Wave Energy Technology

The concentrated power of breaking waves shapes shorelines and erodes beaches. However, it is the kinetic energy associated with up-and-down oscillations within the water column that is transformed into electricity by most wave energy technologies.

Many regions of the world have commercially viable wave resources, including the northeastern and northwestern coasts of the United States. For shoreline and nearshore applications, most technologies include semi-enclosed steel or concrete structures anchored to the ground or integrated within a breakwater.

Oscillating water column (OWC) devices are partially submerged boxes with an opening to the sea at the bottom and an opening to the land at the top. Waves cause the enclosed water column and the air on top of it to rise and fall. This motion alternately forces and draws air through a turbine located in the landward outlet.

Pendulum or flap devices employ a box with an opening on the seaward side. Incident waves cause the pendulum or flap within the opening to move back and forth, driving a hydraulic motor that powers a generator.

Tapered channel devices have walls that rise several meters above water level. A wave grows progressively higher as it travels through the narrowing channel, spilling water into a storage area. The stored water returns to the sea through an outlet that contains a turbine.

Both seafloor-tethered and seafloor-anchored wave technologies are being examined for higher-energy offshore environments, where water depths are more than 40 m. Many concepts exploit the differential motion of floats attached to one another, while others employ floats that move relative to the seafloor. For these technologies, up-and-down motions are used to drive hydraulic pumps or to force water through a turbine. Candidate offshore technologies also include tapered channel and OWC devices constructed on floats.

More than 1,000 wave energy patents exist, and numerous prototype or precommercial systems have been tested in shoreline, nearshore, and offshore environments. Only one commercial wave power station has been developed, however. This 500-kW plant, sited on the shoreline in Islay , Scotland , employs OWC technology. It began operation in 2000, and a second commercial installation is being developed for the Faroe Islands . A 500-kW demonstration facility, the first shoreline-based application of wave energy technology in the United States, is planned for Point Judith, near Narragansett, Rhode Island.

Dual-use applications of wave energy technology may prove cost-effective in the near term. For example, power generation technologies could be incorporated into breakwaters, harbor walls, or other structures, or they could be integrated with other commercial activities, acting as artificial reefs for mariculture operations or as platforms for desalination facilities.

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