HYDROELECTRIC POWER

Dams are what people most associate when it comes to hydroelectric power. Water flows through the dam’s turbines to produce electricity, known as pumped-storage hydropower. Run-of-river hydropower uses a channel to funnel water through rather than powering it through a dam.

Benefits

Hydroelectric power is very versatile and can be generated using both large scale projects, like the Hoover Dam, and small scale projects like underwater turbines and lower dams on small rivers and streams. Hydroelectric power does not generate pollution, and therefore is a much more environmentally-friendly energy option for our environment.

Current Limitations

Most U.S. hydroelectricity facilities use more energy than they are able to produce for consumption. The storage systems may need to use fossil fuel to pump water.[3]  Although hydroelectric power does not pollute the air, it disrupts waterways and negatively affects the animals that live in them, changing water levels, currents, and migration paths for many fish and other freshwater ecosystems.

How Hydroelectric Work

Parts of a Hydroelectric Plant

Most conventional hydroelectric plants include four major components (see graphic below):

1. Dam. Raises the water level of the river to create falling water. Also controls the flow of water. The reservoir that is formed is, in effect, stored energy.
2. Turbine. The force of falling water pushing against the turbine's blades causes the turbine to spin. A water turbine is much like a windmill, except the energy is provided by falling water instead of wind. The turbine converts the kinetic energy of falling water into mechanical energy.
3. Generator. Connected to the turbine by shafts and possibly gears so when the turbine spins it causes the generator to spin also. Converts the mechanical energy from the turbine into electric energy. Generators in hydropower plants work just like the generators in other types of power plants.
4. Transmission lines. Conduct electricity from the hydropower plant to homes and business.
   

Now all we need to do is a little mathematics. Engineers have found that we can calculate the power of a dam using the following formula:

Power = (Height of Dam) x (River Flow) x (Efficiency) / 11.8

Power	The electric power in kilowatts (one kilowatt equals 1,000 watts).
Height of Dam	The distance the water falls measured in feet.
River Flow	The amount of water flowing in the river measured in cubic feet per second.
Efficiency	How well the turbine and generator convert the power of falling water into electric power. For older, poorly maintained hydroplants this might be 60% (0.60) while for newer, well operated plants this might be as high as 90% (0.90).
11.8	Converts units of feet and seconds into kilowatts.

For the dam in our area, lets say we buy a turbine and generator with an efficiency of 80%.

Then the power for our dam will be:

Power = (10 feet) x (500 cubic feet per second) x (0.80) / 11.8 = 339 kilowatts

To get an idea what 339 kilowatts means, let's see how much electric energy we can make in a year.

Since electric energy is normally measured in kilowatt-hours, we multiply the power from our dam by the number of hours in a year.

Electric Energy = (339 kilowatts) x (24 hours per day) x (365 days per year) = 2,969,000 kilowatt hours.

The average annual residential energy use in the U.S. is about 3,000 kilowatt-hours for each person. So we can figure out how many people our dam could serve by dividing the annual energy production by 3,000.

People Served = 2,969,000 kilowatts-hours / 3,000 kilowatt-hours per person) = 990 people.