The Ocean, a Treasure Trove of Energy

The ocean covers more than 70 percent of the surface of the Earth. Essential for our survival, the ocean is where the first living things were born. Although humans do not live in the sea, many people depend on it for their livelihoods, food, and resources.

The ocean can also provide us with energy. The idea that energy can be obtained from the ocean has been around for quite some time. Published in 1870, Twenty Thousand Leagues Under the Sea, written by French novelist Jules Verne, describes the adventures of those who happen to be aboard the Nautilus, steered by Captain Nemo, and presents the idea of obtaining energy from the ocean.

Captain Nemo shows the guests around the Nautilus and explains that the submarine is run by electricity obtained from the ocean. Sodium extracted from seawater is used to make batteries. The captain says that the ocean gives life to the Nautilus as the energy produced from the ocean can give the Nautilus light, heat, and power.

Today, we do not get electricity from the ocean this way. However, electricity can be generated from the ocean in other ways. One of them is tidal power, a method of generating electricity using the high and low tides that occur twice a day. This is like hydroelectric power given that it uses the power of water to run the turbine to produce energy.

When the tide is high, the sea water rises. If seawater is drawn into a lake near the sea during high tide, the power of the flowing water can operate the turbine. Conversely, the turbine also runs when the water drawn into the lake is returned to the sea at low tide. Additionally, the turbine can be turned in both directions at high and low tides. South Korea’s Sihwa Lake Tidal Power Station generates electricity by drawing in seawater at high tide.

Similarly, the power of waves can be harnessed as well. A turbine is turned to generate electricity using the power of the movement of water waves or when water stored at tide is flowing down. This is called wave power. On the other hand, ocean current power harnesses consistent ocean currents. Seawater flows constantly through wind and temperature differences. Therefore, installing turbines in the ocean with strong currents can get us electricity.

Using the movement of water is not the only way. The ocean thermal gradient between deep and surface seawater is also used to produce electricity. For this, liquids with low boiling points, such as ammonia, are utilized. Ammonia is evaporated from the warm surface seawater, and the pressure of the steam turns a turbine to generate electricity. Cold deep seawater turns ammonia vapor into a liquid. This process is repeated to produce power.

Some people came up with the idea of using the thermoelectric effect without turning the turbine. The thermoelectric effect refers to a phenomenon in which an electric current flows by making a ring with two types of metal and keeping the temperature of the two junctions at different temperatures. Electricity is produced by using such an effect and the temperature difference of seawater, depending on the depth.

With the ocean, we can generate power in a clean and eco-friendly way without causing global warming or pollution. We do not need to worry about resource depletion. However, locations are limited, and it could create hazards for the marine ecosystem. Although it is theoretically possible, we still need to address efficiency and economy for full-fledged application.

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Living in abundance in the ocean, microalgae, a.k.a., phytoplankton, are also gaining attention as an energy source. These can be used to make biofuels for transportation or heating. Biofuels are usually produced from plants, such as corn or sugarcane. When biofuels are burned, carbon dioxide is released, but the concentration of carbon dioxide in the atmosphere does not increase since it had been absorbed from the atmosphere by plants during photosynthesis.

Microalgae multiply rapidly in the right environment. As it has no extra tissues, such as stems or roots, it can produce more biofuels than plants grown in the same environment. Another advantage is that it does not take up space to grow food for humans or animals since it grows in the ocean.

The ocean holds a lot of energy. If we can make the full use of its energy, we can curb global warming while solving the energy problem. As it could involve other negative consequences, however, we should always use caution.