Newer technology renews interest in wind power

By Jeffrey Krasner, Globe Staff, 8/6/2001

The would-be developers of a giant wind farm proposed for the shallow waters off the coast of Hyannis in Nantucket Sound want you to know: These are not your father's windmills.

Wind power acquired a flaky image in the 1980s when windmills sprouted from the landscape, spurred in part by federal tax incentives, and began spinning - only to quickly self-destruct and grind to a halt. Giant blades would shear off, entire rotors would fall to the ground, or the machines would just shake themselves to death.

Today's turbines are bigger, more efficient, and more reliable, say energy experts. And while the windmills look pretty much the same, a host of detail improvements have made modern windmills practical devices for generating renewable energy.

The blades on today's mills have been subtly modified to make them more efficient. That enables the windmills to capture more of the wind's energy and transform it into torque, or rotation.

''The shape is optimized to perform under unsteady air dynamics'' that windmills are subject to, says Susan Hock, wind energy technology manager at the National Renewable Energy Laboratory in Golden, Colo. They're now made out of fiberglass composites that are easier to manufacture and lighter than the steel once used.

Engineers have been able to make windmills more durable, partly out of simple experience: After watching windmills fail for a couple of decades, engineers know more about which parts of the machine are subject to the highest stresses. At the same time, designers are using computer-aided design programs to strengthen vulnerable parts without adding weight and bulk to the entire machine.

''You can design a lot smarter,'' says James F. Manwell, head of the Renewable Energy Research Laboratory at the University of Massachusetts in Amherst.

Perhaps the biggest advances have come in the controls that govern the windmill's operation. Attached to each windmill is an anemometor, which measures wind speed and direction. Then, motors inside the nacelle rotate the entire contraption atop the support shaft, so the blades are always facing directly into the wind.

A separate set of motors rotates the blades on the central hub, changing their angle for optimal performance for different wind speeds. The latest systems are able to change the blade angles within the course of a single rotation, thereby enabling the windmill to best exploit different wind speeds at different heights.

Another improvement are switches that instantaneously alter the power output of the turbines. The spinning blades turn a shaft, which through a gearbox turns a generator, producing electricity that is transmitted to the electric grid. But in the past, variable wind speeds produced varying power outputs, and big stresses on the windmill's drivetrain. The new switches enable the windmill to absorb the changes while producing a steadier power output, in much the same way that an automatic transmission in a car smooths gear changes.

And engineers are putting redundant controls into some windmills, such as two computer boards instead of one. That way, a single failure doesn't knock out the windmill. ''It's cheap to install redundancy,'' says Bob Gates, senior vice president of Enron Wind, a unit of the Houston energy company. ''It's expensive to send out a crew in a boat to make repairs.''

Meanwhile, windmills are getting bigger. The wind farm proposed by Cape Wind Associates LLC of Boston would use blades spinning 426 feet above the ocean at the blade tip. There are two reasons for the increase: The higher you go, the faster the wind tends to blow, creating more energy for the windmill to capture. Moreover, bigger windmills give a developer more bang for the buck: As you increase size, costs go up in a straight line, while the amount of power the windmill can generate grows geometrically.

The bottom line is that the windmill is able to capture more of the wind energy, more of the time. Hock, of the national energy laboratory, says that 10 years ago, a typical windmill could generate its full capacity 25 percent of the time. Now, 35 percent is common.

Jeffrey Krasner can be reached by e-mail at krasner@globe.com.

© Copyright 2001 Globe Newspaper Company.