With politicians pushing adoption of renewable energy in the United States and Europe, the last few years have seen a surge in plans for wind farms–both on land and sea. But wind power isn’t viable everywhere, and prime coastal spots are often already de

So some wind-turbine makers are shifting their focus toward

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building bigger wind turbines that can harvest the lower-speed winds

that are more readily available. This next generation of wind turbines

is no small matter: their rotors have a diameter the size of a football

field.

In general, wind turbines get more powerful and efficient with

taller turbine towers and larger areas swept by the blades, according

to the American Wind Energy Association. A turbine’s swept area is a

key indicator in how much power output potential the turbine has.

“Lower wind-speed turbines certainly open up more land for

development,” said Rich Reno, platform leader for General Electric’s

new 2.5-megawatt wind turbine. “Larger turbines open up the opportunity

to get more megawatts out of a given piece of land.”

Finding

new sites for wind farms is essential to the sector’s growth because

many of the places with the most attractive wind conditions tend to be

developed already. More efficient turbines also make wind power a more

realistic option for countries like Germany, which is not very windy

and has relatively limited shoreline, where winds tend to be stronger.

Despite those obstacles, the country has the world’s second largest

installed base of wind power.

Wind farm development continues to push into new regions–particularly

in the U.S. and parts of Europe, where politicians are encouraging

renewable-energy R&D.

“We see continued growth in Europe, notably because of EU legislation

to derive 20 percent of its energy from renewable sources,” Victor

Abate, vice president for the renewables arm of GE Energy, told Reuters

in an interview. The European Union issued a directive in December 2008

to have 20 percent of its energy come from renewable sources by 2020.

Europe contains more than half of the world’s installed wind power

capacity.

The U.S. is now the country with the world’s largest installed base of

wind power, according to the World Wind Energy Association. More than

8,300 megawatts of wind power was installed in 2008, expanding the

nation’s total wind power generating capacity by 50 percent in a single

calendar year.

Although that growth is expected to slow in 2009, according to both the

AWEA and investment bank HSBC, the wind industry is still getting

support stateside. As part of the economic stimulus plan signed in

February, President Obama extended tax credits for wind and increased

the amount the government will spend on those credits by 30 percent.

Industry watchers predict much of the growth in the wind market will be

in the low- to medium-wind segments. And as that trend continues, wind

turbines in general have been increasing in size–from typical 18-yard

rotors 25 years ago to about 110 yards in recent years. The average

wind turbine installed in 2007, with a capacity of 1.6 megawatts, is

twice as powerful as the average wind turbine installed in 2000 (0.76

MW), according to AWEA.

Several manufacturers are rolling out new low-speed turbines to help

meet that demand. Siemens, Vestas, and Nordex all recently released

new, large wind turbines directed at low-wind markets. Last year,

General Electric released its largest turbine for low-wind use.

Siemens predicts that the low-wind market alone should represent

one-third of the total global wind-power market in the coming years.

Its new turbine, the SWT-2.3-101, has a “nominal” (that’s maximum in

wind-engineering speak) power output of 2,300 kW, enough to power

approximately 700 homes, depending on wind conditions. The turbine is

enormous, with a 110-yard rotor diameter–larger than an American

football field.

Designed to harvest weaker winds, SWT-2.3-101 has a swept area of

86,111 square feet, 17 percent larger than Siemens’ previous 2,300 kW

turbine.

“The new wind turbine will open up many potential new sites for our

customers,” Andreas Nauen, CEO of Siemens’ Wind Power Business Unit,

said in a statement.

Danish wind-power company Vestas recently unveiled its V 112,

a 3 MW low-wind turbine the company claims is the world’s largest

mass-produced wind turbine for low- and medium-wind-speed sites.

The wind turbine has a nominal power output of 3,000 kW, the

same as the company’s previous largest turbine. But because of its

larger blade diameter, it’s able to reach that potential with lower

speed winds. It can generate electricity at wind speeds as low as 6.7

miles per hour and reach maximum power at about 31 mph. The previous

model required 8.9 mph winds to deliver power, and 34 mph to attain

maximum output.

Three factors have made it possible to make modern turbines so

big, according to General Electric: controlling the load on the grid,

new blade design, and new materials to reduce the weight of the

turbine.

“As the technology increases in those areas it allows advancement,” said Reno, of GE Energy.

New materials and construction techniques make it possible to build

even larger wind turbines. Siemens says it uses a proprietary

manufacturing process, which casts the 53-yard, fiberglass-reinforced

epoxy blades in one piece. The process eliminates weaknesses from

gluing parts together, as is done with traditional blades and thus

makes it possible to make turbines this size.

Vestas is increasingly using composite materials and has a

low-weight-design philosophy. In March, Vestas teamed up with U.S.

aerospace company Boeing for projects in areas such as aerodynamics and

composite-materials fabrication processes, design, and analysis.

But there are limits to how big these turbines can get. GE says

the grid’s ability to handle more powerful loads is one limiting

factor. And in the future, problems with transportation could limit the

size of new land-based turbines. Going around road corners and narrow

bridges with 50-yard blades is already a problem, and the only thing

that could alleviate that would be technology for making multiple-piece

blades. Offshore this transport problem doesn’t exist so the turbines

could be bigger there. GE thinks the size increase of the turbines will

plateau, but that won’t happen for a while.

“I think 70 meters (77 yards) was a pretty big rotor 10 years

ago. Today 110 is out there,” Reno said. “Can they grow another 30

meters (33 yards) in 10 years? I think it is possible.”

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