Catch the Wave!
AbstractThere is a lot of energy that can be harvested from moving water. Energy can be extracted from water rushing over a waterfall and from the regular patterns of the ocean's tides. The energy that propels waves forward in the oceans can also be extracted and used. But can wave energy power plants be built anywhere there is water? In this energy science fair project, you will use ocean buoy data and mathematics to determine which locations along the coasts of the United States can sustain a wave energy power system.
Michelle Maranowski, PhD, Science Buddies
This science fair project is based on an activity found at the following website:
- Virginia Sea Grant Marine Advisory Program. (n.d.). An Alternative Energy Source: Waves. Retrieved March 20, 2009.
To determine if any locations along the coasts of the United States are appropriate for building wave energy power systems.
It's a beautiful day and you're walking along the beach, when an ocean wave hits the shore and almost pushes you over. Just like your high-energy friend who runs over to tag you as "it," moving water also has energy. But from where does this energy in the form of ocean waves come? Waves are generated by disturbances, ranging from underground earthquakes to a boat moving through the water, but the wind is the most common source of waves. The wind causes ripples on the surface of the ocean, but the strength of the wind, the distance in which the wind blows, and the duration of the wind gust all determine how big the ripples will become.
Waves are characterized by their wavelength and their height. Every kind of wave-whether it is a sound wave, a light wave, or an ocean wave-has a crest and a trough. The crest is the highest point of the wave and the trough is the lowest point of the wave. The wavelength is the distance between two consecutive wave crests. The height is the difference between the wave crest and the next wave trough. Another important characteristic of waves is the wave period. This is defined as the time between two consecutive crests (or troughs) as the crests (or troughs) pass a stationary point. Scientists gather data from the oceans—such as water temperature, wind speed, wind direction, wave height, and wave period—using ocean buoys, which are devices that float in the oceans.
Diagram of a wavelength describes certain characteristics of a wave. The crest is the highest point on the wave while the trough is the lowest point. The difference between the crest and trough is the wave height and the distance between two crests or two troughs is the wavelength.
Figure 1. This figure shows some of the characteristics of a wave. (Courtesy of the Office of Naval Research, 2009.)
As ocean waves move forward, you might think that the water is moving forward; however, this is not the case. The water actually moves in vertical circles and there is little forward motion of the individual water particles in a wave. A wave is just forward motion of energy or momentum.
How can we capture the energy associated with the waves and convert it to something we can use, like electricity? According to the U.S. Department of Energy (U.S. DOE), at any given moment there is enough energy in the oceans' waves around the world to provide up to 2 trillion watts (W) of electricity! Since the oceans will always provide waves, wave energy is a renewable and sustainable form of energy. There are certain parts of the world that are especially rich in wave power. These include the western coasts of Scotland, Australia, South Africa and northern Canada. The northeastern and western coasts of the United States are also good locations to extract wave energy.
The U.S. DOE separates wave energy power systems into two categories: onshore systems and offshore systems. Onshore wave energy power devices include oscillating water column, tapchan, and pendulor devices. In an oscillating water column, a partially submerged structure has an opening below the waterline to the ocean. It encloses a column of air on top of a column of water. As the column of water rises, due to incoming waves, the column of air is compressed and is forced past a turbine. This causes the turbine to rotate and generate electricity. When the wave recedes, the column of air is depressurized and air rushes past the turbine in the other direction. This causes the turbine to rotate again and generate more electricity. When the wave recedes, the column of air is depressurized and air rushes past the turbine in the other direction. This causes the turbine to rotate again and generate electricity. An example of a commercially operating oscillating water column was the LIMPET (Land Installed Marine Powered Energy Transformer) system, originally located on the island of Islay off Scotland's west coast (but shut down in 2013). A tapchan is a tapered channel that feeds into a reservoir that is positioned on a cliff. As a wave enters and proceeds along the tapered channel, its height increases. Eventually, the wave spills over the channel and into the reservoir. The kinetic energy of the wave is converted to potential energy. The generation of electricity is similar to a hydroelectric plant. When water shifts from the reservoir back into the ocean, it is fed through a turbine that generates electricity. A pendulor device is a box with a hinged end that is open to the ocean. As waves pass by the opening, the hinged end swings back and forth. The hinged door is connected to a hydraulic pump and generator. This swinging door causes the generator to create electricity. Offshore wave energy power systems are located where the depth of water is at least 40 meters (m). Examples of offshore wave energy systems are the Salter Duck and the Pelamis systems. Both systems bob up and down, as a result of wave action. The bobbing powers a pump and a generator.
How much energy do these systems generate? The power that the LIMPET system extracts from a wave is expressed in terms of the length of the wave, and is shown in Equation 1.
|J =||0.5 × (HS)2 × TP|
The amount of power produced by the LIMPET system is based on the length of the LIMPET, which is 20 m long. The power produced by the LIMPET system is shown in Equation 2.
|E =||J x 20 m|
When discussing power consumption, the unit of measure is kilowatt-hour (kWh). To convert the result in Equation 2 to kilowatt-hours, simply multiply by 1 hour (h). If you want to calculate the amount of power generated in a week, simply multiply the power output by the number of hours in a week. For example, the power output of the LIMPET system is 20 kW and the number of hours in a week is 168 h, then the power generated is 20kW x 168 h= 3,360 kWh.
The power produced by a Pelamis system is calculated using a complicated mathematical model. However, knowing the significant wave height and the dominant wave period and using the power matrix derived by the marine power engineers at Pelamis Wave Power, you can arrive at the power produced by the system. The power matrix is shown in Figure 2. The Power period in the matrix is the dominant wave period.
