Power from ocean temperature differences

How far are we from ocean temperature differences generating commercial power?

Ocean thermal energy conversion (OTEC) makes electricity from the temperature gap between warm surface water and cold deep water. Small plants have produced power: the Mini-OTEC operational results, published in 1981, report about 15 kW net. A 100 kW closed-cycle plant at the Natural Energy Laboratory of Hawai'i Authority (NELHA) was dedicated in 2015 and connected to the grid, but its output is a company rating, not a measured record. Larger demonstrations and floating platforms are planned or in early installation. The sources reviewed show no OTEC plant running for months with a full net energy balance, and no verified cost figures.

AI illustration · Illustrative scene, not a photograph of the specific device or experiment.
WHERE WE AREPilots

Close. Early pilots are running in the real world.

Net electricity has been reported from a test plant (Mini-OTEC, published 1981), and a 100 kW closed-cycle plant at NELHA was dedicated on 21 August 2015 and connected to the grid. That is more than a laboratory result, but it is a single small plant, and its output figure is a rating rather than a measured record. The Kumejima project is a demonstration, the Dominique platform is set to deploy with no published date, and the 2026 floating platform at PLOCAN is in early installation. No commercial OTEC plant in the sources reviewed has been shown running for months with a full net energy balance, so the stage is pilot.

The tech tree

Everything recorded on Vrulum that this future needs, oldest foundations at the top and the goal at the bottom. Lines show what each step requires.

What it takes: Power from ocean temperature differences Unlocked Being researched Locked
  1. 1979Ocean thermal energy conversionResearch and prototypes Being researched.
  1. 1981Net electricity from a test plantDone Unlocked.
  2. 2015Grid-connected 100 kW closed-cycle plantDone Unlocked.
  3. 2023Demonstration with heat exchangers at Kumejima, OkinawaIn progress Being researched.
  4. 2026Floating prototype with intake riser at PLOCAN, Gran CanariaIn progress Being researched.
  5. Date not recordedDominique floating plant in São Tomé and PríncipeNot started Locked.
  6. Date not recordedEnvironmental baseline and monitoring at plant scaleNot started Locked.
  7. Date not recordedFull-plant net output over monthsNot started Locked.
  1. GoalPower from ocean temperature differencesGoalRequires: Ocean thermal energy conversion, Net electricity from a test plant, Grid-connected 100 kW closed-cycle plant, Demonstration with heat exchangers at Kumejima, Okinawa, Floating prototype with intake riser at PLOCAN, Gran Canaria, Dominique floating plant in São Tomé and Príncipe, Environmental baseline and monitoring at plant scale, Full-plant net output over months. Locked.

The road so far

2 of 7 steps done, 2 in progress.

  1. Done · 1981Net electricity from a test plant

    Mini-OTEC operational results, published in 1981 in the Journal of Solar Energy Engineering, report about 50 kW gross and about 15 kW net at an average seawater temperature difference of 21 °C. Cold water came from about 670 metres depth through a 0.61 metre polyethylene pipe. The longest continuous run was 10 days. [1]

  2. Done · 21 Aug 2015Grid-connected 100 kW closed-cycle plant

    Makai Ocean Engineering's plant at NELHA was dedicated on 21 August 2015 and described as the first closed-cycle OTEC plant connected to the US grid. The company and press coverage give a rating of 100 kW of continuous electricity. The sources reviewed give no measured net output, availability over time, or power sales. [2]

  3. In progress · 24 Mar 2023Demonstration with heat exchangers at Kumejima, Okinawa

    Mitsui O.S.K. Lines (MOL) announced in March 2023 that its Kumejima project had been selected by Japan's Ministry of the Environment. Xenesys proposed the project and manages the test facility, with Saga University and Kumejima Town taking part. MOL says large titanium heat exchangers, with performance verified from FY2022 to FY2024, are equivalent to 200 kW of power generation, and it aims for the world's first 1 MW-scale OTEC commercialisation by around 2026. The announcement gives no measured plant output. [3]

  4. In progress · 23 Apr 2026Floating prototype with intake riser at PLOCAN, Gran Canaria

    In April 2026 Global OTEC reported that it had installed a purpose-built floating OTEC platform prototype and its vertical seawater intake riser at PLOCAN, the Oceanic Platform of the Canary Islands, a pre-consented test site off Gran Canaria. The article gives no rated capacity, generation or net output. [4]

