Hands-on Activity: Power Your House with Water
Educational Standards :
Pre-Req Knowledge (Return to Contents)
A basic understanding of the concepts of kinetic and potential energy, work and power. To complete the worksheet, ability to solve basic algebraic equations.
Learning Objectives (Return to Contents)
After this activity, students should be able to:
Materials List (Return to Contents)
Each group needs:
For the entire class to share:
Introduction/Motivation (Return to Contents)
How many of you have ever seen the Hoover Dam in Nevada or seen a picture of Hoover Dam? One reason for building the Hoover Dam was to help keep silt and sediment out of the Colorado River. Does anyone know what other role the Hoover Dam plays? That's right; it is also a power plant. The Hoover Dam converts energy from the moving water of the Colorado River into electricity. Hydroelectric power plants are found all over the world. When the Hoover Dam was completed in 1935, it was the largest electricity-generating power plant in the world. Currently it is only the 34th biggest hydroelectric power plant in the world. Engineers continue to make significant improvements in the design of dams to harness the power of water.
Hydroelectric power plants like the Hoover Dam produce electricity from the flow of the water through the dam. Once the water reaches the turbines of the Hoover Dam, it is traveling at about 38 meters per second (85 mph). Given that the entire flow of the Colorado River goes through the Hoover Dam, that flow contains a lot of kinetic energy. The water gets this kinetic energy because of a drop in elevation from the reservoir to the outlet. This drop in height converts the water's potential energy into kinetic energy. The difference in the height of the water is known as the head.
The water is also sped up by forcing the flow through a smaller opening, similar to the effect when you place a finger over a faucet or hose. What you are doing is decreasing the area of the flow of the water, and to make up for the decrease in area, the water flows faster (in keeping with the law of conservation of mass). By combining the two effects, narrowing the cross-section through which the water flows and increasing the energy transfer from potential to kinetic, engineers designed the Hoover Dam to generate a maximum of 2,080 megawatts of power.
Dams like the Hoover Dam are also able to control their power output. When demand is high, adjustments are made so more water flows through and more electricity is produced. Hydroelectric power is not always generated in the same way as the Hoover Dam. Some hydroelectric technologies use just the head between a reservoir and the outlet to generate electricity. Instead of a dam, other hydropower plants just use a small canal to channel the river water through a turbine. Still other plants only pump water through a pipe and then turbines, using the flow of the river to generate electricity.
How a turbine works is fairly simple. Water strikes the turbine blades and spins the turbine, which is connected to a generator with a shaft. The shaft turns the generator causing it to produce a current. The electricity generated is sent through power lines of the power grid to where it is needed. Not all the water's energy transfers into electrical energy; during the transfer, some energy is lost through friction between the shaft and generator, and between water and the blades. Even so, many turbines operate at efficiency ratings of greater than 90%.
Several different types of turbines are currently in use around the world. They each have advantages and disadvantages related to the amount of head and the flow rate of the water. Engineers must analyze everything about the dam, river and resultant reservoir to determine the best type of turbine to use.
Traditionally, power plants used coal to generate electricity. Why might a community want to use water instead of coal as a source of energy and electricity for its buildings? Coal is an example of a non-renewable energy source, or an energy source that is not naturally replenished in a short amount of time. Water though, is a renewable energy source. The Earth's water cycle ensures that rivers and lakes are kept full. Water is also a cleaner way to produce electricity because pollutants and carbon dioxide are not released into the atmosphere during the process. Burning coal releases numerous pollutants into the air affecting people's health and disturbing the environment. One way engineers help us increase the use of renewable energy sources is by designing and building hydroelectric dams.
The Hoover Dam is an example of a huge hydroelectric power plant that generates enormous amounts of electricity for the nation's power grid. But hydroelectric power is a viable renewable resource at smaller scales, too; it is what some people use when they live in remote areas near year-round streams. In thinking about designing an energy-efficient house, taking advantage of water power is one way to generate some "off the grid" electricity and increase the efficiency of our housing design. Today we are going to develop and analyze water turbine models and how they could be used to generate some electricity for energy-efficient houses.
