wiki article states "Up to 10,000 TWh/yr of power could be generated from OTEC without affecting the ocean's thermal structure". which converts to about 500GW which... isn't that much
10,000 TWh/y = 1e+7 GWh/y, divide it by 365.25 days/y to produce daily output of 27,379 GWh/day, then by 24 h/day to get pure power of 1,141 GW. It's still more than a terawatt, three orders of magnitude larger than the largest nuclear reactors.
