New Control Approaches Could Deliver Commercial Energy-Harvesting Drones, Researchers Hope

Researchers at the University of Bristol's School of Civil, Aerospace and Design Engineering, working with colleagues at Universidad Carlos III de Madrid and specialist Kitemill, have received funding to push the technology behind Airborne Wind Energy Systems (AWES) — drones that harvest, rather than consume, energy.

"Airborne wind energy has enormous potential and is anticipated to generate €70 billion per year worth of electricity by 2050," says project lead Duc H. Nguyen, PhD, of the potential behind the team's work. "However it is still an emerging technology. In many cases, a trade-off has been made: new designs have been rapidly deployed for test flights before their flying characteristics are fully understood.

"This has prevented many AWES prototypes from achieving full capacity in operation, leading to early termination of the program and hindering commercialization. This project seeks to address this challenge through the use of bifurcation and continuation methods."

Traditionally, an airborne drone is an energy consumer — it draws power from batteries or an engine to keep it in the air and provide control over its movements. While there have been efforts to create self-sufficient drones — harvesting solar energy to keep themselves aloft, for example — an AWES goes a step further by producing excess energy that can be use elsewhere.

Current AWES designs use a fixed-wing drone, which is tethered to a ground station, flying at altitudes above the height of existing wind turbines. As the wind pulls the drone further away from the base station, the tether drives the generator to harvest the wind energy and convert it to electricity.

"AWES technology, with its exceptional material efficiency and higher energy yields, has the potential to become a dominant force in the energy industry," claims Kitemill co-founder and chief executive officer Thomas Hårklau, whose company claims that its AWES prototypes require less than 10 percent of the materials required for a similar-capacity wind turbine while delivering improved energy density.

There's a problem, though, and one which means that earlier attempts to create AWES using simpler devices like kites and parasails have struggled: the airborne part of the system needs to fly in complex patterns according to prevailing wind conditions, both to maximize the energy harvesting and to prevent an accident that would see it crashing to the ground.

"By replacing existing techniques with bifurcation methods," Nguyen explains of the project, referring to non-linear dynamics methods that can deliver more stable control over spin recovery and wing rock motion than rival approaches, "AWES can achieve significant cost savings and improved performance that will ultimately bring this technology closer to commercialization."

More information on the Kitemill system is available on the company website.