Environmental Engineering Reference
In-Depth Information
In the following, plants equipped with rotation parabola profiles are referred to
as dish/Stirling systems or parabola power plants, and large-scale plants with seg-
mented rotation profiles as solar tower power plants (due to the focal plane being
located on a tower). In case of line-focussing plants equipped with extruded pa-
rabola profiles the common technical terms are parabolic trough power plants or
linear Fresnel collector power plants.
Besides the optical properties of the material applied for the reflector, achiev-
able efficiencies are largely influenced by the geometry of the reflectors and the
precision of the sun-tracking system. In practice, mainly optical measuring meth-
ods are used to assess the concentrator quality and the performance.
Typical concentration factors and parameters of different solar power genera-
tion technologies applying concentrating collectors are summarised in Table 5.1.
To allow for a comparison, technical data of non-concentrating solar-thermal
power plants have also been added.
Table 5.1
Concentration factors and technical parameters of selected solar thermal power
generation technologies
Solar tower
Dish/Stirling Parabolic
trough
Fresnel
reflector
Solar
pond
Solar up-
draft tower
30 - 200
c
0.05
1
0.7 - 1.2
grid
+
a
by interconnection of many individual plants within a farm;
b
conversion of radiation energy into
electrical energy, annual average is site-specific;
c
assuming a solar multiple of 1.0;
d
incorporated into
a conventional power station;
e
0 successful operation of demonstration plants, + successful continuous
operation of demonstration plants, ++ commercial plants in operation.
0.01 - 1
a
0.025
up to 3,000
15 - 25
grid/island
+
10 - 200
c
80
50 - 90
10 - 23
grid
++
10 - 200
c
0.3
d
25 - 50
9 - 17
d
grid
0
Typical capacity in MW
Real capacity in MW
Concentration factor
Efficiency
b
in %
Operation mode
Development status
e
30 - 200
10
600 - 1,000
10 - 28
grid
+
0.2 - 5
5
1
1
grid
+
5.1.2
Radiation absorption
All materials absorb part of the incident solar radiation. The absorbed incident
radiation causes atoms of the material to vibrate, whereby heat is generated. This
heat is either transferred within the absorbing material by heat conduction and/or
released by heat radiation or convection back to the atmosphere.
The major portion of solar radiation consists of visible light (Fig. 2.8); i.e. the
short-wave portion of radiation is predominant (Chapter 2.2). The distribution of
luminosity of the different wavelengths corresponds approximately to that of a
black body radiator of a temperature of approximately 5,700 K. In contrast, with
regard to the temperatures relevant to solar thermal plants (approx. 100 to
1,000 °C) bodies radiate mainly medium and short-wave radiation (Wien's Law).
When observing only a small spectral range, the absorption coefficient and emis-
sion coefficient are identical (Kirchhoff's Law). However, suitable "selective"
coatings ensure that short-wave sunlight is well absorbed while (long-wave) heat
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