OTEC Basics

Basic OTEC System

Ocean Thermal Energy Conversion (OTEC) technology uses a turbine generator to create renewable energy from the temperature difference between cold, deep seawater circulating in the ocean and surface seawater warmed by the sun. In order to produce power with the low temperature range, a working fluid with low boiling point is used.

The amount of energy created is dependant on the amount of water available to cool or heat the working fluid. The Okinawa OTEC project has a maximum capacity of 100kW, but since it does not always have access to the maximum capacity due to other seawater users, will often produce less electricty. This is due to the previous use of water by local industries and the Okinawa Deep Seawater Research Center, and does not hinder the project's goal of demonstration and testing.

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Q: What are the characteristics of OTEC power generation?

A: Since seawater temperature does not change rapidly, the power output is stable and prediction of potential power generation is more reliable than many other renewable sources. The seawater pumped in for use at an OTEC plant can be used for many different applications, offsetting the cost of initial pipeline investment.

Q: What is the history of OTEC?

A: Physicist Jacques-Arsène d'Arsonval of France first proposed the idea in 1881. Development has been intermittent since, but in response to the recent growth in interest in renewable energy, development has increased in countries such as the United States, France, China, and Japan.

Q: Where is OTEC possible?

A: With current technology, an annual temperature differeance of 20℃ or more is needed. This difference is found in sub-tropical and tropical regions such as the Okinawa, Kuroshio, and Ogasawara areas in Japan.

Q: What is the potential of OTEC?

A: The potential power generation in Japan is 5,952MW within 30km of the shore. With no offshore distance limitation the potential is 173,569MW (Both in areas where the seawater temperature difference is 20 ℃ or more. The impact on marine environment is negligible due to comparatively small water intake).

In Okinawa, the potential for power generation is 2,797MW within 30km and 79,992MW without offshore distance limitation. Since the current power generation of Okinawa is 2,000MW, the potential could cover all needs in Okinawa. Source: NEDO report “A Business Understanding of Ocean Energy Potential” March 23, 2010

Q: What is the cost of commercial power generation at this time?

A: According to OEA-J the cost is estimated at 20 yen per kWh at 10,000kW class output and 10 yen per kWh with 100,000kW class output. There is currently no commercial class plant in operation anywhere in the world, however, several countries have projects in development.

Current Surface Seawater Temperature


Current Deep Seawater Temperature


(Updated 11/15/2019)

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