Hydroelectric Power Generation - Renewable Energy: Technology, Economics and Environment - page 370

within a transformer that enables feeding the electrical energy into the public ser-
vices grid at its specific voltage level.

Losses. Within the energy transformation chain considerable technically unavoid-
able losses occur; the result is a lower level of energy at the plant exit than the
available energy in the water between the head and tailwater. Therefore Fig. 8.16
shows the respective losses and their average range within the individual energy
transformation steps and components.

Location &
plant
specific

Location &
plant
specific

Location &
plant
specific

8 - 15 % 2 - 5 % 1 - 5 % 1 - 2 % 1 - 2 %

Losses related to energy input at the respective transformation levels

Fig. 8.16 Energy flow inside a run-of-river hydroelectric power station (see /8-5/)

The losses within the plant mainly occur at the water intake, at the screen,
within the channels, pipes, penstocks, and the shut-off valves (if applicable),
within one or more turbines, possibly within one or more transmissions and one or
more generators. In larger plants there may also be corresponding conversion
losses within the transformer. An additional loss is the potential energy of the wa-
ter released at the dam (e.g. at times of flooding). The energy losses in the hydrau-
lic part in particular are very location and plant-specific. A generally applicable
and transferable indication of the magnitude is therefore not possible; at the very
best there are only losses of a few percent. Together with the losses inside the
other system components, total efficiencies clearly over 80 % can be achieved at
full load; sometimes 90 % and above can be achieved. The total efficiency is the
ratio of the electrical power at the plant exit and the power difference between
head and tailwater minus the water released over the spillway. As hydroelectric
power stations are often run at partial load, the annual average utilisation factors
are generally lower; in modern and properly designed hydroelectric power stations
they range between 70 and a maximum of 90 %; in older plants, especially within
the low power range, they can be significantly lower, at 50 to 70 %. In connection
with the total working capacity of the water the utilisation factors are significantly