Tidal energy is a unique form of renewable power that harnesses the predictable, rhythmic movement of ocean tides, driven primarily by the gravitational pull of the moon and the sun. Unlike intermittent sources such as solar and wind power, the timing and magnitude of tides are known years in advance, offering a reliable power generation schedule. This predictability makes tidal power highly attractive for grid stability. Although the United States possesses significant theoretical tidal energy resources, large-scale infrastructure is not yet in place.
The Definitive Count
The definitive answer to how many commercial, utility-scale tidal power plants currently operate in the United States is zero. No commercial tidal energy power plants are presently generating electricity for the commercial grid. This is due to the distinction between pilot projects and full commercial operations.
The U.S. has hosted several small-scale demonstration and research projects designed to test the technology and gather environmental data. For instance, the Roosevelt Island Tidal Energy (RITE) project in New York’s East River and various projects in Maine’s Cobscook Bay have deployed underwater turbines. These pilot sites, often with a capacity of a few hundred kilowatts, are intended for research and development, not for mass power generation. The U.S. Department of Energy continues to fund these efforts, aiming to transition from single-device testing to commercial-scale arrays.
Types of Tidal Energy Technology
Tidal Barrage Technology
The first and older method is the tidal barrage, which functions much like a hydroelectric dam. A barrage is a large, dam-like structure built across the mouth of a bay or estuary to create a basin. Sluice gates control the flow, allowing the basin to fill at high tide and then releasing the stored water through turbines at a controlled rate during low tide to generate power.
Tidal Stream Technology
The newer, less disruptive method is tidal stream or tidal current technology, which utilizes underwater turbines resembling submerged wind turbines. These devices are placed directly into fast-moving currents in narrow channels, straits, or inlets to capture the kinetic energy of the flowing water. Because water is approximately 800 times denser than air, these turbines can generate significantly more power with smaller blades than air-based wind turbines. This technology is the focus of most modern development efforts due to its smaller physical footprint and lower potential for environmental impact compared to large barrages.
Geographical and Economic Constraints
The lack of commercial development stems from a combination of geographical limitations and high economic hurdles.
Geographical Limitations
For a tidal barrage system to be economically feasible, the area must exhibit an extreme tidal range of at least 10 feet. This condition is rare along the majority of the US coastline, as most coastal areas do not experience the necessary vertical change in water level to support high-efficiency power generation.
Economic Hurdles
The financial barriers are substantial, as the upfront capital costs for building robust tidal infrastructure are significantly higher than for other renewable sources. Tidal stream turbines must be sturdier and heavier than wind turbines to withstand the immense forces of dense, moving water, making them expensive to manufacture and deploy. This high initial investment makes it difficult for tidal power to compete with the rapidly falling prices of utility-scale solar and wind power projects.
Regulatory Complexity
Environmental concerns and the resulting regulatory complexity also slow development considerably. Tidal barrages can drastically alter the local ecosystem by changing water salinity, sediment distribution, and disrupting fish migration patterns. While tidal stream turbines have a lower impact, concerns remain about their effect on marine mammals and fish, leading to protracted and expensive permitting processes. For instance, one tidal project in New York required obtaining 23 different permits from 14 separate agencies, illustrating the significant regulatory burden.
High-Potential Resource Areas
Despite the current absence of commercial plants, specific regions of the US possess exceptional tidal resources that are the focus of future development. The Gulf of Maine, particularly the area bordering the Bay of Fundy, is recognized for having the highest tidal range on the East Coast, making it a prime location for both barrage and stream projects. Alaska’s Cook Inlet holds the distinction of being the largest tidal energy resource in the United States, offering immense potential for utility-scale power for remote coastal communities. The Pacific Northwest, particularly the Puget Sound area in Washington State, is another high-potential region, favored for its strong tidal current velocities. These areas represent the most geographically suitable locations where the high costs of tidal technology could potentially be justified by the magnitude and predictability of the available energy resource.