A new type of transmission technology uses a variable-speed rotor to maximize power capture. It also contains fewer parts than traditional technologies, which allows it to be built with a high-volume, low-cost assembly process.
The heart and soul of a wind turbine is its gearbox and drivetrain. Early turbines turned at a constant speed, regardless of how fast the wind was blowing, so the electrical generator could synchronize with the grid and deliver power to the grid smoothly. These wind turbines were simple and reliable, but sacrificed power generation capacity by turning the rotor at a less than efficient speed much of the time.
The next generation, which includes most of the turbines running today, allows the rotor to turn at different speeds as the wind speed varied, and then use power electronics to synchronize with the grid and deliver power.
“They get more power from the rotor, but are more complex and expensive, and give up some of the additional power from the rotor as a result of losses in the electronics,” says John Langdon, CEO of Viryd Technologies. “These turbines also use permanent magnet generators, which are expensive and require rare earth minerals that may be subject to supply issues in the future.”
Langdon has developed a new type of transmission technology that he claims is naturally suited to wind turbines. “The NuVinci is a simple but variable planetary gear, called a continuously variable planetary gear train, that allows the use of a variable-speed rotor to maximize power capture, but still can use an inexpensive generator synchronized directly to the grid,” Langdon point out.
“It is unique in that it has only about 1/10th the parts count of other variable transmission technologies, and can scale up to multi-megawatt class turbines simply by increasing the size of the drive elements,” adds Langdon. “It can also be made with relatively simple machining processes, such as those used to make precision ball bearings.”
The NuVinci transmission has no metal-to-metal contact within the device, because of the elastohydrodynamic fluid used. “Most parts are standard off-the-shelf items with known performance,” says Langdon. “Each custom part is designed so [that we can] adapt to lower-cost methods as volume grows.
“We are [also looking at using] composites to reduce weight and costs as unit volume grows,” explains Langdon. “We believe that rapidly moving down the learning curve, with an inherently simple design facilitated by the NuVinci transmission, will allow us to reach a lower cost of energy than any other wind turbine design.
Langdon and his colleagues have developed an 8-kilowatt turbine for the fast-growing small-wind market. “They are designed for mass production, but currently built in low volumes as we enter the market,” he points out. “Most of our design team has either automotive or aerospace backgrounds [the chief engineer previously worked for Ford Motor Co.], so their mindset is high-volume, low-cost, with very high conformance to quality standards. As our volume increases, we will continuously look for improvements that will improve the long-term cost of energy.”