THE AERIAL BALLET OF THE POWER KITES

Giant wind turbine blades rotating above fields or the sea will no longer generate much excitement in the future. But how about wind turbines that take off into the skies to dance at lofty heights? In the future, it’s hoped that these types of wind turbine will generate electricity at unbeatable prices. And if you believe the optimists, they could even supply up to 100 times more electricity and heat than we need today. [1]

THIS IS HOW AIRBORNE WIND TURBINES WORK

The principle that lies behind all these airborne wind turbines – be they structures resembling kites made of flexible materials, aeroplanes with rotors, or wind turbines in balloons – is that, unlike traditional wind turbines, they’re not mounted on towers. Their flying components, such as wings or balloons, move through the air, while remaining in contact with base stations by means of cable tethers.

The current prototypes generate power in two different ways. In most models, electricity is generated in pump cycles: first, using quick manoeuvres, the flying device is automatically steered to fly fast in a crosswind direction. The wind causes the tether of the flying device to become taut. More cable is then unrolled by the rotation of a cable drum attached to the ground. The cable drum is connected to a generator, which converts into electrical energy the rotating motion of the cable drum. This is called the traction phase. Once the balloon or power kite has reached a certain height, the flying device is manoeuvred into the wind. In the next phase, the cable tether is rolled back, which causes the drum that’s connected to the generator to function like a winch. The retraction process consumes part of the previously generated energy. For this purpose, part of the energy is temporarily stored, for example by means of flywheels or rechargeable batteries.

In other types of systems, small fast-spinning wind turbines attached to the flying device generate electricity in the air, and this is then transmitted to the base station via the tether. At the base station, the energy is either fed into the power grid or stored in batteries.

But what are the advantages of these new technologies over conventional wind turbines? And what challenges do they bring? Our pros and cons:

AIRBORNE WIND POWER – WHAT SPEAKS FOR THE NEW TURBINES

1. Turbo-generators: Airborne wind turbines use the wind where it’s stronger and more stable, namely at altitudes of 300 to 500 metres. Just to put this in context: tower-mounted wind turbines operating offshore harvest wind at around 200 metres. As a result, the electricity yield from airborne wind power is consistently greater.

2. Money-savers: Energy experts estimate that, compared to ordinary wind turbines, airborne wind energy can lead to significantly lower electricity costs. A 2013 study by researchers from the Fraunhofer Institute for Wind Energy Systems (IWES) even assumes that, at two to four eurocent per kilowatt hour, airborne wind energy will eventually be cheaper than all other known options of energy generation.

3. Quiet operators: Conventional wind turbines whirr, cast shadows and are impossible to overlook. Basically, they disturb the residents living in their vicinity. Airborne wind turbines spin around at much higher altitudes. And are therefore less audible – and almost invisible.

4. Environmental saviours: Airborne wind turbines have less impact on ecosystems than traditional wind turbines, for instance, because they require smaller foundations. They’re also less of a hazard to birds – and to insects, which are threatened by conventional wind turbines, as a recent study (2019) by the German Aerospace Center (DLR) concluded.

5. Resource-savers: Only about ten percent of the material needed for tower-mounted wind turbines is required for the production of airborne wind turbines. [2] That’s because the developers rely on smaller rotor blades – and because tower and foundation are more or less completely redundant and replaced by tethers. In addition, the components are easier to transport than the frequently huge tower segments, blades or machine cabins of conventional wind turbines.

6. All-rounders: Airborne wind turbines can be used in many locations that are not suitable for conventional wind turbines. Even in disaster regions, airborne wind turbines could quickly provide electricity and heat. Just like Kitepower, a spin-off from Delft University of Technology, which equips its power plants with inflatable and flexible membrane wings that are ideal for mobile use. Read more here.

WHAT NEEDS TO HAPPEN BEFORE THIS NEW TYPE OF RENEWABLE-ENERGY POWER PLANT CAN TAKE OFF ON A GRAND SCALE

1. Danger of crashing to earth: Among the challenges researchers and developers will have to address in the future are improvements to the control systems and to the fully automatic steering in order to increase the reliability of the power unit, especially in stronger winds. This is necessary because the latter can lead to overloads during normal operation. Another requirement is finding the perfect mix of materials – light but still able to withstand both the enormous forces at windy heights and the icy conditions.

2. Collision course: Prior to the commissioning of airborne wind turbines, no-fly zones need to be established in the airspace surrounding them – analogous to those near nuclear power plants, for instance. This is necessary because of the risk of collision with aeroplanes, hot air balloons and other aircraft flying at altitudes above 100 metres.

3. It’s all still up in the air: At present, airborne wind power is still a technology for the future. Current commercial use: zero. Experts estimate that mass production may become possible – at the earliest – in five to ten years. But in the long run, a breakthrough is certainly possible. International research associations and start-ups are currently working on the development of prototypes that are already being tested in several countries. One showcase project is the airborne wind energy technology by the US-based company Makani. In August 2019, power kites capable of generating up to 600 kilowatts of electricity were launched for the first time from a floating platform in the North Sea. See more here:

SOURCES

[1] Archer, C. L., & Caldeira, K. (2009). Global assessment of high-altitude wind power. Energies, 2(2), 307–319. http://doi.org/10.3390/en20200307

[2] Blackman, C. (2009). High-altitude winds: The greatest source of concentrated energy on Earth. Retrieved on 25 May 2016, at http://news.stanford.edu/news/2009/june24/high-altitude-winds-062309.html