Which direction should we be looking for the next source of low-carbon energy?… and Kites!
It depends. Which story would you like?
By James Gaines September 2, 2025 in Anthropocene
There’s no telling how low or how high humanity will go in its quest for more energy. The deepest oil well to date, the Z-44 well in Sakhalin Island, Russia (just north of Japan), for example, reaches an astounding depth, drilling through more than 12 kilometers of rock.
But green energy promises to go even deeper. The next generation of geothermal companies are looking to drill an amazing twelve milesunderground.
Other energy innovators are looking upward. They’re dreaming of wind turbines and solar arrays that tower over even the loftiest skyscrapers.
Here we press both buttons. What can renewable energy gain by going ever higher? And is there still more to be gained by digging down?
• • •
Going Down
1. Turning up the heat. The Earth is hot. And it gets hotter the deeper you go. In fact, if you go anywhere on the planet and drill about four kilometers down, on average, the rock itself gets so hot that it can boil water. And yet geothermal currently accounts for less than 1% of the world’s energy production. Why? It’s partly because, except in a few select areas, it’s just too hard to drill deep enough and extensively enough to get good returns. But there’s new tech in the works. Quaise Energy is developing something called a millimeter-wave drill. It uses a beam of energy rather than a drill-bit to vaporize rock. They claim it can reach up to 20 kilometers down, where the rock is a blistering 500 Celsius. Combine that with a few tricks engineers learned from the fracking boom and we might be able tovastly increase geothermal’s share.
Source: Clean Air Task Force
2. Going nuclear. And if the Earth itself isn’t hot enough, maybe a little nuclear fuel can help. This April, Anthropocene did a fascinating article on Deep Fission, a Berkeley-based company that’s proposed what they’re calling “assisted geothermal.” Namely, putting small nuclear fission reactors kilometers underground. These reactors would be comparatively tiny, each sitting snugly in a water-filled borehole only 75 centimeters wide (that’s smaller than the front door of a house). The advantage to doing this would be that, hidden away so deep, we could make the Earth itself function as the reactor’s container, heatsink, and radiation-shield (and possible hideaway for any waste), all in one. No expensive, giant, Simpsons-style concrete building needed.
3. Filling up on gas. In addition to heat, another thing the deep Earth may have in abundance is hydrogen—if we can figure out how to get to it. In the last decade or so, scientists have realized that natural chemical reactions between water and certain types of iron-rich rock tens of kilometers down might be continually producing huge quantities of this gas (which we can use as carbon-free fuel for trucks or ships). There’s just one problem: scientists still need to figure out where exactly it forms, where it collects, and, importantly, how to drill down and retrieve it. But if they do, we may be sitting onthousands of years worth of supplies.
• • •
Going Up
1. Scraping the sky. Let’s talk about wind energy. It turns out that the higher you get off the ground, the stronger and more consistent winds tend to be (partly thanks to there being less stuff, like trees and buildings, to slow things down). And developers have been chasing these super-productive winds. In 2023, the average offshore wind turbine was already a whopping 124 meters at its rotor—roughly the height of a 30-story building. And that number’s been growing about 6% each year. But that might be puny compared to one turbine currently being constructed in Brandenburg, Germany, which would stand 300 meters at its rotor. Put next to the 95-story Shard tower in London, the top of its blades would nearly reach the top!
Source: Bloomberg New Energy Finance
2. Slipping the surly bonds of Earth. But if we really want to reach new heights, perhaps the answer is to leave the ground altogether. Airborne wind energy technologies (which use kites or other aircraft either equipped with their own turbines or which can pull tethers on the ground) are designed to reach at least 800 meters off the ground, with some targeting as high as two kilometers or more. While tech is still largely only found as (pun unintended) pilot projects, airborne tech would need significantly less raw material and be easier to set-up than grounded wind energy. And it could be a real powerhouse. One assessment found it had the potential to produce as much as half the electricity the world uses in a year.
2. Knocking on Heaven’s door. And yet, we can go even higher still. If you go all the way up to the edge of space, the sun shines more than ten times as intensely on average than on the ground. Using solar panels shot into orbit, a single space-based solar energy satellite could laser beam as much power down to Earth as an entire nuclear plant. There’s still a lot to figure out, but the idea’s captured the imagination of engineers all around the world. Last year Caltech wrapped up a technological test run while both the European Union and Chinahave announced plans for their own test runs.
