A radical concept developed by a Swiss firm has upended the popular understanding that capturing wind energy for electricity generation requires tall wind turbines with huge blades erected on land or at sea. TwingTec, a spin-off from the Swiss Federal Laboratories for Materials Science and Technology (Empa), has developed an airborne wind energy (AWE) system that works similar to flying a kite. The core part of this system is an airplane-like drone that has a vertical propeller embedded in each of its two broad wings. The drone is further tethered to a mobile power generator using a pulley-and-cable system. It operates at an altitude of up to 500 meters, taking advantage of the increase in wind strength that correlates to the increase in height above the surface of the Earth.
The impetus behind the development of AWE systems is the desire to bypass the costs and challenges of building gigantic horizontal-axis wind turbines. Their designs thus forego tower construction and yaw mechanism for harvesting winds as well as slip rings for power generation. In the case of TwingTec, the company’s concept is to use gliders and drones pulled by cables to capture wind energy. The idea, also called “tethered wings,” is very similar to flying a kite. First, the drone lifts off into the sky and reaches its operating altitude. Once there, the drone shuts off its propellers and flies in a figure-of-eight pattern. As it does this, mechanical energy is created by the pulling of the cable that is connected to the drone. The power generator then converts the energy into electricity for consumption.
Compared with conventional wind turbines, AWE systems have notable competitive advantages such as lower cost and less space taken up by equipment. AWE systems also appear to be more convenient when it comes to deployment because they do not have to be permanent installations on the ground (i.e. drones can be launched from base vehicles). However, there are some rather tricky challenges in putting the concept of tethered wings into practice. TwingTec’s drones are intended to operate between the altitudes of 120 and 500 meters. Wind power is approximately eight times greater at 500 meters than at 120 meters. The drones therefore have to be agile and durable enough to hover above relatively moderate winds and below severely strong winds, all the while being tied to the generator on the ground.
Rolf Luchsinger, CEO of TwingTec, said that the biggest challenge is not flying the drone but launching and landing it autonomously. To become a viable alternative to wind turbines, “kite power stations” like the ones that his company is developing need to be unmanned as well during their operation.
TwingTec has already developed several models of AWE systems. The prototype of its upcoming flagship product, the TT100, was first introduced in 2017. With a wingspan of 15 meters, the TT100 is launched from the top of a shipping container that has been turned into a mobile power generator. The drone can climb up to 300 meters to take advantage of strong winds. After reaching that height, it glides up and down at high speed, pulling its cable and producing energy. When the cable is extended to its maximum length, the drone slowly descends and lands on top of the container. The whole process, which does not involve any human operators, is then repeated. The maximum generation capacity of the TT100 is 100 kilowatts, or enough to satisfy the electricity demand of 60 single-family homes.
TwingTec is also developing solutions featuring smaller drones. However, the company’s engineers for a while were unable to get their scaled-down models to land autonomously. Breakthroughs finally came in 2018 with the T28, a fully autonomous model with a wingspan of just 3 meters. The T28 already completed a field test during which it circled in the sky for 30 minutes before making a safe landing. Buoyed by the successful trial of the T28, Luchsinger’s team is now working on the next model T29, which serves as a utility-based solution. Not only can the T29 take off and land by itself, but its 10-kilowatt generator can also feed power directly into the grid. The trial for the T29 is scheduled to take place this November.
Additionally, TwingTec is considering developing an offshore AWE solution that involves launching wind-harvesting drones from floating platforms. Luchsinger pointed out that the advantages of the offshore environment, such as plenty of unoccupied space and stronger winds, apply to both wind turbines and his company’s kite power stations.
However, Luchsinger noted that AWE technologies are probably not going to be deployed in densely populated areas because of public safety issues. Remote and off-grid communities including rural villages, mining towns, and island settlements stand to benefit a lot more from TwingTec’s solutions. These places can reduce their reliance on diesel generators by adopting AWE, thereby reducing air pollution and carbon emissions while saving on fuel transportation costs.
Going forward, TwingTec still has to overcome numerous obstacles as it pursues commercialization of its solutions. For one thing, the company has to further improve and guarantee the safety of its equipment. It autonomous drones, in particular, must be durable enough to fly in heavy winds and smart enough to avoid ground or mid-air collisions.
(This article is an English translation of news content provided by EnergyTrend’s media partner TechNews. The first photo at the top of the article shows TwingTec’s CEO Rolf Luchsinger alongside the T29, a prototype of wind-harvesting drones that are being developed by his company. Credits for all photos and images in the article go to Empa and TwingTec.)