Strong ocean currents are generated from a combination of temperature, wind, salinity, bathymetry, and the rotation of the earth. The sun acts as the primary driving force, causing winds and temperature differences that impact currents. Because ocean currents are fairly constant in both speed and flow and carry large amounts of energy, there are many suitable locations for deploying energy extraction devices such as turbines. Turbines capable of harnessing the kinetic energy of ocean currents may be indistinct from other marine current turbines and function according to the same principles. However, they may be designed or optimized for lower flow speeds relative to currents in tidal channels and may not need to account for reversing flow. A major difference is where the devices may be located–both geographically and in the water column. Strong ocean currents tend to be further offshore than tidal currents, which tend to be found in coastal or inland waters. This leads to deployment in deeper water. As ocean currents are strongest higher in the water column, fixed substructures for supporting a turbine become impractical for harnessing ocean current energy. Instead, devices may be suspended from moored surface platforms or attached to buoyant structures tethered to the seabed. Electricity is produced from the ocean currents by coupling a generator to the turbine and power is transmitted back to shore via subsea cable.
The primary environmental concerns associated with ocean current energy typically encompass effects of changes in flow and animal collision. It should be noted that these turbines spin much slower than propellers on ships, lessening the likelihood that a collision would result in substantial harm to an individual. There is also concern that noise from the turbines can affect animals that use sound for communication, social interaction, orientation, predation, and evasion. As with all electricity generation, electromagnetic fields generated by power cables and moving parts may affect animals that use Earth's natural magnetic field for orientation, navigation, and hunting.
Photo: OceanBased Perpetual Energy