Kinetic energy can be obtained from tidal currents by means of free-flow turbines. This can take place at flood defenses as well as on the open sea. Channels with a funneling effect cause an acceleration of the tidal current, so that more kinetic energy can be gained.
Turbines with blades rotating about a horizontal axis are the most mature type of free flow turbines. Other types such as vertical axis turbines and designs using an underwater kite are less advanced. In addition to the open sea, vertical-axis turbines are also suitable for use in rivers and kite concepts can be applied at lower flow speeds, which offers additional market opportunities for free-flow turbines. The Dutch industry is working on all three variants of free-flow turbines (MET support, 2015). As horizontal-axis turbines are further in development, more information is available about this turbine type. This fact sheet generally assumes horizontal axis turbines, unless stated otherwise.