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Lecture: A tidal turbine: Narrator: Listen to part of a lecture in an environmental science class. Professor: Recently, I've been spending some time talking to you about the need to find renewable sources of energy. Well, we've done solar and wind energy. So I thought for today's class we could talk about ways to harvest energy from the sea. Specifically, let's focus on the tidal currents that exist within the ocean. Tidal energy, also called tidal power, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power. A way to get energy from these tidal currents is to use tidal turbines. As the currents pass through the turbines, the turbines will turn, and this will produce electricity. A tidal turbine look: a lot like a windmill, just under the water. And, they actually work in pretty much the same way. The idea isn't that new, it's been discussed for quite some time now. Recently, we have been able to create materials that car withstand the corrosive damage from salt water during extended submersion. And it makes the use of the turbines more prevalent. So, the total availability of tidal power may be much higher than previously assumed, and economic and environmental costs may he brought down to competitive levels. Student: Professor, wait a second. But tidal currents move so slowly, I mean, doesn't wind move a lot faster than water? How could they produce electricity? Professor: Good question, well, simply put, water is over hundred times denser than wind is. Even with a slower current, you still have enough force to generate a large amount of power. Actually, a 10 kilometer per hour tidal current generates enough electricity to match a wind current of 300 kilometers per hour. Student: Oh, wow, I had no idea. And, um, now that I think about it, I guess wind isn't that reliable either, right? Sometimes it just stops blowing. Professor: Very good point, and that's precisely why tidal energy is a better source than wind is. Tidal currents are predictable, day to day, all year round. They never change. And another advantage of using them is tidal turbines can even change their direction underneath the water. So they can turn to their face into or out of the direction of the current. But these aren't the first attempts at using energy from the ocean's tides; there have been some earlier methods that I want to talk about first. First of all, there are tidal dams for instance. A tidal dam is built on an inlet, and when the tide comes in, the dam will fill up. On the contrary, when the tide goes back out, the water is forced over the turbines, turning them. There are a few that are still in use right now, but they haven't been scaled for commercial use. Tidal dams are also built in tidal basins. These areas have fragile ecosystems that could be damaged by tidal dams. The dams would affect the sedimentation and various other components in the ecosystem. Now, another method is to use something called tidal fences. Urn, they stick down about 3 meters into the water and they have turning rotors on them that are connected to two bodies of land. Urn, such as a mainland and an island or two islands. As the tide passes through the fence, it turns the rotors and produce electricity. However, tidal fences also have a downside. They block off the entire space between the two land masses. This could have negative consequences to the shipping industry which might use the corridor between the land masses. But they are cheaper than tidal dams and they don't affect the ecosystem. Well, I suppose they could affect the movement of very large marine mammals, but it's still less damage done than what a tidal dam would do. In order to reduce fish fatality, fences could be engineered so that the spaces between caisson wall and the rotor are large enough to allow fish to pass through. Also, larger marine mammals such as whales or dolphins can be protected from the turbines by a sonar sensor auto-breaking system that automatically shuts the turbines down when marine mammals are detected. Okay, so now we're hack to tidal turbines. Now, I think tidal turbines are really the best way to get energy out of the tides. You see, the turbines are placed 20 meters below sea level. So, tidal turbines are out of sight and out of mind. They won't ruin the aesthetic beauty of the environment. The blades have round edges and turn very slowly, so the negative side effect to the local wildlife is relatively minor. Now, at the moment, the problem is that the installation and maintenance of tidal turbines is very expensive. But, this is a temporary problem as technology decreases in price over time. But the financing of such endeavors is unwarranted today. I'm sure that in the future it will be looked into more seriously as the world's energy demands become more serious. Is there any way to read someone' s mind? Well, the chapter on human personality in your book talks about the fairly new field of personality neuroscience, and fMRI. It's an acronym for Functional Magnetic Resonance Imaging.