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<onlyinclude>'''Ocean thermal energy conversion''' or simply '''OTEC''' is the process of using the ocean itself as a [[solar collector]]. This [[technology]] is still highly theoretical, and utilizes the slight [[temperature]] gradient between the warm surface of the ocean and the cooler water deeper down.</onlyinclude> This technology operates in a similar way that [[solar pond]]s do but on a much larger scale. Although there is a temperature gradient, the overall temperature difference with depth is fairly small. In waters deeper than 1000 [[meter]]s the temperature change might only amount to [[celsius|20°C]].<ref name=boyle>G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref> Because of this very slight temperature gradient the [[efficiency]] of these systems are likely to be extremely low - only about 2%.<ref name=wolfson/>
[[File:Makai otec.png|thumb|Figure 1. Makai Ocean Engineering's 105 kW OTEC plant in Kona, HI.<ref>Wikimedia Commons (2013). (Accessed May 22, 2026). ''Makai 105kW OTEC Plant'' [Online]. Available: https://commons.wikimedia.org/wiki/File:Makai_105kW_OTEC_Plant.png</ref>]]
<onlyinclude>'''Ocean thermal energy conversion,''' or simply '''OTEC''', is the process of using the ocean itself as a [[solar collector]]. This [[technology]] (seen in figure 1) utilizes the slight [[temperature]] gradient between the warm surface of the ocean and the cooler water deeper down.</onlyinclude> This technology operates in a similar way that [[solar pond]]s do but on a much larger scale. Although there is a temperature gradient, the overall temperature difference with depth is fairly small. In waters deeper than 1000 [[meter]]s the temperature change might only amount to [[celsius|20°C]].<ref name="boyle">G. Boyle. ''Renewable Energy: Power for a Sustainable Future'', 2nd ed. Oxford, UK: Oxford University Press, 2004.</ref>


Although the technology is still fairly theoretical there have been more large scale experiments recently. These large scale experiments have taken place in the Pacific ocean and have had moderate success. Even though the tests have been partially successful, the engineering required to make these technologies viable is still a ways off in the future. The amount of [[water]] that needs to be pumped is a major issue, as a single OTEC station producing [[watt|10 MW]] of [[electricity]] would need to pump around 500 [[cubic meter]]s of water per [[second]].<ref name=boyle/>
In the 1990s, the Natural Energy Laboratory of Hawaii Authority was one of the world's leading test facilities for OTEC technology. In 2015, the facility became operational and now supplies electricity to the local electricity grid.<ref>EIA (2026). (Accessed May 21, 2026). ''Hydropower explained: Ocean thermal energy conversion'' [Online]. Available: https://www.eia.gov/energyexplained/hydropower/ocean-thermal-energy-conversion.php</ref> Advances in deep-water piping technology makes OTEC more feasible as a reliable power solution for coastal communities.<ref>Ocean Thermal Energy Corporation (2025). (Accessed May 21, 2026). ''Ocean Thermal Energy Conversion'' [Online]. Available: https://otecorporation.com/otec/</ref>


==How it Works==
==How it Works==
OTEC power plants could be built in several different ways, either as platforms similar to [[offshore oil rig]]s or as free floating structures. OTEC plants could also be constructed as large ships that would move throughout tropical oceans to find areas with the largest temperature differences. Practically speaking, it makes the most sense to put OTEC facilities in tropical areas as these regions of the ocean see the largest temperature differences.<ref name=wolfson/>
As shown in figure 2, OTEC power plants make use of the ocean's vertical thermal gradient, where the temperature differential between surface water and deep ocean can drive a heat engine. In tropical oceans specifically, surface water often exceeds temperatures of 25°C (77°F), while the water 1000 meters down is generally 5°C (41°F).<ref name=":0">Chua, I (2024). (Accessed May 21, 2026). ''Ocean Thermal Energy Conversion (OTEC): A Complete Introduction'' [Online]. Available: https://deepseaenergy.org/blog/otec-a-complete-introduction/</ref> OTEC power plants operate like any other thermal [[power plant]], however they require the use of an [[organic Rankine cycle]].
[[File:Oceanthermalec.png|frame|Figure 2. A diagram showing how an open-cycle OTEC facility uses ocean water to generate electricity.<ref>EIA (2026). (Accessed May 21, 2026). ''Hydropower explained: Ocean thermal energy conversion'' [Online]. Available: https://www.eia.gov/energyexplained/hydropower/ocean-thermal-energy-conversion.php</ref>|center]]


