Wind turbine vendors vigorously pursue intellectual property (IP) advantages in technology and ruthlessly defend them to maintain an edge over their competitors. The 2010 clash between GE and Mitsubishi over low-voltage ride-through and variable speed operation reportedly caused Mitsubishi to start sweeping its cavernous exhibit booth at trade shows, on the lookout for electronic surveillance devices planted by rivals. In another example, IP battles between Kenetech and German supplier ENERCON—the world’s third-largest wind turbine vendor by market share in 2013—resulted in ENERCON abandoning the U.S. market entirely.
One of the latest patent fights to spill into the headlines is between ENERCON and Siemens, over so-called de-rated operation. Who will win this round is anyone’s guess, but it’s another example of the rapidly advancing technology that continues to improve the performance, efficiency, and grid-friendly capabilities of wind turbines.
Slowdown, Not Shutdown
De-rated operation is the ability of a wind turbine or an entire wind plant to operate below its maximum capacity during times of high wind speed. Traditionally, when wind turbines reach their thresholds for maximum wind speed (around the 25 meter per second range), they will enter a cut-out and shutdown mode to protect the rotor, tower, and drivetrain from damaging stress. However, this process takes the electricity production offline, which can destabilize the broader power grid. As the commercial-scale deployment of wind turbines increases, this becomes a larger concern. De-rating uses a range of control methods, from pitch control of blades to generator torque control to operate a wind turbine at below its maximum capacity.
For example, instead of a 2 MW wind turbine shutting off once it encounters its threshold cut-off wind speed parameters, it can reduce its output to (for example) 50% capacity, or 1 MW. This ensures that the wind plant remains operational, balancing the grid, and that kilowatt-hours continue to be produced instead of lost due to a full shutdown. There are also economic inefficiencies associated with stopping and restarting wind turbines that can be avoided by running at reduced load. This approach can be used to continue the operation and revenue generation of a wind turbine that is experiencing high operating temperatures within the turbine drivetrain, which can trip a control system that shuts everything down to prevent damage to the turbine. De-rating can allow power production to continue while temperatures are reduced to acceptable levels without entirely shutting the turbine down.
ENERCON named its system Storm control; Siemens calls its system High Wind Ride Through (HWRT). GE Energy—likely as a way to avoid a similar IP battle with ENERCON—uses a de-rating approach that collectively de-rates all of the wind turbines at a wind plant. Spain’s Gamesa fought a 3-year battle to invalidate ENERCON’s patent, but lost in February 2014. Other vendors currently have or are bringing to market similar strategies—and all are certainly watching this patent fight closely from the sidelines.