Go fly a kite: 7 reasons to believe in high altitude wind power
Published July 2017
In this blog, Everoze Partners and tech-enthusiasts George Gibberd and Zoe Barnes take a leap of faith in examining the prospects for high altitude wind energy,
In recent months kite technology for utility scale wind power has been getting some press exposure. Initial reactions observed have ranged from a polite “let’s change the subject”, through a brusque “go fly a kite!” dismissal. Kites are kids’ toys, right, not power stations? You’re seriously proposing to pull cables across a field, around a drum at high speed, and fly it around in a storm? But is it really as daft as it sounds?
History teaches us to mistrust our intuition. Really radical innovation is unsettling and we are naturally sceptical of anything really novel. So, the Everoze Technology Team felt that it was time to take a closer, objective look at kite power; either we will find an exciting, disruptive technology, or we will emerge in festive schadenfreude to proclaim “I told you so!”.
What we find first is that many of the claimed advantages of kite power are actually real and justified. Here are 7 for starters:
- Stronger winds: Kites extract energy from higher altitudes (typically up to a few hundred metres, although some fly much higher), where the wind blows more strongly, more constantly and with less turbulence.
- Reduced mass: Kites fly very fast across the wind and therefore sweep a large area. A relatively small kite surface area can therefore generate significant lift and power. This means that kites weigh a small fraction of a wind turbine of equivalent annual energy production – a 2-3MW kite operating with a 50% Load Factor, for example, might weigh only a few hundred kg, and require a base station of a few tens of tons.
- Flexible deployment: Kites are smaller, lighter, modular, foldable and much easier to handle and transport than conventional fixed turbines.
- Less infrastructure: The force in the tethers is predominantly a shear force at ground level, not an overturning moment; this makes it highly suitable for deployment in remote areas or poor ground conditions, where short pin piles are sufficient to secure the base station, without the need for huge excavations and mass concrete foundations. The environmental impact and footprint of kites is much lower.
- Offshore potential: The light weight coupled with shear-only loading means that kites show great promise for offshore applications, and especially for floating farms because of the greatly reduced size of floating platform and mooring system needed.
- Coping with extremes: They are unaffected by earthquakes, and can be landed and held out of harm’s way in typhoons.
- Engineering simplicity: Kites are mechanically and structurally simpler than wind turbines, and kite materials can be repaired and replaced if damaged in service. Longer lifetimes and easy repowering at end of life are achievable as a result.
Despite our initial scepticism, our analysis shows that kites have the potential to halve the cost of offshore wind energy, even if making pessimistic assumptions about O&M and availability; this is a truly disruptive level of cost reduction.
With this level of potential cost saving, large utilities, OEMs and industrial investors are starting to put money into kite technology. Google invested in Makani a while ago https://x.company/makani/, and UK outfit KPS http://www.kitepowersystems.com/ has recently received major investment from Shell, EoN, Schlumberger and Scottish Enterprise. (The Everoze Technology Team acted as TA for the Scottish Enterprise investment, which provided the stimulus for this article). There are also around a dozen other kite technology developers out there at various stages of development. Yes, a great deal of engineering development is required (materials, fabrication processes, control systems, tether technology etc. etc.) and it may be as much as ten years before they can make a significant impact, but they are showing no signs of disappearing in a hurry.
“But even so”, I hear you say, “aren’t they really just a crazy idea?” Well, if we are realistic, there are significant challenges to deployment – not least public perception and safety. The idea of a cable catenary winching horizontally at high speed close to the ground will be alarming to many, and they will probably require exclusion zones and long demonstration periods to gain general acceptance. This may restrict onshore deployment to remote sites. However, for offshore, and especially for floating applications, the restrictions are less onerous, and with levels of cost saving being demonstrated, we suspect we might see a lot more of kites in the medium-term.
In fact, the biggest restriction is likely to be one of imagination.
