Building a barrage across an estuary can cause silt buildup that affects plant and sea life. There are some disadvantages to extracting energy from the tides. On either side of the tunnel are vertical grooves for the sluice gates, which control the direction of water flow. This is a model of the inner workings of the Rance tidal barrage. As the turbines move due to the tides, they create electricity.įigure 3. The third type, tidal turbines, places turbines in rows beneath the water. Tidal currents make the turnstiles spin and generate electricity. Tidal fences reach across two land masses and look like turnstiles.
A tidal barrage works by forcing sea water through a turbine that is connected to a generator. There are three types of tidal energy plants, tidal barrage (or dam), tidal fence, and tidal turbine. There are only about 40 places on Earth where this requirement is satisfied. For energy to be harvested from the tides, the tidal range must be at least 5 meters (m) or 16 feet. Since the tides are regularly replenished, tidal energy is a type of renewable energy. The movement of the tides also produces energy, called tidal energy. For instance, there are hydroelectric generators located under the Niagara Falls because there is a tremendous amount of water moving over the waterfall. Hydropower is the power that is extracted from moving water. We can take advantage of this regular motion of water to create energy. All coastal areas experience two high tides and two low tides over a lunar day, which is 24 hours and 50 minutes long. (Courtesy of NOAA, 2008.)īecause the motion of Earth, the Moon, and the Sun are regular and predictable, tidal motion is regular and predictable. This images depicts the tidal bulges due to gravity and inertia. When the Sun and the Moon are at right angles to each other, the tides are of average height and are called neap tides.įigure 1. For example, when the Sun, Moon, and Earth are in alignment, the tides are extra high and are called spring tides. The positions of the Moon and the Sun relative to each other and to Earth affect the heights tides. The gravitational force of the Sun affects the size and position of the two tidal bulges. 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 bulge is due to the fact that gravitational force exceeds inertia. As shown in Figure 1, below, this causes a bulge in the water on the side of Earth facing the Moon.
The gravitational force of the Moon "pulls" the water on the side of Earth facing it, toward itself. 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 difference in height between high tide and low tide is called the tidal range. In this case, the tidal wave is defined as the rise and fall of the water surface accompanied by the tidal current. 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.
The tides are periodic waves that originate in the ocean and are due to the gravitational force of the Moon, the Sun, and inertia. The horizontal movement of the water that accompanies the changing surface is called the tidal current. 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. Over the course of a day, the ocean tide can come in and wipe away all the work you put into building the castle. But if you want your castle to last the day, you had better be careful where you build it. Have you ever spent the day at the beach? It's fun to lie in the Sun and build sand castles.
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