Environmental Engineering Reference
In-Depth Information
Then a rated runoff is established. This is the quantity of water a power plant needs
to produce full output. If the runoff volume of the river rises above the rated runoff,
the surplus water must be diverted unused over a weir. If a large quantity of elec-
tricity is to be generated, turbines with a high rated runoff should be selected.
However, if the runoff volume of the river drops below the rated runoff, there will
not be enough water to enable the power plant to provide its full output. The turbines
will then either work at poor effi ciency in partial load or individual turbines will be
switched off and remain unused. A low rated runoff should be selected to ensure
that optimal use is being made of the turbines. In practice, the rated runoff is deter-
mined based on a compromise between the maximum amount of power to be gener-
ated and optimal use of the turbine.
Power Output of a Run-of-River Power Plant
If the water runoff quantity
Q
and the head
H
of the water at a power plant are
known, then the electric power output of a hydropower plant can be calculated rela-
tively easily based on the effi ciency
η
of the plant, the density of the water
ρ
W
(
ρ
W
≈
1000 kg/m
3
) and the gravitational acceleration
g
(
g
= 9.81 m/s
2
):
P
=⋅ ⋅⋅⋅
η ρ
g Q H
el
W
With an extension runoff quantity of 1355 m
3
/s, a head of 10.1 m and effi ciency of
79% = 0.79, the output for full load at the Laufenburg hydropower plant on the
Rhine can be calculated as
kg
m
m
s
m
s
3
P
el
=⋅
0 79 1000
.
⋅
9 81
.
⋅
1355
⋅
10 1
.
m
=
106
MW.
3
2
At 5940 full - load hours per year, the power plant generates 106 MW · 5940 h =
630 000 MWh = 630 million kWh. This is suffi cient to cover the average electricity
consumption of 180 000 households in Germany.
Approval granting water rights is required to build a hydropower plant. Normally
approval is granted for 30 years, but it may be given for a longer time. The procedure
for obtaining approval can take three to ten years. For large-scale power plants the
approval also includes a test for environmental compatibility. The EU water rights
guidelines stipulate that all water bodies in Europe must be kept in a 'good state'.
Although the water may be used, its ecological functioning must remain intact. In
this context the current state of the water body concerned is also crucial. Therefore,
it is much easier to gain approval to modernize a power plant on a stretch of water
that has already been greatly altered than to build a new plant. Because of this, the
chances of obtaining approval to build new large-scale hydropower plants are not
very favourable.
