Environmental Engineering Reference
In-Depth Information
allows maximum operation temperatures of scarcely 400 °C, but must be kept
under a pressure of at least 12 bar.
From plant SEGS VI onwards, additionally a solar re-heater has been inte-
grated which (together with enhanced steam parameters) increased the thermal
efficiency of the power cycle from 30.6 to 37.5 % (Fig. 5.19). Fig. 5.18 shows an
example of the performance characteristic of this power plant (i.e. the provided
electrical energy as a function of direct radiation).
1.20
1.20
1.00
1.00
0.80
0.80
0.60
0.60
0.40
0.40
0.20
0.20
0.00
0.00
0
0
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
Direct radiation in kWh/(m
2
d)
Direct radiation in kWh/(m
2
d)
Direct radiation in kWh/(m² d)
Direct radiation in kWh/(m² d)
Fig. 5.18
Performance characteristic of the SEGS VI plant
The required steam is either generated directly or indirectly by a secondary cir-
cuit (Fig. 5.19). Typical steam parameters are approximately 100 bar / 371 °C for
indirect generation (due to the temperature limit of the heat transfer fluid) or
80 bar / 430 °C for direct generation. Compared to conventional steam power
plant cycles the indicated values are relatively low. Still, this is to a large extent
compensated by an increased technical effort. However, for a plant within this
capacity range rather unusual process improvements such as intermediate super-
heating
and multiple-stage internal feed water preheating are required. Conse-
quently, in spite of the rather unfavourable steam parameters, for instance, the
30 MW plants SEGS IV to VI reach thermal efficiencies in the power block of up
to 38 %.
Hybridisation is possible by integration of additional firing based on fossil
and/or biogenous energy carriers to ensure operation at times of fluctuating or no
solar radiation. As an alternative, also parallel steam generators may be applied;
this additional technical effort allows for better steam parameters and thus higher
electrical efficiencies.
The concept of SEGS plants is also being applied for more recent parabolic
trough power plants whose operation is predominantly assured by solar power
generation without major additional firing.
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