Seatower's game-changing wind turbine foundations could reduce the cost of offshore wind farming
By Loz Blain
May 13, 2014
Offshore wind farming combines the clean, green, environmentally neutral benefits of land-based wind turbines, while being a lot less visually intrusive ... and restricting the usual NIMBY opposition to crustaceans and invertebrates. It's currently a lot more expensive to install turbines out at sea, though, and that's restricting the sector's development. Which is why the Seatower Cranefree turbine platform could be such a significant step forward. Cheaper and easier to install, and requiring less gargantuan and specialized equipment than standard monopile foundations, the Seatower base could help offshore wind farms reach profitability a lot quicker.
Wind farms are one of the cheapest, greenest and most reliable forms of energy generation. One modern turbine can now power more than a thousand homes, and in many areas they're becoming a significant part of the energy mix.
Offshore wind turbines are even better in a performance sense, and they're a lot further out of the way, so fragile petals like conservative Australian Treasurer Joe Hockey don't have to endure the "utterly offensive" sight of clean energy turbines on their way to work in the morning. Strange how conservative politicians seem to find open-cut coal mines far less offensive.
Still, up to this point, offshore turbines have been much, much more expensive to install. That's because there's a lot of challenges to overcome when you're trying to drive a massive monopile foundation into the sea bed.
For starters, the monopiles are huge, they weigh up to 650 tons each, and they require large, expensive ships to transport them. Ships that can drop legs down to the sea floor and elevate themselves above the waves to provide a stable platform that a giant crane can operate from. Very specialized, very rare and very expensive gear that works in a fairly narrow range of weather conditions.
Norway's Seatower foundations offer a much cheaper installation process that works roughly like this: firstly, the bases are mass-produced and assembled on land. Next, the hollow bases are lowered into the water, where they float in a stable fashion.
From there, they can be towed to the install site by a fairly small boat, at which point two more boats string a line to the base to position it precisely above its resting place.
At this point, a valve opens and water is let into the base to weight it. The structure sinks gradually to the ocean floor. A steel skirt around the outside of the base digs into the sea bed to anchor it, and concrete mix is poured into the gap between the base and the sea floor to provide a 100 percent contact between the base and the ground.
A sandy slurry is then pumped into the top of the structure until it achieves its target weight (usually between 6,000 and 7,000 tons), and then the base is ready for the turbine to be stuck on top of it. Even though this step likely requires the very cool jack-up crane ship to come in, it's certainly required for less time.
Should the tower ever need to be decommissioned, the above steps can more or less be followed in reverse, floating the base back up to the surface and leaving very little effect on the surrounding environment. Except, of course, a few squashed crayfish.
No undersea work is required from divers or submersibles, there's no drilling or hydraulic hammering required to seat the foundation.
"Seatower Cranefree Gravity is most applicable for water depths ranging 35 - 80 meters (115 - 262 ft)," Seatower's Niels Brix tells us. "However in some cases, where you i.e. have rocky seabed (and therefore cannot drill/pile), you might use it at less than 35 meters."
The technology will be demonstrated in early 2015 with a single Seatower and turbine to be installed at the Fécamp wind farm site off the coast of Normandy, France.
Brix believes the relatively simple Seatower installation process could have a significant impact on the high cost of offshore wind generation. "The concept will certainly, taken to larger scale manufacturing, help to drive down the total CAPEX of an offshore windfarm," he says. "Our foundation is easier and much less costly to install than typical steel structures using special purpose vessels and offshore jack up vessels."
While Western Europe, Scandinavia and the British Isles offer immediate opportunities, with large areas of relatively shallow seas, large populations close by and good strong winds, Blix says Seatower has global ambitions. "Many sites in the USA and Asia are potentially very interesting to us."
Power generation is a money-in, money-out game. Coal and gas fired power plants persist not only because of entrenched business and political lobbying, but because they make good economic sense.
Right now, offshore wind is expensive and makes less economic sense. If Seatower and other technologies can help bring the cost of offshore wind generation down, more turbines could be installed offshore where they're not "a blight on the landscape" or "a health hazard," and the likes of Joe Hockey will have to find some other reason to oppose them.