OTEC Power Plant Definition

OTEC Power Plant Definition, Types, Components, Locations, Pros/Cons

OTEC power plant is a part of an OTEC system, comprising of turbines, pumps, evaporators and submarine cables that work to convert thermal energy from seawater to electric power.

This article discusses OTEC power plant definition, types, components, location, advantages and disadvantages, as outlined below;



-OTEC Power Plant Definition

-Types of OTEC Power Plants

-Components of OTEC Power Plants

-OTEC Power Plant Locations

-OTEC Advantages and Disadvantages








OTEC Power Plant Definition

OTEC power plant is an electricity generation facility that utilizes the difference in temperature between surface (shallow) (22-27 °C) and deep (4-7 °C) ocean waters, to produce steam that spins a turbine and generates electricity [3].

Principles behind OTEC power plant technology, include thermal energy transfer, fluid temperature-pressure proportionality, thermo-mechanical conversion, and electromagnetic induction.

These principles are also used in other electricity generation systems like fossil fuel power plants, bio-power plants, steam turbines and gas turbines.

It must be noted that the OTEC power plant is one of the components of an OTEC system, alongside ocean thermal energy resources, techniques, processes and mechanisms.

OTEC plants work by pumping warm surface water from the ocean, either into a heat exchanger that allows it to transfer thermal energy to a low-boiling point working fluid like ammonia, or into a low-pressure vacuum chamber that enables the seawater to vaporize at temperatures below the typical water boiling point, so that the water can be directly used as a working fluid.

Based on the working fluid(s) that is used (seawater, ammonia, or both), OTEC power plants can be distinguished into three types, which are highlighted in the following section.







Types of OTEC Power Plants

The types of OTEC power plants are; closed-cycle, open-cycle and hybrid-cycle OTEC plants. This classification is based on working fluid dynamics, and is identical to the classification used for distinguishing the types of OTEC systems.





1). Open-Cycle OTEC Plant (as one of the Types of OTEC Power Plants)

Open cycle OTEC power plants are those which circulate seawater as the primary working fluid of the system [4].

They are called 'open' because the seawater is generally allowed to flow into and out of the system, so that it is continuously recycled in phases of vaporization and cooling that occur between the power plant and the ocean.

The water that is used as a source of thermal energy for the system is warm, surface seawater, whose maximum temperature hardly exceeds 27 °C.

To produce steam at such temperature, the water is pumped into a low-pressure vacuum vessel or chamber, which reduces its boiling point and enables vaporization to occur. The vapor produced may then be used to spin a turbine and generate electricity.

Types of OTEC Plants: Open Cycle OTEC Power Plant (Credit: Schema_offenes_Ocean_Thermal_Gradient-Kraftwerk_OTEC.png, Lumos3 2011 .CC BY-SA 1.0.)
Types of OTEC Plants: Open Cycle OTEC Power Plant (Credit: Schema_offenes_Ocean_Thermal_Gradient-Kraftwerk_OTEC.png, Lumos3 2011 .CC BY-SA 1.0.)







2). Closed-Cycle OTEC Plant

In closed cycle OTEC plant, fluid does not flow into or out of the system.

Rather, the working fluid is enclosed within the system and capture ocean thermal energy through the transfer mechanism of conduction.

Closed cycle OTEC power plants use fluids with low boiling point, such as ammonia, to capture heat from seawater.

The heat captured converts the working fluid to vapor, which is then released into the turbine chamber where it exerts impulsive force on the turbine rotor blades as it expands, causing them to rotate.

Types of OTEC Plants: Closed Cycle OTEC Power Plant (Credit: Schema_geschlossenes_Ocean_Thermal_Gradient-Kraftwerk_OTEC.png, Lumos3 2011 .CC BY-SA 1.0.)
Types of OTEC Plants: Closed Cycle OTEC Power Plant (Credit: Schema_geschlossenes_Ocean_Thermal_Gradient-Kraftwerk_OTEC.png, Lumos3 2011 .CC BY-SA 1.0.)





3). Hybrid-Cycle OTEC Plant (as one of the Types of OTEC Power Plants)

A hybrid cycle OTEC plant combines some of the typical characteristics of both open and closed cycle plants.

Generally, hybrid cycle OTEC power plants are equipped to produce both steam by low-pressure vaporization of seawater, and gaseous working fluid that is used for turbine rotation.

Seawater steam is usually the source of heat for the working fluid.

