2 Solar Spectra
23
Fig. 2.4 Variation in the solar spectrum measured by King et al. [6], for three different times of the
day (different air mass ratio values). The spectra are normalised to the intensity of AM1.5 spectrum,
see text
Thereby three different curves result: the red curve for 7.18 a.m. (AM4.70); the
blue curve for 8.24 a.m. (AM2.46) and the black curve for 10.43 a.m. (AM1.5).
The curves in Fig. 2.4 are normalized, so as to obtain the same area beneath each
curve. This area corresponds to a solar radiation of 856 W/m
2 (which is the solar
radiation received at 10:43 a.m., whereas earlier in the morning, less solar radiation
is received). Thanks to the normalization, the relative changes in the spectral irradiance at different wavelengths, for different times of the day, become clearly visible.
However, the information on the total solar radiation, for the different times of the
day, is lost.
In Fig. 2.4, we can clearly see that in the early morning (at 7:18 a.m. and 8:24
a.m.), the solar spectrum contains relatively more red light components than later in
the day (at 10:43 a.m.).
(b) Shift of spectrum towards blue on cloudy days, and towards red in the
presence of snow in the nearby environment
The atmospheric conditions of clouds also change the solar spectrum as shown in
Fig. 2.5. Similarly, the presence of snow and ice, or of large water surfaces will also
modify the solar spectrum, as received by a PV module.
In Fig. 2.5, we can clearly see that under cloudy conditions, the solar spectrum
contains relatively more blue light or light with short wavelengths. With partially
cloudy conditions, the spectrum shifts towards the AM1.5 solar spectrum. However,
in presence of snow, and clear sky condition,
3 the solar spectrum contains more
3 Clear-sky condition is generally defined as the absence of visible clouds in the sky dome.
23
Fig. 2.4 Variation in the solar spectrum measured by King et al. [6], for three different times of the
day (different air mass ratio values). The spectra are normalised to the intensity of AM1.5 spectrum,
see text
Thereby three different curves result: the red curve for 7.18 a.m. (AM4.70); the
blue curve for 8.24 a.m. (AM2.46) and the black curve for 10.43 a.m. (AM1.5).
The curves in Fig. 2.4 are normalized, so as to obtain the same area beneath each
curve. This area corresponds to a solar radiation of 856 W/m
2 (which is the solar
radiation received at 10:43 a.m., whereas earlier in the morning, less solar radiation
is received). Thanks to the normalization, the relative changes in the spectral irradiance at different wavelengths, for different times of the day, become clearly visible.
However, the information on the total solar radiation, for the different times of the
day, is lost.
In Fig. 2.4, we can clearly see that in the early morning (at 7:18 a.m. and 8:24
a.m.), the solar spectrum contains relatively more red light components than later in
the day (at 10:43 a.m.).
(b) Shift of spectrum towards blue on cloudy days, and towards red in the
presence of snow in the nearby environment
The atmospheric conditions of clouds also change the solar spectrum as shown in
Fig. 2.5. Similarly, the presence of snow and ice, or of large water surfaces will also
modify the solar spectrum, as received by a PV module.
In Fig. 2.5, we can clearly see that under cloudy conditions, the solar spectrum
contains relatively more blue light or light with short wavelengths. With partially
cloudy conditions, the spectrum shifts towards the AM1.5 solar spectrum. However,
in presence of snow, and clear sky condition,
3 the solar spectrum contains more
3 Clear-sky condition is generally defined as the absence of visible clouds in the sky dome.