However, there is plentiful wind where the turbines can’t reach. Just a few thousand feet over our heads, there’s an untapped resource of wind. The wind can be harvested if the turbine is not bound to earth on a short tower. The newest frontier in the wind energy movement is airborne turbines that fly in the higher—and windier—altitudes.
Windlift Inc., in Raleigh, N.C., has developed a fabric wing that flies into the windy altitudes that fixed turbines can’t reach. The wing is sent into the air on a tether. One wing can generate 12 kilowatts (kW), the equivalent of a tower-mounted wind turbine. “The wing captures power as it lifts, then captures even more energy on the way back,” says Matt Bennett, control engineer at Windlift. “While the wing is out, you fly it back and forth in a figure eight for maximum lift.”
Automation tools come into play in controlling the wing to get maximum energy capture. “The wing is controlled by a system of steering servos,” says Bennett. “You pull the wing right or left to get it to bite into the air. Right now, it’s done manually with a semi-automatic joy stick.”
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Bennett notes that there are a number of semi-automatic features to direct the wing to the greatest amount of energy generation. “We want the wing moving at a certain speed, so we’re constantly adjusting the torque to go downwind slower or faster to get the sweet spot,” says Bennett.
The system uses controls from National Instruments Corp., the Austin, Texas, test and automation supplier. “We use a compact embedded computer and the LabView real-time processor,” says Bennett. “There’s an FPGA (field programmable gate array) that shares the tasks of handling the control of the wing.”
Presently, a pilot has to be involved to steer the wing, but the company is developing a version of the system that is fully automated.
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