Editing Ocean thermal energy conversion (section)

== Description ==
OTEC uses the [[ocean thermal gradient]] between cooler deep and warmer shallow or surface [[seawater]]s to run a [[heat engine]] and produce useful [[Work (physics)|work]], usually in the form of [[electricity]].  OTEC can operate with a very high [[capacity factor]] and so can operate in [[base load]] mode.

The denser cold water masses, formed by ocean surface water interaction with cold atmosphere in quite specific areas of the North Atlantic and the [[Southern Ocean]], sink into the deep sea basins and spread in entire deep ocean by the [[thermohaline circulation]]. [[Upwelling]] of cold water from the deep ocean is replenished by the [[downwelling]] of cold surface sea water.

Among ocean energy sources, OTEC is one of the continuously available [[renewable energy resource]]s that could contribute to base-load power supply.<ref name=":0">Lewis, Anthony, et al. IPCC: Special Report on Renewable Energy Sources and Climate Change Mitigation, 2011</ref> The resource potential for OTEC is considered to be much larger than for other ocean energy forms.<ref>World Energy Council, 2000</ref> Up to 10,000&nbsp;[[TWh]]/yr of power could be generated from OTEC without affecting the ocean's thermal structure.<ref>Pelc and Fujita, 2002</ref>

Systems may be either closed-cycle or open-cycle. Closed-cycle OTEC uses working fluids that are typically thought of as [[refrigerant]]s such as [[ammonia]] or [[1,1,1,2-Tetrafluoroethane|R-134a]]. These fluids have low boiling points, and are therefore suitable for powering the system's generator to generate electricity. The most commonly used heat cycle for OTEC to date is the [[Rankine cycle]], using a low-pressure turbine. Open-cycle engines use vapor from the [[seawater]] itself as the working fluid.

OTEC can also supply quantities of cold water as a by-product. This can be used for air conditioning and refrigeration and the nutrient-rich deep ocean water can feed biological technologies. Another by-product is [[fresh water]] distilled from the sea.<ref name="PopSci95"/>

OTEC theory was first developed in the 1880s and the first bench size demonstration model was constructed in 1926. Currently operating pilot-scale OTEC plants are located in Japan, overseen by [[Saga University]], and Makai in Hawaii.<ref>{{Cite web|url=https://www.makai.com/ocean-thermal-energy-conversion/|title=Ocean Thermal Energy Conversion|access-date=2021-07-09|archive-date=2022-02-17|archive-url=https://web.archive.org/web/20220217122357/http://www.makai.com/ocean-thermal-energy-conversion/|url-status=dead}}</ref>