Engineers Look to River and Ocean Currents for Clean Energy

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CLIMATEWIRE | The next frontier for renewable energy may be found in underwater currents.

The Department of Energy is looking to tap that resource through its funding of 11 projects designed to harness the power of moving water in rivers and ocean tidal currents.

The long-term goal is to have sources of renewable energy that can operate 24 hours a day, seven days a week, said Mario Garcia-Sanz, the program’s director.

” This puts this technology in an excellent position with other renewables,” he stated in an interview.

One reason is the limitations on other forms clean energy. Solar power is not always available at night. Wind power can be destructive during storms and is irregular. However, the movement of the underwater currents is predictable and stable.

Using running water to generate energy is not a new concept. Hydroelectric dams can have a significant environmental and financial impact. The latest generation of engineers and scientists is working to improve the concept without causing as many problems.

However, the design and control for underwater turbines to convert energy into electricity are still in the experimental phase. One factor is cost. It remains too expensive to be commercially viable. It is a prime candidate for DOE’s Advanced Research Projects Agency – Energy (ARPA-E), which has the mission of “changing what’s possible” through taking risks.

In this case it’s a $38 million bundle of grants made by ARPA-E in November 2020 to 11 projects put together by a group of companies, universities and nonprofits. Collectively, the acronym SHARKS stands for Submarine Hydrokinetic And Riverine Kilowatt Systems.

SHARKS helps put machines in the water, with names like “Manta” or “Tidal Power Tug .”

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The Tidal Power Tug is topped with a white buoy that rises from the water. It is moored to a seabed, but a pylon hangs beneath it and houses a turbine that looks like an airplane propeller. It is powered by the current and spins like a generator. It transmits the electricity it produces to a shore-based energy grid.

The Tidal Power Tug’s goal is to harness energy from the Gulf Stream, which flows along the east coast of the United States from Florida to North Carolina. It creates gyres, which are circular currents. According to Aquantis, who is the inventor of Tidal Power Tug, this approach provides the United States with “a vast strategic renewable energy resource close to large population centers.”

Several other experimental turbines function as kites. One of these experimental turbines is the Manta. It was inspired by the manta ray’s swimming. It was created by SRI International, a non-profit scientific research institute located in Menlo Park (Calif.), with the help of the University of California at Berkeley.

It is a small generator that is moored at the sea bottom. It has a spool made of rope that is attached to a kite-like, foam-filled, polymer-coated object that spins the pool as the tide pulls it away. An attached generator generates electricity and can be connected to a local grid. It also has a small motor that can pull the Manta back in, deflate it, or redirect it if it encounters a large ship or storm.

Manta can be used to power small, isolated communities close to rivers or tidal inlets. Roy Kornbluh (SRI’s principal researcher engineer), stated that there is a trillion watts (1 trillion W) of untapped energy in the oceans, rivers, and estuaries around the world, waiting to be converted into clean, renewable energy.

Michael Lawson is the group manager for water power research and the development at the National Renewable Energy Laboratory. He said that the laboratory is currently working with four SHARK projects, using a computer model to predict the performance of underwater blades based on data from wind turbines.

According to NREL there is enough energy potential to produce 94 terawatt hours of energy per annum. This is enough electricity for approximately 9 million homes. Tidal inlets can produce a large portion of this. They can be channels that run between the coast and barrier islands or they can be splits in the coastline large enough to allow tidal forces access. They include Cook Inlet, Alaska; Puget Sound, Seattle; and similar inlets throughout northern Maine.

Multiple turbines can provide “utility-scale resources” for large communities, he explained. He explained that single turbines, or small groups of them, could also be used to provide power to smaller or less isolated communities.

Small towns, Lawson said, often rely on diesel generators which are often expensive and subsidized or subsidized by the federal government. Supporters believe that underwater turbines may be cleaner and more affordable.

Europe has been the leader in the development of underwater turbines. However, Lawson stated that China and other Asian countries are also developing them.

According to Garcia-Sanz from ARPA-E the biggest challenge for underwater turbines will be the same as that faced by wind turbines in the 1990s — the cost.

The underwater turbines being tested now can produce electricity for about 25 cents per kilowatt-hour in tidal areas. The projects must reduce that price to 4 cents in order to be competitive.

” It’s hard to predict who will be more successful at this stage. He said, “We just started this a whole year ago.” They all look promising .”

Reprinted from E&E News with permission from

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