A rising number of businesses believe that employing tethered kites and drones to harness the stronger and more consistent high-altitude winds is a realistic option. Will this technology allow wind power to reach its full potential, or will it always be a niche solution?
According to latest estimates from the US Energy Information Administration, wind power generated five times more electricity in 2018 than it did in 2008.
Despite this, it only produces roughly 4% of the world’s electricity.
The fact that the wind does not always blow – the intermittency problem – is cited by critics as rendering this type of renewable energy unreliable.
Winds are stronger and more steady at higher elevations, such as above 500 metres (1,640 feet). High-altitude winds alone might provide 100 times the global energy demand, according to a groundbreaking 2012 analysis from California’s Lawrence Livermore National Laboratory.
“In order to access winds at high altitude, wind turbines have been getting bigger and bigger,” explains Udo Zillmann of trade group Airborne Wind Europe. “However, this necessitates the construction of massive, expensive structures.”
As a result, he claims, high-tech drones and kites are increasingly recognised as low-cost additions.
“Airborne wind energy is a simplified form of a turbine, with only the essential components: a blade and a tether with a diameter of a few centimetres,” he adds.
“These devices consume between 1% and 10% of the resources used to build a turbine and can also be grounded if necessary, such as to allow migrating birds to pass through.”
One of the companies working in the high-altitude wind space is Makani, which is owned by Google’s parent company Alphabet.
Its massive prototype kite is tethered to the ground and controlled by flying processors that utilise GPS and other sensors to guide it in loops.
Rotors on the 26m (85ft) wing spin in the wind as the kite completes its loops, generating generators that provide electricity for the grid.Makani started testing its current version in 2015, which is capable of producing up to 600 kilowatts of electricity, enough to power around 300 households.
It is also going to test a new offshore system installed on floating buoys in collaboration with oil giant Shell.Fort Felker, the company’s CEO, states, “We plan to install Makani’s kite on a small spar buoy tied with a synthetic line and gravity anchor.”
“Makani’s kites are 90 percent lighter than turbines with equal power ratings, making this conceivable. It’s a technical challenge that I’m looking forward to taking on.”
Given that certain energy-capturing kites or drones can reach 600 metres in each direction, flying them offshore makes sense from a regulatory standpoint.
“To operate even one gadget, you need a large area,” Mr Zillmann explains, “which is one reason many enterprises are moving offshore.”However, a number of firms are researching on ways to employ drones that generate wind power over land.
Start-up in Switzerland Skypull, for example, has built an autonomous drone that can fly up to 600 metres, which is almost three times the height of a typical wind turbine.Its current prototype is a multi-copter “box-wing” drone with solid wings that can take off and land without the use of a launcher or ground wind.
The take-off is battery-powered, but the battery is replenished every time the kite loops back down to the ground while it’s in the air.
“Once the drone has climbed to operating height, it switches to kite mode by turning 90 degrees from upright and generating traction on the rope, which is hooked to a winch linked to a generator,” explains Skypull CEO Nicola Mona.
“It’s a mechanism that allows us to fly anywhere between 200 and 600 metres above the ground.”
Mr Mona admits that initial use would likely be confined to smaller projects, but he believes the Skypull technology will one day be utilised to fulfil large-scale energy demands.
“I envisage our technology being used for remote off-grid systems, including as mining operations and disaster relief initiatives, in the mid-term,” he says.
“However, in the long run, I envision larger wind farms capable of generating up to 100MW [megawatts] of power.”
Altaeros Energies, a Massachusetts-based technology startup that received financing from Mitsubishi Heavy Industries in 2015, is another onshore high-altitude wind player.