New Marine Energy Harvesting Devices Are (Finally) Heaving Into View: From the mixing of 1 m^3 of river water with 1 m^3 of sea water, 0.5 kilowatt hours of electricity can theoretically be obtained at 25 °C. This corresponds to a power of 1.8 MW from a flow rate of 1 m^3/s fresh and 1 m^3/s salt water...
Many of the world's major cities are on river estuaries where sea and fresh water are easily available, and Statkraft estimates the total global potential of osmotic power to be around 1700 terawatt-hours per year — about 10% of the world's current electricity consumption...