Page 309 - Managing Global Warming

Hydropower 269

6

1 MWh ¼ 1000 kWh 10 Wh
9

1 GWh ¼ 1000 MWh 10 Wh
12

1 TWh ¼ 1000 GWh 10 Wh
The power output, P, in Eq. 8.2 is limited to P Max (nameplate capacity) at the max-
imum flow capacity of the turbine, Q Max . If the inflow becomes larger than this, water
will be lost (spilled) unless there is a reservoir for storage. In most cases, a hydropower
plant will be designed with capacity considerably below the maximum possible
inflow, and consequently normally spill some water. At periods where the flow is
much less than the capacity, the power plant may have to run at reduced capacity
and efficiency or even have to stop and bypass water to avoid damage to the turbines.
The capacity factor of a power plant, C f , is the ratio of the actual output of a power
plant over a period of time (typically 1 year) compared to its potential output if it had
operated at full capacity over the entire period (year). Typical capacity factors for
hydropower plants are in the range of 0.4–0.6 [1], but lower and higher values can
also be found. World average C f is 0.45 for hydropower.

8.3 Technology

Hydropower is a renewable energy source derived from the potential or kinetic energy
of water, by moving water from higher to lower elevations. It is a proven, mature, pre-
dictable, highly efficient and price-competitive technology. Hydropower has among
the best conversion efficiencies of all known energy sources, for modern power plants
this is typically >90% efficiency, “water to wire.”
A hydropower plant typically includes civil structures to collect, store, and trans-
port water, and mechanical and electrical components to convert energy to mechanical
and electrical energy. During planning and operation, it is very important to include
information about hydrology, hydraulics, and environmental impacts together with
information of social and political issues, in order to find an optimal design.
A hydropower plant typically consists of an intake, a “head race” consisting of tun-
nels and/or pipes, the power station with electrical and mechanical equipment
(“Elmek”), and finally a “tail race” consisting of tunnels and/or pipes to the outlet.
It may or may not include a dam and a reservoir for water storage. The three main
components of Elmek equipment are: turbine(s), generator(s), and transformer(s).
In addition, there will be many other components such as gates and valves, electronic
equipment for controlling the operation of the station, power cables, switchyards, and
grid connections.
A hydropower plant is nearly always tailored to utilize the available water and
head, and many different types of turbines have been developed; the most common
is the Pelton and Francis turbine for high and medium head situations, and Kaplan
and Bulb turbines for lower head and large flow systems. Examples of typical