Download Hydroelectric power: How it works

HYDRO POWER
Hydroelectric power: How it works
So just how do we get electricity from water?
Actually, hydroelectric and coal-fired power
plants produce electricity in a similar way. In
both cases a power source is used to turn a
propeller-like piece called a turbine, which
then turns a metal shaft in an electric
generator, which is the motor that produces
electricity. A coal-fired power plant uses
steam to turn the turbine blades; whereas a
hydroelectric plant uses falling water to turn
the turbine. The results are the same.
The dam stores lots of water behind it in the
reservoir. Near the bottom of the dam wall
there is the water intake. Gravity causes it to
fall through the penstock inside the dam. At
the end of the penstock there is a turbine
propeller, which is turned by the moving
water. The shaft from the turbine goes up
into the generator, which produces the
power. Power lines are connected to the
generator that carry electricity to your home
and mine. The water continues past the
propeller through the tailrace into the river
past the dam. By the way, it is not a good
idea to be playing in the water right below a
dam when water is released!
"A hydraulic turbine converts the
energy of flowing water into
mechanical energy. A hydroelectric
generator converts this mechanical
energy into electricity. The operation
of a generator is based on the
principles discovered by Faraday. He
found that when a magnet is moved
past a conductor, it causes electricity
to flow. In a large generator,
electromagnets are made by
circulating direct current through
loops of wire wound around stacks of
magnetic steel laminations. These are
called field poles, and are mounted
on the perimeter of the rotor. The
rotor is attached to the turbine shaft,
and rotates at a fixed speed. When
the rotor turns, it causes the field
poles (the electromagnets) to move
past the conductors mounted in the
stator. This, in turn, causes electricity
to flow and a voltage to develop at the
generator output terminals."
Pumped storage: Reusing water for peak electricity demand
Demand for electricity is not "flat" and constant. Demand goes up and down during the
day, and overnight there is less need for electricity in homes, businesses, and other
facilities. For example, here in Atlanta, Georgia at 5:00 PM on a hot August weekend day,
you can bet there is a huge demand for electricity to run millions of air conditioners! But, 12
hours later at 5:00 AM .... not so much. Hydroelectric plants are more efficient at providing
for peak power demands during short periods than are fossil-fuel and nuclear power plants,
and one way of doing that is by using "pumped storage", which reuses the same water more
than once.
Pumped storage is a method of keeping water in reserve for peak period power demands by
pumping water that has already flowed through the turbines back up a storage pool above
the powerplant at a time when customer demand for energy is low, such as during the
middle of the night. The water is then allowed to flow back through the turbine-generators
at times when demand is high and a heavy load is placed on the system.
Electricity from Hydropower
Hydropower is considered a renewable energy resource because it uses the Earth's water
cycle to generate electricity. Water evaporates from the Earth's surface, forms clouds,
precipitates back to earth, and flows toward the ocean.
The movement of water as it flows downstream creates kinetic energy that can be
converted into electricity. A hydroelectric power plant converts this energy into electricity
by forcing water, often held at a dam, through a hydraulic turbine that is connected to a
generator. The water exits the turbine and is returned to a stream or riverbed below the
dam.
Hydropower is mostly dependent upon precipitation and elevation changes; high
precipitation levels and large elevation changes are necessary to generate significant
quantities of electricity. Therefore, an area such as the mountainous Pacific Northwest has
more productive hydropower plants than an area such as the Gulf Coast, which might have
large amounts of precipitation but is comparatively flat.
Water Discharges
Hydroelectric power plants release water back into rivers after it passes through turbines.
This water is not polluted by the process of creating electricity.
Solid Waste Generation
The use of water to create electricity does not produce a substantial amount of solid waste.
Air Emissions
Hydropower's air emissions are negligible because no fuels are burned. However, if a large
amount of vegetation is growing along the riverbed when a dam is built, it can decay in the
lake that is created, causing the buildup and release of methane, a potent greenhouse gas.
Environmental Impacts
Although hydropower has no air quality impacts, construction and operation of
hydropower dams can significantly affect natural river systems as well as fish and wildlife
populations. Assessment of the environmental impacts of a specific hydropower facility
requires case-by-case review.
Although power plants are regulated by federal and state laws to protect human health and
the environment, there is a wide variation of environmental impacts associated with power
generation technologies.
The purpose of the following section is to give consumers a better idea of the specific
ecological impacts associated with hydropower.
Water Resource Use
Hydropower often requires the use of dams, which can greatly affect the flow of rivers,
altering ecosystems and affecting the wildlife and people who depend on those waters.
Often, water at the bottom of the lake created by a dam is inhospitable to fish because it is
much colder and oxygen-poor compared with water at the top. When this colder, oxygenpoor water is released into the river, it can kill fish living downstream that are accustomed
to warmer, oxygen-rich water.
In addition, some dams withhold water and then release it all at once, causing the river
downstream to suddenly flood. This action can disrupt plant and wildlife habitats and
affect drinking water supplies.
Although large hydroelectric plants can be
operated economically, the cost of land
acquisition and of dam and reservoir
construction must be included in the total
cost of power, since these outlays generally
account for about half of the total initial
cost. Most large plants serve multiple
purposes: hydropower generation, flood
control, storage of drinking water, and the
impounding of water for irrigation. If the
construction costs are properly prorated to
the non-power-producing utility of the unit,
electricity can be sold very cheaply.
About $10.5 million depending on the size
of the plant. A large plant could be
upwards of $50 million. Small geothermal
plants can be anywhere from $3,000 to
$5,000.