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Products & Applications Energy kites for green electricity

| Author/ Editor: Rainer Klose* / Erika Granath

The energy revolution is here. You can feel it, or more accurately see it, in the air. Light “kites” on thin ropes can now convert wind energy to electrical energy. They might even come to replace traditional wind turbines. At least if we’re to believe the Swiss startup Twing Tec that recently ran a successful test on a pilot plant with energy kites. Let’s look closer into how this slightly unusual method for generating electricity works.

The TwingTec prototype T 28 measures three meters between the wings.
The TwingTec prototype T 28 measures three meters between the wings.
(Source: TwingTech)

Flying a kite is a fun way of spending a windy summer or spring afternoon. However, kites can be more than just a hobby to spend your leisure time on. Rolf Luchsinger, CEO at the Empa spin-off Twin Tec, has proven that they can also be used to generate electricity. The startup is one of the first companies in the world to develop air wind power plants.

How to generate wind with a kite

The wind is up to eight times more powerful 500 meters above the ground than it is 120 meters up. Capitalizing on the strong wind half a kilometer up in the air is the main idea behind Twin Tec’s wind kite project. Since building 500 meters tall wind towers isn’t a sufficient solution, the startup started to look into other possibilities to generate wind at that altitude instead. The solution they came up with was kites.

The Twing Tec uses the power of the wind to rise up in circular movements and then pulls a rope in a pulley system. A generator that generates electricity is connected to the axis of the pulley. In a nutshell, this mechanism is what makes the Twing Tec generate electric power out of wind power.

When the kite’s rope has been unwound, the kite sinks back towards the launching platform. Then, when the rope has been wound up, the kite scents again.

"The big challenge is not flying the kite. The problem is automated take-off and landing," says Luchsinger.

“After all, our goal is that the kite power plant should generate electricity without a human touch”.

Successful test flight with no human involvement

The wind kites first test flight was carried out on a power plant in Chasseral in western Switzerland in late 2018. The T 28 prototype with its three-meter wingspan started from the base vehicle and spiraled upwards. There it circled autonomously in the air for 30 minutes, produced electrical energy, and finally landed safely again on the launch platform.

In the next phase, the goal is that the kite should generate electricity for consumers. Luchsinger's team is currently working on the T 29 prototype, which is scheduled to make its first flights at the Chasseral later this year. T 29 will not only take off and land automatically, it will also generate up to 10 kW of electrical power and feed it into the grid.

Wind Energy 2.0 launching from above.
Wind Energy 2.0 launching from above.
(Source: TwingTech)

The test carried out with T 29 so far has been successful, so successful that a slightly modified version of the kite will be put into series production soon. The modified kite, named TT100, will have a 15-meters wingspan and start from a shipping container. TT100 should be able to both take off and land automatically and is calculated to generate up to 100 kW–enough for 60 single-family homes.

Why kites belong over the ocean

If you’re living in a crowded city, you’re not likely to see a wind kite from your window any time soon.

"We are talking to mines, remote settlements, and islands. These areas are our potential customers," says Luchsinger. He continues:

"Diesel generators that generate exhaust gases and noise and whose fuel has to be delivered at great expense are still used in most of these areas today."

Automated kites could save diesel and take over the entire energy production in these areas in the future.

The energy kite project

The wind kites didn’t take off without problem in the beginning, metaphorically speaking. The research team behind the kites have been working hard to move the project forward. The journey between the first sketch of the kite and its first produced kilowatt hour was bumpy. Early prototypes had a construction more inspired by kite surfing than kites. At one stage, the kite was attached to the platform underneath by several ropes.

However, this design was soon discarded. By start and landing, the Twing Tec kite uses small rotors, similar to those on drones. The startup has filed a patent application for the kite’s take-off and landing technology, which has been granted in several countries.

Putting Twing Tec’s kite into series production is a costly project. The T 29 prototype is supported by the Swiss Federal Office of Energy (SFOE). However, Twing Tec is still looking for private investors and partners from the energy industry for the subsequent commercialization phase.

The video shows Twing Tec test flight in 2018:

This article was first published in German by Elektronikpraxis.

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