Environmental Engineering Reference
In-Depth Information
7.3.1 Concentrating Solar Thermal Power Plants
Concentrating solar power plants can only utilize the direct irradiance portion of the
sun. This portion of irradiance can be refl ected by mirrors and ultimately concen-
trated. For non-concentrating solar systems the global irradiation intensity, thus the
sum of direct and non-directional diffuse sunlight, is important. The effi ciency of
these systems is therefore related to the global irradiation intensity. With concentrat-
ing systems the direct-normal radiation intensity on a surface orientated vertically
towards the sun serves as a reference quantity (see Figure 7.14). In the technical
jargon this is abbreviated to DNI, which stands for 'direct normal irradiance'. The
DNI values can lie somewhat below but also somewhat above the values for global
radiation.
Figure 7.14 Differentiation of types of solar radiation.
Annual Electricity Production of Solar Power Plants
The annual output yield of a concentrating solar thermal system can be estimated
using the average effi ciency
, the annual total of solar direct-normal irradiance
DNI and the aperture area A of the mirrors:
η
E
=⋅⋅
η
A DNI
.
electrical
With an effi ciency
of 15% = 0.15, a solar thermal parabolic trough system with
an overall aperture area of 500 000 m 2 at a Spanish location and a DNI of 2200 kWh/
(m 2 a) achieves an annual yield of:
η
kWh
ma
million kWh
a
2
E =⋅
0 15 500 000
.
m
2200
=
165
.
2
This is suffi cient to cover the electricity needs of around 50 000 Spanish
households.
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