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Hydrokinetic Energy and Its Uses

Utility-scale hydrokinetic energy facilities can generate electricity that is sent to energy consumers via electric transmission systems. On a smaller scale, hydrokinetic energy can be used to deliver electrical power directly for commercial, residential, agricultural, or public facilities.

What Is Hydrokinetic Energy?

Hydrokinetic energy is the energy that can be captured from flowing water that occurs in rivers or ocean currents. This includes ocean wave energy, tidal energy, river in-stream energy, and ocean current energy. Because the ocean currents in general are far from the United States shoreline and outside the jurisdiction of Native American tribes, this energy resource is not included further in this discussion.

To date, there are few hydrokinetic energy projects in commercial operation; however, there are several proposed wave energy projects worldwide, and a number of operating prototype systems are being tested. The Makah Indian Nation was a partner in a proposed wave pilot project that had received a license from the Federal Energy Regulatory Commission (FERC); however, the licensee filed an application to surrender its license for economic considerations.

There are only a few operating tidal energy plants, including three barrage tidal facilities, in the world with a few more projects in development. River in-stream generating facilities are also in the development stage with several operating prototypes being tested. FERC has issued some preliminary permits for proposed tidal, wave and river in-stream facilities. Despite this relatively low level of development, hydrokinetic energy resource potential is significant, particularly for wave energy, and it is a renewable resource which does not produce greenhouse gas emissions.

What Is Wave Energy and How Can We Use It?

Wave energy is energy derived from the movement of ocean waves. Waves are generated by wind passing over the ocean surface. Therefore, the height of sea waves and, hence, the amount of energy transferred depends on the wind speed; the duration of wind from a particular direction; and the fetch, or the expanse of water surface over which the wind blows. In deep water, the energy of the waves can travel thousands of miles before dissipating on shore.

Wave Energy System
Wave Energy System
Source: EERE
Wave Energy System
Source: EERE
Click to enlarge

Wave energy devices extract energy from the surface motion of the waves or from pressure fluctuations below the surface. This energy is converted to mechanical energy that drives a generator to produce electricity.

Current examples of wave energy devices include point absorbers, attenuators, and terminators. See Chapter 3 of the Final Programmatic Environmental Impact Statement for Alternative Energy Development and Production and Alternate Use of Facilities on the Outer Continental Shelf for more information on these and other hydrokinetic energy technologies.

What Is Tidal Energy and How Can We Use It?

Tidal energy is derived from capturing energy in ocean tides. There are two basic types of systems used to convert tidal energy to mechanical or electrical energy: barrage systems and tidal turbines.

Barrage Systems

A barrage is a dam placed across an inlet or estuary that allows a basin to fill during the incoming high tide and then water is directed through turbines during the outgoing tide. A barrage facility operates like a hydroelectric dam and power plant. In general, a tidal range of about 7 m is required for economical development of a tidal barrage. There are both existing and planned barrage facilities located throughout the world.

Tidal Energy Farm
Tidal Energy Farm
Source: BOEMRE
Tidal Energy Farm
Source: BOEMRE
Click to enlarge

Tidal Turbines

A tidal turbine, similar to a wind turbine, converts the horizontal movement of the water from the incoming and outgoing tide into electricity. Tidal turbines can be placed wherever there is a reliable tidal flow and where there is minimal conflict with existing uses (e.g., ship traffic) or where conflicts can be minimized or are otherwise acceptable. For tidal flows, a current of more than 9.3 km/h (5.8 mph) would be needed to provide for economical operation.

What Is River In-Stream Energy and How Can We Use It?

River in-stream energy is derived from the movement (kinetic energy) of water in rivers, streams, and canals. This differs from low-head hydropower systems, which rely on the elevation difference (head) between the intake and turbine. River in-stream devices are placed directly in the flowing water of rivers. River in-stream energy is extracted from rivers with turbines similar to those used in tidal installations. The major difference is that the river current is unidirectional. This energy is converted to mechanical energy that drives a generator to produce electricity.

How Is Electricity from Hydrokinetic Energy Sent to Users?

Electricity generated from hydrokinetic energy is sent to users through a transmission system consisting of underwater transmission lines connected to an electrical substation on shore, and then to the land-based electrical transmission grid.

Environmental impacts of construction and operation of underwater transmission lines are largely related to the disturbance of the sea floor caused by trenching operations to bury the lines. These impacts are discussed in Potential Impacts. See Potential Impacts of Energy Transmission Projects to learn more about potential impacts of construction and operation of land-based transmission lines. The integration of hydrokinetic energy into a transmission system requires careful planning to balance the input of hydrokinetic energy with other sources of energy generation.