Tropical oceans absorb approximately 278 petawatt-hours of solar energy on an average day. Harvesting just 1/4000 of this energy could meet the daily electricity needs of the entire world. Of course, it is very difficult to collect even this much of the incoming energy, but ocean-based thermal energy conversion appears as a possible method for this.Unlimited ocean-based thermal energy
Obtaining energy from the temperature difference between the hot surface and the cold deep ocean is not actually a new idea, it was first tried 142 years ago in 1881, and a 22 kilowatt OTEC (Ocean thermal energy conversion) facility was built in Cuba in 1930. was built. The basic idea of this method is to take advantage of regions where there are constantly large temperature differences. Generally, in tropical regions, the surface temperature of the ocean near the land is around 25 degrees. At a depth of 800 meters below the surface, the temperature drops to 4 degrees. When such a region is found, it is possible to establish a thermal facility with a liquid that can reach a boiling point between these two values (for example, ammonia). The operating principle is the same as that of thermal facilities on land: Hot water on the surface boils a liquid such as ammonia, the boiling liquid expands as a gas and turns the turbine to produce electricity. This gas is then directed deep into the ocean, condensed again and included in the cycle.
However, this system has some efficiency problems. OTEC and similar facilities use a large portion of the energy they produce to keep the facility running (such as the use of pumps that bring cold water to the surface), and therefore, even though the energy source is unlimited, the efficiency remains very low. Of course, there are other difficulties. Tropical regions are not calm places and storms can damage the floating facility. As with any ocean-based project, it is necessary to combat biofouling and the corrosive properties of seawater. At the same time, this method is an early stage technology that does not yet benefit from economies of scale. In order to compete with other options in terms of cost, this type of facility needs to be built at a scale of approximately 100 megawatts.
A commercial facility will be established in 2025
Still, London-based company Global OTEC says it’s time to bring this idea to life once again. At the recent Vienna International Forum on Energy and Climate, the company presented a new concept for an OTEC barge called Dominique, which it expects to enter service in 2025 off the coast of São Tomé and Príncipe, a small island nation off the west coast of Africa.The barge Dominique is designed to provide 1.5 megawatts of net generation throughout the year. This production amount is enough to meet approximately 17 percent of the country’s 78 million-odd kilowatt-hour energy consumption. In terms of Levelized Cost of Energy (LCoE), OTEC barges will have a unit cost of $150-$300 per megawatt-hour, the company says. This is a high but reliable 24/7 production capacity compared to other energy sources, which may be more suitable for use in some conditions where geography and other factors are favorable. Despite all this, the issue of cost and efficiency still remains a question mark.
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