Researchers have discovered that two tiny, counter-rotating wind turbines working in tandem can generate 37% more power than a single turbine alone.
This finding could unlock more efficient ways to provide decentralized power, from remote environmental sensors to personal electronic devices.
While most people associate wind power with towering turbines, a team of researchers led by Shuo Zhang has been focusing on the potential of micro wind turbines, those with a diameter of less than 200 millimeters.
These diminutive powerhouses are critical for a world increasingly reliant on remote technology, from environmental sensors monitoring climate change in the Arctic to Internet of Things (IoT) devices powering smart agriculture.
However, their small size has traditionally meant lower aerodynamic efficiency and a higher cost per kilowatt, limiting their widespread adoption.
Harnessing hidden “twist” advantage
The team’s investigation into the interaction between pairs of these small turbines has yielded promising results for maximizing their energy-harvesting capabilities.
Using a sophisticated technique called stereoscopic particle image velocimetry—a 3D mapping method that uses lasers and tracer particles to visualize airflow—the team analyzed the wake created by the front turbine.
Using advanced imaging techniques, the scientists analyzed the turbulent airflows, or wakes, created by a micro wind turbine. They found that this wake still contains a significant amount of rotargy that is typically lost.
However, by placing a second, counter-rotating turbine directly behind the first at a distance of 12 radii, this rotational energy can be captured and converted into additional electricity.
“Surprisingly, the counter-rotating arrangement consistently outperforms the co-rotating one — even at short distances, where wakes are highly turbulent and energy recovery is challenging,” said Michaël Pereira, an author on the study.
The key to this enhanced performance lies in the unique physics of smaller turbines. Operating at lower speeds and with higher torque, they impart a distinct “twist” to the wind that a specially designed downstream partner can harness.
Providing resilient power for critical infrastructure
This breakthrough offers a new perspective on designing compact wind energy systems.
“It suggests that, much like multi-stage turbines in jet engines, micro wind turbines could benefit from tailored downstream designs — harvesting not only the wind’s push, but also its twist,” concluded Pereira.
The researchers hope their findings will spur further innovation in micro-scale renewable energy, making it a more viable option for a wide range of applications disconnected from a traditional power grid.
Micro-turbine systems enhanced with this tandem design could provide resilient power for critical infrastructure, off-grid communities, and mobile applications, such as charging stations for drones or field robotics.
“This study provides an experimental foundation that guides in designing an optimized system in terms of tip-speed ratios of the rotors and the distance between them,” concluded the study.
The study has been published in the Journal of Renewable and Sustainable Energy.