American Offshore Energy (AOE) says it has submitted novel patents for the floating wind turbine industry.
The AOE VAWT design, the “American Turbine,” is a wind turbine that has no center shaft; the bearings and electrical generation move to the perimeter, where there are high surface speeds even at low RPMs, eliminating the need for rolling bearings, gearboxes and oil. The team at AOE used design principles to completely avoid moment forces being transmitted to the floating base; this means the floats may be made from fiberglass, saving thousands of tons of steel. They built a lightweight but powerful aerodynamic rotor that may be “trimmed” to conditions.
The idea is that to make a floating wind turbine, it makes more sense to reach up into the wind with a lightweight structure, like a cross between sailboat masts and bicycle wheels, keeping the heavier bearings and generator near sea level. The key technologies enabling the opportunity are water-based hydrostatic perimeter support bearings, direct drive HVDC generation at the perimeter and tension and compression design principles.
The AOE design leads to sustainability advantages, the company says. Because of the fluid film bearing technology, axial and radial loads are separated; this means that the axial bearings, carrying the weight of the rotating assembly, may push down or pull up on a float, but cannot introduce a moment load. Because the floats are loaded in only tension or compression, they may be made from fiberglass at a tenth of the weight per megawatt of the oil derrick-like floats required for HAWT designs. HAWT have the loads and masses at the top of a long pole, they are cantilevered, so a 50-ton force at the top of a 100-meter tower puts more than 500 tons of force into a floating base that is holding the bottom 10 meters. This is why they require so much steel. The AOE design avoids this.
“It goes back to our ‘No Shaft’ design,” says CTO Drew Devitt about what distinguishes AOE from other VAWT offerings. “All the other VAWT offerings employ a center shaft. The center shaft VAWT have an advantage over HAWTs in regard to floating, by having the mass of the bearings, gearbox and generator at or below sea level. But they still are on the wrong end of 10 to 1 leverage, and in their case, this force is transmitted through rolling element bearings. And still, they need a gearbox, as generating power at 10 RPM would require a huge generator. The cost, the shafted VAWTs will pay, that shafted HAWT guys do not have, will be trying to keep saltwater out of oil-lubricated turbine bearings, gearbox and generator that is at or below sea level.”