Engineers look to river and ocean currents for clean energy

CLIMATE WIRE | The next frontier for renewables may be in undercurrents.

The Department of Energy is seeking to harness this resource by funding 11 projects designed to harness the power of moving water in rivers and ocean tidal currents.

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

“It puts this technology in a very good position with other renewable energies,” he said in an interview.

One of the reasons, he explained, is the constraints on other forms of clean energy. The unavailability of solar energy occurs at night. Wind power is erratic and can be destructive during storms. But the movement of undercurrents is relatively stable, reliable and predictable.

Using running water for energy is not a new concept. But hydroelectric dams come at a huge cost and environmental impact. So, the latest generation of scientists and engineers are trying to advance the concept without so many downsides.

However, the design and control of the underwater turbines needed to convert energy into electricity are at the experimental stage. Cost, on the other hand, is a factor – it’s still far too expensive for commercial use. That makes him a prime candidate for the DOE’s Advanced Research Projects Agency-Energy (ARPA-E), whose mission is to “change what’s possible” by taking risks.

In this case, it is a $38 million grant package awarded by ARPA-E in November 2020 to 11 projects set up by a group of companies, universities and organizations in non-profit. The projects are collectively known by the acronym SHARKS – which stands for Submarine Hydrokinetic And Riverine Kilo-megawatt Systems.

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

As designed, the Tidal Power Tug begins with a machine topped with a white tubular buoy that sticks out of the water. It’s moored to the seabed, but a pylon suspended below contains a turbine driven by what looks like a large airplane propeller. It is rotated by current and the rotation powers a generator. It sends the electricity it produces to an onshore power grid.

One of the purposes of the Tidal Power Tug is to capture the energy of the Gulf Stream which flows along the eastern seaboard of the United States from Florida to North Carolina. It creates many circular currents called gyres. The approach offers the United States “a vast, strategic resource of renewable energy near major population centers,” according to a statement from Aquantis, the inventor of the Tidal Power Tug.

Several other experimental turbines function as kites. One is called the Manta, inspired by the way a manta ray swims. It was developed by SRI International, a nonprofit scientific research institute in Menlo Park, California, with assistance from the University of California, Berkeley.

It has a small generator, moored to the bottom of the sea, which has a reel of rope attached to an inflated, foam-filled, polymer-covered kite-like object that spins the reel as the tide moves it. took of. Spinning an attached generator produces electricity and can power a connection to a local grid. It also operates a small engine that can redirect the Manta, bring it back, or deflate it in case it encounters a storm or a large ship.

Manta is designed to supply small isolated communities near rivers or tidal inlets. “There are terawatts (1 trillion watts) of untapped energy in the world’s oceans, rivers and estuaries waiting to be converted into clean, renewable energy,” said Roy Kornbluh, senior research engineer at the SRI, in a press release.

Michael Lawson, head of the hydropower research and development group at the National Renewable Energy Laboratory, said he’s been working on four SHARK projects using a computer model that can help predict the performance of underwater turbines on the database previously obtained from wind turbines.

According to NREL, there is enough potential energy to produce 94 terawatt hours of energy per year. That’s enough electricity to power around 9 million homes. Tidal inflows will produce a good portion of it. These may be channels between the shoreline and barrier islands, or clefts in the shoreline large enough for tidal forces to operate there. Among them are Cook Inlet near Anchorage, Alaska; Puget Sound near Seattle; and similar creeks in northern Maine.

Multiple turbines have the potential to offer “utility-scale resources” to power large communities, he explained. Alternatively, he said, single turbines or small groups of them could provide electricity to smaller or more isolated communities.

Small communities, Lawson pointed out, frequently depend on diesel generators, which are often expensive and subsidized by the state or federal government. Proponents say underwater turbines could prove both cleaner and cheaper.

So far, Europe has led the development of underwater turbines, but China and other Asian countries are also starting to develop them, Lawson said.

The biggest challenge for underwater wind turbines, according to ARPA-E’s Garcia-Sanz, will be the same one faced by wind turbines in the 1990s: cost.

Underwater turbines currently being tested can generate electricity for around 25 cents per kilowatt hour in tidal areas. To be competitive, projects must reduce this price to around 4 cents.

“It is difficult to know at this stage who will have the most success. We just started this a year ago,” he said. “They all look promising.”

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2022. E&E News provides essential information for energy and environmental professionals.

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