When most people think of renewable energy, they think of common sources such as solar, wind, or maybe even geothermal. However, people rarely think of tidal or wave energy. Interestingly, tidal energy has been used by thousands of years after being first developed by the Romans to power mills. Despite this, these forms of renewable energy are not nearly as frequently used as wind or solar, but they represent a huge amount of potential. The picture below shows possible locations for power generation. Alaska has the greatest amount of recoverable energy, totally over half of the country’s available tidal and wave energy, according to the Bureau of Ocean Energy Management.
Courtesy of BOEM
There are many different kinds of technology that harness the energy of the ocean. Here are a few:
Tidal Turbines:
Tidal turbines are very similar to wind turbines. Like wind turbines that are placed in areas that experience higher speed winds, tidal turbines are placed in areas that experience more extreme tides. Ocean turbines are sunk into the seabed in shallow water ranging from 65-100 feet deep. Here, they are placed facing the current. As the current moves with the tide, the turbine spins and produces energy. Tidal lagoon systems work in a similar way. Rather than sinking the turbines offshore, these turbines are placed at the openings of lagoons that fill up with water with the tide. As the water leaves these lagoons, it travels quickly past the turbines, generating electricity.
Courtesy of EPA
Wave Terminators
Wave terminators are placed perpendicular to incoming waves either on the shoreline or in very shallow water. These machines are able to capture or reflect the energy of the wave. New, floating versions of these shore terminators have recently been designed and can be placed offshore. Another type is the oscillating water column. This kind of terminator has an opening where water enters and traps the air above it. Similar to a piston in a car engine, the waves cause this captured water to move up and down. As the water pushes up on the air above it, it exerts pressure and pushes the air through a turbine. This turbine in turn generates power.
Courtesy of the EPA
Attenuators:
Attenuators are long, floating, buoy-like structures that run perpendicular to the shore. They follow the motion of the waves and extract energy by using restraints that run along the length of the apparatus. As the wave brings the attenuator up and down, the device stretches at the connectors of the segments, which are connected to hydraulic pumps. These pumps are what converts the waves into usable electricity. This electricity is then transported to land by using a cable that runs underground from the device.
Courtesy of BOEM
Benefits:
While there are multiple different kinds of technology that utilize the energy waves and tides produce, the United States has yet to tap into this source of clean energy. In addition to the nearly zero-emission source of power that is provided by the sea, it is very reliable. Apart from massive storms such as hurricanes, tidal patterns are very stable. Tides follow the lunar cycle which can be predicted in advance. This greatly contrasts with most forms of renewable energy such as wind and solar, which rely on weather conditions to produce electricity.
Wave and tide energy is widely available as well. As shown in the map above, these systems can be implemented wherever there is a coastline. After accounting for unusable coastal areas that must remain open for shipping and other purposes, wave and tidal energy could produce one third of the total energy need in the entire United States.
Disadvantages:
There are significant reasons that the United States has yet to build any large scale energy farms utilizing sea currents. According to Conserve Energy Future, “The biggest disadvantage to getting your energy from the waves is location. Only power plants and towns near the ocean will benefit directly from it.” While this is true, 39% of the US population lives in a county bordering the coastline. Another large reason they are not widely used is the physical obstruction of the devices. Any kind of large object in the water can become a hazard to shipping vessels as well as the marine environments they are invading. They can also be a visual obstruction. Beaches and coastlines represent some of the most beautiful areas of the country, and large machines capturing energy from waves can be a noisy eye sore. Overall, there are many areas that these machines could be useful at producing electricity, and the United States should start looking to more abstract sources of energy to promote a green and sustainable future.