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 great. Anyone who has been white water
rafting knows that!
Hydropower is called a
renewable energy source because it is replenished by snow and rainfall. As long
as the rain falls, we won't 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 pertaining 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.
But by the late 1940s,
the best sites for big dams had been developed. Inexpensive fossil fuel (coal,
oil) plants also entered the picture. At that time, these plants could make electricity
more cheaply than hydro plants. Soon they began to underprice the smaller
hydroelectric plants. It wasn't until the oil shocks of the 1970s that people
showed a renewed interest in hydropower.
Hydroelectric Power 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 (or
hydro plants, as they are usually called) are very different. They use mode
turbine generators to produce electricity just as thermal (coal, oil, nuclear)
power plants do.
How a Hydro Plant
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
a dam that can be opened or closed to control
a reservoir (artificial lake) where water can
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
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.
More about 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. First, 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.)
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.
Some hydro plants also
use pumped storage systems. A pumped storage system operates much as 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 or may not be
pumped back to an upper pool. Pumping water to the upper pool requires
electricity so hydro plants usually use pumped storage systems 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.
How much electricity do
we get from hydropower today? Quite a bit. Depending on whether the year has
been wet or dry, hydro plants produce from eight to 10 percent of the
electricity produced in this country (almost 8.5 percent in 1994), far more
than any other renewable energy source. In Oregon and Washington, hydropower
supplies over 85 percent of the electricity each year.
Currently, there are
about 75 million kilowatts of hydroelectric 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 country 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 utility
companies buy this imported electricity.
What does the future look
like for hydropower? The best sites for hydropower dams have already been
developed so the development of big hydro plants is unlikely. But existing
plants could be enlarged to provide additional generating capacity. Plus, many
flood-control dams not equipped for 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.
Good source of
base load 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.
companies have to produce electricity to meet these changing demands. Base load
power is the electricity that utilities have to generate all the time. For
that reason, base load 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, especially at plants with pumped storage systems.
Hydro 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
Hydro plants also run 85
percent of the time, about 50 percent more than thermal plants.
Economics of Hydropower and the Environment
Hydropower is the cheapest
way to generate electricity today. No other energy source, renewable or
nonrenewable, can match it. In 1994 it cost less than one cent per kWh
(kilowatt-hour) to produce electricity at a typical hydro plant. In comparison,
it costs coal plants about four cents per kWh and nuclear plants two cents per
kWh to generate electricity.
from hydropower is cheap because, once a dam has been built and the equipment
installed, the energy source-flowing water-is free.
Another reason hydro
plants produce power cheaply is 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.
There is one thing that
may increase hydropower's costs 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 times 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 dam.
Hydropower and the
Hydropower does present a
few environmental problems. Damming rivers may destroy or disrupt wildlife and
natural resources. Fish, for one, may no longer be able to swim upstream.
Hydro plant operations
may also affect water quality by churning up dissolved metals that may have
been deposited by industry long ago. Hydro plant operations may increase
silting, change water temperatures, and lower the levels of dissolved oxygen.
To some degree, these problems can be managed by constructing fish ladders,
dredging silt, and carefully regulating plant operations.
On the plus side,
hydropower's fuel supply (flowing water) is clean and is renewed yearly by snow
and rainfall. Unlike fossil fuel plants, hydro plants do not emit any
pollutants into the air because they bum no fuel.
Hydropower is also the
only energy source that offers a whole range of added benefits. Dams control
flood waters, and reservoirs provide lakes for boating, fishing, and swimming.