Environmental Engineering Reference
In-Depth Information
dams are not used, but pipes divert some of the flow, dropping it down a gradient and through a
turbine before returning it to a stream (University of Nottingham 2011). Pico hydro is of greatest
interest to persons concerned with rural electrification in developing countries and with very small,
remote off-grid applications in the United States.
Pumped storage projects differ from conventional hydroelectric projects. They normally pump
water from a lower reservoir to an upper reservoir when demand for electricity is low. Water
is stored in an upper reservoir for release to generate power during periods of peak demand.
At times of low electrical demand, excess generation capacity is used to pump water from a
lower elevation to a higher reservoir. When there is higher demand, water is released from the
higher reservoir through a turbine back into the lower reservoir (USDOE 2003, 4). Pumped
storage facilities currently provide the most commercially important means of large-scale
storage and improve the daily capacity factor of hydroelectric generation. These projects are
uniquely suited for generating power when demand for electricity is high and for supplying
reserve capacity to complement the output of large fossil-fueled and nuclear steam-electric
plants. Start-up of this type of generation is almost immediate, thus serving peak demand for
power better than fossil-fueled plants that require significantly more start-up time. Like con-
ventional projects, they use falling water to generate power, but they use reversible turbines
to pump the water back to the upper reservoir. Because they are designed to meet only peak
demand, pumped storage reservoirs are much smaller than those designed to provide base
load power and therefore have lesser environmental costs than large hydro reservoirs. Pumped
storage facilities in the United States range from less than 100 MWe to almost 1,600 MWe in
generating capacity (USFERC 2010).
Because projects with a small reservoir surface area minimize natural habitat losses and hu-
man resettlement needs, pumped storage facilities entail lower environmental costs than do large
hydro facilities.
Environmental Costs of Utilizing Hydropower
The “fuel cycle” for hydropower involves exploration, power plant construction, generation and
transmission of electricity, decommissioning, and reclamation of the generating site, as illustrated
in
Figure 8.2.
The basic components of hydroelectric power generation facilities include a dam
and reservoir for large hydro, a powerhouse with hydraulic generators, turbines, and electrical
grid interconnection equipment. Small hydro may or may not require a dam and reservoir, and
connection to a high-voltage transmission network. Riverine areas and geologic depressions must
be evaluated, dams and reservoirs constructed, generating facilities operated, and eventually
dams, reservoirs, and generating equipment must be decommissioned. Potential environmental
costs of using hydroelectric technologies include alteration of landscapes through formation of
reservoirs; land disturbance and major ecosystem changes; alteration of aquatic and streamside
habitats; effects on water quality and quantity; climate-changing air emissions; displacement of
human, fish, or wildlife populations; interruption of migratory patterns for fish; injury or death to
fish passing through turbines; and risk of catastrophic failure of a dam, depending on the design
and scale of the technology employed.
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