Makai Ocean Engineering Inc. has built an Ocean Thermal Energy Conversion (OTEC) demonstration plant in Hawaii. The project was funded by Makai, Hawaii Natural Energy Institute, and the U.S. Navy and cost about $5 million to build.
The 105-kilowatt demonstration plant is located on the big island of Hawaii and is connected to the main electrical grid, generating enough electricity to power 120 homes.
Makai has also signed a memorandum of understanding to build a 1 megawatt Ocean Thermal Energy Conversion plant in Japan.
Here is a great video about the Hawaiian demonstration plant and how the technology works: