What is Hydropower?
Hydropower (from hydro meaning water) is energy that
comes from the force of moving water. The fall and flow
of water is part of a continuous natural cycle. The sun
draws moisture up from the oceans and rivers, and the
moisture then condenses into clouds in the atmosphere.
The moisture falls as rain or snow, replenishing the
oceans and rivers. Gravity drives the water, moving it
from high ground to low ground. The force of moving water
can be extremely powerful.
Hydropower is called a renewable energy source because it
is replenished by snow and rainfall. As long as the rain
falls, we will not run out of this energy source.
History of Hydropower
Hydropower has been used for centuries. The Greeks used
water wheels to grind wheat into flour more than 2000
years ago. In the early 1800s, American and European
factories used the water wheel to power machines. The
water wheel is a simple machine. The water wheel picks up
flowing water in buckets located around the wheel. The
weight of the water causes the wheel to turn. Water
wheels convert the kinetic energy (energy pertain to
motion) of water to mechanical energy. The mechanical
energy can then be used to grind grain, drive sawmills,
or pump water.
In the late 19th century, the force of falling water was
used to generate electricity. The first hydroelectric
power plant was built at Niagara Falls in 1879. In the
following decades, many more hydroelectric plants were
built. At its height in the early 1940s, hydropower
provided 33 percent of this country's electricity. By the
late 1940s, the best sites for big dams had been
developed. Inexpensive fossil fuel plants also entered
the picture. At that time, plants burning coal or oil
could make electricity more cheaply than hydro plants.
Soon they began to under price the smaller hydroelectric
plants. It was not until the oil shocks of the 1970s that
people showed a renewed interest in hydropower.
Hydro Dams
It's easier to build a hydro plant where there is a
natural waterfall. That's why the first hydro plant was
built at Niagara Falls. Dams, which are artificial
waterfalls, are the next best way. Dams are built on
rivers where the terrain will produce an artificial lake
or reservoir above the dam. Today there are about 80,000
dams in the United States, but only three percent have
power-generating hydro plants. Most dams are built for
flood control and irrigation, not electric power
generation.
A dam serves two purposes at a hydro plant. Fist, a dam
increases the head or height of a waterfall. Second, it
controls the flow of water. Dams release water when it is
needed for electricity production. Special gates called
spillway gates release excess water from the reservoir
during heavy rainfalls.
Hydropower plants
As people discovered centuries ago, the flow of water
represents a huge supply of kinetic energy that can be
put to work. Water wheels are useful for generating
mechanical energy to grind grain or saw wood, but they
are not practical for generating electricity. Water
wheels are too bulky and slow. Hydroelectric plants are
different. They use modern turbine generators to produce
electricity, just as thermal (coal, oil, nuclear) power
plants do.
How a Hydro Plant Works
A hydro plant uses the force of falling water to make
electricity. A typical hydro plant is a system with three
parts:
-An electric plant where the electricity is produced.
-A dam that can be opened or closed to control water
flow.
-A reservoir (artificial lake) where water can be stored.
To make electricity, a dam opens its gates to allow water
from the reservoir to flow through a large tube called a
penstock. At the bottom of the penstock, the fast-moving
water spins the blades of a turbine. The turbine is
connected to a generator to produce electricity. The
electricity is then transported via huge transmission
lines to a local utility company.
Head and Flow
The amount of electricity that can be generated at a
hydro plant is determined by two factors: head and flow.
Head is how far the water drops. It is the distance from
the highest level of the dammed water to the point where
it goes through the power-producing turbine.
Flow is how much water moves through the system. The more
water moving through a system, the higher the flow.
Generally, a high-head plant needs less water flow than a
low-head plant to produce the same amount of electricity.
Storing Energy
One of the biggest advantages of a hydro plant is its
ability to store energy. The water in a reservoir is,
after all, stored energy. Water can be stored in a
reservoir and released when needed for electricity
production. During the day when people use more
electricity, water can flow through a plant to generate
electricity. Then, during the night when people use less
electricity, water can be held back in the reservoir.
Storage also makes it possible to save water from winter
rains for summer generating power, or to save water from
wet years for generating electricity during dry years.
