Environmental Engineering Reference
In-Depth Information
I
mpoundment
The most common type of hydroelectric power plant is an impoundment facility. An
impoundment facility, typically a large hydropower system, uses a dam to store river
water in a reservoir. This type of facility works best in mountainous or hilly ter-
rain where high dams can be built and deep reservoirs can be maintained. Potential
energy available in a reservoir depends on the mass of water contained in it, as well
as on overall depth of the water. Water released from the reservoir flows through a
turbine and makes it spin, which in turn activates a generator that produces electric-
ity. The water may be released either to meet changing electricity needs or to main-
tain a constant reservoir level.
d
IversIon
A diversion (sometimes called
run-of-river
) facility channels all or a portion of the
flow of a river from its natural course through a canal or penstock, and the current is
used to drive a turbine. This approach may not require the use of a dam. This type
of system is best suited for locations where a river drops considerably per unit of
horizontal distance. The ideal location is near a natural waterfall or rapids. The chief
advantage of a diversion system is the fact that, lacking a dam, it has far less impact
on the environment than an impoundment facility (Gibilisco, 2007).
p
umped
s
torage
When demand for electricity is low, a pumped storage facility stores energy by pump-
ing water from a lower reservoir to an upper reservoir. During periods of high electri-
cal demand, the water is released back to the lower reservoir to generate electricity.
KEY DEFINITIONS
•
Dam facilities
have substantial water storage and a powerhouse at the base
of the dam.
•
Run-of-the-river
typically features a small diversion dam that delivers
water into a penstock, a pipe that delivers water to the powerhouse, which is
located farther down the river.
DID YOU KNOW?
The potential energy in a specific slug or parcel of water is expressed in
newton-meters (N⋅m). The newton is the standard unit of force, equivalent to
1 meter per second squared (1 m/s
2
). This is the product of the mass of the slug
in kilograms, the acceleration of gravity in meters per second squared (about
9.8 m /s
2
), and the elevation of the parcel in meters (the vertical distance it falls
as its energy is harnessed). The equivalent kinetic-energy unit is the joule (J),
which is in effect equal to a watt-second (W⋅s).
