 is now to go from space back to Earth and try to use drones, so autonomous flying vehicles for power generation. So this is the second part. So the outline here is, thank you very much. So the outline is that first I will introduce the source here and motivate why it is a good idea to harvest high altitude winds and produce energy from them. The technologically part will come in the second part here. This is about the technology which is called airborne wind energy. And in the third part I want to show how you can build a wind drone for low cost for yourself and experiment with this kind of technology. So let's start with the first part. And here as a reminder is the conventional energy supply of wish list, so probably what your global players in conventional energy would think about it or tell you. They would say that it's a surely clean enough resource and meaning on time scales here it is exploitable of the order of one human life expectancy, it's controllable especially economically and politically, it is depreciable economically and leads so to a very high profit for some players. Unfortunately there's also the technological part and here sometimes it's driven by hope saying it will be okay but as we know it might be mostly harmless. So as we see here for instance there are catastrophes like Chernobyl. This is after the catastrophe where you have the memorial for the people who died. Then you have scenarios during the catastrophe here. This is deep water horizon being like desperately tried to extinguish the fire by the US Coast Guard and fire degrades. And of course what I don't have to mention here but in times of fake news is important to mention we are before the catastrophe. So this is here a plot of the carbon dioxide concentration in the atmosphere taking from ice. And as you see here the ice ages give these variations over 500,000 years and now we are at this spot here that points up and if you resolve this into the time scale extend this time scale from the last 1000 to 2000 years here. So we are here at this spot at 2000, year 2000, then you see that this rise has started at the industrialization. So it's a clear sign that we have to do something and we have to do it quickly. So now let's try to propose something which can be part of the solution namely sustainable energies and here's a wish list of what probably you would think it should be. It should be sustainable, ubiquitous, continuous, accessible and profitable at the very end. So does such a source exist and first I should define what it means. So sustainable means it should serve present needs without compromising the future and this is clearly not what we are doing now. So it should be available on time scales which are like the lifetime of our central star if possible. It should be ubiquitous meaning that it should be present almost on any location on earth so that we can without very complicated long range infrastructure have access to the energy. It should be continuous meaning it should be present at almost any daytime and seasons so that we can plan of what we produce and of course it should be accessible meaning it can be tacked by the technology and lead to a significant contribution to our energy mix. And profitable should of course also be. So does it exist and the answer is yes and I want to show that this airborne wind energy can be a big part of it. So here I have a table of some sustainable energy sources and the wish list items are written here and I put some of the sustainable sources so there is fusion, there is solar energy, terrestrial and also the spatial energy of which both presented by Anya and by Stefan before, hydro energy, geothermal energy and conventional wind energy whereby conventional wind energy I mean wind energy up to approximately 100 meter which is the hub height of wind turbines approximately and as you can see some of these items here are not fulfilled by all these different approaches. So for example the spatial energy is clearly not ubiquitous because you have this beam as we heard which is just like basically hitting a certain spot on the earth and they are transferred into energy so you have to distribute this energy. Also it is not yet accessible. On the other hand, conventional wind energy is not ubiquitous because you can only select certain spots and it is not continuous because you cannot really plan when the wind is blowing and when it's not blowing. So let's add to this list what is called high altitude wind and high altitude wind is clearly sustainable because it's also wind energy so it's like driven as all the other wind energy as well and high altitude means to go to heights which are above 200 meters and try to drain energy from these winds. So let me argue why it is a ubiquitous source and for this Philip who is also here and part of the team I'm very happy has made this very nice plot here which shows the western part of Europe and it shows the ratio of wind power which you can extract at an optimal height which should be below the 1000 meter so this is just an arbitrary at the moment limit to say that we can have a system which can basically get up to 1000 meter height and compare it to this wind energy which is basically available at 100 meter and in this plot you can see at the coastline there is a line here and this line is the line where in the interior you have already a doubling of the wind power so meaning at the coastline itself if you go to higher altitude you have the double wind power available than at 100 meter even better directly at the coastline there is another line which is a factor of four better so as soon as you put your wind turbines on land site you will be a factor of four you have better you have access to a factor of four higher wind power and here in the region slightly south of Leipzig there is another line this is a factor of eight where you become better in wind power in high altitude wind power so seeing that the coastal regions have already a factor of four in this ratio better and the inland between four and eight oh there are the signs sorry there should be reversed of course so saying that here the site of conventional in vintage harvesting which are now very limited and where you put for instance all the wind turbines in the north they become much more accessible if you go to higher heights because there you can basically use all the land sites so this is with more sites available when you harvest at optimal height and here as an example about why does a continuous source you see a time distribution of the wind velocity in January 2016 in Leipzig the wind velocity he's here increasing from yellow to red and the altitude is displayed here and this is the time scale of the month and what you can see is at 100 meter height you have almost like only in the lower parts you have winds whereas if you go to higher heights you have the reddish parts where you have high violent velocities so this shows that continuity is already improved if you go to higher altitude especially for land sites and this is almost impossible for continue for conventional wind turbines you would have to build a must hire and much much bigger structures and also what is displayed here is the optimal harvesting height so this is the height again below 1000 meter where it would be optimal to harvest wind at a certain time over the display over the whole month and if one goes from this plot to the histograms to the so to the time distribution of the different wind velocities you get this picture here so this is other spots the histograms of hundred hundred seventy five hundred thousand