conversion. The kinetic energy present in marine and tidal currents can be converted to electricity using
relatively conventional turbine technology. Harnessing the kinetic energy in waves presents a different set
of technical challenges and a wide variety of designs have been suggested. Ocean thermal energy
conversion is possible in locations with large temperature differences, extracting energy using a heat
engine. Salinity gradients can be exploited for energy extraction through the osmotic process. The
cultivation of marine biomass can yield many useful products, including renewable fuels for electricity
generation. Marine current refers to water that moves continuously and is driven by the motion of the
ocean from solar heating and wind near the equator. Marine current moves in one direction with relatively
constant flow. Only a fraction of the global ocean energy resource can be found in sites economically
feasible to explore with available technology. However, this fraction could still make a considerable
contribution to the European electricity supply and the marine renewable sector is currently the focus of
much industrial and academic research around the world. A variety of new ocean power technologies are
poised on the threshold of commercial development. In various places around the world, pilot projects are
under way or have been completed, and several energy plants are being planned or are under
development. Progress in this area has been slow, however, due mainly to the fact that these systems,
based on emerging technologies with high research and development and startup costs, have significant
engineering hurdles to overcome and are not competitive with current prices of fossil fuels. Wave energy
is captured by devices that are stationary or move up and down with the frequency of waves. Energy
conversion devices also capture waves in reservoirs by overtopping the device and channeling sea water
through a hydro turbine to generate electricity. Wave height and frequency determine wave energy. Wave
power varies depending on location; more powerful waves are a result of stronger winds blowing over the
water’s surface. Globally, this occurs primarily in the areas between 30° and 60° latitude, both north and
south (Fig. 1). According to the U.S. Department of Energy, traditional (barrage) tidal power requires a
difference between high tide and low tide of at least 16 feet. There are only about 40 such sites worldwide
(Fig. 2) Tidal stream, on the other hand, simply needs a strong current and, in the case of a tidal fence, a
narrow inlet to span.