Innovators develop devices to tap vast stores of ocean energy

Ocean energy technologies lag decades behind wind and solar power. But they’re catching up.

According to the European Technology & Innovation Platform for Ocean Energy, by 2050, wave, tidal and salinity gradient systems could deliver up to 100 gigawatts of capacity to the European grid — 10% of current European power consumption. 

Global estimates are similar, and many companies are trying to harness and distribute that energy.

At annual exhibitions of Ocean Energy Europe, the world’s largest network of ocean energy professionals, inventors present their best methods for harvesting the estimated terawatts of energy stored in the motions of Earth’s oceans. Those include wave energy converters that bob up and down in turbulent seas, tidal turbines secured to the bottom of boats or anchored to the floor of narrow straits and metallic kites that surf underwater currents. 

Devices of this sort are designed to be assembled into arrays of six or a dozen. They are capable of surviving ferocious ocean conditions for long periods, tied into coastal power grids and serviceable year-round.

The technical challenges, though, are huge, UK engineer Mike Robinson explained.

“What you’re trying to do is turn a linear motion or an oscillating motion from the wave into a rotational motion,” Robinson said. “You’ve got to turn that into electricity that you and I can use at home, which is quite difficult.”

Equally challenging, he said, is generating a revenue stream.

“If you look at the amount of capital equipment that has to be installed to actually generate the electricity, you [have to ensure] that you’re actually going to get more energy out than you’re putting in,” Robinson said. “That’s not a simple solution.”

Tweaking prototypes is essential.

Fred Gardner, founder of Symphony Wave Power, has tested out a wave energy converter off the Dutch port of Den Helder, in the North Sea. Now, it’s ready to be tweaked.

“Ocean waves can contain up to megawatts of energy, a thousand times more than on the North Sea,” Gardner said.

“The energy is less” in the sea, Gardner said. “But your device goes up much faster. So, you can get more energy out. And the other thing is, it’s cheaper.”

Flowing with nature 

A three-hour drive south of Den Helder, in the town of Vlissingen, where the Scheldt River flows into the North Sea, Dutch start-up Water2Energy has tested its tidal turbine in a small sluice and is now tweaking its turbine blades. The blades spun one way as Scheldt River waters moved up the sluice and then back again when the tide reversed, generating a hundred kilowatts of power 20 hours a day — sufficient for a hundred households.

Like airplane wing flaps, the turbine’s blades are adjustable, boosting efficiency, and they can adjust themselves.

Water2Energy’s tidal turbine blades don’t endanger fish, according to its marketing director, Willem Molenaar. Through the use of underwater cameras, the fish have been seen swimming safely past the turbine’s blades, up the sluice and then back to the Scheldt again.

Off the coast of the Dutch island Texel, another device called Slow Mill actually attracts sea life. As its floater bobbed up and down in North Sea waves, driving a piston that generated a hundred kilowatts of power, kelp, mussels, clams and fish turned Slow Mill’s anchor into a fertile reef, a magnet for biodiversity — and an unobtrusive source of power for Texel swimmers and beachcombers who appreciate being able to charge up their smartphones. East of Texel, a totally different ocean energy facility is equally unobtrusive.

In the middle of the 20-mile-long Afsluitdijk dike road separating the Dutch provinces of North Holland and Friesland, in a barely noticeable trailer straddling the dike — salty seawater to the west, freshwater to the east — fresh and salt water are being pumped in opposite directions through a stack of membranes. Positive sea ions get sent one way, and negative ions the other, just like charging a battery — generating an electrical potential that can be tapped for power. 

The salinity gradient facility, now in experimental mode, generates a kilowatt of electricity. The system’s designer, a Dutch company called REDStack, has just secured an investment to scale up and commercialize.

A similar system is being tested out at the mouth of the Rhône River, flowing into the Mediterranean Sea. Power potential there is estimated at four terawatt/hours per year.

The future

UK engineer Mike Robinson believes that salinity gradient, wave and tidal energy technologies do have a future.

“You’ve only got to look at the curve with other types of energy,” he said. “For example, offshore wind, you would have never thought that would be economically viable. But as the technology develops, then you make cost savings, and you become more efficient. So, you’ve got to be prepared to go through the pain at first.”Ocean energy systems certainly have a future in Europe. Under Europe’s Green Deal, they’re also pegged to generate half a million jobs — stabilizing grid supply when winds stop and the sun goes down.