Tidal energy can be captured on the basis of the potential energy of the head difference between high and low
tides, which creates a gravity flow. Tidal barrages are effectively conventional hydro dams, deployed in estuarine
settings. Tidal impoundments are essentially offshore self-contained dams. Both tidal barrages and tidal
impoundments require large capital investments and have been developed with multiple purposes to improve project
economics, e.g., providing roadways across estuaries and flushing for enclosed bays in addition to electricity generation.
Tidal current devices convert the kinetic energy of a moving water current. Several different device technology concepts have been proposed and tested in recent years. The main differences between the device types are related to the method of securing the turbine in place, the number of blades and how the pitch of the blades is controlled. Devices may be seabed mounted or floating. Tidal current devices are generally small (<1 MW), modular and intended for deployment in multi-unit arrays for utility-scale generation.