Go figure: how a high-altitude drone could be the future of wind power

AmpyxPower is taking inspiration from water-skiers and drones in a project to harness the power of high-altitude wind for energy. Currently a start-up, how close are they to bringing airborne wind power to the world’s energy mix?


The AP3 Protoype

In many ways, the story of Ampyx Power is a classic start-up tale, beginning with a flash of inspiration to reaching financial backing, via a stint in a university lab.

In 2004, while kite-flying at the beach, ex-astronaut and professor WubboOckels burned his hand on the tether of his kite. Struck by an idea, he returned to work at the University of Delft to investigate how the force created by a kite could be harnessed to make electricity. As research progressed, Richard Ruiterkamp - the eventual founder of Ampyx Power - joined the team, honing the technology from a kite-based to a fixed-wing product.

The team began to see the commercial viability of the technology they were developing, and eventually, Ampyx Power was spun out from the university in 2008.

The fastest route to wind energy

PowerPlane is a type of certified, fully autonomous aircraft attached to a power generator on the ground by a tether. As the plane flies in a figure of eight motion, taking advantage of crosswinds, it pulls on the tether; it is the tensile strength of the tether that creates power for the grounded generator.

"PowerPlanes are able to achieve significantly higher yields by flying across the wind"

The figure of eight motion is important. Much like a water-skier uses the side to side action to gather speed, PowerPlanes are able to achieve significantly higher yields by flying across the wind. The tether is reeled in as the plane descends, and out again as it rises.

The aircraft can fly up to 450m from the ground, and is deployed and put away autonomously, using complex sensors to inform the autopilot of conditions.

A potential game-changer

"We are set to disrupt the energy market," says the director of Ampyx Power, WolbertAllaart. "In the future, our Ampyx Power parks will provide abundant renewable energy at market utility scale, at cost levels below any other method of electricity generation."

How can an emerging technology make such a claim? Founder of Ampyx Power, Richard Ruiterkamp, says it's all down the amount of materials required. Compared to a V-80 wind turbine, a PowerPlane designed to produce the same amount of energy, 2MW, requires just 8% of the material. The quality of the material is more expensive but this is significantly mitigated by the sheer overall reduction.

As the company and technology evolves, Ruiterkamp says that a firm price will be released and that it will be significantly cheaper than turbines, both for manufacture and installation. At the moment "a large part of the uncertainty comes from the inability to negotiate large volume deals in terms of raw materials", says Ruiterkamp.

"If you asked me for a gut feel, it should be completely possible to introduce our system at 30%-40% less, compared to the installation and capex costs of a wind turbine of the same power nameplate value."

This becomes all the more compelling when it comes to offshore wind. Ruiterkamp says, "Because offshore installation costs are even more staggering than onshore installation costs we have an even better economic proposition."

Not only are there savings to be made in capital expenditure, but the yield from PowerPlanes could be significantly more than turbines. Data collated by scientists at the Polytechnic University of Turin shows a significant increase in average wind speed as the distance from the ground increases. At 80m above ground, average wind speed was 4.6m per second (mps); at 800m the wind speed was 7.2mps.

Another reason for going higher is the constancy of high-altitude wind. This could combat the intermittency issue that plagues turbine generation.

A long way to go?

A commercial offering could be available as soon as 2018, but there is a long way to go yet. The team is part-way through the certification process with the European Aviation Safety Agency (EASA), after which it will need to begin proving that its models stack-up with reality.

Enter AP3, the biggest prototype yet. A wingspan of 12m produces around 250kW of energy, enough to supply 250 homes with electricity. Ampyx Power has finished the conceptual and preliminary design phase and is in the construction drawing stage. According to Ruiterkamp, the team expects to have two of these prototypes ready to fly by December.

"The commercial model, AP4, will have a wingspan of 30m-40m, producing 2MW."

AP3 will be used to demonstrate that the concept and prototype can be scaled up. The commercial model, AP4, will have a wingspan of 30m-40m, producing 2MW. This is enough to power 2,000 homes.

It is one thing to ensure the concept works technically, but another to prove the PowerPlane is safe for operation on a large-scale. Ruiterkamp says this is why the company is working with the EASA.

"One of the positive effects of doing the certifications process is that everything we do is safety driven," he says. "The payback of this is that our commercial PowerPlane will be on par with the safety of general aviation."

One thing you can say about traditional turbines is, they don't crash. So what happens if things go wrong? Ampyx Power says that, in the unlikely event of a tether break, the PowerPlane's automatic security mechanism allows the plane to land safely. However, this has not been tested in a space with multiple systems on-site, or other infrastructure surrounding it.

"Our first demonstration park will be in a secluded area so we can have a large influence on who is underneath that system," explains Ruiterkamp. "We will have to show the reliability through a large number of safe operational hours before people will actually believe us and trust it."

Another potential snagging point is the effect of PowerPlanes on the environment. Ampyx Power is actively partnering with environmental consultancies to carry out impact studies on noise, bird strikes, and flora and fauna.

In terms of noise, Ampyx theorises that levels will be relatively low; as the PowerPlanes fly twice as high as turbines, the noise being heard at ground level will be four times less. This is yet to be tested with full prototypes so we'll have to wait and see if the theory stacks up.

Material developments: An old idea made reality

Harnessing high-altitude crosswind isn't a new idea. In 1980, Miles L Loyd published a paper in the Journal of Energy describing the potential to harness the kinetic energy from kites on the crosswind. The major obstructions at the time were a lack of interest in renewable technologies and the availability of lightweight materials.

Ruiterkamp says that advancement in materials has made ideas conceived in the 1980s possible, which is why different types of airborne wind energy are being prototyped at the moment.

"What is funny is that what happens quite often with inventions is that they pop-up simultaneously in lots of different places at the same time," he says. "This is basically because the state of the art is sufficiently developed to spawn new ideas."

The kite fight

The ways in which different companies are making airborne wind energy a reality vary wildly. Two of the most prominent systems in development are the Makani and Altaeros BAT.

Along similar lines to Ampyx Power's PowerPlanes, Makani is a tethered kite-type system. However, it aims to operate like the tip of a turbine blade, the part which produces up to 70% of the energy. The kite flies in a circular motion, driving a generator which passes electricity down the tether to the ground. The Makani project was acquired by Google in 2013 and is still in development for commercial use.

Secondly, the Altaeros BAT, is an autonomous tethered airborne platform which lifts wind turbines up to 600m above ground. Blimp-like in appearance, the BAT uses helium to gain lift and is marketed as a good option for rural communities, although it is yet to be seen how scalable the technology is.

Little is known about the viability and timescales for commercial production of either of these technologies compared with the PowerPlane, and developments are shrouded in secrecy. Whoever makes it first will be a popular entrant to the market, whether they snaffle all the custom for themselves or blaze a trail for competitors to follow.

According to Ruiterkamp, "Commercial viability does not just mean that we are capable of building something, it means that this whole value chain needs to be addressed to show that this is a new technology that can survive in a competitive market."

The journey is ongoing and Ampyx Power is highly aware that commercial viability is not the holy grail, but convincing people to buy the system is. Persuading the public that the PowerPlane is both safe and practical is the next challenge.