22
A. Funde and A. Shah
(2) Solar spectral irradiance equivalent to AM1.5
(3) Solar Cell temperature of 25 °C.
The deviation between operating conditions in the field and STC can be significant. This can be in the form of deviation in intensity from 1000 W/m
2 , deviation
in solar spectrum from the AM1.5 or deviation in the operating temperature of the
solar cells in the module from 25 °C. The deviation in spectral characteristics and
intensity will be addressed in this Chapter, whereas the effect of temperature on the
performance of solar cell will be addressed in Chap. 3. (The overall effect on the
energy yield of an installation is detailed in Chap. 10.)
At a given location, the noon referred to as “local solar noon” is the time when the
sun’s position in the sky is crossing the longitude of that location. This comes from
the varying sun-earth geometry at every moment of the day and throughout the year.
The detailed account of the sun-earth geometry is beyond the scope of this book and
readers are encouraged to consult other literature for this. e.g. “Energy Conversion”
by Yogi Goswami and Frank Kreith [4] or “Renewable Energy Engineering” by
Jenkins and Ekanayake [5].
At the local solar noon, the air-mass ratio experienced at different latitudes will be
different as the path traversed by solar radiation through the atmosphere (and, thus,
the air mass ratio) will be different for different latitudes: e.g. the cities of Astana
in Kazakhstan, Peshawar in Pakistan, Ahmedabad, Mumbai and Kochi in India and
Colombo in Sri Lanka have the same “local solar noon” because their longitudes are
the same, near 75 °E, although their latitudes are different. Therefore, at any given
time of the day, on any day of the year, these cities will experience different values
of the air mass ratio.
Similar observations can be made for the cities of Cambridge and Greenwich in
UK, Paris in France, Barcelona in Spain, Tiaret in Algeria, Niamey in Niger, Benin
City in Nigeria as they all lie on almost same longitude position of near 0° E/W.
2.1.3 Spectra of Sunlight, for Different Times of the Day
and for Different Atmospheric and Environmental
Conditions
(a) Shift towards red, in mornings and evenings
There is a significant alteration in the nature of the solar spectrum at different
values of the air-mass ratio—as the composition of the atmosphere is different for
different air mass ratios. Even between mornings and evenings the solar spectrum
on the surface of the Earth is different, because of changes in the atmospheric constituents: in the morning the air has a different relative humidity than in the evening.
However, in both cases, there is a relative enhancement of the red part of the solar
spectrum. Figure 2.4 shows the variation in the solar spectrum, as measured by
King et al. [6], for three different times of the day at Sacramento (California, USA).
A. Funde and A. Shah
(2) Solar spectral irradiance equivalent to AM1.5
(3) Solar Cell temperature of 25 °C.
The deviation between operating conditions in the field and STC can be significant. This can be in the form of deviation in intensity from 1000 W/m
2 , deviation
in solar spectrum from the AM1.5 or deviation in the operating temperature of the
solar cells in the module from 25 °C. The deviation in spectral characteristics and
intensity will be addressed in this Chapter, whereas the effect of temperature on the
performance of solar cell will be addressed in Chap. 3. (The overall effect on the
energy yield of an installation is detailed in Chap. 10.)
At a given location, the noon referred to as “local solar noon” is the time when the
sun’s position in the sky is crossing the longitude of that location. This comes from
the varying sun-earth geometry at every moment of the day and throughout the year.
The detailed account of the sun-earth geometry is beyond the scope of this book and
readers are encouraged to consult other literature for this. e.g. “Energy Conversion”
by Yogi Goswami and Frank Kreith [4] or “Renewable Energy Engineering” by
Jenkins and Ekanayake [5].
At the local solar noon, the air-mass ratio experienced at different latitudes will be
different as the path traversed by solar radiation through the atmosphere (and, thus,
the air mass ratio) will be different for different latitudes: e.g. the cities of Astana
in Kazakhstan, Peshawar in Pakistan, Ahmedabad, Mumbai and Kochi in India and
Colombo in Sri Lanka have the same “local solar noon” because their longitudes are
the same, near 75 °E, although their latitudes are different. Therefore, at any given
time of the day, on any day of the year, these cities will experience different values
of the air mass ratio.
Similar observations can be made for the cities of Cambridge and Greenwich in
UK, Paris in France, Barcelona in Spain, Tiaret in Algeria, Niamey in Niger, Benin
City in Nigeria as they all lie on almost same longitude position of near 0° E/W.
2.1.3 Spectra of Sunlight, for Different Times of the Day
and for Different Atmospheric and Environmental
Conditions
(a) Shift towards red, in mornings and evenings
There is a significant alteration in the nature of the solar spectrum at different
values of the air-mass ratio—as the composition of the atmosphere is different for
different air mass ratios. Even between mornings and evenings the solar spectrum
on the surface of the Earth is different, because of changes in the atmospheric constituents: in the morning the air has a different relative humidity than in the evening.
However, in both cases, there is a relative enhancement of the red part of the solar
spectrum. Figure 2.4 shows the variation in the solar spectrum, as measured by
King et al. [6], for three different times of the day at Sacramento (California, USA).