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October 11, 2019
Hydropower plants capture the energy of falling water to generate electricity. A turbine converts the kinetic energy of falling water into mechanical energy. Then a generator converts the mechanical energy from the turbine into electrical energy.
Hydroplants range in size from "micro-hydros" that power only a few homes to giant dams like Hoover Dam that provide electricity for millions of people.
The photo on the next shows the Alexander Hydroelectric Plant on the Wisconsin River, a medium-sized plant that produces enough electricity to serve about 8,000 people.
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.
How Much Electricity Can a Hydroelectric Plant Make?
The amount of electricity a hydropower plant produces depends on two factors:
1. How Far the Water Falls. The farther the water falls, the more power it has. Generally, the distance that the water falls depends on the size of the dam. The higher the dam, the farther the water falls and the more power it has. Scientists would say that the power of falling water is "directly proportional" to the distance it falls. In other words, water falling twice as far has twice as much energy.
2. Amount of Water Falling. More water falling through the turbine will produce more power. The amount of water available depends on the amount of water flowing down the river. Bigger rivers have more flowing water and can produce more energy. Power is also "directly proportional" to river flow. A river with twice the amount of flowing water as another river can produce twice as much energy.
Can I Figure Out How Much Energy a Dam in My Area Can Make?
Sure. It's not that hard.
Let's say that there is a small dam in your area that is not used to produce electricity. Maybe the dam is used to provide water to irrigate farmlands or maybe it was built to make a lake for recreation. As we explained above, you need to know two things:
1. How far the water falls. From talking to the person who operates the dam, we learn that the dam is 10 meters high, so the water falls 10 meters.
2. Amount of water flowing in the river. We contact the United States Geological Survey, the agency in the U.S. that measures river flow, and learn that the average amount of water flowing in our river is 5 stere per second.
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) *9.81
For the dam in our area, let’s say we buy a turbine and generator with an efficiency of 80%.
Then the power for our dam will be:
Power = (10 M) x (5 m³ per second) x (0.80)*9.81 =392kilowatts
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