The airstream 30 km offshore blows at an average 10 m per second, a prime condition for wind turbines. But it’s prohibitively expensive to build a turbine in deep water, and the ocean floor that far off most of the coastal United States is a long way down. Two companies are testing floating turbine prototypes in Europe that are designed to operate at great depths, and at low cost. Officials with the US Department of Energy are evaluating both real-world tests for domestic use. – By Stephanie Warren
WindFloat’s base adjusts the water level in three columns to keep the turbine level. Engineers designed Sway’s tall, slender tower so that its centre of gravity lies below the structure’s centre of buoyancy, allowing it to remain steady even when seas are turbulent.
WindFloat saves steel by placing its tower on a column instead of on a platform. The Sway design economises and gains structural support with steel cables. Its blades are mounted downwind – the opposite of most turbines – to keep them clear of the cables.
WindFloat’s 91-ton nacelle, or gear housing, turns to meet the breeze, like a typical landbased turbine. The Sway’s entire tower rotates on a universal joint that connects the turbine to the tension-leg anchor; the blade clearance from the wires remains constant.
Developer: Principle Power, Seattle
Height above water*: 50 m
Depth below water: 13 m
Power produced: 2 megawatts
Developer: Sway AS, Norway
Height above water*: 13 m
Depth below water: 15,8 m
Power produced: 7,2 kilowatts
* Without blades