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.
Take a look at this diagram (courtesy of the Tennessee Valley Authority) of a hydroelectric power plant to see the details:
The theory is to build a dam on a large river that
has a large drop in elevation (there are not many hydroelectric plants
in Kansas or Florida). 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!
This diagram of a hydroelectric generator is courtesy of U.S. Army Corps of Engineers.
As to how this generator works, the Corps of Engineers explains it this way:
"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."