Environmental Engineering Reference
In-Depth Information
unless storage is available. This same problem exists in
many countries, and each will have to make its own
choice. It is unlikely that another big dam will be built
any time soon in the United States or Europe, but Asia
has made different decisions based on their need for
energy and perhaps the world
'
s need to limit emissions
from fossil fuels.
Smaller hydropower facilities generate less environ-
mental concern and there seems to be a signi
cant poten-
tial, at least in the United States, where a detailed study
has been done by the DOE. Hydropower is broken down
into four classes: large are those that can produce more
than
MWa, small are in the
to
MWa class, low are
less than
MWa.
A recent study by the DOE evaluated all low and small
hydropower sites in the United States [
MWa, and micro are less than
.
]. They surveyed
over
potential sites and after applying their selec-
tion criteria came down to
with an electrical poten-
tial of
GWa. Whether any of these will actually be
developed depends on costs.
Hydropower systems can be easily turned on or off so
that electricity can be generated when needed (limited by
the need to keep up
fish and agriculture). That
capability leads to an application of hydropower called
pumped storage. The idea is that with a lake at some high
elevation and another at a low elevation, electric power
can be generated by letting the water run downhill when
needed, and then pumping the water back uphill to be
used again when the electricity is not needed. With the
right kind of equipment, the same turbines that generate
electricity from falling water can be run as pumps to send
the water back to the top. Turbine ef
flows for
ciencies are about
