Bluewater develops tidal power platform

Bluetec is a modular floating platform for harvesting tidal power. The prototype was shown to the press in Amsterdam last weekweek; and Bluetec aims to deliver its first power to Texel this summer.

Bluewater has delivered large floating platforms to the offshore oil and gas industry for over 30 years. Now it’s trying the waters of renewable energy with this modular unit called Bluetec. Anchored to the seafloor in a tidal current, the unit carries a generator with a large propeller that converts current into power. A heavy submarine cable transports the electric power to the nearby island where it feeds into the grid.

The structure at the Amsterdam wharf looks a bit like a yellow submarine. The middle part is essentially a container with a large hole in the middle to support the underwater turbine. It also houses a switchboard that connects the leads from the turbine to the marine power cable that runs to the shore. In front and aft two half containers with pointed edges have been attached to improve the structure’s stability and to reduce the drag. The modular design allows easy reconfigurations and extensions. Four special anchors (30 square meters and 15 tonnes) will keep the powerboat in its place.

Allard van Hoeken MSc. is Bluewater’s head of new energy. He studied offshore engineering at the TU. “We’re applying the skills and expertise that we’ve learnt in the oil and gas industry in renewable energy”, he explains. For a firm that anchors structures as big as oil tankers in the high seas, securing a floating container near Texel is hardly a challenge. The challenge here is to make tidal energy a commercial success.

After its launch later this year, Bluetec will first support a 100 kW tidal turbine from Tocardo. After three months, it will be exchanged with an experimental 50 kW turbine from Schottel. Finally, a 200 kW Tocardo with a span of 10 meters will be fitted underneath the platform.

Meanwhile, Dr. Janine Nauw from the Texel based Royal Netherlands Institute for Sea Research (NIOZ) will monitor changes in the current and possible modification on the seabed.

The Tocardo turbines feature two blades that automatically flip around their length axis when the tide turns. This way both in- and outgoing tide will generate power. The Schottel blades work in one direction only.

Even when working both ways, the system will produce its full power for only a fraction of the time. People in the new energy sector have a name for that: performance factor. It equals the average power divided by the maximum power. Van Hoeken estimates the performance factor near Texel will be less than 40 %. With current technology, he regards tidal currents with speeds from 2,5 to 3,5 meters per second as minimal requirements. Such currents occur around the UK and Ireland, near Norway, Italy, Canada, Korea and Japan.

These are the potential customers if the consortium* succeeds in making the Texel project successful. Texel has a modest current of 2,0 – 2,5 meters per second, which is on the low side for commercial tidal energy production. Its sheltered location from open seas however and the nearby harbour of Den Helder make Texel an ideal test bed for tidal energy systems.

In fact, Bluetec at Texel is not about generating on blue energy or making the island self-sustainable. Bluetec is an effort to develop a modular floating tidal power platform that can be deployed and made to measure for any location with strong enough currents. The consortium sees Bluetec mainly as an innovative Dutch energy solution for the export.

“We’ve lost the competition in wind turbines to the Danes and the Germans”, says Tocardo director Hans van Breugel. “I hope we won’t blow it again this time.”

Van Breugel is trying to convince the Ministry of Economic Affairs to apply the same tariff of 16 cents/kWh for offshore wind to offshore tidal current as well. Currently, it’s only 8 cents/kWh. The higher tariff should apply at least for the first 100 megawatt installed power. That way, Van Breugel argues, the Ministry would provide this budding new energy industry with the room it needs to grow.

–> Lees ook De oceaan als energiebron, TU Delta, 9 maart 2015

(*) The Bluewater consortium includes Van Oord, Vrijhoff anchors, NIOZ, Tidal Testing Centre, Tocardo, TKF marine cables, Schottel, Damen shipyards, Niro staal, Acta Marine and Nylacast.

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