American Offshore Energy unveils floating vertical-axis wind turbine

4C Offshore | Tom Russell
By: 22/11/2022 AOE

American Offshore Energy (AOE) unveiled its patent for a floating vertical-axis wind turbine (VAWT). The AOE VAWT design, the "American Turbine", is claimed to be the first 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 design aims to completely avoid moment forces being transmitted to the floating base; this means the floats may be made from fiberglass. Then they designed a lightweight but aerodynamic rotor that may be "trimmed" to conditions.


According to AOE, the fluid film bearing technology, axial and radial loads are separated; which 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 MW 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. AOE stated that its design avoids this.


Furtheremore, AOE stated its design has no need for forgings, castings, rolling element bearings, gearboxes, conventional generators, or AC/DC conversions at sea. Being lighter, they can be manufactured and launched from sites not appropriate for launching floating HAWTs, and towed and serviced by existing Jones Act-compliant vessels.


Drew Devitt, CTO of AOE commented: "Being completely American-made, we will avoid having to wait to buy European-made nacelles; that is another reason we may be able to deploy faster and less expensively.


"We are not competing with HAWT; we really offer a completely different 'Iron in the Fire' with regard to deploying utility-scale floating wind turbines."


Devitt added, "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 10rpm 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."


AOE further stated that the turbines may be sunk in the face of a hurricane, allowing them to ride out the storm just below the ocean surface. The turbines can be raised after the storm by remotely releasing compressed air cylinders in the fiberglass floats. General maintenance at sea is facilitated as the bearings and generator components are at deck level for service boats and because the turbines are arranged in a mooring field, they may be unplugged and towed back to port in a day by existing Jones Act-compliant tugs for maintenance if necessary.


Devitt, said: "I think speed to deployment is the key. Steel and fiberglass fabrication have relatively low capital requirements. Combine that with low real estate costs, near the proposed wind farms, and you have a recipe for franchising manufacturing. Once the facility and tooling to make the turbines have been developed, they can be duplicated, and other manufacturing sites could pop up quickly near deployment sites. This would be a great way to help us meet our renewable energy targets and put Americans to work quickly."