Innovators around the globe are working on prototype airborne wind turbines to bring high-altitude energy down to earth. R&D concepts range from little airplanes flying in circles to tethered aerostats or kites. “The technology has attractive features that are sufficiently compelling, it makes sense to continue to investigate it,” says Fort Felker, director at the National Renewable Energy Laboratory (NREL). “The challenges are huge, but the potential is immense.” And with a much higher premium on lightweight design, components like the blades and frame will use advanced composites.

Airborne turbines over land-based windmills

High-altitude winds have the necessary power density, consistency and geographic availability to potentially become a predominant renewable energy resource of the future. Scientists estimate that energy in the jet streams are 100 times the amount of power used worldwide annually. What’s more attractive is that the winds are stronger and steadier the higher you go. Consequently, airborne systems can be built smaller, more lightweight and cheaper than fixed-bottom turbines on the ground. It’s much more economical to deploy flying turbines on a lightweight tether that transmits the electricity back to the ground than installing an enormous cantilever steel tower that needs to be drilled into land or the sea floor. Those savings can bring the cost of high-altitude wind energy down to be competitive with the grid.

Airborne turbines can also be deployed over challenging, complex terrain without roads, over rocky ridges or offshore, opening up new territories for harvesting clean energy. For now, high-altitude wind companies are focusing on the playing field below 2,000 feet, where winds are still up to 2.5 times stronger than where traditional land-based windmills can reach. Complex federal airspace restrictions kick in above 2,000 feet.

Unprecedented yet challenging characteristics

Before larger-scale deployment of airborne wind turbines comes within reach, the industry has to overcome major challenges. “Systems would need to be manufactured in quantity at a low enough capital cost to make them attractive to investors,” Felker says. He predicts a large use of advanced composites in future airborne systems for the “fantastically good fatigue characteristics.”

The bigger challenge is operational. How do you keep an airborne system flying autonomously 24/7 for months upon months, even decades? “No one has demonstrated a flight vehicle operating continuously even for a day, much less 20 years, which is about the lifespan of a land-based wind turbine,” says Felker. It will take time to accumulate sufficient operational experience to understand how wind energy companies will insure sufficient reliability. The wind energy expert speculates we are probably 10 years away from significant deployments.