Basic Facts:  A temperature differential of 38 degrees Farenheit (roughly 21 degrees Celsius) is needed to make OTEC optimally feasible.  Sea surface temperatures versus deeper ocean temperatures are a key determiner of feasibility, making warm water / deep water locations the most likely sites for Ocean Thermal Energy implementation.  This includes much of the South Atlantic, the Caribbean, the Pacific, the South China Sea and the Indian Oceans bordering areas where billions of people live and work.   Further, far off sites could do many useful tasks regardless of location such as desalinating water for wind-driven tankers and performing other energy intensive functions.  Great links of power stations could span many thousands of miles between distant sea locations and major population centers in China, the US West, the Middle East and Europe.

Ocean Thermal Resource Map (Orange and, to some extent, yellow show feasible areas)

Source: Robert Cohen

Thermocline map

Wikipedia on Sea Surface Temperatures