Engineers at Pelamis Wave Power created a color coded chart to determine the power produced by the Pelamis system based on the significant wave height and dominant wave period. The chart is color coded by values, higher values are marked as red and lower values are a light blue.
Figure 2. Power Matrix for the Pelamis offshore wave energy system. (Courtesy of Pelamis Wave Power, 2009.)
In this energy science fair project, you will determine which sites along the coasts of the United States would be appropriate sites to build either an onshore or an offshore wave energy power system.
Terms and Concepts
- Renewable energy
- Sustainable energy
- Oscillating water column
- Pendulor device
- Salter Duck system
- Pelamis system
- What causes wind to form?
- What is a Wells turbine? What is special about the design?
- How does a Salter Duck extract energy from waves?
- What is the difference between wave energy and tidal energy?
- Are there any other systems for extracting energy from ocean waves?
- Are there any disadvantages to extracting energy from the ocean waves?
This website, from the Office of Naval Research, discusses how ocean waves are formed.
- Office of Naval Research. (n.d.). Science and Technology Focus—Ocean in Motion: Waves. Retrieved June 6, 2017.
WaveGen, the company that originally designed the LIMPET system, closed in 2013 and their original website is no longer available. However, several publications related to the LIMPET project are still available online:
- Whittaker, T.J., et. al. (n.d.) The LIMPLET Wave Power Project—The First Years of Operation. Renewable Energy. Retrieved June 6, 2017.
- The Queen's University of Belfast (April 2002). Islay LIMPET Wave Power Plant. Retrieved June 6, 2017.
This is the website of Pelamis Wave Power, the company that manufactures the Pelamis Wave Energy Converter.
- Pelamis Wave Power Ltd. (n.d.). Pelamis Wave Power. Retrieved March 20, 2009.
This website offers buoy data, which you will need for this science fair project.
- National Oceanic and Atmospheric Administration's (NOAA) National Data Buoy Center. (2009, March 25). National Data Buoy Center. Retrieved June 6, 2017.
This website contains a large amount of data about electricity generation and consumption in the United States. You can use this site to see how much electricity your state used in a certain year and the sources of the electricity.
- United States Department of Energy's Energy Information Administration. (n.d.). Electricity. Retrieved June 6, 2017.
Materials and Equipment
- Computer with a connection to the Internet and Microsoft® Excel® or other spreadsheet software
- Lab notebook
- To work on this science fair project, you will need access to ocean buoy data. You can access buoy data at the National Oceanic and Atmospheric Administration's (NOAA) National Data Buoy Center page. This website has ocean buoy data from around the world.
- A lend on the page should describe the different types of buoys. Some buoys have recent data, and some only have historical data. Not all of the buoys give the data that you need, which are the wave height and the dominant wave period. You will have to investigate the different buoys and see which ones collect the data in which you are interested. Use the on-screen controls and your mouse to move around and zoom in and out of the map. Look for buoys that have Significant Wave Height and Dominant Wave Period listed in the pop-up window, which will appear once you've clicked the buoy. For this project, choose at least three onshore locations and three offshore locations. Note these locations, and the states where they are located, in your lab notebook.
- Hints: As you can see on the website's map, there are a lot of buoys, all over the world. To help you begin your search, possible offshore locations could be in one of the Great Lakes. Southern California has multiple onshore locations with wave height and dominant period data, as do locations in Maine and North Carolina.
- Begin retrieving and recording data in your lab notebook for your three onshore locations. On the buoy data website, click on a yellow buoy that is producing data. Note the wave height and the dominant wave period and see how it varies over a day, a week, a month, and a year, as follows.
- You can look at the daily data by clicking View Details on the pop-up window.
- To take a look at historical data, click View History on the pop-up window. You'll see a Historical data bullet, with a Standard meteorological data sub-bullet. Click on the year that you want to look at.
- Follow the instructions and import the data from each of the locations into Excel®. If you need help using Excel (or another spreadsheet program), use the tutorials that are part of the software package, or an online tutorial.
- Use a new Excel worksheet for each location. Create your own table in each one to organize the data.
- To import daily data, simply copy the data directly from the website and paste it into Excel.
- To import historical data, use "Method Two" from the website (you'll see this option after you've clicked on a previous year to view). The file will open in another Internet browser window. You can copy and paste the data or save it as a text file. The file is delimited (surrounded) by spaces, so you can then open it in Excel. This file will have a whole year's worth of data, so you can look at various time frames.
- Plot the wave height and dominant period data for each of the locations and then see how it varies. Use Equations 1 and 2, from the Introduction, to calculate the potential power generated if there were a LIMPET system built at each of the onshore locations that you chose. Use Excel to plot how the power output varies over a day, over a week, and over a year.
- How does the power output vary over a day for each onshore location? What is the highest power output and what is the lowest power output? What is the average power output for a day? Repeat this step for a week, a month, and a year. How does the data over the different time periods compare to each other?
- Calculate the amount of power that the systems can provide in a year, in units of kilowatt-hours.
- How much power did each of the onshore sites you pick generate? Looking at the data, where would you build an onshore wave energy power system? How many power systems would have to be built, assuming they gave the same amount of power as the original, to provide enough power for the state you live in for one year? You can look up information about electrical power consumption in the United States at the U.S. Department of Energy's Energy Information Administration's website.
- Repeat steps 3–8 for each of the three offshore locations. Use the wave height, the dominant period, and the power matrix from Figure 2 to determine the power a Pelamis system could generate if one were placed at the locations you picked.
- Reviewing your data and calculations, is wave energy a viable source of energy?
Ask an Expert
- Look at ocean data from the coasts of other countries. Are there other sites that could serve as locations for wave energy power systems?
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