Mike Bergey was sailing along in his silver sedan with the "WINDPWR" license plate, streaming toward one of the electric windmills he seeded around central Oklahoma's prairie, when a warning siren howled out of nowhere.
Five years ago, a fat tornado rolled over this stretch of plain south of Oklahoma City. It killed 44 people and scrambled 8,000 homes. At one farm, it also ripped a blade tip off a turbine made by Bergey's wind power company.
En route this day to check it, he considered the charcoal sky, then wheeled around. "I'm not superstitious," he muttered, "but I'll take my chances this way."
For more than 25 years, Bergey has been trying to outguess the vagaries of the winds.
They fluctuate hourly here, sway and buckle metal, and in tornado season sometimes transplant windmill parts in a neighbor's field.
In central Oklahoma, a little wind turbine designed for a single home or small business can generate enough electricity to pay half its yearly bill -- and pay for everything in a windy spring. Giant, commercial-scale machines can churn out enough power for hundreds of homes.
Yet the United States gets merely 0.3 percent of its electricity from wind. Even the American Wind Energy Association, a trade group, predicts that figure will be no more than 6 percent by 2020.
In other words, wind power works -- but probably cannot carry the burden when fossil fuels start running thin.
At its core, wind power is low tech and old tech. Blades catch passing winds to spin a generator.
Most systems forgo expensive batteries that can store power for times when winds are still. In the more common on-grid systems, wind power flows into an existing electrical box and home outlets. Any surplus flushes into the local power line for credit. When winds calm, the power line takes over.
To cut down on moving parts and upkeep, Bergey's turbines are built with neither gearbox nor bearings needing periodic lubrication. With patience, a manual, a few helpers and a crane for some models, a buyer with the ambition can assemble one himself, mounting its 23-foot-span blades on a 100-foot tower bolted to a concrete pad.
Since the early 1980s, 37,000 wind turbines sold by dozens of companies have sprouted across the country, the industry estimates. The bigger commercial ones produce by far the bulk of the electricity. Sleek and modernistic, they poke from California ridges or alternate with oil rigs on the wide Texas horizon. A battery of 130 has been proposed for choppy waters off Cape Cod.
While less powerful, little turbines for single homes and small businesses are more abundant. Bergey Windpower has sold about two dozen in the Norman area alone.
Why aren't there more around the country?
First, winds do not blow hard or steadily enough in many places.
Then there are the aesthetics: Even small turbines may whew-whew-whew ceaselessly, thrumming through a restless night like a distant freight train. Also, in many towns windmills violate height restrictions.
There are infrastructure problems, too. To make full use of wind power, the Midwest, for example, would need an expensive web of high-voltage lines between wind sites and cities, industry advocates say. Commercial farms pay penalties for power interruptions from variable winds.
In the late 19th century, thousands of windmills made farming practical in Oklahoma, mechanically pumping water for livestock and settlers who swarmed here in the Great Land Rush. The technology had been eclipsed when in the early 1970s, with oil supplies short, an engineer decided Oklahoma's winds could again be harnessed.
That engineer -- Mike Bergey's father, Karl -- was teaching aircraft design at the University of Oklahoma at Norman. He had co-designed the popular Piper Cherokee light plane.
With $40,000, he and his engineer son founded Bergey Windpower Co. in 1977. It was a quixotic idea: No market for small turbines existed then.
"When Mike graduated, I asked him a simple question: 'How little can you live on?' " recalled his father, who is now CEO. His son is president.
Within three years, Bergey Windpower put its first turbine -- a one-kilowatt generator, one-tenth as powerful as most of today's -- on a tower beside Karl Bergey's house. They soon sold dozens more, with the help of federal and state tax credits worth as much as $7,500 for each turbine.
While simple in theory, a durable turbine is tricky to design. The blades pivot edge-on to let storms slip by, but must be stout and slightly flexible so they do not snap in ordinary gusts.
