Comment: Tidal gaining traction in the U.S?

Clint Robertson

The U.S. Department of Energy says ocean power has the potential to provide 15 percent of the nation's electricity by 2030. And while 15 percent may not seem like much, it would more than double the US' current renewable energy generation.

According to the Institute for Renewable Energy Research, only 12 percent of the power generated in the U.S. came from renewables in 2012. And despite growing environmental concern and presidential support for green energy, the renewable energy industry is still held back by one thing — the power grid.

Most forms of renewable energy pose a problem for the electrical grid in the United States because the grid doesn't have the capacity to store energy. Instead, energy is distributed to homes and businesses as it is generated. Utilities have to find balance between the supply and demand of energy. If the demand for energy is higher than anticipated, there's not enough power to go around. On the other hand, if demand is lower than expected, energy is simply wasted.

Factoring in renewable energy makes the system even more complex. The amount of energy obtained from renewable resources ebbs and flows, making it hard to predict how much clean power will be transported on the grid.

Solar energy, for instance, produces less power when the sky is cloudy. Additionally, wind energy can't be generated if the wind isn't blowing hard enough to spin a turbine's blades. Short of developing a smart grid that includes the capacity to store a supply of energy, the flux of renewable power availability remains variable and therefore an option many utilities don't want to depend on.

However, tidal energy is a reliable — though relatively up and coming — form of renewable energy that could work well with the current grid. Because water continuously flows and tides can be forecast accurately, it makes it easier to know how much power tidal energy will bring to the grid each day. With a contribution of renewable tidal energy, less fossil fuel-generated energy needs to be burned to keep up with America's energy consumption.

The first U.S. grid-connected tidal turbine

The United States launched its first commercial tidal turbine off the coast of Eastport, Maine, in 2012. The turbine, built by the Ocean Renewable Power Company, is situated in the Bay of Fundy, which often sees tidal ranges of 50 feet or more. Each day more than 100 billion tons of water flow through the area with a force of 8,000 locomotives, making the location a powerful place to harness the ocean's energy.

The project is also the first ocean energy project of any kind, including offshore wind turbines and wave power projects, to feed energy to the U.S. electric grid. The turbine is connected to an on-shore substation through an underwater transmission line. Once electricity is transported through the wire it is fed to the power grid by the Bangor Hydro Electric Company in Maine and delivered to the homes in the area.

The single turbine produces enough energy to power 75 to 100 homes, according to the U.S. Department of Energy. ORPC plans to add two more tidal turbines in the same location in the fall of 2013. Along with a few more additions in the following years, the site should generate about 5 megawatts of energy — enough to power about 2,000 homes — by 2016.

ORPC's power system for the turbine is built around its Turbine Generator Unit, or TGU. The system works very much like a wind turbine. It has foils that rotate and power a permanent magnet generator. However, these TGUs are built to handle the power of water, which is 800 times denser than air. ORPC built the TGUs out of non-corrosive materials that would hold up in saltwater. Additionally, the system is gearless so it requires no lubricants and leaks nothing into the surrounding water.

It does appear that the US Government is also finally starting to take a serious look at tidal energy, the US Energy Department recently announcing an investment of US$16 million in seventeen projects to capture energy from waves, tides and currents in a sustainably and efficient way.

The projects are intended to increase the power production and reliability of both wave and tidal devices and help gather valuable data on how deployed devices interact with the surrounding environment (A full list of the seventeen projects is available here).

About: Clint Robertson is a freelance writer who has held numerous positions in the energy industry. His work promotes ways to educate the general population and reduce the carbon footprint for the betterment of the world by focusing on our need for renewable energy sources.

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Energy infrastructure  •  Wave and tidal energy