Environmental Engineering Reference
In-Depth Information
These correlations can also be described by the power duration curve schemati-
cally represented in Fig. 8.18 for a typical run-of-river power station. According
to this plan, a run-of-river power station with a defined design is characterised by
a specific flow at a corresponding head; together this results in a certain power
output over time. Considering these design conditions, the values change with in-
creasing and decreasing flows.
He
ad durat
ion curv
e
Rated head
Design power
Design discharge
Usable flow
0
100
200
300
365
Fig. 8.18
Discharge, head and power duration curves of a run-of-river power station (see
/8-2/)
Time in days
−
Power generation decreases with decreasing flows. The corresponding head
rises as the tailwater drops slightly due to the smaller flow. If the discharge is
very low, the plant has to be switched off at a certain point, as turbines cannot
operate flows below a certain minimum. Under these conditions no power can
be generated if the turbines are dimensioned correctly; this is only - if at all -
the case on very few days of the year (Fig. 8.18).
−
Power generation also decreases with increasing discharge. The turbine cannot
process discharges exceeding the design capacity. The power generation is re-
duced as the difference between the head and tailwater level decreases with an
increase in the discharge. The additional flow has to be spilt and can therefore
not be used energetically. In the worst case, power generation is no longer pos-
sible, as the difference in height between head and tailwater is too small. That
is normally the case if the gates of the dam or barrage are opened (i.e. during
floods).
8.3
Economic and environmental analysis
Hydroelectric power stations have contributed to meet the energy demand for over
100 years. The costs related to this and the evaluation of the relevant environ-
mental impacts is analysed in the following paragraphs. We will, however, define
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