Lesson: Generators: Three Mile Island vs. Hoover Dam

Contributed by: Techtronics Program, Pratt School of Engineering, Duke University

A row of seven gigantic cylindrical devices in a concrete room.
Hydroelectric turbines at the Hoover Power Plant.
Copyright © U.S. Department of the Interior


Students are given a history of electricity and its development into the modern age—an energy lifeline upon which our society so depends. A range of methods of electrical power generation are introduced—turbines, hydroelectric, steam, fuel cells, solar power and wind power—along with further discussion of each technology's pros and cons.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Understanding energy issues is an important part of engineering, as is the ability to clearly explain technological concepts in terms suitable for one's audience.

Learning Objectives

After this lesson, students should be able to:

  • Describe important discoveries leading to electricity.
  • Name different sources of power generation and how they work.
  • List the pros and cons of each method of power generation.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • New products and systems can be developed to solve problems or to help do things that could not be done without the help of technology. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • The use of technology affects humans in various ways, including their safety, comfort, choices, and attitudes about technology's development and use. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Throughout history, new technologies have resulted from the demands, values, and interests of individuals, businesses, industries, and societies. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • The use of inventions and innovations has led to changes in society and the creation of new needs and wants. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Energy can be used to do work, using many processes. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Power is the rate at which energy is converted from one form to another or transferred from one place to another, or the rate at which work is done. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Much of the energy used in our environment is not used efficiently. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Explain the implications of the depletion of renewable and nonrenewable energy resources and the importance of conservation. (Grade 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Explain the environmental implications associated with the various methods of obtaining, managing, and using energy resources. (Grade 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Evaluate human behaviors in terms of how likely they are to ensure the ability to live sustainably on Earth. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Evaluate alternative energy technologies for use in North Carolina. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
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Get students geared up for this lesson with a 15-minute demonstration to the class of anything electronic, preferably involving sparks, noise and/or moving parts. Many demonstrations and explanations are available at the Society for Amateur Science's webpage at http://www.amasci.com/scied.html. Because different schools have different resources available, a specific activity is not outlined here. Be sure to verify the safety of an experiment from the web before performing it around students. Then present students with the content information in the Lesson Background section.

Have students brainstorm in pairs or small groups to come up with criteria for electric power plants and constraints in their design. Then have them report out and use their ideas to lead a brief discussion. Possible student answers will hopefully include:

  • A power plant should be capable of generating enough electricity for thousands of people (large-scale)
  • Generated electricity should be affordable
  • Energy sources used to supply a power plant should be renewable
  • Energy sources should be from local/national supplies
  • A power plant should not pollute the air, land, or water
  • A power plant should not cause irreparable damage to local ecosystems
  • A power plant should not be an eyesore

Tell students to keep these ideas in mind as you discuss the types of electricity generation outlined below. Ask them if any type meets all or most of these criteria and constraints.

Lesson Background and Concepts for Teachers

Key points in the history of electricity are provided below, serving as a historical background for the teacher.

Early Qualitative Observations

  • As early as 600 BC, it was known that amber could be charged by rubbing it with a cloth.
  • William Gilbert, the father of modern electricity, observed this process on many substances around 1600.
  • In 1660, Otto von Guericke invented a machine that generated static electricity.
  • Robert Boyle recognized that attraction and repulsion were related, which contributed to C.F. Du Fay recognizing two types of charge, later named positive and negative by Benjamin Franklin and Ebenezer Kinnersley.
  • In 1729, Stephen Gray recognized conductors and nonconductors as the two types of materials known to exist.


  • Pieter van Musschenbroek invented an early form of capacitor that could store and discharge electricity, leading William Watson to discover current and the modern circuit in 1747.
  • Henry Cavendish began measuring conductivity (how easily electricity flows through a material) and Charles Coulomb came up with mathematical expressions relating force and charge—a fact not always appreciated by introductory physics students.
  • In 1786, Luigi Galvani observed a relationship between muscle tissue and electricity and the exciting field of electrobiology was born.
  • Alessandro Volta invented the battery shortly thereafter. In 1827 and 1841 respectively, G.S. Ohm and J.P. Joule stated their laws, and soon after Kirchoff contributed his as well. These statements that describe natural "laws" led to the quantitative analysis of electric circuits.
  • James Maxwell came up with his famous equations describing electromagnetic fields in 1873 and Heinrich Hertz proved them.
  • Andre Ampere gave mathematical form to Oersted's discovery that currents in a wire create a magnetic field.
  • Michael Faraday and Joseph Henry independently developed the generator.

Key concepts on power generation methods are as follows

Methods of Power Generation

  • Electricity is a naturally occurring phenomena.
  • The majority of power generating systems involve mechanical power being converted into electrical power through the use of turbines, which work like motors, only backwards.
  • These turbines can be driven by any moving fluid; however, most operate as heat engines driven by steam.
  • Steam can be produced in a variety of ways: nuclear, geothermal and fossil fuels.
  • Coal plants produce the vast majority of power in the U.S.

Hydroelectric Power

  • Hydroelectric power plants operate on the flow of water from human-made or naturally occurring bodies of water. Gravity provides the energy source that causes water to move downstream or through dams.
  • Turbines transfer this into a power output when their rotors are turned by the flow.
  • They are highly efficient (~80%) and utilize an abundant renewable resource.
  • They require a body of water and altitude gradient.
  • They pose serious environmental threats because they
  1. Disrupt flooding cycles needed to deposit rich nutrients on surrounding land,
  2. Prevent spawning of many fish species,
  3. Flood large plots of land, destroying valuable habitats and even entire ecosystems.
  4. Are not permanent; reservoirs silt up over time.

