[00:00.00]Listen to part of a lecture in an environmental engineering class.
[00:05.37]Professor Okay, we've talked about renewable energy as an alternative way of generating electricity, alternative to what? [00:12.64]To non-renewable energy, such as coal or petroleum or natural gas. [00:17.95]Something that will eventually run out of because we're consuming it at a faster rate than it's being regenerated.[00:23.74] OK, so what's our primary source of renewable energy? Ken?
[00:28.58]Ken: The sun?
[00:29.85]Professor Yes. But it's not so easy to use it to generate electricity because…
[00:35.04]Ken: It doesn't work at night.
[00:37.24]Professor Okay?
[00:38.43]Ken: And It doesn't work very well in places where it's cloudy a lot of the time.
[00:42.75]Professor That's right. And the sun's energy is not that easy to capture. [00:46.81]We're trying to use giant panels called solar cells to capture the sun's rays and convert them into electricity. [00:53.12]We've had some success, but let's just say that the idea of using the sun as the principal source of energy in the United States is, well, as someone once said, it's kind of like the sun itself - big and bright, but further away than it seems.[01:07.84]Now, let's talk about the ocean as another source of renewable energy. [01:12.49]The ocean has 2 kinds of mechanical energy that we can use, the tides and the waves. [01:18.88]In order to use tides, to generate electricity, the difference between high and low tide has to be at least 5 meters or uh about 16 feet. [01:27.57]They're only about 40 places on the planet with that kind of tidal range. [01:31.46]There's actually only one really big title energy power station in the world that's in France, Susan.
[01:38.64]Susan: So do they build a dam like they do it on some rivers?
[01:43.68]Professor Yes, They build a dam across a bay and they have gates and turbines in the dam, and when the tides produced the required difference in the water level on opposite sides of the dam, the gates are opened and waters forced through the turbine, which turn a generator which produces electricity.[02:01.03]So what about the waves? [02:03.76]There are 2 kinds of power systems we can use to convert the energy and waves into electricity. [02:08.85]There's what we call an offshore system where you have devices that are installed in deep water that float on the waves in the open sea. [02:16.89]Then you have what we call an onshore system where you install your devices along the shoreline to extract the energy from waves that are breaking on the shore. [02:26.45]And there are several varieties of these systems.
[02:29.56]Susan: I've never heard of that.
[02:30.88]Professor No, most people haven't. [02:32.63]Because wave power is a lot like tidal power. [02:35.82]You only have a handful of places in the world where it's practical to, use waves to produce electricity.[02:40.94]There's a fundamental problem with trying to harness the ocean's mechanical energy. Ken.
[02:47.23]Ken: What about using the heat energy in the ocean? [02:50.52]Has anybody tried to do that? [02:52.15]I know the ocean has to absorb a lot of heat from the sun.
[02:55.76]Professor Yes. They have. [02:57.39]As a matter of fact, we have a process called ocean thermal energy conversion or OTEC to convert that heat into electricity. [03:05.70]The ocean covers more than 70 % of earth's surface. [03:09.16]It's like a huge solar panel, a huge solar cell collecting solar energy and heating up. [03:15.20]The sun warms the surface water, a lot more than the deep ocean water. [03:19.30]And that temperature difference creates thermal energy. [03:22.16]Ocean, thermal energy conversion works best when the temperature difference between the surface water and the deeper water is about 20 ℃. [03:30.30]You have those conditions in a lot of tropical areas.[03:33.62]Actually, the idea of tapping the thermal energy of oceans goes way back. [03:37.88]The first OTEC system was built around… I think it was 1930. [03:42.54]Unfortunately, OTEC systems are very expensive. [03:45.97]Still, there are some energy experts who believe that they might be a major power source in the future. [03:51.37]If we can figure out how to make them more efficient, and OTEC might have a significant side benefit. [03:57.52]There are a number of valuable minerals dissolved in ocean water. [04:00.97]But when they've studied the possibility of mining, extracting minerals from the ocean, they've always said it wasn't feasible because it would cost too much money, one to pump all that ocean water and two to extract the elements. [04:13.42]But if you have OTEC plants already pumping the water, you don't have to worry about that cost. [04:18.49]You just have to figure out how to reduce the cost of extraction.
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