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WHAT IS OTEC

Did you know that we can use the natural temperature difference in our tropical oceans to create electricity day and night all year round? 

Makai-Plant-Hawaii

Ocean Thermal Energy Conversion (OTEC) harnesses the power of the ocean to provide a continuous, cost-effective supply of clean energy. It possesses significant environmental advantages over fossil fuels and nuclear power; requires less land than renewable energy technologies such as solar, wind, biomass and hydroelectric power; and has the potential to produce far more useful and affordable energy than could be generated from other renewable sources.

How does it work?

Ocean Thermal Energy Technology (OTEC) provides a baseload power source that works day and night, year-round; offering a clean alternative to diesel that can be used alongside peak load solar or wind. It works by using warm surface seawater to produce electricity: 

1.

The barge draws in warm surface seawater (of around 26°C) which has been heated by the sun’s rays

2.

This warm water is used to evaporate a working fluid with a low boiling point

3.

This produces a vapour which spins a turbine to produce electricity using a generator

4.

At the same time, cold deep water (of around 4°C) is drawn up through a pipe from the depths of the ocean

5.

The cold water cools the vapour, turning it back into a liquid which can then be immediately reused

6.

The cycle runs continuously whilst the power generated is transmitted to the grid using a sub-sea cable

Electricity grids use two types of power: baseload (the unchanging amount of energy needed throughout the day and night) and peak load (shorter periods when more energy is needed). Renewable energy sources like solar panels provide peak load power during the daytime when the energy from the sun can be captured. But most tropical nations require oil imports for constant baseload power the rest of the time. Because the tropical ocean is always warm whatever the weather, time of day or year, OTEC can continuously generate electricity 24 hours a day, 365 days a year.

History of OTEC

The idea of creating energy from the temperature differences between the surface and deeper levels of the ocean isn’t new. In fact, the idea is over 140 years old. Decades of research and development in the lab have already been undertaken. 

1881 to 1930:
The Concept

If using the ocean’s temperature to create energy sounds like fiction, you might not be far off. Jules Vernes’ famous novel Twenty Thousand Leagues Under the Sea – first published around 1870 – includes a fictional character – Captain Nemo – thinking about how to make electricity using temperature differences in the ocean. Perhaps this inspired the French physicist Jacques-Arsène d'Arsonval who proposed it was possible to harness the ocean’s energy to create power in 1881. In 1930 an entrepreneurial student of d’Arsonval, called Georges Claude, tested the idea. He built an Ocean Thermal Energy Conversion plant in Cuba but it was destroyed by a storm. Low-level research into OTEC continued through the 1940s and ‘50s but, by this time, the world’s focus was on cheaper energy sources such as nuclear and fossil fuels.

1970s to 90s

It wasn’t until the 1970s that OTEC returned to the spotlight. With the energy crisis causing oil prices to skyrocket, the USA and Japan decided to revisit OTEC as a source of clean, reliable energy. In 1974, the Natural Energy Laboratory of Hawaii Authority (NELHA) was founded to conduct research into clean energy technologies. In 1979, former President Jimmy Carter passed the Ocean Thermal Energy Conversion Act to ensure the USA had a wide range of energy sources. This led US researchers to develop two OTEC plants based off the coast of Hawaii, (mini-OTEC and OTEC-1) which successfully generated net power. Then, around 1981, Japanese companies tested an OTEC system off the coast of Nauru, in the Pacific, which generated 35 kilowatts of net power before being destroyed by a storm. By 1999, one of NEHLA’s plants could generate 250 kilowatts of energy.

2013 to date

After another lull in the progression of OTEC, the pace picked up again in the 2000s as people became more concerned about climate change. At this point, the OTEC energy pioneers of the 1980s were coming to the end of their careers. They had spent decades testing how to create the most efficient cycle and permanent projects in Hawaii, Japan and South Korea had proven that, alongside wind and solar, OTEC can provide a viable, clean energy solution to help the world move away from diesel. Despite this, OTEC hasn’t yet been commercially successful. Most plans to upscale have struggled to secure funding. Huge 100-megawatt plants needed billions in investment to get off the ground and failed because they tried to grow too quickly. Global OTEC plans to change this. We have designed the first small-scale commercial Ocean Thermal Energy Conversion system to transform the energy landscape for tropical islands.

THE FUTURE

Global OTEC aims to transform the future of Ocean Thermal Energy Conversion and believes success is possible with collaboration between the public and private sector. The company plans to standardise as much of the OTEC platform as possible so it can be mass-produced for the widest deployment possible. Over the last five years, our team has designed a series of small floating OTEC concepts to serve small island nations. An agreement was signed with SIDS DOCK in 2021 to pilot a 1.5-megawatt barge in São Tomé and Príncipe. The success of this project will show the rest of the world how diesel fuel can be replaced with clean ocean energy and will allow Global OTEC to scale up to more and larger barges in the coming years.

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