Editorial Feature

How Will Ocean Thermal Energy Conversion Help the Environment?

Ocean thermal energy conversion (OTEC) is an energy technology that makes use of the ocean’s temperature difference between the warm surface water and the cold deeper water to drive a turbine connected to a generator to produce electricity.

OTEC systems are operated based on the principle that the temperature difference of the fluid can be used to generate an increase in pressure which is in turn applied for generating mechanical work.

OTEC works best when the difference in temperature between the warm top layer and cold deep layer of the sea is around 20 °C (36 °F). This condition commonly exists in tropical coastal areas.

OTEC plants require an expensive, large-diameter intake pipe submerged to more than a mile into the ocean to bring cold water to the surface. Cold water obtained as a by-product from OTEC can be used for air conditioning and refrigeration.

Some energy experts suggest that OTEC can be used to produce billions of watts of electric energy, if it becomes cost-effective when compared to other conventional power technologies.

Ocean Thermal Energy Conversion Technologies

There are basically three types of OTEC systems:


Closed-cycle systems use working fluids with low boiling point, such as ammonia for rotating a turbine to produce electricity. Warm surface seawater is pumped via a heat exchanger where vaporization of the low-boiling-point fluid takes place.

The turbo-generator is rotated upon the expansion of vapor. Cold deep seawater is, in turn, pumped via a second heat exchanger where the vapor is condensed back into a liquid recycled through the system.

The Natural Energy Laboratory along with several private-sector partners carried out the mini OTEC experiment in 1979 which successfully achieved the production of net electrical power at sea with the help of closed-cycle OTEC.

In 1999, the Natural Energy Laboratory experimented with a 250-kW pilot OTEC closed-cycle plant, which is the largest of its kind.


Open-cycle systems make use of warm surface water of the tropical ocean to generate electricity. The expanding steam formed due to the boiling of warm seawater in a low-pressure container drives a low-pressure turbine connected to an electrical generator. The steam is then condensed back into a liquid upon exposure to cold temperatures from deep-sea water.

The Solar Energy Research Institute developed a vertical-spout evaporator in 1984 for the conversion of warm seawater into low-pressure steam using open- cycle plants and achieved 97% of energy conversion efficiencies.

An open-cycle OTEC plant developed at Keahole Point, Hawaii, in 1993 generated 50,000 W of electricity during a net power-producing experiment.


Hybrid system is a combination of open- and closed-cycle systems. In this system, warm seawater is flash-evaporated into steam in a vacuum chamber like the open-cycle evaporation process. The steam is then vaporized into a low-boiling-point fluid that in turn drives a turbine for producing electricity.

Benefits of OTEC

The key benefits of OTEC include the following:

  • OTEC systems produce fresh water and electricity as well, which is highly beneficial for island regions where fresh water availability is limited.
  • It makes use of renewable, clean, natural resources. Fossil fuels are replaced by warm surface seawater and cold water from deep sea to generate electricity.
  • OTEC plants do not pollute the environment by releasing carbon dioxide emissions or other polluting substances.
  • It helps reduce the country’s dependence on imported fossil fuels.

Disadvantages of OTEC

Some of the major drawbacks of OTEC include the following:

  • Construction of OTEC plants and pipes in ocean may cause damage to onshore marine ecosystems and reefs.
  • As this technology has been tested only in small-scale, it is not feasible for an energy company to invest in this project.
  • Electricity produced from OTEC would currently cost more than that produced from fossil fuels.
  • Discharging of cold and warm sea water needs to be carried out several metres away from the shore to avoid any dwelling impact on marine ecosystems.
  • Energy required to pump the sea water from depths may be huge, which otherwise need a diesel generator.


Power generated from OTEC technology will be inexpensive when compared to the unit cost of power from other plants like hydro, diesel and wave. As a result, several proposals for the development of OTEC in Pacific island countries have been submitted to the investors for consideration.

Therefore, the OTEC technology is the best solution to meet the world’s increasing energy demands thereby reducing the need for importing petroleum products.

Some of the areas related to the OTEC technology currently being considered in research include the development of new materials from cold water pipe and the improvement of the heat transfer coefficient for heat exchanges for a period of time.

However, the OTEC researchers believe that involvement of the private sector firms is very limited owing to the need of enormous initial investment. Another major factor that hinders the OTEC plant development is the limited availability of land-based sites in the tropical regions where deep-sea water is close enough to the shore to make the operation of the plant feasible.

Upon resolving these issues related to the OTEC development, the technology could easily change the face of energy consumption by causing a shift from fossil fuels.

Sources and Further Reading

Kris Walker

Written by

Kris Walker

Kris has a BA(hons) in Media & Performance from the University of Salford. Aside from overseeing the editorial and video teams, Kris can be found in far flung corners of the world capturing the story behind the science on behalf of our clients. Outside of work, Kris is finally seeing a return on 25 years of hurt supporting Manchester City.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Walker, Kris. (2020, October 15). How Will Ocean Thermal Energy Conversion Help the Environment?. AZoCleantech. Retrieved on June 13, 2024 from https://www.azocleantech.com/article.aspx?ArticleID=343.

  • MLA

    Walker, Kris. "How Will Ocean Thermal Energy Conversion Help the Environment?". AZoCleantech. 13 June 2024. <https://www.azocleantech.com/article.aspx?ArticleID=343>.

  • Chicago

    Walker, Kris. "How Will Ocean Thermal Energy Conversion Help the Environment?". AZoCleantech. https://www.azocleantech.com/article.aspx?ArticleID=343. (accessed June 13, 2024).

  • Harvard

    Walker, Kris. 2020. How Will Ocean Thermal Energy Conversion Help the Environment?. AZoCleantech, viewed 13 June 2024, https://www.azocleantech.com/article.aspx?ArticleID=343.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Your comment type

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.