
solar cells connected in series and parallel to satisfy the terminal properties of the
whole generator. Accordingly, the solar cell is the basic element in the PV generator.
This element is the basic solar radiation converter into electricity.

1.2 THE SOLAR RADIATION
One must be able to describe the solar radiation as it is the input power source to the
PV generators. The sun emits electromagnetic radiations as a black body having a
surface temperature of about 6000 K. This is because of the nuclear reaction running
in it, where the sun is converting hydrogen into helium. The radius of the sun
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amounts to 1.39 10 m. The total radiation power received from the sun on a
unit area perpendicular to the sun rays at the mean earthesun distance, termed an
astronomical unit, is called the solar constant (SC), where 1 astronomical unit ¼ 1
AU ¼ 1.496 10 11 m. The solar radiation intensity at other distances is expressed
2
in terms of SC with SC ¼ 1.353 kW/m [2]. Like a black body radiation, the
sun’s radiation covers a wide spectrum of wavelengths from deep ultraviolet to
far infrared. The power spectral distribution of the sunlight [3] is shown in Fig. 1.2.
The vertical axis represents the spectral irradiance I(l) while the horizontal axis
represents the wavelength in mm. The irradiance I(l) is equal to the incident solar
2
2
power/m /dl ¼ [W/m /mm], where dl is the respective wavelength range in mm. It
is clear from this figure that the maximum spectral irradiance lies at l ¼ 0.5 mm.
The spectral irradiance decreases because of the presence of air in the atmosphere.
The air molecules scatter and absorb the solar radiation. There are multiple absorp-
tion bands for O 2 ,H 2 O, and CO 2 . It is important to notice that the solar irradiance
resembles the black body radiation at w6000 K represented by the dashed line.