Coastal tides are a naturally occurring process caused by the moon’s gravitational pull on the oceans of the world. In the U.S., tidal changes vary wildly from coast to coast, with the highest tidal range in Anchorage, Alaska spanning up to forty feet. While the natural movement of water flowing downstream in a river has been harnessed as a power source for a millennium, tidal energy generators are technology still in its earliest stages in the U.S., but could have potential to contribute to the country’s energy needs.
There are three main types of tidal energy: tidal stream, barrages, and tidal lagoon systems. Unlike other sources of renewable energy which face intermittency issues, tidal changes are predictable and can be easily harnessed by turbines that are placed in tidal streams. The density of the water, combined with the predictability of the tides means that these turbines are most effective in shallower water. Turbines are then connected to a generator via undersea cable.
Learn about conventional hydropower here.
A barrage system consists of a low-lying dam that water can spill over. As the tide rises the barrage collects water and shuts, trapping a large amount of water that is then released into its turbines, generating power. Barrages have a large impact on the local environment, with tidal range shifts, water salinity, and fish populations all affected by the barrage’s restriction of water. Tidal lagoons systems are constructed with low permeability materials and force large amounts of water through narrow passages, which turn turbines. When the tide rises, the turbines are turned generating power and vice versa. Lagoon systems are much less environmentally impactful, as they can be constructed with natural materials like rocks and appear as a seawall during low tides and would be completely submerged during high tides.
The potential energy that can be harnessed from tidal hydropower facilities largely depends on the tidal range of the particular area of coastline. Making energy production economical, a minimum of 10 feet of tidal range is needed. Several locations in the U.S. possess immense potential for tidal power, however most of those locations are concentrated in northern states. While several pilot projects are being tested, there are currently no active tidal energy facilities in the U.S.
A 254 MW tidal power station in South Korea and a 240 MW tidal power facility in France are the two largest facilities in the world respectively. Due to tidal being one of the more recent additions to renewable energy options, construction of many larger-scale tidal facilities remains an expensive undertaking.
However, as with every new piece of technology that emerges on the market, improvements and innovations quickly follow. Tidal energy’s small land use requirement means that the 12.5 kilometer long tidal energy generator in South Korea takes up only a fraction of the space as other land-based renewables. Larger turbines, like the one constructed by SIMEC Atlantis can generate more electricity at a much lower cost for maintenance and operation. The predictability of tidal energy means that electricity generated from the tide can be a crucial substitute source of power if other renewables, like wind or solar, are not capable of functioning effectively. Finally, tidal energy technology is built to last much longer than other renewables, with facilities built to run for over fifty years. This is in keeping with the longevity of conventional hydroelectric dams, which have an average lifespan of around 100 years.
Tidal energy will only become a more widely known and utilized source of renewable energy if costs continue to fall and the effects of the technology on the surrounding environment are more rigorously understood. The environmental impacts of the noise, vibrations, and electricity generation on surrounding marine life needs more research. In order to attract serious attention from both the national and state governments in the U.S., tidal energy needs to continue to produce innovative ways to demonstrate it is a viable, cheap, and worthwhile energy investment.
Want to learn more about energy resources? Read our hydropower brief here.
Written by Roy Mathews, Public Policy Associate
The Alliance for Innovation and Infrastructure (Aii) is an independent, national research and educational organization. An innovative think tank, Aii explores the intersection of economics, law, and public policy in the areas of climate, damage prevention, energy, infrastructure, innovation, technology, and transportation.