Justin Martino, Associate Editor, Power Engineering
April 02, 2014 | 7 Comments
Tulsa, OK -- Wind power capacity has increased dramatically in the U.S. recently — and accompanying that, the turbines that produce it have become more powerful, more efficient and more affordable for power producers.
"If you go back 10 years ago and look at wind power and then look at where is today, it's just dramatically different," said Keith Longtin, wind products general manager at General Electric.
Those differences come in many different areas — rotors, controls, electronics and gearboxes — but the advancing technology used in wind power production have always aimed for the same goal: making wind power a better choice for power generation.
Breakthroughs in control technology has allowed GE to use a 120-meter rotor on its GE 2.5-120 turbine, the company's largest. Photo credit: GE
While a previous focus of the industry was increasing the total nameplate capacity of wind turbines, the focus has shifted to the capacity factor of the turbine, which helps keeps energy cost low by providing the most possible power.
"That is really the direction we're going," Longtin said. "If you go back 10 years ago, the turbine was at about 25 percent capacity factor. Today, it's over 50 percent. As we've improved the capacity factors and improved the cost of energy, that enables us to go into more and more locations where the wind is lower."
One of the deciding forces so far for increasing capacity factors has been an increase in the size of the rotors used on wind turbines. Longtin said GE's predominant turbine in the U.S., which has a 1.6 MW capacity, currently comes with a 100-meter rotor, compared to a 70-meter rotor in the past.
Increasing the size of the turbine rotors creates new challenges for manufacturers, however. Longtin said rotors scale poorly with size, so the cost can go up faster than the revenue generated by the increased capacity factor.
Turbine rotors are affected by two different forces: torque, which turns the rotors and creates energy, and thrust, which pushes against the turbine. Dealing with thrust can be difficult when designing a rotor.
"The thrust is equivalent to five F-18 engines just trying to pull it over," Longtin said. "There are tremendous loads of forces up there, and so it goes to great engineering technology to be able to create these very reliable turbines."
Breakthroughs on turbine controls led to being able to handle the additional thrust generated by wind, Longtin said. He compared the controls used on turbines to anti-lock braking systems on cars, saying the way the turbine is controlled and shut down, along with how it responds to wind gusts, allows for a bigger rotor on a turbine.
Alstom has made similar changes in the size of rotors for its platforms. The company took its eco100, a 3-MW turbine with a 100 meter rotor, and upgraded it to a 110-meter rotor in 2010. Last year, the company increased that to a 122-meter rotor.
"We were able to increase by nearly 40 percent the area of the rotor in less than five years," said Albert Fisas-Camanes, Director of Innovation for Alstom Wind North America. "That lets us deliver a more efficient wind turbine to our customers. When you increase the area of the rotor, you are able to get more energy at lower wind speed."
While the focus on increasing the power produced from wind turbines may be on the capacity factor, another way is to make sure wind turbines are operational and available. Longtin said GE has made major strides int hat area in the past 10 years.
"The availability of wind turbines 10 years ago was about 80 to 85 percent," he said. "And the wind industry was OK with that because before that they were available 70 percent. We took a power generation mindset to it and said 98 percent is what we do. That's what gas turbines run at, that's what nuclear plants run at, that's what steam turbines run at, so that's what we're going to do. We've made lots of investments to improve the overall availability of a wind turbine so that today we have 22,000 wind turbines with an average production-based availability around 98 percent."
To help achieve that sort of industry reliability - and to continue improving on it - Longtin said the company has worked to improve the individual components used in turbines, both electronics and gearboxes.
For gearboxes, GE has combined the manufacturing processes and design processes so they're designing components that can be reliably manufactured. In addition, the company does highly accelerated lifetime testing on all its gearbox designs to validate the design on all new gearboxes.
Longtin said the company is looking at the manufacturing of the parts used in the gearbox. GE is looking at ways to harden gears as well as different types of bearings and bearings configuration.
"Gearbox reliability is something we're incredibly focused on," he said. "There's a lot of work that goes into trying to maximize that reliability."
In the future, Longtin said the company will also focus on how to minimize the downtime when a gearbox does have a mechanical failure.
"We're trying to make our gearboxes so if a problem occurs, we're able to service that uptower as opposed to bring a crane in and replace the whole thing," he said. "That is probably one of the best things we can do."
Challenges in Offshore Production
While the onshore wind turbine industry is going strong, the U.S. is looking toward the possibility of adding offshore wind capacity in the future. Alstom recently signed a contract with Deepwater Wind to supply turbines for the 30-MW Block Island Wind Farm three miles off the coat of Rhode Island, and the company is also part of Dominion Virginia Power's Virginia Offshore Wind Technology Advancement Project, which was one of seven picked by the U.S. Department of Energy's advanced technology demonstration projects.