Steam & Nuclear Power

  • Geothermal sources of steam exist that can power turbines, but are location specific and require geothermally active sites.
  • Efficiencies of up to 80% can be reached using mechanical power to generate electrical power. Most losses occur due to heat loss from friction in turbines, and also from direct heat transfer out of imperfectly insulated systems.
  • The laws of thermodynamics dictate the maximum efficiency possible for a system.
  • Simply stated, they are as follows:
  1. Matter and energy are always conserved. This means that a finite amount of energy exists in the universe. Energy can neither be created, nor destroyed.
  2. After an energy transformation, a system cannot return to its original energy state because there is always an increase in disorder. In other words, entropy always increases.
  • Efficiency is further limited by heat limits and safety concerns. Most steam plants operate at efficiencies of around 40%, nuclear at 30%.
  • Environmental concerns are very important with such power plants.
  1. Huge problems arise from combustion of fossil fuels because of their harmful byproducts that are released into the environment. Expensive methods exist to reduce the amount of pollution that gets into the air.
  2. Nuclear power leaves us with fission byproducts, which remain highly dangerous for millions of years and must be stored somewhere.
  3. Improper control of fission reactors can lead to meltdown, a disastrous situation that causes the reactor fuel to melt into the earth, releasing massive amounts of pressure, heat and radioactive material that could affect millions. Extensive regulation exists along with numerous safeties to prevent this from ever happening; they arose in part from the two near meltdowns that occurred at Three Mile Island and Chernobyl.
  4. A huge amount of heat must be released into the environment, regardless of how it is generated. This often ends up in streams and lakes, destroying fragile ecosystems.

Fuel Cells

  • Convert chemical power of hydrogen and some other substances directly into electrical power.
  • Require production of hydrogen by some other means.
  • Hydrogen can be stored and distributed much like oil and gasoline as a fuel source, but is more environmentally friendly in the event of a release.
  • The technology is currently very expensive due to requirement of platinum as a catalyst in the process.
  • Are highly efficient, 50-60 % currently, however theoretically this could reach values much closer to 100%.
  • The byproduct of this process is water, and nothing is consumed.

Solar Power

  • Photovoltaic cells directly convert light radiation to electrical power.
  • Solar power is a renewable resource.
  • Real-time energy source that cannot store energy (or else requires storage systems).
  • They are clean, quiet and give off no harmful byproducts.
  • Requires presence of sunlight, thus are not ideal where days are very short for much of the year, though often no other options exist in remote locations.
  • Panels are expensive and have a broad range of efficiencies up to about 30% (typically 10-15%) depending on panel type.

Wind Power

  • Clean and efficient renewable power source.
  • Requires presence of wind; often placed on ridgelines to accomplish this.
  • Must be maintained to reduce noise pollution.
  • Are often perceived as an eyesore.


catalyst: An element that causes a chemical reaction to begin; in a fuel cell, it is usually platinum.

energy: A measurement of ability of a system to do work.

fuel cell: A device that directly transforms hydrogen gas and oxygen into water and electricity.

photovoltaic cell: A device that directly transforms light radiation into electricity.

power: A measure of the amount of energy being used or generated per unit of time (energy/time).

renewable resource: An abundant resource that is not consumed during the process of power generation.

turbine : A device that produces electricity through the action of fast moving liquid, steam or gas.

Associated Activities

  • Win that Bid! Selling Your Power Solution - Students hone their problem solving and presentation skills as they create market studies and persuasive presentations to sell specific power solutions to a growing community.

Lesson Closure

Although electricity's existence has been known for thousands of years, it has not been until the last two centuries that we have begun to understand its true nature.

Only in the last century have we been able to harness electrical power for general use.

Original coal and oil-fueled steam turbines release harmful hydrocarbons and other substances into the environment, but provide a cheap energy source.

Hydroelectric plants provide a cleaner source of power, but their negative effects have made them unpopular in recent years.

Nuclear power originally promised to provide an inexhaustible source of power, but lost popularity in the late 1970s, when among other things, the very-close-to-home Three Mile Island in Harrisburg, PA, had a near disastrous meltdown due to negligence. Then the 1986 meltdown at Chernobyl increased public fears immensely.

Solar power used in conjunction with fuel cell technologies provide us with hope for the future; however, high initial costs are making this renewable energy source slow to take off.



  • Divide the class into teams and play a fact game on electricity and power.
  • The winning team gets a prize; make sure they know about this at the start.
  • Popcorn questions to students while presenting the information to them to make sure they are on their toes.


  • Have students list two pros and two cons for each type of power plant.

Lesson Extension Activities

Have students investigate and describe areas of cutting-edge power source and power supply research.


Physics Demos & Science Exhibit Designs. Accessed June 22, 2004.http://www.amasci.com/scied.html

History of Electricity, HighBeam Encyclopedia. http://www.encyclopedia.com/html/section/electity_historyofelectricity.asp, 06-22-04

Sources of Electrical Energy, HighBeam Encyclopedia. http://www.encyclopedia.com/html/section/power-el_ SourcesofElectricalEnergy.asp, 06-22-04

What is a simple defintion of the laws of thermodynamics? http://www.physlink.com/Education/AskExperts/ae280.cfm, 06-22-04


Brandon Jones


© 2013 by Regents of the University of Colorado; original © 2004 Duke University

Supporting Program

Techtronics Program, Pratt School of Engineering, Duke University


This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: August 29, 2017