[[File:Otec_Closed_Diagram_in_English.JPG|400px|framed|center|Figure 1. A diagram showing how an OTEC facility uses ocean water to generate electricity.<ref>Wikimedia Commons. (August 13, 2015). ''OTEC Closed'' [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/b/bd/Otec_Closed_Diagram_in_English.JPG</ref>]]
=== Closed-cycle vs. open-cycle ===
In closed-cycle plants, the warm surface sea water heats up some [[fluid]] with a low [[boiling point]] (that is ''not'' the sea water itself). The fluid needs a low boiling point because the surface water itself isn't very warm, so generally [[ammonia]] is used (which has a boiling point of -33°C at [[atmospheric pressure]]). The warm water heats this fluid, turning it into a [[gas]] that drives a [[turbine]] to [[electricity generation|generate electricity]]. This vapour then comes into contact with a cold [[reservoir]], chilled with cold water from below the ocean surface. This condenses the vapour and the process begins again.<ref name="boyle" /><ref name=":0" />


OTEC power plants operate like any other thermal [[power plant]], however they require the use of an [[organic Rankine cycle]]. In these plants, warm surface sea water heats up some [[fluid]] with a low [[boiling point]]. The fluid needs a low boiling point because the surface water itself isn't very warm, so generally [[ammonia]] is used (which has a boiling point of -33 °C at [[atmospheric pressure]]). The warm water heats this fluid, turning it into a [[gas]] that drives a [[turbine]] to [[electricity generation|generate electricity]]. This vapour then comes into contact with a cold [[reservoir]], chilled with cold water from below the ocean surface. This condenses the vapour and the process begins again.<ref name=boyle/>
In open-cycle systems, the seawater itself is the working fluid. To drive the turbine, warm surface water is flash-evaporated in a low-pressure environment. Then, the steam is condensed by the cold deep water. This system yields both electricity and desalinated water as a byproduct.


==Environmental Impacts==
==Environmental Impacts==
The primary concern with OTEC facilities is the potential harm to marine life that could occur as a result of the mixing of warm and cool ocean waters. This mixing changes the temperature gradient of the ocean in a specific area, disrupting the ecosystem. For example, nutrients that are brought to the surface with the cold deep water could increase the number of fish or lead to [[algae]] blooms.<ref name=wolfson>R. Wolfson. ''Energy, Environment and Climate'', 2nd ed. New York, U.S.A.: Norton, 2012</ref> If these facilities are large scale, the average ocean surface temperature could even be affected and this would lead to changes in the [[weather]], [[climate]], and ocean circulation.<ref name=wolfson/>
The primary concern with open-cycle OTEC facilities is the potential harm to marine life that could occur as a result of the mixing of warm and cool ocean waters. This mixing changes the temperature gradient of the ocean in a specific area, disrupting the ecosystem. For example, nutrients that are brought to the surface with the cold deep water could increase the number of fish or lead to [[algae]] blooms.<ref name=wolfson>R. Wolfson. ''Energy, Environment and Climate'', 2nd ed. New York, U.S.A.: Norton, 2012</ref> If these facilities are large scale, the average ocean surface temperature could even be affected and this would lead to changes in the [[weather]], [[climate]], and ocean circulation.<ref name=wolfson/>
 
== For Further Reading ==
 
* [[Solar collector]]
* [[Organic Rankine cycle]]
* [[Ocean heat]]
* [[Ammonia]]
* Or explore a [[Special:Random|random page]]


==References==
==References==
{{reflist}}[[Category:Uploaded]]
{{reflist}}[[Category:Uploaded]]

Revision as of 21:33, 22 May 2026

Figure 1. Makai Ocean Engineering's 105 kW OTEC plant in Kona, HI.[1]