  5. Not startedDominique floating plant in São Tomé and Príncipe

    Global OTEC describes Dominique as a first-of-a-kind 1.5 MW floating OTEC platform, with installed capacity to reach 10 MW through additional platforms. Lloyd's Register has granted Approval in Principle, and a cold-water riser installation method was approved by ABL Group in 2023. The project page shows no deployment, commissioning or completion dates and says only that the platform is set to deploy. [5]

  6. Not startedEnvironmental baseline and monitoring at plant scale

    A 2010 NOAA-sponsored workshop report says a minimum baseline of marine life and seawater conditions is required before installation, that a longer baseline may be needed to capture multi-year variability, and that monitoring should continue through installation and operation. Suggested parameters include temperature, salinity, dissolved oxygen, pH, trace metals and changes in marine organisms. The sources reviewed include no monitoring results from a plant at full intended scale. [6]

  7. Not startedFull-plant net output over months

    The sources reviewed do not report a run of several months with measured gross output, all pumping loads, net export, shutdowns and maintenance. The longest continuous run in the Mini-OTEC results was 10 days. [1]

Why it matters

Warm surface water and cold deep water can be tapped day after day, unlike wind or solar output. An April 2026 Global OTEC announcement cites more than 25 GW of existing fossil fuel capacity on tropical islands that OTEC could replace over time, a figure from the company rather than an independent estimate. Whether that value is real depends on the whole plant. Gross output and net electricity delivered to users are different numbers, and the gap between them decides the case.

What stands in the way

  • Gross and net output differ widely. In Mini-OTEC, about 50 kW gross output fell to about 15 kW net, so the net figure is the one that reaches users.
  • The sources reviewed do not establish long-term effects on marine life. A 2010 NOAA-sponsored workshop report calls for baseline data before installation and monitoring during operation, and no plant-scale monitoring results are in the sources reviewed.
  • Full-plant net output over months has not been published in the sources reviewed. The longest Mini-OTEC run was 10 days, and no measured output has been published for the NELHA plant.
  • The sources reviewed give no verified cost figures for OTEC plants, so the cost of OTEC power cannot yet be compared with solar, wind or diesel.

Published forecasts

What others have predicted. These are their estimates, not ours.

WhoForecastTimeframeMade
Mitsui O.S.K. Lines (MOL), with Xenesys, Saga University and Kumejima TownAims for the world's first commercialisation of OTEC on a 1 MW scale by around 2026. This is a project target stated in a 2023 company announcement, not an independent forecast. [3]202624 Mar 2023

Signals to watch

  • A multi-month offshore run that reports gross output, pumping loads, net export, shutdowns and maintenance.
  • Deployment and commissioning dates for the Dominique platform in São Tomé and Príncipe, and results from the PLOCAN floating prototype.
  • Whether the Kumejima demonstration reports measured output against the 1 MW commercial-scale goal set for around 2026.
  • Whether the NELHA plant in Hawai'i publishes measured net output, or a sale of its power is reported.

Sources

  1. peer reviewed paper
    Mini-OTEC Operational Results
    W. Owens, L. Trimble. Journal of Solar Energy Engineering (ASME), record hosted by Tethys Engineering (PNNL), Aug 1981.
  2. news
    Makai Ocean Engineering connects world's largest OTEC plant to U.S. grid
    Power Engineering, 31 Aug 2015.
  3. company announcement
    Ocean Thermal Energy Conversion Demonstration Project in Okinawa Selected by Japan's Ministry of the Environment - Aiming to Commercialize World's 1st Ocean Thermal Energy Conversion by around 2026
    Mitsui O.S.K. Lines (MOL), 24 Mar 2023.
  4. news
    Global OTEC Completes Installation of World's First Purpose-Built Offshore Platform for Ocean Heat Energy
    ECO Magazine (environment coastal & offshore), 23 Apr 2026.
  5. company announcement
    Dominique
    Global OTEC, 2022.
  6. government report
    Ocean Thermal Energy Conversion: Assessing Potential Physical, Chemical and Biological Impacts and Risks
    J. Cunningham, Z. Magdol, N. Kinner. University of New Hampshire, prepared for NOAA (record hosted by Tethys), 22 Jun 2010.

Last reviewed 21 Oct 2026.