New Alternative Energy Sources: OTEC, Hydrogen Gas & Fuel Cells

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

In this lesson you will learn about two potential future alternative energy sources: OTEC and hydrogen fuel cells. Discover the benefits and drawbacks of each, and then test your new knowledge with a quiz following the lesson.

What is Alternative Energy?

Humans use a lot of energy. The population of the Earth is growing and countries are becoming more developed. This has created a relentless increase in demand for energy that isn't going away anytime soon. In the process of creating energy, we also produce huge amounts of pollution, including carbon dioxide (which is primarily responsible for climate change). Something needs to be done, and one promising solution is alternative energy.

Alternative energy is electricity that is generated in ways that do not use up natural resources or harm the environment. It is generally considered synonymous with renewable energy. However, while alternative energy can sometimes apply to efficient energy sources that do get used up, renewable energy by definition can never be used up.

There are many types of alternative energy, including wind, solar, hydroelectric, and geothermal. Today we're going to talk about some new ideas in the area of alternative energy, and how they work.

Ocean Thermal Energy Conversion (OTEC)

Ocean Thermal Energy Conversion or OTEC is a way of generating electricity from the temperature difference between different layers of sea water. This is possible because lower layers are colder than upper layers. There is currently only one power plant of this type in the world, found in Japan. There are two types of OTEC systems: closed and open.

Closed OTEC systems have fluids inside them that undergo the process of heating and cooling, driven by the sea outside. They work by having a low boiling point fluid inside them (such as ammonia), which is vaporized (boiled) deep under the ocean where it's warmer, and then rises in the same way that a submerged cork bobs up out of water. As vapor rises, it pushes a turbine. This generates electricity just like in every other kind of power plant: the turbine moves a piece of metal near a magnet, producing an electric current. When the fluid reaches the top, it cools again and sinks. This cycle continues. All of this energy originally comes from the Sun, since it's the Sun that gives the ocean its heat energy.

Open OTEC systems work nearly the same way, except that the sea water itself is used as a liquid. This is possible if the water is put in a low-pressure environment, since under low pressure substances boil more easily. Maintaining this environment uses up extra energy, but you do get usable pure water as a byproduct.

Diagram Showing How OTEC Byproducts Can Be Used
Diagram Showing How OTEC Byproducts Can Be Used

The biggest weakness with OTEC is that it isn't very efficient. This is because the difference in temperature between the top and the bottom is relatively small. One of the main benefits is that such a power plant could operate 24 hours a day, unlike other renewable energy sources like solar (which requires the Sun) and wind (which requires windy conditions).

Ocean Depth Gradients: Higher Gradients Means More OTEC Potential
Ocean Depth Gradients: Higher Gradients Means More OTEC Potential

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