Technology
Marine energy resources include mechanical energy from currents, tides and waves, and thermal energy from the sun's heat, captured in surface waters.

Tidal power can be generated by barrages, similar to hydroelectric dams, such as the La Rance scheme in Brittany, France, or extracted from currents, using devices similar
to underwater wind turbines. Conditions are good for tidal power generation in both the Pacific Northwest and the Atlantic Northeast regions of the United States. 

Wave-power devices convert the motion of surface waves to electricity. Wave-power rich areas of the world include the western coasts of Europe and Canada, southern Africa, Australia and the northeastern and northwestern coasts of the United States. A wide range of device concepts are under small- and large-scale testing in the United States, Europe and Australia.

Ocean thermal energy exploits the small temperature difference between surface and deep waters. Much larger differences are available on land at industrial sites and these can usually be exploited more cost effectively.

Market / Advantages
Ocean energy is renewable, generally unobtrusive to the public and has been successfully deployed.  Although the commercial market is relatively small, in the past few years investment in marine energy has doubled.

Issues
Although there are a handful of commercial marine power generation operations, much of the technology is still in its infancy and costs are usually high compared with traditional and other renewable generation.  Tidal power barrages that dam estuaries can impede navigation and sea life migration. Silt build-ups behind such facilities can impact local ecosystems. Wave energy devices must be designed to interact strongly with moderate size waves to attain decent efficiency yet survive large storm waves without overloading structure or moorings.