A "generator" and "motor" are essentially the
same thing: what you call it depends on whether electricity is going
into the unit or coming out of it.
A generator produces electricity. In a generator, something
causes the shaft and armature to spin. An electric current is generated,
as shown in the picture (lighting bolt).
Lots of things can be used to make a shaft spin - a pinwheel, a
crank, a bicycle, a water wheel, a diesel engine, or even a jet
engine. They're different sizes but it's the same general idea.
It doesn't matter what's used to spin the shaft - the electricity
that's produced is the same.
A motor uses electricity. In a motor, the electricity comes
in through wires attached to the positive (+) and negative (-) terminals.
The electric current causes the armature and shaft to spin. If there's
just a little current and it's a small motor,
it won't do very much work (i.e. it can only spin a small fan).
If it's a large motor and it's using a lot of electricity, it can
do a lot of work (i.e. spin a large fan very fast; lift a very heavy
load; or whatever the motor is being used for).
Electric generators are essentially very large quantities of copper
wire spinning around inside very large magnets, at very high speeds.
A commercial utility electric generator -- for example, a 180-megawatt
generator at the Hawaiian Electric Company's Kahe power plant on Oahu
-- can be quite large. It is 20 feet in diameter, 50 feet long, and
weighs over 50 tons. The copper coils (called the "armature")
spin at 3600 revolutions per minute. Although the principle is simple
(copper wire and magnets), it's not necessarily easy!
Steam turbine generators, gas turbine generators, diesel engine generators,
alternate energy systems (except photovoltaics), even nuclear power
plants all operate on the same principle - magnets plus copper wire
plus motion equals electric current. The electricity produced is the
same, regardless of source.
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So where do all the different fuels come in? It's all
a question of how to get (and keep) the system moving (i.e.
how to keep the copper wire spinning around).
In a steam power plant, fuels (such as petroleum,
coal, or biomass) are burned to heat water which turns into
steam, which goes through a turbine, which spins...turning
the copper wire (armature) inside the generator and generating
an electric current.
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A geothermal power plant is pretty much a steam
power plant, since what comes out of the earth is steam. Rainwater
soaks into the ground and goes down, down, down...far enough until
it reaches a region which is really hot (in Hawaii, that's about 6000
feet). A well is drilled, the steam comes out, goes through a heat
exchanger, and spins a turbine... turning the copper wire (armature)
inside the generator and generating an electric current. By the
time the steam has gone through the heat exchanger, it has cooled
off and become warm water. It is then re-injected into the ground.
In a gas turbine power plant, fuels are burned to
create hot gases which go through a turbine, which spins...turning
the copper armature inside the generator and generating an electric
current.
In a nuclear power plant, nuclear reactions create
heat to heat water, which turns into steam, which goes through a turbine,
which spins...turning the copper armature inside the generator
and generating an electric current.
In a wind turbine, the wind pushes against the turbine
blades, causing the rotor to spin...turning the copper armature
inside the generator and generating an electric current.
In a hydroelectric turbine, flowing (or falling)
water pushes against the turbine blades, causing the rotor to spin...turning
the copper armature inside the generator and generating an electric
current.
Consumers expect electricity to be available whenever they plug in an appliance,
turn a switch, or open a refrigerator. Satisfying these instantaneous demands
requires an uninterrupted flow of electricity. In order to meet this requirement,
utilities and nonutility electricity power producers operate several types
of electric generating units, powered by a wide range of fuel sources. These
include fossil fuels (coal, natural gas, and petroleum), uranium, and renewable
fuels (water, geothermal, wind, and other renewable energy sources).
| Coal was the fuel used to generate the largest share (51.8 percent)
of electricity in 2000 1,968 billion kilowatthours(kWh). This is over
one and a half times the annual electricity consumption of all U.S. households
(1,141 billion kWh). Natural gas was used to generate 612 billion kWh
(16.1 percent), and petroleum accounted for 109 billion kWh (3 percent).
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Steam-electric generating units burn fossil fuels, such as coal, natural
gas, and petroleum. The steam turns a turbine that produces electricity through
an electrical generator. Natural gas and petroleum are also burned in gas
turbine generators where the hot gases produced from combustion are used to
turn the turbine, which, and in turn, spins the generator to produce electricity.
Additionally, petroleum is burned in generating units with internal-combustion
engines. The combustion occurs inside cylinders of the engine, which is connected
to the shaft of the generator. The mechanical energy provided from the engine
drives the generator to produce energy.
In 2000, approximately 40 quads of energy were used to generate electricity.
Roughly one-third of this was converted into the 13 quads of electricity that
reached end-users (3,800 billion kilowatthours). The other two-thirds wound
up mostly as waste heat and dissipated into the environment.
In nuclear-powered generating units, the boiler is replaced by a reactor
in which the fission of uranium is used to make steam to drive the turbine.
Nuclear generating units accounted for the second largest share (20 percent)
of electricity generation in the United States in 2000, 754 billion kWh.
Hydro electricity units use flowing water to spin a turbine connected to
a generator. In a falling water system, water is accumulated in reservoirs
created by dams, then released through conduits to apply pressure against
the turbine blades to drive the generator. In a run-of-the-river system, the
force of the river current applies the pressure to the turbine blades to produce
electricity. In 2000, hydroelectric generation had the fourth largest share
(7 percent) of electricity production at 273 billion kWh..
Nonwater renewable sources of electricity generation presently contribute
only small amounts (about 2 percent) to total power production. These sources
include geothermal, refuse, waste heat, waste steam, solar, wind, and wood.
Electricity generation from these sources in 2000 totaled 84 billion kWh.
Total electric power industry generation in 2000 was 3,800 billion kWh, 2.5
percent greater than the 1999 total of 3,705 billion kWh. Of this total, utilities
net generation for 2000 was 3,015 billion kWh, and net generation by nonutility
power producers was 785 billion kWh.
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