The necessary fast flowing currents are produced by features, such as headlands, inlets and straits, that constrict the flow and act to magnify its speed. Tidal stream technologies exploit the movement of coastal tidal waters induced by the interaction of the gravitational fields of the earth, moon and sun. A few larger-scale projects are under development but generally dependent on further cost reductions/financing for viability.

Up to ten demonstration projects have been deployed (up to 1.2MW capacity), many for a number of years. They typically use submerged horizontal axis turbines but designs with vertical axis turbines and oscillating hydrofoils are also possible. Tidal stream power plants directly extract energy from the flow of water due to the tides. A 240MW commercial tidal barrage has been operating for more than 40 years in France (EDF) however globally there are few other examples of this technology. Tidal barrage system: When using a tidal barrage system the technology required to convert tidal energy into electricity is very similar to hydropower as water flows into and out of gates through turbines set along a dam or barrage built across a tidal bay or estuary. Marine renewables are, in general, at a relatively early stage in their development and, as such, the methods of converting these potential energy sources into useful electrical power are still highly diversified, with many technologies competing for commercial viability.

Marine renewables, also known as ocean energy, refers to a broad range of technologies that extract energy from the ocean this energy can be in the form of ocean waves, tidal movements or thermal gradients.

Tidal energy