|May 17: Tapping the waves
Fundamentally there are three different ways of harvesting the energy of the waves, says Jane Kruse. As manager of the Test station for Wave energy near Helligso, she has seen dozens of different attempts.
The Test station for Wave energy is located at the north shore of the Limfjord, an open and scenic waterway between the North Sea and the Baltic Sea. This most western part of the Limfjord is called Nissum Bredning. The water at the site is about four meters deep, at which depth you can still see the sea floor through the clear water. A 150 meter long pier leads to a small hut and a docking station for wave generators. An electricity meter at the base of the pier shows that in total 161,950 kilowatthour has been fed into the grid.
The 'Wave Star' is hooked up at the test facility
The 'logbog' lists 33 tests since 2000 onwards. Some inventors have returned several times, others made unique trials. Anyone who wants to test their device for tapping energy from waves can book the Nissum Bredning test facility via the Folkecenter for renewable energy at nearby Ydby.
Today, with a stiff breeze from the east, the waves are choppy at best. But they can get monstruous as well. Strong western winds cause considerable waves at the North Sea, which can enter the Limfjord virtually unhindred. Jane Kruse shows a blurred picture (shaken by the wind) where a wave is about to hit the hut at the far end of the pier. It made quite a dent, she tells.
At such circumstances, it's no wonder that not all tests have an happy ending. Once there was a contraption that simply sank to the sea floor (no details given), and only last January the successful Wave Dragon was beaten off it's moorings by the waves. It ended down the beach a little distance away. The facility itself remained undamaged, which was mostly due to luck and the right wind direction.
Development of wave energy lacks behind in comparison to wind energy, Kruse observes. “At the beginning they didn't know to choose two, three or twelve blades. Now the three blade system has been universally accepted. In wave energy, we are still at the beginning.”
Nonetheless, most inventions can be classified in only three categories: hydraulic systems, overpasses and floaters. The system that is currently hooked, the 'Wave Star', belongs to the first category. Its pairs of half balls float on the water at a distance of about half a wavelength. As waves pass underneath, they rock the metal support of the floaters, pumping up the hydraulic pressure which is then converted into electrical energy.
The mentioned Wave Dragon is the best known example of overtopping devices. Its wide arms converge incoming waves, thus increasing their height. At the base of the arms, the wave then runs up a ramp, filling a horizontal but elevated basin. As water pours down the basin to sea level, it drives generators making electricity.
The floaters are devices that bob on the waves (or just beneath them), thus converting the wave's motion into a vertical movement, which then, as you probably guessed, drives a generator.
Which if these types will win, you can't tell, says Kruse. Different locations have other wave characteristics and also the structure of the sea bed plays a role. Most probably, each of the three different techniques will find their own niche.
The Nissum Bredning test site at Helligso is low threshold, says Kruse. Its relative sheltered location provides more friendly operating conditions than out at the North Sea. Besides, the facility offers relatively easy access to the devices. A second mooring has recently been added and more fragile prototypes may be tested nearer to the shore.
After successful tests here, inventors can take their installations to the Orkney islands where the European Maritime Energy Centre (EMEC) operates a test facilty in one of the most atrocious waters in the world. It's the ultimate the maritime endurance test. We'll visit EMEC later this trip.