The 28th Conference of the Parties to the United Nations Framework Convention on Climate Change (COP28) will be held in the United Arab Emirates from November 30 to December 12 to discuss climate change countermeasures, a pressing issue amid increasingly severe abnormal weather on a global scale. In this first installment, we will focus on the “Ocean Thermal Energy Conversion (OTEC)” demonstration project being implemented on Kumejima Island, Okinawa Prefecture, and the “Kumejima Model,” which includes industrial promotion through the combined use of deep seawater and ocean thermal energy. JICA is now studying the possibility of introducing this model to island countries. What are the possibilities of the Kumejima Model, which simultaneously realizes sustainable clean energy and the creation of industry?
Ocean Thermal Energy Conversion Demonstration Facility (100 kW) on Kume Island, Okinawa
Energy Transformation Necessary for Decarbonization
Global warming and other factors are said to be causing abnormal weather. The world’s major energy sources are fossil fuels such as oil, coal, and natural gas, but their combustion emits carbon dioxide, which causes global warming, and an energy transition is needed to achieve decarbonization. Many island countries, in particular, rely on imported fossil fuels (diesel) as their energy source. In addition to high transportation costs, the spread of the new coronavirus infection and Russia’s invasion of Ukraine have caused fuel prices to soar even higher, resulting in higher energy bills and other impacts. Therefore, economic circumstances have also forced a shift in energy sources. Island countries are introducing solar power, wind power, and other renewable energy sources with the goal of achieving 100% renewable energy generation. However, variable renewable energy sources, whose generation fluctuates greatly depending on weather and seasonal changes, require storage batteries and backup power sources if the supply is not stable. The higher the proportion of variable renewable energy, the higher the cost of power generation.
Ocean Thermal Energy Conversion” attracting attention
Now, Ocean Thermal Energy Conversion (OTEC) is attracting attention as a clean, renewable energy source with a stable supply.
Ocean Thermal Energy Conversion (OTEC) is a technology that utilizes the temperature difference between warm surface water and cold deep water to generate steam using ammonia, which has a low boiling point, as a medium to turn turbines and generate electricity. Compared to variable renewable energy sources such as solar power and wind power, this technology is less susceptible to weather conditions and can provide a stable 24-hour power supply. Since the suitable sites for power generation are those where the temperature difference between surface water and deep water (600 to 1,000 meters deep) is about 20°C, there are many suitable sites near the equator, and this technology is attracting attention as an energy source especially in island countries.
Source: Okinawa Prefecture Ocean Thermal Energy Conversion Demonstration Facility
The “Kumejima Model” has achieved great results in 10 years.
Since 2013, Okinawa Prefecture has been conducting a demonstration project for ocean thermal energy conversion in Kumejima Town, a remote island about 100 km west of the main island. At the time, Okinawa’s energy self-sufficiency rate was low at around 0.5% (the national average is 4.8%), and the prefecture was dependent on fossil fuels as its energy source. While the prefecture was trying to diversify its energy sources and improve its self-sufficiency rate, Kumejima Island had facilities to take in deep seawater, and the temperature difference between surface seawater and deep seawater around Kumejima Island was about 20°C, which was suitable for OTEC power generation.
The demonstration project, now in its 11th year, is an industry-government-academia collaboration between Saga University, which has been researching ocean thermal energy conversion for more than 50 years, the town of Kumejima, and a private company that aims to develop a deep seawater utilization business. This was the world’s first case in which power was successfully generated using actual seawater, and it has attracted attention as the “Kumejima Model” because of the success of the industry that utilizes the deep seawater in addition to power generation. So far, 69 countries around the world have visited Kumejima to inspect the project.
Imari Satellite of the Institute of Ocean Energy, Saga University
A major feature of ocean thermal energy conversion is that deep seawater can be used for complex projects after it has been used for power generation. Deep seawater has a constant low temperature throughout the year and is rich in nutrients such as minerals with few bacteria. Since the quality of the water does not change even after power generation, it can be used for cultivation of marine products such as prawns, sea grapes, and oysters, and can also be used for drinking water and cosmetics.
Currently, Kumejima Town’s total business using deep seawater amounts to about 2.5 billion yen, of which cosmetics business sales account for about 1 billion yen in fiscal year 2022. The population of Kumejima Town is approximately 7,000, and the deep seawater business has created approximately 140 jobs, demonstrating the high economic and employment effects of the project,” said Seiichiro Ezu, Kumejima Town Project Promotion Section Chief.
Naoki Ota, Director of Kumejima Town Project Promotion Division (right) and Seiichiro Ezu, Chief Inspector
The town’s research institute is also developing technology to produce coral seedlings using deep seawater. Photo shows coral seedlings being placed in the sea.
Kumejima Model” to solve the problems of island countries
JICA has taken notice that the “Kumejima Model,” which generates both electricity and industry, could contribute to solving issues such as securing clean energy and water and promoting industry on the islands of developing countries. JICA has begun a study to introduce this model to island countries. The first field survey was conducted in Palau in May 2023 to study the feasibility of introducing the model to the Republic of Palau and other Pacific island countries, and a year-and-a-half-long information gathering and confirmation survey is underway.
