Kume Island, Okinawa, Japan: Using seawater temperature difference to generate electricity

A new project to generate electricity from thermal energy using deep seawater is underway on Kumejima Island in Okinawa Prefecture. A demonstration has been started to expand the scale of the plant, and the creation of this project is nearly underway.

The phenomenon of Kumejima Island in Okinawa Prefecture

Kumejima Island is located about 90 km west of the main island of Okinawa Prefecture. Although it is not very easy to get around, it is known as a beautiful island and a mecca for deep diving and scuba diving. The Congo Basin is isolated, with a population of about 8,000, and 95% of its electricity supply comes from thermal power plants that use fuel oil as an energy source.

In June 2012, OTEC (Deep Ocean Thermal Energy Conversion) is gradually operating on the island in other parts of the world. In collaboration with Saga University, a demonstration facility with a power of 100kW set up by Okinawa Prefecture succeeded in producing electricity from specific seawater, the first of its kind in the world.

Kumejima Town has long set a goal of supplying 100% of the electricity in the Congo Basin from renewable energy by 2040, and using thermal control generation as a source of support power. The main objective is to become a "carbon seeping island" and to promote the economy by reusing the water bottom for seawater breeding and other thematic activities.

Deep-sea thermal energy conversion

Ocean thermal energy conversion was first proposed in 1881 by the French physicist Jacques-Arcène d'Arsonval. Since then, the development trend has been intermittent, but as people in the country expect more and more renewable energy, today Japan, France's, our country and other countries are proactive in developing designs. With the current expertise, it is able to be applied in subtropical climates and tropical climates, and the average annual temperature difference between the surface and deep seawater in that place is around 20°C.

From the offshore account 2.3 km 612 meters deepest pumped up about 9 ℃ underwater attack and defense alliance 23-29 ℃ temperature difference between the surface water caused electricity. Selectable CFCs and ammonia with melting and boiling points are vaporized in warm boiling water to turn the turbine engine to produce electricity, and later vaporized again in cool water and circulate the system.

Ltd., Saga University and Xenesys Corporation (Koto-ku, Tokyo), which operates the plant, officially started a demonstration project at the beginning of this year to expand the scale of the plant in the face of commercialization, according to Nikkei News. The performance of the heat exchanger, which is suitable for generating electricity equivalent to 200KW, twice the current volume, will be confirmed.

Using solar power and electric batteries to "fill" the temperature difference between seawater and electricity

Solar photovoltaic panels and power batteries are combined on the roof to efficiently supply renewable energy. The cost of assembly is recovered by selling the remaining electricity under a power agreement contract. The electricity cost per kwh for home use is 29.7 yen. When the demand exceeds a certain level, the price per kwh is less than that of the Okinawa Prefectural Electric Power Company. The application of power battery is expected to be the emergency power source.

Remote islands sometimes lose power for several days due to strong typhoons. By introducing solar power plants and electric batteries, it can complete the rise of renewable energy and ensure its own energy needs.

It will be a sustainable turn for remote islands

Japan is at the forefront of the world in many basic technologies that cannot be lacking in seawater temperature difference power generation, such as shipbuilding technology that can extract seawater and heat exchangers that can vaporize liquid.

On the other hand, the supply of electricity to remote islands with thermal power plants is largely affected by soaring fuel consumption. According to the data, the overall income and expenditure of the remote islands was 2.2 billion yen in the financial performance as of March 31, 2010. If renewable energy sources such as deep-sea thermal energy conversion and solar power plants can be used to give local manufacturing and local trading power (regional distributed power supply) to borrow water, it will be a step towards creating sustainable development of remote island society.