With tidal energy, large bodies of water such as oceans and seas are acted upon by the gravitational forces of the sun and moon, which in combination with the rotation of the earth on its axis, cause movements of the oceans and seas, known as tides. The motion of the moon and sun relative to the earth causes a periodic variation in the forces that generate the tides. Vertical movement (range) can be seen in the difference in water level at high and low tide, and horizontal motion of water is known as a tidal current.
The tidal energy sector is reaching a significant milestone in the development of the industry; tidal technologies are taking a step towards commercial viability, with the more advanced device developers now progressing beyond single unit demonstration devices and proceeding to array development and multi-megawatt projects. The backing of major OEMs will enhance the ability of technology developers to continue to optimise the development process, potentially unlocking further investment from utilities as array scale projects enter the planning phase.
The operating principle behind tidal energy converters is that the energy contained within the moving current is harnessed by a device that extracts kinetic energy from the flow and imparts this into a mechanical motion of a rotor or foil. The device then converts the mechanical motion of the structure into electrical energy by means of a power take-off system. Before connection to the electricity grid, the electrical power output from the device will need to be conditioned in order to make it compliant with grid code regulations. In essence, tidal device operation is synonymous to that of a wind turbine, albeit operating within a different fluid medium.
More detail on each of the types of tidal energy converter, and their principles of operation can be obtained from the SI OCEAN project:
SI Ocean - Technology Status