Ocean thermal energy conversion, or simply OTEC, is the process of using the ocean itself as a solar collector. This technology (seen in figure 1) utilizes the slight temperature gradient between the warm surface of the ocean and the cooler water deeper down. This technology operates in a similar way that solar ponds do but on a much larger scale. Although there is a temperature gradient, the overall temperature difference with depth is fairly small. In waters deeper than 1000 meters the temperature change might only amount to 20°C.[2]

In the 1990s, the Natural Energy Laboratory of Hawaii Authority was one of the world's leading test facilities for OTEC technology. In 2015, the facility became operational and now supplies electricity to the local electricity grid.[3] Advances in deep-water piping technology makes OTEC more feasible as a reliable power solution for coastal communities.[4]

How it Works

As shown in figure 2, OTEC power plants make use of the ocean's vertical thermal gradient, where the temperature differential between surface water and deep ocean can drive a heat engine. In tropical oceans specifically, surface water often exceeds temperatures of 25°C (77°F), while the water 1000 meters down is generally 5°C (41°F).[5] OTEC power plants operate like any other thermal power plant, however they require the use of an organic Rankine cycle.

Figure 2. A diagram showing how an open-cycle OTEC facility uses ocean water to generate electricity.[6]

Closed-cycle vs. open-cycle

In closed-cycle plants, the warm surface sea water heats up some fluid with a low boiling point (that is not the sea water itself). The fluid needs a low boiling point because the surface water itself isn't very warm, so generally ammonia is used (which has a boiling point of -33°C at atmospheric pressure). The warm water heats this fluid, turning it into a gas that drives a turbine to generate electricity. This vapour then comes into contact with a cold reservoir, chilled with cold water from below the ocean surface. This condenses the vapour and the process begins again.[2][5]

In open-cycle systems, the seawater itself is the working fluid. To drive the turbine, warm surface water is flash-evaporated in a low-pressure environment. Then, the steam is condensed by the cold deep water. This system yields both electricity and desalinated water as a byproduct.

Environmental Impacts

The primary concern with open-cycle OTEC facilities is the potential harm to marine life that could occur as a result of the mixing of warm and cool ocean waters. This mixing changes the temperature gradient of the ocean in a specific area, disrupting the ecosystem. For example, nutrients that are brought to the surface with the cold deep water could increase the number of fish or lead to algae blooms.[7] If these facilities are large scale, the average ocean surface temperature could even be affected and this would lead to changes in the weather, climate, and ocean circulation.[7]

For Further Reading

References

  1. ↑ Wikimedia Commons (2013). (Accessed May 22, 2026). Makai 105kW OTEC Plant [Online]. Available: https://commons.wikimedia.org/wiki/File:Makai_105kW_OTEC_Plant.png
  2. ↑ 2.0 2.1 G. Boyle. Renewable Energy: Power for a Sustainable Future, 2nd ed. Oxford, UK: Oxford University Press, 2004.
  3. ↑ EIA (2026). (Accessed May 21, 2026). Hydropower explained: Ocean thermal energy conversion [Online]. Available: https://www.eia.gov/energyexplained/hydropower/ocean-thermal-energy-conversion.php
  4. ↑ Ocean Thermal Energy Corporation (2025). (Accessed May 21, 2026). Ocean Thermal Energy Conversion [Online]. Available: https://otecorporation.com/otec/
  5. ↑ 5.0 5.1 Chua, I (2024). (Accessed May 21, 2026). Ocean Thermal Energy Conversion (OTEC): A Complete Introduction [Online]. Available: https://deepseaenergy.org/blog/otec-a-complete-introduction/
  6. ↑ EIA (2026). (Accessed May 21, 2026). Hydropower explained: Ocean thermal energy conversion [Online]. Available: https://www.eia.gov/energyexplained/hydropower/ocean-thermal-energy-conversion.php
  7. ↑ 7.0 7.1 R. Wolfson. Energy, Environment and Climate, 2nd ed. New York, U.S.A.: Norton, 2012
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