Two-Blade Turbines the Future of Offshore Wind Energy?

Two Blade

Published Sep 23, 2015 3:54 PM by The Maritime Executive

The energy industry is in a constant search for new ways to harness clean, renewable energy. Wind energy, particularly offshore wind, is the most commonly utilized natural resource industry leaders look to in hopes of meeting the world’s energy demands. Offshore wind farms are in planning and construction phases throughout Europe, and the U.S. has several projects in development as well.

Farms featuring three-bladed turbines are the industry standard, but as manufacturers seek to increase efficiency, many are constructing two-bladed and spinning the rotor 180 degrees to face downwind.

2-B Energy, a Netherlands-based company, is set to build a prototype two-bladed offshore wind turbine with a 6 megawatt capacity off Eemshaven. The turbine is expected to power about 5,000 households by 2030.

The 2B6 wind turbine is being financed by the Ministry of Economic Affairs, Shell and Capital Truffle, a European investment company.

And on September 15, the Crown Estate, a semi-independent public body with the U.K.’s largest property portfolio, announced plans to construct two-bladed offshore wind turbines with Forthwind Limited, a subsidiary of 2-B Energy. This 6-megawatt turbines will be constructed off Methil, Scotland.

While the potential benefits of two-bladed turbines are numerous, there are engineering issues to consider.

The benefits of two-bladed turbines include cheaper construction because they require fewer less material to construct and are easier to install. Industry leaders estimate that two-bladed turbines could cost about 20 percent less to construct and install while still generating the same amount of power as three-bladed turbines.

Removing the third blade makes the rotor lighter and allows engineers to place the rotor on the downside of the tower. In addition, two-bladed rotors are often easier to install than three-bladed turbines which must be constructed on-site. Because they often weigh up to 40 tons less than conventional rotors, two-bladed rotors can be built onshore and transported to its designated location on a ship because it is light enough to be lifted onto the tower.   

But there are still some engineering issues that must be addressed before two-bladed turbines become commonplace. Because the blades are lighter and more flexible, it is possible that the blades will spring back and hit the turbine tower in strong wind conditions.

Two-bladed turbines also suffer from dynamic imbalances. For instance, when the top blade is in the wind the bottom blade is being shaded by the tower. This causes problems with yawing and puts unnecessary wear on the bearings. This makes them particularly unsuitable for high wind areas.

While two-bladed turbines may eventually be a viable alternative, three-bladed turbines will likely remain the industry standard until these issues are resolved.