Along the northern coasts of Germany, wind turbines speckle the landscape, capitalizing on the flat, breezy countryside to generate renewable energy.
But this region is far from the country’s industrial core, so the energy created here has to be transported across a great distance—an inefficient process. In contrast, the hilly Swabian Alps, which enjoy plenty of wind, directly border Germany’s industrial core. You might think this would be the ideal place for Germany’s wind energy installations. The problem here is that wind turbines work optimally when the breeze blows horizontally. And entrepreneurs worry that the wind turbulence created by the region’s undulating hills could kibosh the efficiency, and thus the success, of new wind energy installations.
Here’s where drones equipped with turbulence sensors can help. These drones have the ability to scout out spots where the wind blows strongly and horizontally enough for turbines to be practical.
Satellites don’t have the spatial or temporal resolution to measure this turbulence. And human-piloted aircraft are expensive and can’t always fly low and often enough to acquire the necessary data, explains the University of Tübingen’s Jens Bange, a meteorologist and physicist who has been using unmanned aerial vehicles (UAVs) to study turbulence since 2002.
In addition to scouting out new sites for wind parks, Bange is also looking at the turbulence created by the spinning blades themselves—even on optimal, flat terrain. “A wind turbine creates wakes and eddies that interfere with the operation of other turbines,” he says. “The second row of turbines in any wind park produces significantly less power compared with the first.”
Furthermore, as wind turbine blades get increasingly longer—now, upward of 50 meters—the turbulence produced by a spinning blade can bend it, cutting its lifetime short.
Turbulence data provided by drones can help turbine engineers develop solutions, such as flaps on rotor blades, to minimize this bending, Bange says.
To do their measurements, Bange and his team often use small, fixed-wing drones equipped with a tiny device called a five-hole probe, through which air can pass. Air pressure sensors at the entryway of the five holes can be used as a proxy to measure the turbulence. The relatively light drones—often weighing about 5 kg—that Bange’s group uses to study wind parks were helpful in initially convincing companies that the machines were safe to fly near turbines. “It’s easier to get permission to fly at a wind park when the UAV is not heavier than a fat seagull,” Bange says.
But as UAV-based measurements have proven their worth, larger drones are also being equipped to do wind park studies. For example, a team of researchers led by Jan Denzel and Dominique Bergmann at the University of Stuttgart has used larger 60-kg helicopter drones equipped with lidar to study the turbulence near wind turbines. Lidar, a laser-based version of radar, helps the drones detect aerosol particles in the air. Turbulence is measured by the changes in laser light reflection as the aerosols twist and turn in the wind.
Given that drones disrupt the air as they fly, researchers have had to develop techniques to subtract the wind patterns produced by the devices’ own flight from the natural turbulence of the air. But with this challenge met, these tiny flying robots are helping expand the places wind turbines can operate and improving the steady spin of their blades.