Innovative technology to harvest reliable wind power has the potential to really take off

In Sherman Island, California, a huge robotic kite tethered to a truck is flying in perfect circles some 500m up in the air.

From a distance, the scene is like an unusually unimaginative aerobatics display. But get closer and the expressions of those in charge of the spectacle as they crane their necks skyward and pore over monitoring screens inside the truck suggests anything but frivolity.

It’s test flight day for high altitude wind pioneers Makani Power. On today’s agenda: autonomous flight and power generation. Achieving this would be another noteworthy stride towards grabbing a sizeable chunk of the global wind turbine market (worth some $35bn last year and growing), and achieving technological dominance of an entirely new wind energy frontier.

Makani Power chief executive Corwin Hardham anticipates going to market in 2015 with the unveiling of a 1MW airborne wind turbine (AWT). This will use 80% less materials than its conventional, terrestrially rooted counterpart, and generate energy that is 40% cheaper (which is conservatively estimated to reach price parity with coal).

“There are two main challenges to wind power,” says Prof Ken Caldeira, a feted atmospheric scientist at Stanford University and a longstanding proponent of high altitude wind.

“Firstly, winds are inconsistent and intermittent, and secondly wind turbines cost a lot to produce and maintain. If you go higher off the ground, wind becomes both stronger and more consistent. The energy source is truly huge.”

Indeed winds typically double in power density at Makani Power’s chosen altitude of 500m.

High-altitude wind has been on the agenda of adventurous engineers since the 1970s. But while the resultant ideas have always piqued the imagination, the logistical realities have tended to scupper any realistic hope of reliable, scalable power generation.

In June, the US National Research Council published a report on renewable energy. This briefly acknowledged the possibilities of high-altitude wind power but essentially dismissed it as “pie in the sky” thinking that was at least a quarter of a century away.

“You need to basically convert some of the kinetic energy of the wind into lift to keep the device afloat, and you need to make the blades rotate,” says high altitude wind expert Cristina Archer, assistant professor of energy, meteorology, and environmental science at the department of geological and environmental science of California State University Chico.

“You need to design your device so it can sustain itself up in the air as well as generate electricity. This is a pretty interesting mechanical engineering challenge.”

Growing flock

Intriguingly, there is today an ever-growing band of companies intent on moving the debate forward. The Airborne Wind Energy Consortium was formed this year to promote research, development and deployment of airborne wind energy worldwide.

Names to watch include Joby Energy and its multi-wing structure of six square segments, each corner fixed with turbines, Ampyx Power with its Power Plane and Megenn’s blimp-like helium-filled Power Air Rotor System.

Makani Power, buoyed by a $15m investment from Google’s groundbreaking RE

Autonomous flight with power generation was demonstrated in 2007, and ramped up to a 30-hour test a year later. In 2009, the Makani Power team demonstrated autonomous flight on high-performance, rigid wings, and power generation was proven this year.

Other recent breakthroughs include a filed patent for a new tether design that significantly reduces weight and drag. While Hardham refuses to reveal any specifics, he is confident the design is “different to anything we’ve seen before”.

Within the next six months, a seventh wing prototype is scheduled to achieve the next milestone of autonomous launch-and-land with power generation at 20KW.

“We are the furthest along,” Hardham says. “To my knowledge, no one has demonstrated autonomous crosswind flight, particularly at the flight speeds that we have recently.”

So how does it all work?

The biggest internal intellectual property, according to Hardham, is a comprehensive mathematical model of the entire system.

“Our experience is that a wing will behave just as we expected in the model. This means you can optimise several different aspects of the design, and then be very confident what you are building is going to be a functional system that realises the objectives you’ve set,” Hardham says.

On the nuts-and-bolts side of things, the Makani system comprises a high performance rigid wing (the 1MW prototype will have a wing span of 35m) mounted with several small turbines and attached to a ground station via a high strength fibre jacket tether with an electrically conductive core.