Palau, like other island countries, relies on diesel power generation for energy. In addition to the fact that a shift to cleaner and cheaper energy was being sought, the country has few major industries other than tourism, and many areas rely on rainwater for water, which causes drought and water shortages during typhoons and natural disasters.
If ocean thermal energy conversion could be introduced, it could not only play a role as a base load power source (a stable power source that can generate electricity day and night), but could also contribute to the creation of industries using deep seawater. If fresh marine products and leafy vegetables can be supplied to hotels and restaurants, the added value of Palau as a tourist destination will increase, and it can be expected that the number of tourists visiting Palau will also increase. In addition, if water can be efficiently desalinated and supplied, it will be possible to supply large quantities of drinking water at low cost even in times of drought, thus contributing to national security.
In island countries, a common problem is that young people who have received higher education outside the islands by studying abroad do not return to the islands. For the multiple use of deep seawater, professionals with business management know-how with an eye on overseas markets and research and technical staff in fields such as fisheries, agriculture, and life sciences that use deep seawater are needed onsite. Research and technical personnel in fields such as fisheries, agriculture, and life science are needed in the field. It can be said that the combined use of deep seawater has great potential in terms of providing opportunities for young people to play active roles and revitalizing the island’s economy and society.
Many Pacific (Oceania) island countries are sincerely trying to become carbon neutral and protect nature. In addition, although they were battlegrounds during the Pacific War, many people have confidence in the Japanese people. They are also located on important sea lanes for Japan today. We are conducting a survey first in Palau with the aim of spreading the Kumejima Model to these island countries.
However, in order to promote the introduction of the Kumejima Model in island countries, it is essential to establish a cooperative system among industry, government, and academia, and to have actual businesses participate. Therefore, during the field survey in May, we held a briefing session on the “Kumejima Model” for local ministries, agencies, and public enterprises to deepen the understanding of local officials.
Briefings conducted in Palau for local ministries and utilities
G.O. Farm Corporation, which participated in the first survey as a private-sector representative, has realized complete land-based cultivation of oysters on Kume Island using deep sea water and developed “Ataranai Oyster. The company is considering overseas expansion of this land-based aquaculture system and says there is potential for island countries. Kyoko Washidari, COO and director of the company, says, “With the ocean environment changing dramatically due to rising temperatures, we feel that the Kumejima model, which enables land-based aquaculture through the use of deep seawater, will become globally important in the future. We would like to share our knowledge with Palau in a speedy manner that only a private company can provide.
Kyoko Washidari, Director and COO of G.O. Farm Ms. Washidari and other members of the research team touring a fish aquaculture facility in Palau
Contributing to the World with Japan’s Leading Renewable Energy Technology
The study is currently underway to select a candidate site for a power generation plant and to propose a business model and economic analysis utilizing deep seawater. Once validated, we then plan to proceed with the actual introduction of the “Kumejima Model” in cooperation with other national aid agencies and international organizations.
JICA is also considering the possibility of expanding the Kumejima model to other island countries, and plans to use existing data from several countries, including Solomon Islands, to study suitable sites. At present, the Permanent Mission of Japan to the United Nations and other island countries are inquiring about visiting Kume Island, and some have expressed a desire to implement the model in their countries.
Kumejima is one of the few renewable energy technologies in which Japan leads the world. I expect that the Kumejima Model will become a Japanese model that can contribute to the island regions, and I believe that it is necessary to do so,” said Professor Yasuyuki Ikegami of the Institute of Ocean Energy, Saga University, who is leading the research on this power generation. Yasuyuki Ikegami, a professor at the Institute of Ocean Energy Research, Saga University, who is leading the research on this power generation, says so.
Professor Yasuyuki Ikegami of the Institute for Ocean Energy Research at Saga University. He succeeded the late Professor Haruo Uehara of the same university, who invented the efficient ocean thermal energy conversion system “Uehara Cycle,” and is leading research worldwide.
Kumejima has set forth an “Energy Vision” to be self-sufficient in renewable energy by 2040, with solar power as the main source and 24-hour ocean thermal energy conversion as the base load power source. In the current demonstration project, the electricity generated is used to run the demonstration facility, but based on the results so far, the project is about to move forward to the commercialization of power generation. MOL plans to expand the current 100-kilowatt facility to a 1-megawatt-scale power plant by 2026.
The Kumejima Model is a sustainable island development model that utilizes the local resource of deep seawater to generate electricity, water, and food. We would like to make it a commercial success here in Kumejima first, and we also hope that it will spread overseas as well.
In 2015, Japan announced its support for the promotion of renewable energy using Japanese knowledge and technology for island countries that face difficulties in being vulnerable to environmental changes such as climate change. In response to this, JICA is also promoting the “Hybrid Island Program” to optimize the introduction of renewable energy in addition to diesel and other power sources currently used by the island countries. Starting with the introduction of the “Kumejima Model,” JICA will continue to cooperate with island countries to solve their problems and those of the earth.
© Source JICA
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