Japan's power-from-seawater project attracts global attentionーNHK WORLD-JAPAN NEWS

Key Concepts

• Ocean Thermal Energy Conversion (OTEC): A technology that generates electricity by utilizing the temperature difference between warm surface seawater and cold deep ocean water.
• Temperature Gradient: The difference in temperature between two locations, in this case, surface and deep ocean water.
• Working Fluid: A substance (like ammonia) with a low boiling point that is vaporized by warm water and condensed by cold water to drive a turbine.
• Base Load Power: A continuous and stable supply of electricity that is available 24/7, regardless of external conditions.
• Marine Farming: The cultivation of marine organisms, such as seaweed and oysters, often utilizing the temperature-modified water from OTEC systems.

Ocean Thermal Energy Conversion (OTEC) Technology

OTEC is a renewable energy technology that aims to generate clean electricity directly from the sea. It leverages the significant temperature difference that exists between warm surface seawater and cold water found at greater depths.

Core Mechanism

The process relies on a temperature gap in seawater. Specifically, the technology utilizes a temperature difference of approximately 20°C between surface seawater and colder water pumped up from depths exceeding 600 meters.

1. Vaporization: Warm surface seawater is used to heat a liquid with a low boiling point, such as ammonia. This causes the ammonia to vaporize.
2. Turbine Generation: The ammonia vapor is then directed to spin a turbine, which in turn generates electricity.
3. Condensation: Cold water pumped from the deep ocean is used to cool the ammonia vapor, causing it to condense back into a liquid.
4. Cycle Repetition: The condensed liquid ammonia is then ready to be heated again, continuing the cycle to produce electricity continuously.

Test Facility in Kumijima, Okinawa, Japan

A test facility on Kumijima Island in Okinawa Prefecture, Japan, serves as a demonstration site for OTEC technology. This facility, funded by Okinawa and Koujima, is based on research and technology developed at Saga University.

• Current Output: The test plant currently produces 100 kW of electricity.
• Operational History: It has successfully provided a stable electricity supply for over 10 years.
• Expert Insight: Professor Iikami Yasuyuki of Saga University, a leading expert in OTEC, explains the process: "When I open this vapor valve, the pressure will rise and rapidly spin the turbine. This is how it generates electricity."

Advantages of OTEC

• Stable Electricity Supply: The primary advantage of OTEC is its ability to generate stable electricity 24 hours a day, irrespective of weather conditions. This makes it a reliable source of base load power.
• Long-Term Research: Saga University has been researching ocean energy for approximately 50 years, seeking alternatives to fossil fuels. Kumijima was identified as an ideal location due to the readily available warm surface and deep ocean water.

Challenges and Cost Mitigation

• High Cost: OTEC is currently a costly method for power generation.
• Cost Offsetting through Marine Farming: To address the high costs, Saga University has implemented a strategy of recycling the seawater used in the OTEC process.
  • Sea Grapes Cultivation: The cold deep-sea water, after warming up, is ideal for marine farming. On Kumijima, this warmed water is used to cultivate a type of edible seaweed known as "sea grapes." This initiative has made Kumijima Okinawa's leading producer of sea grapes.
  • Oyster Farming: The warmed water is also utilized for onshore oyster farming.
  • Other Seaweed Cultivation: Another facility, opened in spring, uses the water to farm different types of seaweed for food and medicinal purposes.
• Economic Impact: These marine farming businesses generate approximately $17 million annually and have created about 140 jobs. This additional revenue stream significantly helps to reduce the cost of generating electricity through OTEC.

International Collaboration and Future Expansion

Japan's OTEC research is extending its reach globally, benefiting other nations.

• Malaysia Facility: A facility designed by Saga University commenced operations in Malaysia in October of the previous year.
• Palao Interest: Officials from the Pacific Island nation of Palao have visited Kumijima and are planning to establish their own OTEC plant.
• Global Impact: Professor Iikami Yasuyuki expresses his hope: "I would like the research at Saga University to help not just people in Kajima but many others around the world. There are many people struggling from shortages of electricity."

Conclusion

The OTEC technology, nurtured over decades by Saga University, represents a significant step towards building a world powered by sustainable energy. The ongoing development and innovative cost-mitigation strategies, such as integrating marine farming, demonstrate the potential of harnessing ocean resources for clean and reliable electricity generation. The technology's expansion beyond Japan highlights its promise in addressing global electricity shortages and promoting a sustainable energy future.