Useful energy can be generated from marine currents using completely submerged turbines comprising of rotor blades and a generator. Water turbines work on the same principle as wind turbines by using the kinetic energy of moving fluid and transferring it into useful rotational and electrical energy. The velocities of the currents are lower than those of the wind, however owing to the higher density of water (835 times that of air) water turbines are smaller than their wind counterparts for the same installed capacity.
The first large ocean-system proposal is for a 2.4-mile system that would link Samar and Dalupiri islands in the Philippines. The Dalupiri project is estimated to cost $2.8 billion, produce 2,200 megawatts at tidal peak and offset 6.5 million tons of carbon dioxide a year
A corruption scandal that exploded and led to the resignation of the Philippine president in January 2001 has put the project on hold, however.