Huge amounts of wind blow over seas whose waters are over 30m deep. Yet installing offshore turbines in deeper waters so that this wind can be captured and transformed into power is cripplingly expensive.

As futuristic as the idea may seem, floating turbines could be the solution. And according to Henrik Stiesdal, Chief Technology Officer for Siemens, writing in the latest issue of Wind Directions, they may be able to take wind energy into deeper, more distant waters as soon as 2020.

Although ideas for floating turbines have been tossed around for decades, 2009 will go down as the first year one was put into (or onto) the sea. StatoilHydro installed a 2.3 MW Siemens model, known as ‘Hywind’, off the west coast of Norway this summer.

Traditionally, offshore turbines have either a gravity based foundation – that sits on the bottom of the sea and is heavy enough to keep them stable, a pole foundation (known as a ‘monopile’) that is driven into the seabed, or a tower of latticed steel known as a ‘jacket foundation’ for greater depths. In contrast, the slim Hywind machine has a floating platform that is tethered to the sea floor.

The major challenge of any floating turbine is ensure its stability. So far, floating models have tackled the problem in various ways - with a weight to pull the turbine down into the water to make it steadier, for example. But in the Hywind project, it is the movement of the turbine’s blades that enables the turbine to be stabilised through a computer program which monitors the movement of the blades and tower.

Stiesdal writes that “floating wind power is in its infancy”, and cites the example of maintenance. Already there are only certain weather windows that allow boats to head out to service an offshore turbine – as turbines go deeper and further from shore, this is likely to become trickier. Not to mention the fact that a floating turbine by nature moves around slightly, making it far harder to work on than a totally stable one.

The Hywind turbine is set to undergo two years of testing, and Stiesdal is confident that the floating sector will not need much more time to become commercially usable. The offshore sector went from baby to large-scale in nine years (1991-2000), he points out, so the floating wind power can do the same.

“Siemens and StatoilHydro expect that floating wind turbines may be commercially viable within five to ten years”.

The full article appears in the latest edition of Wind Directions - out now.

By Sarah Azau