Catching the wind before it arrives

Wind turbines have more moving and parts exposed to harsh elements than most electricity generating facilities. In some respects this is a problem in that there are more things that can go wrong due to external causes including birds, ice, waves (offshore wind) and sudden gusts of wind.

The flip side of all this is that there are also a number of areas where designers, manufacturers and developers may be able to reduce overall costs of wind energy systems beginning at the drafting table and extending through operation and maintenance. (GW)

Laser Sensors for Wind Turbines

A system that detects gusts before they arrive reduces wear, boosts output.

By Tyler Hamilton
Technology Review
November 06, 2008

A new fiber-optic laser system can measure wind speed and direction up to 1000 meters in front of a wind turbine, giving the massive machines enough precious seconds to proactively adapt to gusts and sudden changes in wind direction. The device, developed by Catch the Wind, a startup based in Manassas, VA, could improve the efficiency of wind turbines and keep them from breaking down.

The device could help lower the cost of renewable electricity from wind. Wind turbines lose roughly 1 percent of their operating efficiency for every degree their blades are out of alignment with the oncoming wind. Catch the Wind claims that its laser system can boost turbine power output by 10 percent by improving orientation accuracy. The pitch of the blades can also be adjusted in advance of the wind to reduce wear and tear on turbine gearbox components and blades, lowering repair and maintenance costs by up to 10 percent and extending the operating life of a wind farm, the company says.

John Kourtoff, chief executive officer of offshore wind developer Trillium Power, calls Catch the Wind's approach "conceptually intriguing" if it can both reduce wind-farm costs and increase revenues. "On the face of it, it makes sense. It would be advantageous for us," he says. "But I'd have to see real field data."

Current wind-energy measurement systems--both mechanical anemometers and more advanced LIDAR (light detecting and ranging) devices--are used primarily to determine if a location is suitable for a wind farm. The systems are also kept as part of on-site weather stations used for longer-term wind forecasting. Real-time data can also be gathered by mounting a small anemometer on the back of a turbine's nacelle, Kourtoff says. The problem with this setup is that the air is so disturbed after passing by the turbine blades that measurements are often skewed and unreliable. Also, the turbine can only respond to wind changes after its blades have been hit, leaving them vulnerable for a few seconds to a range of punishing forces caused by wind shear, gusts, and turbulence.

Catch the Wind has adapted LIDAR so that it can be mounted on wind turbines and used to measure wind changes in time to make adjustments to the turbine. It pulses three invisible laser beams in front of the turbine that can simultaneously measure both vertical and horizontal wind speeds at different distances, as well as sudden changes in direction. Like conventional LIDAR, it does this using the Doppler principle: when the laser bounces off small dust particles carried in the wind, it changes color. The color of the laser is directly proportional to the speed of the particle. The device uses proprietary algorithms to convert this data into measurements of wind speed and direction before communicating a course of action to the turbine's control system. The device provides 20 seconds' advance notice--enough to turn the nacelle and angle the blades so that the turbine can catch more of the wind energy while reducing strain on its parts.

Conventional LIDAR isn't suited for mounting on wind turbines because these devices rely on mirrors, which must be precisely positioned, to project a single beam as a three-dimensional cone, says company president Philip Rogers. Changes in temperature or sudden movement can knock the mirrors out of alignment. Rogers's company's device replaces mirrors with fiber optics that project three separate beams. This design makes it rugged, small, and lightweight enough to be permanently mounted onto a turbine nacelle and integrated into its control system. "It's very much akin to solid-state electronics," Rogers explains. "It makes for a very compact and robust system that's not susceptible to shock, temperature change, and other things caused by movement."

Catch the Wind's system is currently being field-tested at the Wind Energy Institute of Canada on the windy shoreline of Prince Edward Island. Paul Dockrill, director of technology at the institute, says that the device performed well under initial ground tests atop a tripod. It will soon be mounted onto the nacelle of a turbine as part of a more in-depth study.

Rogers envisions the fiber-optic system being integrated directly into new turbines at the point of manufacture, and also being retrofitted to the thousands of turbines already in operation today. "We are in discussions with a number of manufacturers, and we've seen significant interest," he says, adding that beta versions of the device will come next spring, and commercial production is targeted for late 2010.