• • •
What To Keep An Eye On
1. China and other competitors. With the new Trump administration, with its slashed science budgets and apparent ire towards green energy in particular, the U.S. seems to have ceded its influence over the global market. In the meantime, China and the EU have been happy to forge ahead, with China in particular now making up a third of the world’s clean energy investment. If there are new breakthroughs, they may not be coming from the USA.
2. The price tag. Any new technology is going to have to compete with existing wind and solar technologies, and these are continuing to drop in price year over year. Wind in particular has become cheaper than fossil fuels in all major markets. No matter how cool any given technology is, it’ll either need to compete on price or offer something current tech doesn’t have if it’s going to survive on the market.
3. Diving instead of digging. We’ve explored ways to harness energy from the earth and sky, but what about the ocean as well? On the clean energy side of things, a technology known as ocean thermal energy conversion uses a combination of warm, surface water and cold, deep ocean water to drive turbines to provide carbon-free energy, for instance. Meanwhile some fossil fuel researchers are eyeingfrozen methane deposits found scattered across the ocean floor as well. Maybe the deep ocean will be the next place clean vs. carbon-based energy dukes it out.
After a Shaky Start, Airborne Wind Energy Is Slowly Taking Off
Numerous companies are developing technologies, such as large kites, that can harvest wind energy up to a half-mile above ground. While still in its nascent stages, airborne wind power could potentially be used in remote locations or flying from barges far offshore.
BY NICOLA JONES • FEBRUARY 23, 2022 in e360 Yale
Look up over the white sand beaches of Mauritius and you may see a gigantic sail, much like the kind used by paragliders or kite surfers but the size of a three-bedroom apartment, looping figure-eights overhead. The sail isn’t a tourist attraction — it’s creating electricity for the power grid of this island nation off the coast of East Africa.
Launched in December by German company SkySails Power, the massive wing is the world’s first fully autonomous commercial “airborne wind energy” (AWE) system. For the past two months, the company says, it has been delivering a little under its goal of 100 kilowatts —typically enough to power up to 50 homes. That’s just a tiny fraction of the island’s electricity demand, but, SkySails hopes, a sign of the future.
As the world heads towards net-zero emissions, pretty much every pathway for future electricity production foresees a big role for wind. The International Energy Association forecasts wind energy skyrocketing 11-fold by 2050, with wind and solar together accounting for 70 percent of the planet’s electricity demands. Thanks to the expanding number of wind turbines dotting fields and adorning ridgelines worldwide, the cost of wind power has plummeted about 40 percent over the past decade.
But some experts say those massive turbines aren’t always the best solution — they can be expensive or logistically impossible to install in remote locations or deep waters, and just can’t reach the lofty heights where the wind blows hardest. To harvest these spots, the key may be to fly a kite. Dozens of companies and a handful of academic institutions are now investigating a plethora of airborne options. These range from soft wings that convert the tug and pull on a kite’s line to useful energy, to complex rigid craft that carry turbines and generators on board and shuttle electricity down a tether.
Advocates envision wind farms hosting hundreds of kites tethered to barges in deep waters far offshore.
Airborne systems have some key advantages, says Lorenzo Fagiano, an engineer at the Polytechnic University of Milan who is on the board of the industry association Airborne Wind Europe, founded in 2019. In some countries, suitable land for wind farms is getting slim: Wind farms typically need a whopping 71 acres to generate a megawatt, compared to 12 acres for a fossil fuel plant, and the ideal locations will eventually run out. “The first farms are in the best spots, and the best spots are limited,” says Cristina Archer, director of the Center for Research in Wind (CReW) at the University of Delaware.
Plus, in general, the higher you go, the faster the wind. “For a two-fold increase in windspeed, that’s eight times the power,” says Fagiano. An airborne system can reach up to 800 meters high (half a mile), far above the 200- to 300-meter tip of the tallest wind turbines. The theoretical global limit of wind power at high altitude has been estimated to be about 4.5 times greater than what could be harvested at ground level.
It’s relatively cheap and easy to bring a wing to a remote location, adds Fagiano; these systems come in a container and can be dropped off wherever there’s a road or dock. They can also be tethered to an anchored barge in deep waters, where a traditional wind turbine cannot stand firm. Their height is adaptable, so they can be moved up or down to wherever the wind blows the hardest, which often changes with the seasons. “It’s such a good idea,” agrees Archer. “The attraction is its simplicity in terms of materials and costs.”
“It’s not going to replace conventional wind,” adds Archer. But advocates envision wind farms hosting hundreds of kites floating on barges in deep waters far offshore, while single wings — or smaller arrays — could unfurl to help power remote islands, temporary military installations, or mining operations in the mountains.
