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Wind turbines are a mature technology for offshore harvesting of wind power. They can manage themselves in variable wind speed and shut down safely when it gets too strong. The largest systems have blade lengths of 80 to 120 meters (even longer are being explored) with maximum power of 8 to 12 MW or more.

Since blades need to be replaced from time to time, there is now work to make them from materials more suitable for recycling or reuse.

Tethered or crosswind kites are still in the development stage. Since they "fly" they can reach higher up where winds may be stronger and steadier. Some use work done by kite on the tether (reeling in and out) others put propellors and generators on the kites themselves and end up looking a lot like multi-prop airplanes. They have the potential to be lighter and cheaper per unit, but without long term demonstration at scale it may be difficult to compare them directly to wind turbines.

No matter, I'd like to ask anyway:

Question: What are the tradeoffs between wind turbines and tethered kites for offshore wind power? For a given site how would one know which is likely to be better? For example, will one be cheaper per square km of "wind farm area" while the other cheaper per MW?

Potentially helpful:

Ground-tethered kites have the potential to reach higher than conventional turbines, to access strong, reliable winds (Credit: SkySails Group)

Ground-tethered kites have the potential to reach higher than conventional turbines, to access strong, reliable winds (Credit: SkySails Group)

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    The other metric that would be useful would be, which would give a higher MW per square kilometer & even maximum MW per device: kite or wind turbine. The picture in the question shows a key difference between the two. Wind turbines occupy a specific area of land & they need to be positioned so they don't interfere with one another. I get the impression that due to the length of the tether & the 3D movement of kites, each kite may occupy a larger area of land than a wind a turbine.
    – Fred
    Mar 11 at 21:13
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    I haven't heard of offshore kites being explored. To my knowledge kites are mostly of interest when it comes to temporary, small scale energy production, while wind farms are a huge, long term investment.
    – Erik
    Mar 14 at 13:41
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    Makani were very interested in offshore kites. The big advantage is that areal density was less of an issue and the lower torque meant smaller platforms. Plus no-one cared if they dropped one in the sea 5km from their tower, but people get excited on land. End of doco is all about the water option: youtu.be/qd_hEja6bzE?t=4624
    – Móż
    Mar 15 at 22:53
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    The problem with fabric kites is durability, it's just hard to make lightweight, flexible, durable fabrics. Makani went with a solid glider for that reason. They also put the generator into the kite since they needed a motor to launch it. The fabric setups tend to use the winch motor as the generator AFAIK, which means it's on the ground but also harder to launch and recover. FWIW I've got no ties to Makani, I know a couple of the people but they know I think it's a stupid idea, but because I know them I know more about that project than other kite generators.
    – Móż
    Mar 15 at 22:55
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    The brutal answer is: wind turbines. They actually work, kites don't. Kites might work in the future, but in the next decade they're not going to be able to be deployed at any useful scale.
    – Móż
    Mar 15 at 22:59

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