electric utility power station uses either a turbine, engine,
water wheel, or other similar machine to drive an electric
generator or a device that converts mechanical or chemical
energy to electricity. Steam turbines, internal-combustion
engines, gas combustion turbines, water turbines, and wind
turbines are the most common methods to generate electricity.
of the electricity in the United States is produced in steam
turbines. A turbine converts the kinetic energy of a moving
fluid (liquid or gas) to mechanical energy. Steam turbines
have a series of blades mounted on a shaft against which steam
is forced, thus rotating the shaft connected to the generator.
In a fossil-fueled steam turbine, the fuel is burned in a
furnace to heat water in a boiler to produce steam.
petroleum (oil), and natural gas are burned in large furnaces
to heat water to make steam that in turn pushes on the blades
of a turbine. Did you know that coal is the largest
single primary source of energy used to generate electricity
in the United States? In 1998, more than half (52%) of the
county's 3.62 trillion kilowatt-hours of electricity used
coal as its source of energy.
gas, in addition to being burned to heat water for steam,
can also be burned to produce hot combustion gases that pass
directly through a turbine, spinning the blades of the turbine
to generate electricity. Gas turbines are commonly used when
electricity utility usage is in high demand. In 1998, 15%
of the nation's electricity was fuelled by natural gas.
can also be used to make steam to turn a turbine. Residual
fuel oil, a product refined from crude oil, is often the petroleum
product used in electric plants that use petroleum to make
steam. Petroleum was used to generate less than three percent
(3%) of all electricity generated in U.S. electricity plants
power is a method in which steam is produced by heating
water through a process called nuclear fission. In a nuclear
power plant, a reactor contains a core of nuclear fuel, primarily
enriched uranium. When atoms of uranium fuel are hit by neutrons
they fission (split), releasing heat and more neutrons. Under
controlled conditions, these other neutrons can strike more
uranium atoms, splitting more atoms, and so on. Thereby, continuous
fission can take place, forming a chain reaction releasing
heat. The heat is used to turn water into steam, that, in
turn, spins a turbine that generates electricity. Nuclear
power is used to generate 19% of all the country's electricity.
the source for 9% of U.S. electricity generation, is a process
in which flowing water is used to spin a turbine connected
to a generator. There are two basic types of hydroelectric
systems that produce electricity. In the first system, flowing
water accumulates in reservoirs created by the use of dams.
The water falls through a pipe called a penstock and applies
pressure against the turbine blades to drive the generator
to produce electricity. In the second system, called run-of-river,
the force of the river current (rather than falling water)
applies pressure to the turbine blades to produce electricity.
power comes from heat energy buried beneath the surface
of the earth. In some areas of the country, magma (molten
matter under the earth's crust) flows close enough to the
surface of the earth to heat underground water into steam,
which can be tapped for use at steam-turbine plants. This
energy source generates less than 1% of the electricity in
is derived from the energy of the sun. However, the
sun's energy is not available full-time and it is widely scattered.
The processes used to produce electricity using the sun's
energy have historically been more expensive than using conventional
fossil fuels. Photovoltaic conversion generates electric power
directly from the light of the sun in a photovoltaic (solar)
cell. Solar-thermal electric generators use the radiant energy
from the sun to produce steam to drive turbines. Less than
1% of the nation's electricity is based on solar power.
is derived from the conversion of the energy contained in
wind into electricity. Wind power like the sun, is usually
an expensive source of producing electricity, and is used
for less than 1% of the nation's electricity. A wind turbine
is similar to a typical wind mill.
(wood, municipal solid waste (garbage), and agricultural waste,
such as corn cobs and wheat straw, are some other energy sources
for producing electricity. These sources replace fossil fuels
in the boiler. The combustion of wood and waste creates steam
that is typically used in conventional steam-electric plants.
Biomass accounts for less than 1% of the electricity generated
in the United States.