Science

Floating counter-rotating wind turbines promise unprecedented power generation

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Norwegian startup World Wide Wind has developed a technology to improve the efficiency of offshore wind projects. These are floating vertical axis turbines, consisting of two sets of counter-rotating blades. According to the developers, these wind turbines can generate more than twice as much energy as current offshore wind turbines.

Offshore wind farms are typically based on horizontal axis wind turbines (or HAWT, for horizontal axis wind turbine) whose rotation axes are parallel to the ground. The blades rotate in a plane perpendicular to the ground, and the longer they are, the higher the masts must be. However, installing them off the coast, where the ocean gets deeper, is a real challenge: the heaviest components (motor and blades) are at the top of the mast, so assembling them on a floating platform is especially difficult.

Vertical axis turbines (or VAWT, for vertical axis wind turbines) from World Wide Wind (WWW) get around these difficulties. The generator and rotor are located at the foot of the windmill under water, acting as stabilizers and counterweights; the upper turbine rotates in one direction, while the lower turbine and the outer part of the mast rotate in the other direction. The structure leans against the wind. The WWW says its thick-bottomed, co-axial, tilting and counter-rotating turbines can solve massive offshore wind restrictions.

Reduced wake effect, higher turbine density

These wind turbines are distinguished by their dual turbine: the top turbine is attached to a shaft located in the center of the mast (and which is connected to the base, all the way to the rotor), and the bottom turbine is attached to the outer shell of the mast. mast (itself connected to the stator). Each part rotates in the opposite direction to the other. This configuration makes it possible to double the relative rotational speed compared to a static stator.

Diagram of a floating vertical axis wind turbine developed by World Wide Wind. © World Wind

Another advantage of these wind turbines is that they can use wind from any direction. The blades are not facing the wind: two sets of three blades are arranged in a cone. WWW also indicates that this design results in a significant reduction in the wake effect, which corresponds to a decrease in wind speed after the wind turbine after capturing some of its kinetic energy.

This effect makes it necessary to place HAWTs at a sufficient distance from each other in wind farms to limit the reduction in production. Here, the distance between the turbines can be reduced by 50%, which makes it possible to install four times more turbines in a given area of ​​the sea.

Another benefit of this technology is less impact on wildlife, as the rotating turbine is perceived as a natural obstacle. “The low rotor blade speed prevents bird strikes, and our design also allows for more recyclable materials,” the company’s website says.

Masts 400 meters high, 40 MW

The fact that these floating towers can tilt with the wind allows them to withstand strong winds, limiting damage. The parts requiring the most maintenance are located at the base of the wind turbine under the floating platform, making maintenance easier, unlike the HAWT. It remains to be proven that these wind turbines are as resistant to the elements as expected.

The current trend is more towards giant offshore wind turbines. GE Wind Energy (a subsidiary of General Electric) distinguished itself in 2019 with its 12MW Haliade-X wind turbine. The company recently unveiled its new prototype, the 14 MW Haliade-X, which can generate up to 74 GWh of gross annual energy production while saving up to 52,000 tons of CO2. “The ability to produce more electricity with a single turbine means that fewer turbines need to be installed in each wind farm. In addition to reducing capital costs, it also simplifies operation and maintenance,” said Vincent Schellings, Chief Technology Officer, GE Renewable Energy Offshore Wind.

The largest wind turbine in the world today remains the MySE 16.0-242 (16 MW) turbine, introduced by the Chinese company MingYang Smart Energy in August 2021: with a height of 264 meters, it has a rotor with a diameter of 242 meters and blades 118 meters long, which allows it to cover an area of ​​almost 46,000 m2. It is designed to withstand strong winds, including typhoons. Such a turbine could generate 80,000 MWh of electricity per year, enough to power more than 20,000 homes.

But the WWW windmills could completely overshadow these already impressive projects: according to the company, they could reach 400 meters in height with a power of 40 MW! Thus, these counter-rotating vertical turbines can drastically improve the efficiency and reduce the LCoE (Level Cost of Energy) of floating offshore wind projects; the latter, according to company officials, could be less than $50 per megawatt.

WWW promises rapid prototyping. By 2026, it is planned to commission a 3 MW model; The 40 MW juggernaut could be ready by 2029.

World Wind

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