The device is steered using the same physics as an aircraft under autonomous computer control. An onboard navigation system calculates the wing’s position and adjusts the control surfaces to vary heading and angle.

“The on-wing control system has evolved to the point where the wing can predict its position seconds into the future corresponding to a path deviation of less than a few metres,” Hardham explains.

If there’s a temporary lull in the wind, energy can be despatched up the tether to fly the system like a plane. For prolonged periods of stillness, the wing is landed via computer control to a perch on the ground.

Makani Power’s edge comes from an ability to sweep through high-density winds across an area nearly ten times greater than that of a similarly scaled wind turbine, a feat that enables electricity to be generated at much lower wind speeds. According to Makani Power’s studies, a conventional 1MW turbine reaches its rated power at wind speeds of 12 metres per second, whereas an AWT can achieve the same at 9m/s.

Tipping point

A crucial point is that the wing’s flight path mimics the movement of the tip of a conventional wind turbine, which is the most effective part (in some cases the final 25% of a terrestrial blade is responsible for 75% of the energy generated).

Hardham estimates that the system’s cost efficiency, lightweight form and ability to generate power beyond the reach of the conventional wind power industry will radically extend the developable terrestrial wind resource area. This means unlocking vast tracts of previously undevelopable lands such as dips and hollows. In the US alone this could potentially bring a remarkable 85% of the land surface into play. Such flexibility means a Makani Power system could even be co-sited with existing wind farms.

Nevertheless, the technology’s biggest potential is thought to be offshore.

“If we are to make a dramatic impact on global warming and climate change we need technological steps that are not incremental,” says Geoff Sharples, who previously worked in commercial operations at Clipper Windpower and as an energy investment expert at Google. He is currently working as an independent adviser to Makani Power on commercial issues.

“Makani represents a large stride forward – in many ways the endgame of a wind turbine: the least amount of material providing the most energy.”

Vibes and fresh bread

Makani HQ is a converted air traffic control tower on the former Alameda US Naval Air Station on the Oakland side of San Francisco Bay. There is a distinctly hip, familial 1990s Silicon Valley start-up vibe about the place. Everyone cycles to work, there’s kite-boarding equipment prominently in view, and the tower’s control room, now the company lounge, has microbrews on tap. Most lunchtimes, Hardham bakes fresh bread for the 14-strong team of scientists and engineers.

“Every one of our team is a rock star within their field,” says Makani Power co-founder Don Montague, adding that each is enviably blessed with both analytical and practical, prototype-building skills.

“You can go in there at 1am and they are still working, and it is all personally driven, not because some manager or anyone is cracking the whip. They are doing it for themselves, not because anybody is asking them to. They are passionate about solving this problem.”

Named after the Hawaiian word for breeze, Makani Power began life when Montague – a wind surfing and kite surfing professional who had branched out into the R&D and design of his own equipment – floated the idea of developing a “kite boat”.

Initially, the purpose was to draw people’s attention to the millennia-old potential of kites, but the ambition and focus dramatically shifted when Montague teamed up with polymathic inventor Saul Griffith and Hardham, a mechanical design expert.

Montague – who was well known among Silicon Valley’s adrenaline junkies – casually mentioned the idea of developing an autonomous, electricity generating kite system to Google’s top brass during a kite surfing trip. One formal pitch later, the fledgling company had a priceless financial vote of confidence from one of the biggest and most high-profile innovators on the planet.

“The founders of Google are just amazing people,” Montague enthuses. “Their approach is to seed a new technology, and support it. They don’t see it as a risk, just a technology that has a longer run.”

Hardham echoes the sentiment. “Google is led by some of the best minds I have ever encountered – they understood the opportunity before we even got there ourselves,” he recalls.

He admits that he was initially sceptical. Even when the preliminary analysis showed interesting results, “we had no idea that it was going to be as tractable as it seems to be. And not only does it look pretty damn doable, it looks like it’ll be game-changing once we get it to work.”