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  • Writer's pictureNed Patton

So, What’s Up with Kites for Wind Energy Generation?

And what does a kite have to do with composites anyway, or even sustainable composites? Well, this post is intended to answer that question. And, again, please excuse my focus on wind energy and wind power devices. I did my Master’s degree essentially in low speed aerodynamics, calculating the power coefficient of a horizontal axis wind turbine. So, windmills and wind energy devices have sort of a soft spot in my heart.

Yes, this isn't some guy flying a kite - this thing actually generates electricity

First – how does this thing work? This image is from a test that was being run on an airborne wind energy (AWE) device designed and built by SkySails power. This company, based in Northern Germany, initially wanted to build huge kites to propel container ships across the Atlantic rather than having those ships use bunker crude. It was a novel idea in 2001 when they developed the design and built their first prototype. That was when the price of oil was skyrocketing, so their intent was to use the fact that the fuel for these large ships would have been much more expensive than buying and using a kite like what you see above. SkySails product might have made a huge splash if the price of crude had not plummeted in 2009, and then plummeted again in 2014 and 2020. So, being enterprising Germans, in 2015 they modified their initial concept and shifted to harnessing energy from the wind using their sails. So now they call themselves SkySails Power.

Their new concept uses a winch to fly the kite in a figure-8 pattern at an altitude of 200-400 meters (600 to 1200 feet) where the energy in the wind is twice what it is at the upper tip of even the largest land or offshore wind turbines. And electricity is not transmitted down the kite tether line, it is actually extracted from the winch as it flies the kite back and forth. Even though the winch has to expend a little energy at the end of each cycle to put the kite back up in altitude, the net result is a fairly large positive output. Hopefully you can see the pattern in this image – which is directly from the SkySails website - This is actually a little video graphic where the sail flies along the dotted green line with the winch alternatively pulling it in and letting it out. They call this the “yo-yo principle” and it seems to work because they have demonstrated a fairly significant positive net output power. One of these sails can generate about a megawatt, or enough to power on the order of 50 homes. And, of course, they have a maintenance mode where if there is a problem with the kite or if there is very bad weather coming, the system automatically reels in the kite so that it can be stored safely.

This system is going to be installed in Ireland soon. The Irish Composites Testing Laboratory (CTL) has launched a project that they are calling Hawk – Hibernian Airborne Wind energy Kites that will be based on the SkySails airborne wind energy sails. This project is funded by the Sustainable Energy Authority of Ireland with collaborations from Zero Nexus, TU Delft, and Airborne Wind Europe. Currently the HAWK project is going through materials testing and prototype testing to enable certification of the SkySails units for use in wind energy farms in Ireland. Of course, the end goal is to enable deploying these airborne wind energy systems all over Europe. That is of course why the Dutch are also involved – they have windmills galore, and may be responsible for what we now know as the farm windmill seen all over the Midwest US being used to pump water, grind grain, etc.

Since this is a newsletter about composites, and not necessarily about wind power per se, I need to explain why I am focusing on this particular development or on airborne wind energy in general. It is the advent of advanced composite fibers that have made such a thing possible. Conventional fibers and ropes are just too heavy and not nearly strong enough to enable the SkySail to exert the high forces on the winch that it has to exert. One of these devices, as I said earlier, can generate as much as a megawatt of electricity. And that’s just from letting out the tether rope and having to reel it back in. The forces on the tether rope are enormous. To enable this to work, SkySails uses a Dyneema® fiber rope and also a “synthetic” (I’m guessing either Dyneema or Spectra® sailcloth) fabric for the sail. This permits rapid deployment because both the tether rope and the sail itself are very light weight. Essentially, SkySails is using technology that has been used in the large yacht racing community ever since the introduction of these two ultrahigh molecular weight polyethylene fibers. And, the winches are very probably quite similar to the sheet winches that are electrically operated on most modern sailing yachts. They at least operate on the same principles and use the same fibers for both sails and all of the running rigging (for you that aren’t sailors, please just ask me what “running rigging” means).

So, there you have it. I did finally make this about composites, even if I did take a few back alleys along the way. For me, I’m fascinated by this stuff, and quite happy to see that at least the Europeans are very serious about developing technologies that will help us get off the fossil fuel train. Hopefully these ideas will also come to the US and get implemented here. There is enormous wind power potential in the Midwest US as well as at both coasts, and systems like this that are light weight and have a small footprint because they are made from advanced composite fibers can be made to be less expensive and easier to install than the equivalent coal fired or gas fired power plant. Plus, once they are installed, there is zero fuel cost – wind is free.

That’s about it for this week. Again, if you like this, please visit my website and subscribe to the newsletter. The URL is And also, please take a look at the pre-sale page for my book. My publisher says it will probably be out in August or if I’m lucky the end of July. The Pre-Sale like is:

See all of you next week.


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