Turning the ocean into a battery

A UK-based startup, Global OTEC, is breathing new life into a century-old technology that could power tropical island nations with virtually limitless, consistent, renewable energy by treating the ocean like a battery. Ocean thermal energy conversion (OTEC) might produce at least 2,000GW globally, rivalling the combined capacity of all the world’s coal power plants.

French physicist Jacques Arsene d’Arsonval invented ocean thermal energy conversion in 1881 when he realized that the temperature difference between the surface and the cold depths of the ocean could be used to  generate electricity.  Now, says Global OTEC, innovation and partnerships can prevent the 50 million people who live on tropical islands from having to seek refuge because island life has become untenable.

This educational video is the result of a cooperation between Global OTEC, environmentalist Kane Baker, of the George F. Baker Trust Foundation and Schoolyard Films.

By transferring heat from warm surface waters to evaporate a low-boiling point fluid like ammonia, OTEC creates steam that drives a turbine. As the vapour cools and condenses in contact with cold seawater pumped from the ocean’s depths, it completes the energy cycle. It can run 24/7 and generates electricity at a consistent rate. 

But the costs of setting up plants held back its wide scale adoption until Global OTEC developed its floating barge design, Dominique, which it presented at the International Vienna Energy and Climate Forum. With support from UNIDO’s Green Climate Fund, it is being installed in São Tomé and Príncipe. UNIDO will share lessons through the Global Network of Regional Sustainable Energy Centers, benefiting future OTEC projects.

Global OTEC photo

Dominique is designed to be modular and much cheaper than previous prototypes. It needs only one large cold-water pipe travelling straight down into the ocean’s depths. “We know Dominique is a life-changer for small islands and coastal nations, and that’s why we see the pace of the project on track for success,” says Dan Grech, CEO and founder of Global OTEC.

 “This project is not just important for São Tomé and Príncipe but has high potential for replication across other SIDS”, says Martin Lugmayr of UNIDO. The efforts are part of the Global Ocean Energy Alliance (GLOEA), launched by UNIDO, SIDS DOCK and other partners at the UN Ocean Conference in Lisbon, Portugal, in 2022.

São Tomé and Príncipe is proving to be the shining example to the rest of the world of how diesel fuel imports can be replaced with clean baseload energy from the ocean. It will be the catalyst for a whole portfolio of OTEC projects, with needs for ocean energy already identified in countries such as Antigua and Barbuda, Belize, Fiji, Grenada, and Tonga, among others.

“OTEC is a new opportunity for São Tomé and Príncipe to explore renewable energy, meeting the national ambitions and goals of the National Determined Contributions,” says Gabriel Mquengo, who is with the Ministry of Infrastructure, Natural Resources and Environment of São Tomé and Príncipe.

Dominique has the potential to decarbonize 10 GW of installed diesel capacity across 32 island countries, and the company believes that developing partnerships with these countries will secure clean and sustainable energy, leveraging the vast, untapped technology that is OTEC.

“The GLOEA has highlighted 700 MW of OTEC projects which are required urgently. Our first-of-a-kind platform de-risks this floating technology for infrastructure investors and will accelerate the technologies rollout through our standardised, modular systems”, Grech says.


140-year-old ocean heat tech could supply islands with limitless energy. The Next Web, Nov. 9, 2023

140 year old tech to bring unlimited clean energy to island nations Interesting Engineering, Nov. 10, 2023


Cover image: UNIDO/Global OTEC

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