Civil Engineering Reference
In-Depth Information
2 Solar Energy
Nicolae Badea
Solar energy is available all over the world in different intensities. According to the
widely accepted terminology [
7
], the two concepts of solar (i.e., short wave) irra-
diation are used. The term irradiance is used to consider the solar power (power
density) falling on unit area per unit time [W/m
2
] or irradiance is a measure of
the rate of energy received per unit area, and has units of watts per square meter
(W/m
2
). The term irradiation (or radiation) is used to consider the amount of solar
energy falling on unit area over a stated time interval [Wh/m
2
]. This interval can be
one minute, day, month, or year. Irradiation is radiant exposure and is a time
integral (or sum) of irradiance. Thus, one minute radiant exposure is a measure of
the energy received per square meter over a period of one minute. Therefore, a
1 min radiant exposure = mean irradiance (W/m
2
)
60(s), and has units of joule(s)
per square meter (J/m
2
). For example: a mean irradiance of 500 W/m
2
over 1 min
yields a radiant exposure of 3,000 J/m
2
or 3 kJ/m
2
. Both irradiance and irradiation
have the same symbols, namely H. The two concepts can be differentiated by
context or by the attached units. H
h,i
is the monthly or yearly average of daily global
irradiation on the horizontal or inclined surface. (Note: Depending on the country
and manufacturer of solar equipment is also used notation G [W/m
2
] for irradiance
and for irradiation is used notation E [Wh/m
2
].)
Irradiation is essential when looking at how much power can be derived from a
certain area of real estate of an energy source. Low irradiation indicates that too
much real estate is required to provide the power we demand at reasonable prices.
Irradiation for most people is from 150 to 300 W/m
2
or 3.5 to 7.0 kWh/m
2
/day. The
global mean irradiance is 170 W/m
2
.
Theoretically, the solar energy available on the surface of the Earth is enough to
support the energy requirements of the entire planet. In reality, progress and
development of solar science and technology depends to a large extent on human
desires and needs.
The potential for using solar energy in EU is relatively important (Fig.
3
). There
are areas where the annual solar energetic
×
2,200 kWh/m
2
/year,
flux is up to 1,800
-
like the Black Sea coast and Mediterranean countries.
The solar energy potential depends primarily on the latitude and local climatic
conditions like cloudiness and, secondly, on air temperature. Simulations with the
Photovoltaic Geographical Information System [
8
] show that the average sum of
global irradiation per square meter received by optimally orientated modules lies
between 1,000 kWh/m
2
/year for Oslo region and 2,200 kWh/m
2
/year in Andaluc
í
a
region of Spain. In the majority of the countries, the annual solar energetic
flux is of
1,400 kWh/m
2
/year.
…
1,000
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