These ideas have been around for decades, but the path to using kites, wings, or drones to capture wind energy has been bumpy. In 2020, for example, an airborne wind energy company acquired by Google famously folded operations after engineers couldn’t make their system work economically. But others pursuing lighter, simpler versions of the technology, like SkySails, are now going commercial. A 2021 U.S. Department of Energy report to Congress concluded that the idea has a lot of potential, with airborne systems likely capable of harvesting the same order of magnitude of energy as ground-based wind systems in the U.S. But, they add, the technology has a long way to go before it could become an important part of the nation’s energy solution.
SkySails actually started back in 2001 with a different purpose: building soft kite wings to pull ships along at sea. The shipping industry has traditionally relied on a crude, dirty fossil fuel called bunker fuel, and the idea was that a wing could, like the sails of old, help to dramatically reduce a ship’s fuel requirements. It was a concept ahead of its time. SkySails expected oil prices to keep rising, making their product more attractive. Instead, oil prices crashed in 2009 (and again in 2014 and 2020). Now, with more stringent requirements from the UN’s International Maritime Organization for ships to reduce emissions, other companies, including a spin-off from Airbus, are making wings to tug massive ships. But back in 2015, SkySails shifted focus to producing electricity with SkySails Power.
Kites produce cheaper electricity than many remote locations are paying for diesel generators.
Their system — like several others under development — relies on a roughly 150-square-meter, parachute-like wing to ride on the wind. There are no turbines up in the air, and the tether isn’t an electric wire. Instead, the energy is generated on the ground, from the tug on the line. “The brake on the winch is generating the electricity,” says Fagiano. Software flies the kite autonomously in a figure-eight pattern to get the strongest pull possible to produce energy. The system then changes the wing’s flight pattern so it can be pulled in with minimal resistance, expending a little energy to wind it back. This pattern repeats, creating far more energy than it consumes.
Will floating turbines usher in a new wave of offshore wind? Read more.
It sounds simple, and the power generation system is pretty standard. But Stephan Brabeck, the chief technology officer at SkySails, says it took the team around 7 years to perfect the flying software, particularly so the wing can safely land and launch autonomously. They have now made and sold five units, Brabeck says, with the one in Mauritius the first to get up and running. They reckon that the wing will have to land some 14 times a year because of heavy rain, unsuitable winds, or thunderstorms. Occasional hurricanes, which an airborne system can weather tucked away on ground, is what makes the island unsuitable for traditional wind turbines, says Brabeck, an aerospace engineer.
The sails are less intrusive on the skyline than traditional turbines and quieter too, says Brabeck. And they make economic sense, he says, for anyone currently paying more than 30 cents per kilowatt hour from diesel generators. But there are challenges. Wind turbines can kill or wound migrating birds, and how birds will react to these kites “hasn’t yet been very well studied,” says Fagiano. SkySails has studies underway. The tether on any such system, notes Archer, could theoretically trip up drones or even small aircraft. And if a tether breaks or guidance system fails, a system can crash to the ground.
That might not be a big deal for a soft wing, but other companies are pursuing rigid wings more like a hang glider than a paraglider. These can be more efficient and have better control, but crashes can be a bigger issue, making them a better bet for offshore use. “Essentially, they are aircraft,” says Fagiano. “They will have to reach a level of reliability close to civil airplanes.”
A third, more ambitious option is to make a hard-winged drone that has heavy wind turbines and generators on board and sends the electricity down the tether. This option would produce more consistent energy (without needing to cycle between energy production and energy expenditure), but it’s a hard nut to crack.
“We’re talking about a completely novel technology with a lot of aspects,” says Fagiano. “New turbines. New everything.” Google picked up one such project, led by Makani Technologies, back in 2013. They flew some successful test runs, but the economics weren’t adding up, and in 2020 the Makani project folded. Google released a YouTube movie about the experience and made all Makani’s R&D and patents available for free.
Plenty of other companies are now in the race to pick up where Google left off, or to find a better solution. This includes Netherlands-based Kitepower, which has a project in the Caribbean, and Norway-based Kitemill, which is aiming to make megawatt-scale systems. Others are even designing similar systems that work under the same principle, but underwater instead of up in the air, using ocean currents instead of wind to drive a submarine glider in a figure-eight. SkySails plans to test the concept of an airborne wind farm in the American Midwest before they move offshore. “You need a lot of space,” says Brabeck.
