A mechanical, underwater carpet mimics the motion of the shifting muds beneath the sea.

One day, such a system could harvest that energy to power our homes.

For the past five years, professor Reza Alam has been tinkering with the best way to build the wave carpet.

"Instead of mud, we use generators and springs, and instead of that energy converting to heat, we convert it into useful energy," he says.

"The power that we can get from carpeting an entire soccer stadium by solar panels, we can get from 10 meters of California coast."

2014-02-10

Co.Exist

A Giant, Wriggling Sea Carpet To Harvest Ocean Energy

It's a clean energy dream to harness the power of the ocean's movements, but it's always been a bit impractical. This "wave carpet" at the bottom of the sea is a radical rethinking of how to make it work.

Every June and July, something strange happens off the coast of the southwestern Indian state of Kerala. The turbulent waters go still. Waves disappear. And then, suddenly, the newly tamed coastline invites mountains of shrimp and fish. Locals celebrate the moment, a natural phenomenon they call chaakara.

The mystery of chaakara actually lies in the soft, shifting mud of the ocean floor. During monsoon season, new, loose clay settles in the sea. Then, like a fat rippling blanket, it absorbs the rolling energy of the waves above. The oppositional force calms the water, the fish have a party, and the people eat the fish.

A rendering of the wave carpet (and fish). Credit: Theoretical and Applied Fluid Dynamics Laboratory, University of California-Berkeley.

That same chaakara phenomenon is also a huge, untapped source of energy estimated to be several times richer than the sun's rays, according to researchers at the University of California-Berkeley. And by creating a mechanical, underwater carpet that mimics the motion of the shifting muds, they're hoping to harvest that energy to power people's homes.

For the past five years, professor Reza Alam has been tinkering with the best way to build the wave carpet. "Instead of mud, we use generators and springs, and instead of that energy converting to heat, we convert it into useful energy," he says.

In theory, the carpet would be almost 100% energy efficient, as opposed to the 10% to 20% energy efficiency of solar panels, explains Alam. That's partly because wave energy is far denser than solar. The average square meter on Earth soaks up between 300 to 400 watts of solar radiation, but waves pound the average meter of California coastline with 45 kilowatts of energy. "If I want to generate the same amount with solar panels, I'd need 150 square meters," Alam says. "The power that we can get from carpeting an entire soccer stadium by solar panels, we can get from 10 meters of California coast."

In the lab, Alam and his team have designed a 2-D tank test using a carpet made of rubber to successful effect. But in reality, waves would be multi-directional, and rubber would disintegrate in saltwater over time. That's why Alam is now working on a 3-D tank test, as well as materials that could be used in place of rubber, like silicon or other composites.

Alam isn't the first scientist to dream of the potential of wave energy, but most wave energy harvesters sit on the surface of the water. Alam says his design would be cheaper than those models. For one, it minimizes potential contact with ships or other vehicles. Secondly, unlike other wave energy converters or even wind turbines, the wave carpet wouldn't have to be shut down in the event of a storm. Where strong winds and waves overwhelm turbines and surface wave harvesters, the carpet experiences lesser turbulence on the bottom of the sea.

Another vision of the wave carpet (and boat). Credit: Theoretical and Applied Fluid Dynamics Laboratory, University of California-Berkeley.

Still, no one knows how the wave carpet might affect seabed ecosystems. Alam says that while he expects the environmental effects to be minimal, placing the carpet in an oxygen-deprived "dead zone" with little to no marine life might be the best option for the technology.

The wave carpet's biggest test will take place in 2016, when Alam and his team aim to actually install a prototype in the ocean. They're researching locations now, and hope their design will finally consolidate the vision of mass power generation by sea.

"Wave power today is at the state wind power was 25 years ago. We have an array of designs, and everybody says this is the one that's going to work," Alam says. "From a research point of view, we believe that in the next five to 10 years, we're going to answer the wave power question: Which design is the best design, and if it can provide competitive commercial power to the grid, or not."

The wave carpet is still squarely in the research stage, but Alam's excited about its potential prospects. "We're hoping that within the next 10 years, the overall cost will be competitive with utility power costs today, about $0.10 per kilowatt hour," he says.

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