Date: Nov 07, 2014 Author: Nick Stockton Source: Wired (
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A lidar buoy used for measuring wind. The three lasers are poking out of the white orb above the solar panel. Pacific Northwest National Laboratory
If you're looking for wind energy, the sweetest breezes blow over the open sea. But gathering this energy is risky business, as the strength of offshore winds can easily overwhelm a turbine designed for land. To build better turbines, we need more accurate wind measurements, which scientists are going to get by putting lasers on a buoy and shooting them into the sky.
The project, funded by the US Department of Energy, will measure the wind off both the Atlantic and Pacific coasts of the country. Each buoy will have three upward-facing lasers, angled slightly apart, that can measure the wind's speed and direction continuously up to about 650 feet above sea level. The first buoy is tentatively scheduled to deploy in mid-November off the coast of Virginia. The second will deploy off central Oregon soon afterward.
The goals are to provide long-term measurements of how much power offshore wind can generate, and to help designers prevent wind turbine fatigue. The latter is caused when the wind blows more strongly--sometimes 20 mph or more--at the top of a turbine's rotor sweep than at the bottom. "The blade will bend backward, then forward, which will make a continual flexing at the hub," said the project's leader, William Shaw, a meteorologist at Pacific Northwest National Laboratory. This flexing will wear the material out, similar to bending a piece of foil back and forth.
To build turbines that can withstand this stress, engineers need to understand exactly how the wind behaves at every point between sea level and the top of the highest blade. The buoys do this by bouncing laser pulses off particles in the atmosphere. This technology is called lidar, short for light detection and ranging. Those pulses reflect back to the sensor, bearing information about how fast the particle was moving. Because each laser pulse moves at the speed of light, the sensor can tell the particle's altitude by calculating how long it took the pulse to bounce back. And by using three lasers, it can triangulate the exact direction the wind is moving. Each laser fires off more than 50,000 pulses each second.
Offshore wind energy has a lot of potential, not just because the wind is stronger and more consistent, but because the turbines can be built bigger. Terrestrial turbine parts have to be transported via truck or train from the manufacturing yard to the wind power plant. If the blades are too long, they won't make it through curves in the road or track. Shaw estimates that a single individual offshore turbine could be more than 300 feet high at the central hub, and generate three times the electricity as one on land. This makes knowing the potential dangers from fatigue even more important.
In times past, taking offshore wind measurements for turbines required building stationary structures called meteorological masts. The buoys, called WindSentinels, were developed in 2009 by AXYS Technologies to replace those masts. Not only are they mobile (Shaw says his project plans to move them up and down the coasts to measure wind at a number of different sites), but are about 10-15 times cheaper.
Most WindSentinels are used by private energy companies, and their data is proprietary. Shaw says that the data from these buoys will be available to the public, for the purpose of advancing the wind industry as a whole. This could make it a lot easier for people hoping to break into wind.