Vocabulary/Definitions (Return to Contents)
Procedure (Return to Contents)
For dams that generate power through a difference in elevation of the water, the calculation of the power output can be achieved in a few mathematical steps. Start by finding the energy of the system. If you know the head of the water (or the difference in the height of the water), then the potential energy of the water in the reservoir is equal to:
where PE is the potential energy, m is the mass of the water, g is the acceleration due to gravity (9.8 m/s2), and h is the head of the water. This potential energy can be transferred into kinetic energy using the following equation:
where v is the velocity of the water. Since energy can never be created or lost (law of conservation of energy), the potential energy is equal to the kinetic energy of the system. Use the kinetic energy to determine the velocity of the water flowing through the turbines.
The power generated by a dam is related to the flow rate of the water. The flow rate of the water is simply the volume over time (most common units are m3/s). The easiest way to calculate the flow rate of water is to first calculate or determine the water's velocity. The velocity of the water multiplied by the cross-sectional area it is flowing through gives you the flow rate, Q.
The mass flow rate of the water is simply the mass of the water over time, or kg/s. Use the following equation to calculate the mass flow rate:
where Q is the flow rate and ρ is the density of water (1,000 kg/m3). (Note: any variable with a dot over it simply means that variable is over time. So ṁ [mass flow rate] is simply the mass divided by time.) The power generated by this flowing water is then simply:
Before the Activity
With the Students
Attachments (Return to Contents)
Safety Issues (Return to Contents)
Troubleshooting Tips (Return to Contents)
Some motors have easy-to-spot connectors (two pieces of metal sticking out of the motor with a hole in the middle) that make attaching wires and multimeters/voltmeters to the motor leads straightforward, while others do not. If using a motor in which the connectors are absent on the motor, look for (at least) two slits for connectors on opposite sides of the motor. Have students place the leads of the wires or multimeters in two of these slits. If more than two slits, have students place the leads in one pair of the slits and turn the shaft of the motor manually. If the multimeter/voltmeter reads a voltage or current when the shaft spins, then these are the connectors. If it does not, then the other pair of slits is the connector. Have students check the motor for a voltage and current reading on the multimeter/voltmeter.
One easy way to measure voltage from the motor is to attach electrical wire to the motor connectors and use alligator clips on the ends of the multimeter/voltmeter leads. You can create one or more testing stations this way, and the students can just attach their water turbines to the set-up.
Assessment (Return to Contents)
Brainstorming: In small groups, have students engage in open discussion. Remind students that no idea or suggestion is "silly." All ideas should be respectfully heard. Ask the students:
Activity Embedded Assessment
Worksheet: Have students complete the activity worksheet; review their answers to gauge their mastery of the subject.
Class Discussion: As a class, discuss the following:
Class Presentation: Have student groups present their designs to the rest of the class. Require them to include descriptions of how well the waterwheels worked and what improvements they might make to their designs.
Activity Extensions (Return to Contents)
Have each team work with another group to combine parts of both designs to create a turbine that has a better efficiency rating than either group's original turbine prototypes. Have students write a short paragraph or two describing what they would add and eliminate, and why they think these changes would make their new turbine have a greater efficiency than the individual turbines they originally made.
Problem Solving —- Energy and Water Flow: Have students solve the following math problems:Problem Solving —- Energy and Water Flow: Have students solve the following math problems:
Activity Scaling (Return to Contents)
Additional Multimedia Support (Return to Contents)
See an excellent graphic showing the key parts of a hydropower plant, including the reservoir, intake, control gate, penstock, generator, turbine, transformer, powerhouse, outflow and power lines at this HowStuffWorks website: http://people.howstuffworks.com/hydropower-plant1.htm
References (Return to Contents)
Bonsor, Kevin. How Hydropower Plants Work. September 6, 2001. HowStuffWorks.com. Accessed March 31, 2009. http://people.howstuffworks.com/hydropower-plant1.htm
Hoover Dam, Visiting Hoover Dam. Last reviewed March 2009. Lower Colorado Region, Bureau of Reclamation, US Department of the Interior. Accessed March 31, 2009. http://www.usbr.gov/lc/hooverdam/
Hydropower Basics. Last updated January 8. 2008. Wind and Hydropower Technologies Program, Energy Efficiency and Renewable Energy, US Department of Energy. (how hydropower works, types of hydropower plants, types of hydropower turbines, glossary of terms) Accessed March 31, 2009. http://www.eere.energy.gov/basics/renewable_energy/hydropower.html
ContributorsTyler Maline, Lauren Cooper, Malinda Schaefer Zarske, Denise W. Carlson
Copyright© 2007 by Regents of the University of Colorado. This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326.
Supporting Program (Return to Contents)Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Last Modified: July 30, 2012