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Professor Quester Answers
Questions on Hydroelectric Power

Dear Dr. Quester:
Who discovered that water could be used to make electricity?""(Alex, Fifth grade, Lafayette, CA)

The Professor Answers:
Probably the first turbine to use water was designed by an American mining engineer Lester Pelton. The Pelton wheel had pairs of buckets stopping the water, turning a turbine and is connected to a generator.

The first hydroelectric power station was built in 1882. It could only work 250 light bulbs.

Dear Professor Quester:
What percentage of our energy comes from Hydro-electric? (Alex Fifth grade, Lafayette, CA)

The Professor Answers:
About 27% of California's electricity generation comes from hydroelectric power. About 8.5 % is from out-of-state, the rest is generated in California.

Thanks for asking and if you want more hydroelectric information try the Energy Story.

Dear Professor Quester:
My name is Brandon Suarez and I'm doing a project on hydroelectricity. I am trying to demonstrate a watermill wheel and how it creates energy. I would be pleased if you sent me some information on how these wonderful machines work. You seem to know a lot on this subject, so I selected you to answer my question. I would be obliged if you sent me some information on how watermills, hydroelectricity, or how dams work. Thank you in advance for all your help. (Brandon Suarez, Cotter High School, Winona, MN)

The Professor Answers:
Water wheels were used for irrigation as long ago as 500 B.C.E., (before the common era), but water power was first used for grinding corn around 100 B.C.E. The type of water wheel used depended on how fast the stream or river flowed. There are three types of water wheels: Overshot, Undershot and Horizontal also called "Greek" or "Norse." Overshot wheels (the traditional thought of water wheels) are used where water falls from a great height but is slow moving. The water pulls one side of the wheel around with it as the water falls from the top. Undershot wheels are used in fast-moving water. The water passes under the wheel and pushes blades, which turn the wheel. This could be connected to heavy machinery in factories. Horizontal water wheels were used to grind grain into flour. Grain was placed into the top of a funnel-shaped container, called a hopper, and fell down between the millstones. Horizontal wheel needed fast-moving water to be effective. Water wheels became obsolete when steam turbines came on the scene because steam could be generated anywhere, not just along a river.

Modern dams use similar technology except the stored water is funneled through channels or pipes that push this high pressure water through the blades of a turbine. This turbine generates electricity.

For pictures of these different types of water wheels or dam generation type your library resources or search the 'Net.  A very good book that explains science simply is the Eyewitness Science series...try the Energy series.

We hope that answers your question.

Dear Dr. Q:
I want to know, how to make a model in scale of a Pelton turbine. I need that it produce some energy. I'm in the second semester in the Universidad Pontificia Bolivariana. (Juan Jose, Medellin-Colombia.)

The Professor Answers:
I sorry I'm not able to help you construct a scale model of the Pelton turbine however the Pelton wheel is a flywheel system with pairs of "buckets" to stop the water and turn a belt that is connected to a generator.

Good luck with your project.

Dear Dr. Q:
I was doing a physics project regarding hydroelectricity and these few questions came across my mind that I can't answer. I would like to know if there is a minimum requirement for the speed of the water as it is flowing to convert the energy to hydroelectricity. I would also like to know which country in Southeast Asia has the ability (financially and the geology) to build dams. Also, does a dam require much taking care after it is built? What are the minimum requirements to build a dam? I would appreciate if you could answer these questions. Thank you.

The Professor Answers:
Interesting questions. I'm not certain if I can answer all of them. First, regarding the minimum water speed. It's not the speed of the water that's important, it's the volume, force and drop (the higher the drop and more volume, the more force). There are two main categories of hydroelectric power generation: conventional methods, which produce electricity via water flow in one direction (and are therefore dependent on seasonal runoff), and pumped storage methods, which are both producers and consumers of electricity as the water used to generate electricity can be recycled by pumping it back uphill.

Two types of conventional hydroelectric facilities are dams and run-of-river. Dams raise the water level of a stream or river to an elevation necessary to create a sufficient elevation difference (water pressure, or head). Run-of-river, or water diversion, facilities typically divert water from its natural channel to run it through a turbine, and then usually return the water to the channel downstream of the turbine.

We have some more basic information on hydro. Check out this address

There are also some additional links such as the Bureau of Reclamation. They have a technical report at this address:

If YOU have a question about energy, send your question by e-mail to "Professor Quester."
Ask your parents or teacher first before sending an e-mail. Please tell us your grade level, the name of your school and your city. We will usually respond within four or five days.

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Page updated: May 17, 2002
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