The heat exchangers and pipework required to make a 10MW plant already exist, but the 100MW facility will need a pipe that is not only 1km long (in order to reach the cold water at depth) but ten metres in diameter (in order to bring enough of that cold water to the surface).

ECONOMIST: Ocean heat may be used to generate electricity

The seawater down there is so cold that when natural gas bubbles out of the well into the water it forms methane hydrates, which clog the uptake pipe.

FORBES: BP's Big Box Removed From Leak As Gas Crystals Clog Uptake Pipe