Pumped Storage-Systems
Some hydro plants use pumped storage systems. A pumped
storage system operates much a public fountain does. The
same water is used again and again. At a pumped storage
hydro plant, flowing water is used to make electricity
and then stored in a lower pool. Depending on how much
electricity is needed, the water may be pumped back to an
upper pool. Pumping water to the upper pool requires
electricity so hydro plants usually use pumped storage
systems only when there is a big demand for electricity.
Pumped hydro is the most reliable energy storage system
used by American electric utilities. Coal and nuclear
power plants have no energy storage systems. They must
turn to expensive gas and oil-fired generators when
people demand lots of electricity. They also have no way
to store any extra energy they might produce during
normal generating periods.
Hydro Production
How much electricity do we get from hydropower today?
Depending on the amount of rainfall, hydro plants produce
from eight to 11 percent of the electricity produced in
this country (10.2 percent in 1997, 9.1 percent in 1998),
far more than any other renewable energy source. In
Oregon and Washington, hydropower supplies over 85
percent of the electricity each year. Today, there are
about 75 million kilowatts of hydro generating capacity
in the United States. That's equivalent to the generating
capacity of 70 large nuclear power plants. The biggest
hydro plant in the U.S. is located at the Grand Coulee
dam on the Columbia River in northern Washington.
The United States also gets some hydropower electricity
from Canada. Some New England utilities buy this imported
electricity.
What does the future look like for hydropower? The vest
sites for hydropower dams have already been developed so
the development of big hydro plants is unlikely. Existing
plants could be enlarged to provide additional generating
capacity. Plus, many flood-control dams not equipped with
electricity production could be outfitted with generating
equipment. The Federal Energy Regulatory Commission
estimates 60 thousand megawatts of additional generating
capacity could be developed in the United States.
Hydropower for Baseload Power
Demand for electricity is not steady; it goes up and
down. People use more electricity during the day when
they are awake and using electrical appliances, and less
at night when they are asleep. People also use more
electricity when the weather is very cold or very hot.
Electric utility companies have to produce electricity to
meet these changing demands. Baseload power is the
electricity that utilities have to generate all the time.
For that reason, baseload power should be cheap and
reliable. Hydropower meets both these requirements.
Generating electricity from flowing water is the cheapest
way to generate electricity in the United States, and the
fuel supply-flowing water-is always available.
Hydropower plants are more energy efficient than thermal
power plants too. That means they waste less energy to
produce electricity. In thermal power plants, a lot of
energy is lost as heat. Hydro plants also run 85 percent
of the time, about 50 percent more than thermal plants.
Economic of Hydropower
Hydropower is the cheapest way to generate electricity
today. No other energy source, renewable or nonrenewable,
can match it. In 1998, it cost about one cent per kWh
(kilowatt-hour) to produce electricity at a typical hydro
plant. In comparison, it cost coal plants about four
cents per kWh and nuclear plants two cents per kWh to
generate electricity. Producing electricity from
hydropower is cheap because, once a dam has been built
and the equipment installed, the energy source-flowing
water-is free. Hydro plants also produce power cheaply
due to their sturdy structures and simple equipment.
Hydro plants are dependable and long-lived, and their
maintenance costs are low compared to coal or nuclear
plants.
One requirement may increase hydropower's cost in the
future. The procedure for licensing a dam has become a
lengthy and expensive process. Many environmental impact
studies must be undertaken. And some time as many as 13
state and federal agencies must be consulted. It takes
anywhere from five to seven years just to get a license
to build a hydroelectric dam.
Hydropower and the Environment
Hydropower dams can cause several environmental problems,
even though they burn no fuel. Damming rivers may destroy
or disrupt wildlife and natural resources. Fish, for one,
may no longer be able to swim upstream. Hydro plant
operation may also affect water quality by churning up
dissolved metals that may have been deposited by industry
long ago. Hydro operations may increase silting, change
water temperatures, and lower the levels of dissolved
oxygen. Constructing fish ladders, dredging silt, and
carefully regulating plant operations can manage some of
these problems.
Hydropower has advantages, too. Hydropower's fuel supply
(flowing water) is clean and is renewed yearly by snow
and rainfall. Furthermore, hydro plants do not emit
pollutants into the air because they burn no fuel. With
growing concern over greenhouse gas emissions, hydropower
may become more important in the future. Hydropower
facilities offer a range of additional benefits. Dams can
control floodwaters and regulate water supply, and
reservoirs can provide lakes for recreation purposes,
such as boating and fishing.
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