MIT researchers recently demonstrated the feasibility of “tension-leg” platforms, a technology that oil companies have recently adopted for deep-water rigs. The wind turbines and towers would be assembled at a shipyard and placed on top of large floating cylinders (see images). The canisters would be ballasted on the bottom with high-density concrete to keep the structure from tipping over, and the whole turbine assembly would be tugged out to sea.
There, four steel cables would be attached to the platform, anchoring it to the sea floor. First, though, some water would be allowed into the cylinder, causing the structure to sink more into the water. Once the cables are attached, the water is pumped back out again, allowing the turbine to rise, tightening the cables, and preventing the turbine from bobbing up and down, yet allowing some lateral movement that would help cushion the impact of storm waves on the tower. (The blades themselves would be high enough to avoid even waves from hurricanes.) The cable tension can be adjusted for different weather conditions, says Paul Sclavounos, professor of mechanical engineering and naval architecture at MIT.
Based on wind-speed measurements, researchers at MIT, led by Stephen Connors, director of the Analysis Group for Regional Electricity Alternatives, calculated that large turbines located far offshore could ultimately cost less per power generated than either land-based turbines or near-offshore ones, even factoring in extra costs, such as much longer underground electricity transmission cables. The upside: much more fast and steady wind, which would allow the turbines to generate power at 50 percent capacity on average throughout the year, compared with 30 percent or less with on-land turbines.
Offshore wind farms could also have the advantage of being close to big cities, unlike wind farms in remote areas, which require significant power grid upgrades to transport the power to places where it’s needed. “I personally see this as the endgame,” says GE’s Lyons. “We’ll see gigawatt-scale projects delivering clean energy to the East Coast.
But making the technology cheap enough to be feasible will not be easy. “You’ve got to push all the buttons to get the costs down,” Lyons says. Using a combination of far-offshore and land-based farms, however, one day it may be possible to provide 20 percent of U.S. energy from wind, he says.