While hybrid cycle plants are more complex than other types in terms of operation and design, they are built to achieve greater energy efficiency and power output.







Components of OTEC Power Plants

Components of OTEC power plants are;

1). Offshore foundation of floating platform

2). Heat exchanger

3). Fluid Pumps

4). Turbine

5). Working Fluid

6). Submarine electric cable(s)



Of these components, the core parts of an OTEC power plant are; working fluid, pumps, heat exchanger (or vaporizer) and turbine generator [1].







OTEC Power Plant Locations

OTEC plants are located in deep-sea zones, where the ocean depth allows for a broad hydrothermal gradient between surface and deep seawaters, so that such temperature differences can be used to vaporize and condense the working fluid effectively.

There are two OTEC plants in the world which are operational as of 2023, and these are; the Saga University OTEC plant in Japan, and the Makai OTEC plant in Hawaii, United States.

The largest producer of ocean thermal energy in the world as of 2023 is the United States, with the Makai plant being the largest OTEC power plant, at an output capacity of 105 kW [5]. This is only 5 kW ahead of the Saga University plant, which has a total capacity of 100 kW [2].

OTEC power plant schemes and projects are also ongoing in other parts of the world, such as China [6].







OTEC Advantages and Disadvantages

OTEC advantages are;

1). Renewable supply

2). Relative consistency

3). Minimal environmental impact

4). Low maintenance

5). Relative technical simplicity



OTEC disadvantages are;

1). High capital cost

2). Risk of marine pollution by working fluid

3). Low thermal energy conversion rate

4). Early-stage development

5). Geographic limitation to deep sea locations









OTEC power plant is facility composed of evaporators and turbine generators that work together to capture heat from seawater, and use this heat to generate electricity.


Types of OTEC power plants are;

1. Open-Cycle OTEC Plant

2. Closed-Cycle OTEC Plant

3. Hybrid-Cycle OTEC Plant


Components of OTEC power plants are; offshore foundation, heat exchanger, fluid pumps, turbine, working fluid, and submarine cables.


OTEC plant locations in the world are Okinawa, Japan; and Hawaii, United States.


OTEC advantages and disadvantages are; renewable supply, relative consistency, minimal environmental impact, low maintenance, relative technical simplicity (advantages); high capital cost, marine pollution risk, low thermal conversion, early stage development, and geographic limitation (disadvantages).








1). Adiputra, R.; Utsunomiya, T.; Koto, J.; Yasunaga, T.; Ikegami, Y. (2019). "Preliminary design of a 100 MW-net ocean thermal energy conversion (OTEC) power plant study case: Mentawai island, Indonesia." Journal of Marine Science and Technology 25(1). Available at: https://doi.org/10.1007/s00773-019-00630-7. (Accessed 12 March 2023).

2). Cuartas, J. A. H.; Acuña, S. S.; Ibeas, A. (2021). "Ocean Thermal Energy Conversion and Other Uses of Deep Sea Water: A Review." Journal of Marine Science and Engineering 9(4). Available at: https://doi.org/10.3390/jmse9040356. (Accessed 12 March 2023).

3). Etemadi, A.; Emdadi, A.; AsefAfshar, O.; Emami, Y. (2011). "Electricity Generation by the Ocean Thermal Energy." IEEE International Conference on Smart Grid and Clean Energy Technologies 2011 (IEEE ICSGCE), Energy Procedia 12. Available at: https://doi.org/10.1016/j.egypro.2011.10.123. (Accessed 13 March 2023).

4). Hernández-Romero, I. M.; Nápoles-Rivera, F.; Flores, A.; Fuentes-Cortes, L. F. (2020). "Optimal design of the ocean thermal energy conversion systems involving weather and energy demand variations." Chemical Engineering and Processing 157. Available at: https://doi.org/10.1016/j.cep.2020.108114. (Accessed 13 March 2023).

5). Owano, N. (2015). "Celebrating Hawaii ocean thermal energy conversion power plant." Available at: https://techxplore.com/news/2015-08-celebrating-hawaii-ocean-thermal-energy.html. (Accessed 12 March 2023).

6). Sharda (2019). "World’s Largest Ocean Thermal Energy Conversion (OTEC) Power Plant To Come Up in China." Available at: https://www.marineinsight.com/offshore/worlds-largest-ocean-thermal-energy-conversion-otec-power-plant-to-come-up-in-china/. (Accessed 13 March 2023).

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