As commercial activity ramps up, says Fagiano, one of the biggest hurdles is regulatory: Airspace rules aren’t designed to accommodate these wings. “It’s chicken and egg,” he says. “So long as there aren’t technologies, they don’t make regulations. Without regulations, it’s hard for companies to raise money.”
Three myths about renewable energy and the grid, debunked. Read more.
With the first commercial pilot products now out there, “in remote locations, the costs are already pretty competitive,” says Fagiano. If airborne wind systems start to be mass produced, he says, there’s no question they’ll produce affordable energy. “The question,” he says, “is whether we ever reach mass production.”
Nicola Jones is a Yale Environment 360 contributing editor and a freelance journalist based in Pemberton, British Columbia. With a background in chemistry and oceanography, she writes about the physical sciences, most often for the journal Nature. She has also contributed to Scientific American, Globe and Mail, and New Scientist and serves as the science journalist in residence at the University of British Columbia. MOREABOUT NICOLA JONES →
Exploring the Potential of Kite-Based Wind Power Generation: An Emulation-Based Approach
by
1 Department of Electrical & Electronics Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore 575025, India
2 Department of Water Resources and Ocean Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore 575025, India
3 Institute for Environmental Research and Sustainable Development, National Observatory of Athens (IERSD/NOA), 15236 Athens, Greece
Authors to whom correspondence should be addressed.
Energies 2023, 16(13), 5213; https://doi.org/10.3390/en16135213
Submission received: 27 May 2023 / Revised: 16 June 2023 / Accepted: 5 July 2023 / Published: 6 July 2023
(This article belongs to the Special Issue Advanced Technologies in Wind Power Generation)
Abstract
A Kite-based Airborne Wind Energy Conversion System (KAWECS) works by harnessing the kinetic energy from the wind and converting it into electric power. The study of the dynamics of KAWECS is fundamental in researching and developing a commercial-scale KAWECS. Testing an actual KAWECS in a location with suitable wind conditions is only sometimes a trusted method for conducting research. A KAWECS emulator was developed based on a Permanent Magnet Synchronous Machine (PMSM) drive coupled with a generator to mimic the kite’s behaviour in wind conditions. Using MATLAB-SIMULINK, three different power ratings of 1 kW, 10 kW, and 100 kW systems were designed with a kite surface area of 2.5 m2, 14 m2, and 60 m2, respectively. The reel-out speed of the tether, tether force, traction power, drum speed, and drum torque were analysed for a wind speed range of 2 m/s to 12.25 m/s. The satellite wind speed data at 10 m and 50 m above ground with field data of the kite’s figure-of-eight trajectories were used to emulate the kite’s characteristics. The results of this study will promote the use of KAWECS, which can provide reliable and seamless energy flow, enriching wind energy exploitation under various installation environments.
Keywords:
high altitude wind power; kite-based airborne wind energy conversion system; kite emulator; PMSM; renewable energy
1. Introduction
Renewable energy generation and implementation are crucial for minimising the impact of fossil fuel emissions on the environment. Renewable technology development comes with challenges that restrict endorsement. Wind energy is one option for decarbonising the energy system. Wind turbines were used to generate electricity in the 1880s [1]. Among all renewable energies, wind power is one of the most rapidly growing industries in the world because it has many benefits, such as a high capacity factor, low maintenance costs, and low carbon emissions. By 2030, wind power alone will provide 20% of the world’s energy needs [2]. Various wind turbines have been designed for this purpose, each with unique core subsystems for converting wind into electricity [3,4].
An Airborne Wind Energy System (AWES) is a high-altitude wind energy conversion system that uses one or more kites, gliders, or horizontal flying turbines that are tethered to a ground station to produce energy [5]. The AWES was designed to improve existing technologies by focusing on catching winds at high altitudes and turning them into electricity [6]. Loyd demonstrated that a tethered wing the size of a C-5A aircraft could generate 6.7 MW of electrical power with a wind speed of 10 m/s. The generated power is three times more than the conventional wind turbine-generated power [7]. Since then, most of the prototypes for airborne wind energy systems are still in the early stages of development [8]. AWES technology’s improved availability, stability, and reduced prices make it economically viable [9]. The autonomous takeoff and flying of a tethered aircraft verify the technological viability of the proposed takeoff approach, allowing for deploying this AWES technology in a small area at a low cost [10]. An economic analysis at an existing site indicated that AWES costs less to transport and assemble and has a larger potential capacity, resulting in more significant economic advantages [11]. Consequently, a little increase in the operating altitude of the wind energy system can result in a significant rise in the produced power. AWES can access winds at heights between 0.1 km and 2 km [8,12].