July 31, 2012
Vertical Wind Turbines May Boost Offshore Power
Brett Smith for redOrbit.com - Your Universe Online
A once-promising wind turbine prospect is getting a second look as engineers attempt to refine the technology for use in offshore power generation.
Modern wind power is primarily generated by horizontal axis wind turbines (HAWT), but in the 1970s and 80s, during the early stages of wind power technology, another design was actively pursued because of its simplicity and reliability. Vertical axis wind turbines (VAWT), which have blades that spin parallel to the ground, were compared favorably to their traditional-looking counterparts, until problems with VAWTs became apparent when both designs were scaled up for industrial use.
However, researchers at Sandia National Laboratories are exploring the previously abandoned technology as a way to solve some of the challenges facing offshore wind turbines. The economics of offshore wind power make VAWTs an attractive proposition because of three characteristics: a low turbine center of gravity, less mechanical complexity, and the attractive costs of scaling the technology up to larger sizes.
VAWTs lower center of gravity makes them an attractive choice for offshore turbines that would float, compared to HAWTs that must be anchored to solid bedrock. Additionally, floating VAWTs would have a drivetrain at or near the surface, facilitating turbine maintenance along with fewer parts, lower fatigue loads, and reduced overall costs.
"VAWTs are elegant in terms of their mechanical simplicity," said Josh Paquette, one of Sandia's two main researchers on the project. "They have fewer parts because they don't need a control system to point them toward the blowing wind to generate power."
The financial costs of large-scale VAWTs would also make them an attractive option because the bigger turbine´s pricy blades could be offset by a greater energy production.
Sandia, a public-private partnership, is banking on the five-year, $4.1 million Department of Energy (DOE) funded research project to return substantial advancements in VAWT and other wind turbine technology.
However, several problems surround the development of VAWTs as the next generation of offshore wind power technology.
VAWT blades currently require a complex manufacturing process, which calls out for refined, innovative engineering solutions. Matt Barone, the project's other main researcher, said Sandia´s partners at Iowa State University and TPI Composites plan to refine new techniques and lower the manufacturing costs associated with making the geometrically intricate blade shapes on a massive scale.
The new turbines must also solve problems with stresses their unique design place on its drivetrain. While HAWTs maintain a constant torque in a steady breeze, VAWTs have two "beats" of torque: one for the upwind position and one for the downwind position. This "torque ripple" places an unsteady load on the drivetrain, which causes increased wear and tear.
To solve this problem, Sandia researchers plan to evaluate new rotor designs that will compress the wildly swinging torque amplitudes into a smooth and steady force on the drivetrain.
The wind energy program will have two main phases. A design phase will take place over two years and will revolve around identifying a single, most-workable model. The second phase will focus on building and testing the chosen design over three years.
According to the project officials, how VAWT technology will be developed and implemented will depend less on technological capability and more on economic reality.
"Ultimately it's all about the cost of energy. All these decisions need to lead to a design that's efficient and economically viable," said Paquette.