The first Bergey blades were made of sheet metal and tested on a machine that gave them an energetic workout of flexes and twists. It was not enough. Subjected to buffeting by real winds, the blades cracked. They were replaced at company expense. The blades are now made of tough fiberglass.
Their shape also needed refining, including wind tunnel tests. Not everything worked. Filling the hollowed bottom of an early blade design did little to quiet its pulsating whoosh.
The sound of the turbine on Karl Bergey's second tower, installed on a hillock beside his home, bothered his wife, Jimmie, at first. "At night, I felt like there was a jet plane sitting over the house. It's just this huge white noise," she said.
Over time, she got used to it. "Now," she said, "I don't even hear it."
Blade design has since been transformed by computer software that simulates air flow. The result at Bergey Windpower is slightly thicker, harder-working blades, shaped more like airplane wings. The new design smoothed the leading edge, built up a little ridge in front and tapered the back -- all to mute the rush of air past blades that can whirl at 200 mph.
The Bergey turbine at Jim and Helen Driscoll's kept cranking for more than 20 years, with few breakdowns.
When a tornado knocked their roof into a neighboring field in 1988, the 100-foot-high wind tower stayed put. Its cracked blades kept rotating.
"I think if I were to evaluate that machine with all the machines I have, that's the most perfect," Jim Driscoll said.
In plains on the rural outskirts of Oklahoma City, Delbert Thornhill's turbine also survived a monster 1999 tornado, which sank a neighbor's tractor in a pond. But he has come to a different conclusion about his unit, which was cycling on and off in recent weeks for no apparent reason.
No longer does Thornhill recommend it to inquisitive passers-by. "When I tell the truth, it don't sound very good. It's not making what they said it'd make," he says.
Harold Klusmeyer's little Bergey broke down twice within the first couple of years. He could have replaced parts for several hundred dollars, but it was saving only about $350 a year in electricity, he figures. He gave up and traded in the generator for a photovoltaic system that converts sunlight into electricity.
Jim Hames was saying morning prayers one day when he was jolted by a crash.
A guy wire on his wind turbine tower had snapped in high winds. About 40 feet of steel had come thwacking down into his pasture. The sleek turbine nosed into the dirt like an airplane engine.
Hames felt oddly liberated: "At the time it went down, it hadn't worked in, say, six months. I was relieved to get rid of it."
Bergey is working on a new, more powerful model, but the company's systems already cost around $40,000. Even saving more than $1,000 a year in electricity in some windy spots, they can take more than a generation to pay for themselves.
Without Oklahoma or federal tax incentives, and with electric lines near most homes, hardly any of Bergey's Norman employees have installed wind units of their own. Even Ken Craig, Bergey's vice president, acknowledges that at this point, "it doesn't make economic sense."
To prevail in the long run, some experts say, wind energy must drop well below the price of conventional power. "If it's not cheaper than the fuel, why use it?" asked Robert Thresher, director of the National Wind Technology Center in Golden, Colo.
The vagaries of economics and energy policy have compounded those of the winds. After the oil embargo passed, tax credits for alternative power fell away in the mid-1980s. Many wind companies withered.
Bergey Windpower lost about 90 percent of yearly sales.
Over time, it began sending more battery-equipped turbines to customers in developing countries with rudimentary electrical networks. It now does about half its business abroad, especially in China. It employs almost half of its roughly 50 workers there.
Other parts of the world have outpaced the United States in spreading wind power. Germany has built up three times more capacity, and Denmark derives more than 15 percent of its electricity from the wind. The United States has installed only about 15 percent of the 40,000 megawatts of world wind capacity.
Still, over the past five years, wind power capacity in this country has more than tripled, virtually all from bigger commercial machines. They can beat the economics of conventional power in extraordinarily windy places, such as a point on Boston Harbor where a 150-foot colossus whips out 3 percent of the power for one suburb, Hull, Mass.
Bergey Windpower has rebounded to $4.5 million in annual sales, Mike Bergey said. It has gotten a lift from new state subsidies in California and some other places.
But Bergey acknowledged that the company "goes in and out of profitability." Prospects remain changeable, like the wind.