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Appendix C
Comparison of Different Power-Generation Methods 257

require the protracted economic, engineering, and environmental stud-
ies associated with large projects, and often can be completed much
more quickly. A small hydro development might be installed along with
a project for flood control, irrigation, or other purposes, providing extra
revenue for project costs. In areas that formerly used waterwheels for
milling and other purposes, often the site can be redeveloped for electric
power production, possibly eliminating the new environmental impact
of any demolition operation. Small hydro can be further divided into
mini-hydro, with units around 1 MW in size, and micro-hydro, with
units as large as 100 kW down to a couple of kW rating.
Small hydro units in the range of 1 MW to about 30 MW are often
available from multiple manufacturers using standardized water-to-wire
packages; a single contractor can provide all the major mechanical and
electrical equipment (turbine, generator, controls, switchgear), selecting
from several standard designs to fit the site conditions. Micro-hydro
projects use a diverse range of equipment; in the smaller sizes; industrial
centrifugal pumps can be used as turbines, with comparatively low pur-
chase cost compared to purpose-built turbines.
ptg
Advantages
The major advantage of hydroelectricity is elimination of the cost of
fuel. The cost of operating a hydroelectric plant is nearly immune to
increases in the cost of fossil fuels, such as oil, natural gas, or coal. Fuel
is not required, and so it need not be imported. Hydroelectric plants
tend to have longer economic lives than fuel-fired generation, with some
plants now in service having been built 50 to 100 years ago. Operating
labor cost is usually low because plants are automated and have few per-
sonnel onsite during normal operation.
Where a dam serves multiple purposes, a hydroelectric plant can be
added with relatively low construction cost, providing a useful revenue
stream to offset the costs of dam operation. It has been calculated that
the sale of electricity from the Three Gorges Dam will cover the con-
struction costs after 5 to 8 years of full generation.

Greenhouse Gas Emissions
Because hydroelectric dams do not burn fossil fuels, they do not
directly produce carbon dioxide (a greenhouse gas). Although some car-
bon dioxide is produced during manufacture and construction of the
project, this is a tiny fraction of the operating emissions of equivalent
fossil-fuel electricity generation.