The development of new and larger capacity wind farms in the US sets up a likely conflict between the developers and the US Department of Defense. The large, utility-scale wind turbines that tower some 400 feet from the ground produce interference with military and civilian radar installations.

In a recent incident, the DoD slapped an eleventh-hour stop to a 338-turbine wind farm in Oregon because the department was concerned about interference with long-range surveillance radar. The ban was eventually lifted on the $2 billion project following a study that identified work-arounds to the interference.

As The New York Times reports , there is not yet a single solution to the conflict between wind turbines and radar. Every prospective wind farm is evaluated as if it were the first one the DoD had ever been faced with.

The issue with wind turbines is not new, and is summarized nicely in a DoD report from 2006 called “The Effect of Windmill Farms on Military Readiness”:

“The significant physical size of the turbine blades results in a substantial [radar cross section] target irrespective of whether the blades are viewed face on or edge on by a radar. The tip velocities for these blades fall within a speed range applicable to aircraft. Consequently, the turbine blades will appear to a radar as a ‘moving’ target of significant size if they are within the radar line of sight.”

In other words, the turbine blades spin at speeds that closely approximate an aircraft, and the size of the radar image indicates that the object is somewhat larger than a 747. Military radar, much of which still uses analog signal processors, cannot easily or reliably sort out the turbines from potential bad guys.

Part of the solution lies in technological improvements. Advanced digital signal processors can more easily screen out the clutter caused by wind turbines. Like all things technological, this will cost serious money because most military and civilian radar systems still use analog processors and are decades old.

A simpler, and cheaper, part of the solution rests in the review process for wind farms. Under current regulations, a developer need give the FAA, and by extension the DoD, just 30 days notice before the beginning of construction. As with the Oregon wind farm, if the FAA/DoD review determines that there’s a problem, the agency has no choice but to stop the project. No one is happy with that solution.

To avoid last minute delays or stoppages on new wind farms, the DoD has proposed that the agency get involved earlier and formulate a process that is streamlined and transparent enough to handle the variety of wind farms that are being proposed.

The good news is that there are ways to mitigate wind turbine interference with radar. The bad news is that it’s not cheap.

Paul Ausick

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