Abstract
Renewable energy is the energy that is extracted from natural sources, such the Sun (solar), earth (geothermal), wind, and water (hydropower). These sources are renewable because they can be replenished by the same natural sources within a short period of time. Hydropower energy is extracted from moving water, like ocean wave energy and tidal energy. In this energy science fair project, you will make a model of a tidal barrage (also known as a dam) and investigate how emptying the tidal barrage through different-sized tunnels affects energy production.Objective
To build a model tidal barrage or dam and to investigate how the size of the tunnel affects the speed of rotation.
Introduction
Have you ever spent the day at the beach? It's fun to lie in the Sun and build sand castles. But if you want your castle to last the day, you had better be careful where you build it. Over the course of a day, the ocean tide can come in and wipe away all the work you put into building the castle. What are ocean tides and what causes them? Tides are the periodic (occurring at regular intervals) rise and fall of the surface water level of the oceans, bays, gulfs, and inlets. The horizontal movement of the water that accompanies the changing surface is called the tidal current. The tides are periodic waves that originate in the ocean and are due to the gravitational force of the Moon, the Sun, and inertia. High tide occurs when the crest of the tidal wave hits the shore and low tide occurs when the trough of the tidal wave hits the shore. In this case, the tidal wave is defined as the rise and fall of the water surface accompanied by the tidal current. The difference in height between high tide and low tide is called the tidal range.
While the Sun is a much larger body than the Moon and exerts a larger gravitational force than the Moon, the Moon is closer to Earth and therefore, the effect of its gravitational force on the water is more significant. The gravitational force of the Moon "pulls" the water on the side of Earth facing it, toward itself. As shown in Figure 1, below, this causes a bulge in the water on the side of Earth facing the Moon. The bulge is due to the fact that gravitational force exceeds inertia. On the opposite side of Earth, inertia exceeds the gravitational force of the Moon and as a result, there is a second bulge in the water. The gravitational force of the Sun affects the size and position of the two tidal bulges. The positions of the Moon and the Sun relative to each other and to Earth affect the heights tides. For example, when the Sun, Moon, and Earth are in alignment, the tides are extra high and are called spring tides. When the Sun and the Moon are at right angles to each other, the tides are of average height and are called neap tides.
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| Figure 1. This images depicts the tidal bulges due to gravity and inertia. (Courtesy of NOAA, 2008.) |
Because the motion of Earth, the Moon, and the Sun are regular and predictable, tidal motion is regular and predictable. All coastal areas experience two high tides and two low tides over a lunar day, which is 24 hours and 50 minutes long. We can take advantage of this regular motion of water to create energy. Hydropower is the power that is extracted from moving water. For instance, there are hydroelectric generators located under the Niagara Falls because there is a tremendous amount of water moving over the waterfall. The movement of the tides also produces energy, called tidal energy. Since the tides are regularly replenished, tidal energy is a type of renewable energy. For energy to be harvested from the tides, the tidal range must be at least 5 meters (m) or 16 feet. There are only about 40 places on Earth where this requirement is satisfied.
There are three types of tidal energy plants, tidal barrage (or dam), tidal fence, and tidal turbine. A tidal barrage works by forcing sea water through a turbine that is connected to a generator. Tidal fences reach across two land masses and look like turnstiles. Tidal currents make the turnstiles spin and generate electricity. The third type, tidal turbines, places turbines in rows beneath the water. As the turbines move due to the tides, they create electricity.
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| Figure 2. The Rance tidal barrage at Bretagne, France. (Wikipedia, 2009.) |
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| Figure 3. This is a model of the inner workings of the Rance tidal barrage. The turbine sits in the tunnel. On either side of the tunnel are vertical grooves for the sluice gates, which control the direction of water flow. (Wikipedia, 2009.) |
There are some disadvantages to extracting energy from the tides. Building a barrage across an estuary can cause silt buildup that affects plant and sea life. Tidal barrages and tidal fences also affect sea life migration. The ecological cost of building a tidal energy plant must be weighed against the cost of creating energy from fossil fuels (a nonrenewable energy source). Building a tidal barrage also affects the tides.
In this energy science fair project, you will build a model tidal barrage to experiment with the rate of water release and see how it affects the rotation of a toy boat propeller. In a barrage, as water is forced through the turbine, it will rotate. The rotation causes the generator to create electricity. The more the turbine rotates, the more electricity is created. There are several variables that need to be considered when designing the barrage. Examples of this are the type of turbine and the size of the tunnel. For this science fair project, the propeller in your model will act as the turbine, and differently sized holes in a bucket will act as differently sized tunnels. Have fun and go with the tidal flow!
Terms, Concepts and Questions to Start Background Research
Bibliography
Visit these pages, from PG&E, a California power, gas, and electric company, for more information about electricity:
Materials and Equipment
Experimental Procedure
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| Figure 4. Completed basin and tunnels portion of the tidal barrage model. Note that this bucket has four holes, but your bucket should only have three. |
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| Figure 5. Completed rod and propeller assembly. |
| Hole size | Trial | Rotations in 10 seconds (sec) |
| 1/2-inch | ||
Variations
Credits
Michelle Maranowski, PhD, Science Buddies
Last edit date: 2009-03-02 09:52:00
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