Hydro-electric
Power Plants capture the energy released by water falling
through a vertical distance, and transform this energy
into useful electricity. In general, falling water is
channeled through a turbine which converts the water's
energy into mechanical power. The rotation of the water
turbines is transferred to a generator, which produces
electricity. The amount of electricity which can be generated
at a hydro-electric plant is dependent upon two factors.
These factors are :
the
vertical distance through which the water falls, called
the "head", and
The
flow rate measured as volume per unit time
.
The electricity produced is proportional to the product of the head
and the rate of flow. The following is an equation, which may be used
to roughly determine the amount of electricity, which can be generated,
by a potential hydro-electric power site:
POWER (kW) = 5.9 x FLOW x HEAD
In this equation, FLOW is measured in cubic meters per second and HEAD
is measured in meters. Based on the facts presented above, hydro-electric
power plants can generally be divided into two categories. "High
head" power plants are the most common and generally utilize a
dam to store water at an increased elevation. The use of a dam to impound
water also provides the capability of storing water during rainy periods
and releasing it during dry periods. This results in the consistent
and reliable production of electricity, able to meet demand. Heads
for this type of power plant may be greater than 1000 m. Most large
hydro-electric facilities are of the high head variety. High head plants
with storage are very valuable to electric utilities because they can
be quickly adjusted to meet the electrical demand on a distribution
system. "Low head" hydro-electric plants are power plants
which generally utilize heads of only a few meters or less. Power plants
of this type may utilize a low dam or weir to channel water, or no
dam and simply use the "run of the river". Run of the river
generating stations cannot store water, thus their electric output
varies with seasonal flows of water in a river. A large volume of water
must pass through a low head hydro plant's turbines in order to produce
a useful amount of power. Hydroelectric facilities with a capacity
of less than about 25 MW (1 MW = 1,000,000 Watts) are generally referred
to as "small hydro", although hydro-electric technology is
basically the same regardless of generating capacity.
P = u.g.H.Q, where u = overall coefficient of efficiency.
Most conventional hydropower plants include six major components.
Dam.
Controls the flow of water and increases the elevation to create
the head the reservoir that is formed is, in effect, stored energy.
Penstock.
Carries water from the reservoir to the turbine in a power
plant.
Turbine.
Turned by the force of water pushing against
its blades.
.Generator.
Connects to the turbine and rotates to produce
the electrical energy.
Transmission
lines. Conduct electricity from the hydropower
plant to the electric distribution system
The principal advantages of using hydropower
are its large renewable domestic resource
base, the absence of polluting emissions
during operation,
its capability in some cases to respond quickly to utility load demands,
and its very low operating costs. Disadvantages can include high initial
capital cost and potential site-specific and cumulative environmental
impacts. Potential environmental impacts of hydropower projects include
altered flow regimes below storage reservoirs or within diverted stream
reaches, water quality degradation, mortality of fish that pass through
hydroelectric turbines, blockage of upstream fish migration, and flooding
of terrestrial ecosystems by new impoundments. However, in many cases,
proper design and operation of hydropower projects can mitigate these
impacts. Hydroelectric projects also include beneficial effects such
as recreation in reservoirs or in tailwaters below dams
