How wind turbines work, and why they're getting bigger 

They keep getting bigger.

Just 10 years ago, each turbine in Oregon’s first industrial-scale wind farm churned out enough power to light about 165 homes. That was a respectable showing at the time, but now they seem mere pinwheels.

The generating power of wind turbines in the Columbia River Gorge has jumped more than threefold in the past decade. And bigger towers are on the way.

Driving the trend is a simple motivation: saving money.

“It’s economies of scale,” said Jim Johnson, a senior engineer with the U.S. Department of Energy’s National Renewable Energy Laboratory. “The larger the machine, the less it costs per megawatt.”

Technological advances resulting in longer, more adaptable blades have accelerated the trend. But record-breaking U.S. demand and tapped-out manufacturing capacity have pushed up project costs and prompted developers to go for big and efficient.

So far, the most powerful turbine in the gorge is Siemens Power Generation’s 2.3 megawatt turbine (each megawatt – 1,000 kilowatts – can power about 250 homes continuously). California boasts the biggest: a 3 megawatt turbine in Rio Vista.

Portland-based PPM Energy, one of the country’s largest wind farm developers, owns and operates the Siemens turbines. It plans to expand the Sherman County project, called Klondike III, but hasn’t settled on a turbine size.

PPM Energy has been buying hundreds of turbines of various sizes for future projects. Turbines could be as large as 3 megawatts at Klondike.

“We want to keep our options open,” company spokeswoman Anita Marks said. “We will use whatever is appropriate and economic for a specific area.”

Anything bigger might be pushing it.

“Two to three megawatts is pretty much where the industry says it will be for a while,” said Bob Gates, president of the American Wind Energy Association and senior vice president of turbine maker Clipper Windpower.

The logistics of hauling turbine components to the project site are getting in the way. “As these things get so big and heavy, they get disproportionately expensive to transport,” Gates said.

The towers, well over 200 feet tall, are made in three sections. Each weighs more than 35 tons and fills a semi-trailer bed. Straight, open interstates pose few problems, but winding country roads can prove daunting.

Two cranes – one to lift a tower section and one to serve as backup and guide – position the pieces, which are bolted together.

The bullet-shaped nacelle houses the generator. At 100 tons, it’s the single heaviest component. Like the tower sections, the nacelles are hauled one by one to the project site, then hoisted into place with a special crane.

On-the-ground crews connect the three blades – each about 150 feet long – to the hub, then call in the crane.

“It’s like a big erector set,” Marks said of the assembly process.

From ground to straight-up blade tip, a turbine can approach 400 feet and weigh more than 200 tons.

Roads and mass are limiting factors, said Johnson, of the National Renewable Energy Laboratory. “It’s an issue of transportation and crane capability. If you can physically get them there and get them up, you’ve got it made.”

Open seas and ocean tankers give developers more choices for offshore projects. California-based Clipper has announced plans to develop a record 7.5 megawatt offshore turbine at a research center in the United Kingdom.

The United States has no offshore wind farms. Several are under consideration, but none off the West Coast.

By Gail Kinsey Hill

The Oregonian

12 December 2007