Sometimes progress can be its own worst enemy, with early adopters being stuck with obsolete equipment that leaves them with the choice of living with out-dated technology or an expensive replacement. The green energy field isn’t immune to this, and as part of a US$2 million renewable energy project, GE has developed a way to make smaller, less efficient wind turbines into bigger more efficient ones with a bit of plastic (or carbon composite) surgery.
Windmills have been around for over 2,000 years, and have been used for everything from grinding corn to reclaiming much of The Netherlands from the sea. In these days when global warming is such a political hot potato, many governments have seen wind turbines as a clean, green alternative to conventional or nuclear power sources.
One problem is that wind turbines are not a very efficient power source, with many square miles of land containing thousands of turbine towers needed to replace a single coal-fired plant. Therefore, engineers are working to better understand how wind turbines work, and to come up with more efficient designs that put out a greater amount of power more predictably from each tower.
GE cites a paper in Environmental Science and Technology which states that the key to more efficient wind turbines is to make the towers higher and the rotors longer. This way, the amount of power put out by the wind turbine is increased without a proportional increase in the mass of the installation. The paper states that by following this rule, the average size of commercial wind turbines in the past 30 years has gone from 50 ft (15.2 m) to 500 ft (152 m).
However, that brings its own problems. For one, it’s all very well and good to come up with a better design, but wind turbines aren't cheap and any major improvement in design means that the wind farm operator is faced with a costly quandary: what to do with the old, inefficient turbines?
GE’s answer is to avoid replacing the turbines in favor of lengthening the rotor blades. That may sound simple, but given that the blades are made of composites and the shapes are as carefully engineered as the wing of a fighter plane, that extension has to be very carefully designed. Eventually, the GE team came up with a method to cut a 120-ft (27-m) blade in half, then insert a 23-ft (7-m) extension, which is blended into the original blade’s curve.
According to GE, the extension allows the turbines to gather power at lower wind speeds while boosting power output by 20 percent, and the modifications have exceeded the standards of the International Electrotechnical Commission (IEC) in both static tests and fatigue tests where the blade was put through 6 million cycles.
The video below shows a blade extension being installed.