meter and of the optimal height so if you adjust your height and one of the things that you can see is that the mean is clearly shifted to higher wind velocities if you increase the height and also if you harvest at optimal altitude you shift the whole probability distribution to the right so and what increases there is that the fraction of time below five meter per second which is like the time where the cut in wind speed for your wind turbine so it would like starting produce energy the probability to have such winds is increased from 76 percent to 87 percent which is quite a lot of increase so adjusting to varying optimal harvesting height is not only almost but is really impossible for conventional wind turbines so one has to find another technology which is better and can give you access to this altitude winds so this is the plot again from before so I have now a little bit motivated why the source is ubiquitous and continues now the question is is it accessible and how it is accessible and this is the technological part which is called airborne wind energy so how do we access these high altitude winds so on for these let's come back to the design challenges which would be necessary to go to high height so high altitude means that you don't just can you cannot just increase your tower and have more talk on your foundation and just scale up the system so you should avoid proliferation of mass and proliferation of the tower and foundation and also varying altitude means you shouldn't have passive stabilizing static structure so find but find something which can vary so just as an example here this is the sky walk in the Grand Canyon and this is already a quite scary lever arm you which you have and if and comparison you take your modern wind turbine you rotate it by 90 degrees and compare it in size to this you can see what kind of torque will be like will act on the foundation so this is already a very big piece of technology you have here so we have to do better and this is the second part namely airborne wind energy so the technology itself so the first slide is probably the most important of this part because it explains the the idea behind this technology so you take autonomous drones which are at most flexible connected to the ground via tethers and expect when a wind energy via these drones so how does it work so look at this conventional wind turbine here you have most of the energy is produced by the outer part of the wings they are rotating with the highest velocity and at the same time you have the highest the largest lever arm so you produce most of the energy in the outer part the inner part is more less passive stabilizing structure so you remove that structure and replace it by something which is flexible and the first which comes to mind probably is a tether with which you attach it to the ground and then you have just the active part here which is now a aircraft moving in this circle which before was circulated by the wingtips to extract your energy this is the principle so how do we bring down the power when circulating this aircraft so we have to in some way transform it to electric power so there are which are not shown in the picture before lighter than air systems so you just basically take a balloon you put your wind turbine and high altitude and extract the power and here the tether can please serve as the power line but what we can also do is crosswind flight which was shown in the picture before so here you have a moving arc aircraft which can move in with something which is called the direct mode meaning that you have onboard generators on the aircraft so essentially it's a propeller aircraft but the propellers are reversed in repeller mode so that the repellers produce energy for you and then the tether serves as power line so this is a principle is shown here so here you can see the generators and then the power is brought down by the tether and the second part a second like strategy is using the so-called lift mode so here you have ground-based generators and the tether itself transmits the power there are no power lines in the tether so here you use that the power is given by the pulling force times the real out velocity of the tether so you circulate in some patterns with your aircraft and you lose the lift force acting on the aircraft to unreal this tether from a drum and at the drum on the base station there's a generator attached which helps you to get the energy to transform the energy into electrical energy and of course at some point the tether is maximally reeled out and then you have to have to go to a real in phase where with minimal energy you reel in the tether again and start periodically this phase again so these are the concepts and there is a whole zoo of airborne wind energy devices and proposals which show that this technology is still in the very early stage of being developed so you have people here flying figure of eight patterns with the aircraft so some things are lighter than air turbines which look very exotic like this one probably this one you have seen in media already proposals like this here there are quadcopters which produce the energy by rotating of their of the propellers here and all kind of exotic lever arm and aircrafts which you can use. So let's bring a little bit of more order into the technology in this into the proposals and one of the things I want to discuss which is very probably promising is what is called crosswind flight and so here as an example is a comparison of a conventional lighter than air system with the big wheel in London so this is one of the biggest wind turbines and the harvesting area is so the effective area of such a wind turbine is the swept area of your propellers essentially so now let's look what happens if you move an aircraft instead through the wind then the picture of before is like of that size and if you take an aircraft which is the same wing area as the wing areas of the propeller here your harvesting area is of that size it's much bigger and the reason for this is that the effective area is now given by the wing area times coefficient which is the square fraction of the lift to drag coefficient of the aircraft times the lift coefficient itself and this factors of the order of 200 so it gives you it increases the efficiency of your of your wings dramatically this was already found by light in 1980 and you can now ask why does it take 30 years from this idea to first systems and the answer is in this community for is probably a very interesting is why are these products are appearing only 30 years later it's because sufficient computer power so for the control algorithms which allow you to control such flight modes was not available so as an example here's an illustration of one of the current leaders in the field called Ampix power showing a crosswind airborne wind energy system versus a conventional system so here's the conventional wind turbine for two megawatts and the conventional this is a conventional system and the airborne wind system is this is the ground station and this is the aircraft so one of the things which are I mean visible in this picture is that it is much less like even sight impact in the environment so having something like this is much less disturbing from the even from the aesthetic of volume to view than this huge wind turbine so now the next step would be to look at closer to the technology and see what are the AV system components with that that you need that you need to build such a device so first of all there is the drone or the fixed wing aircraft we have seen that it's very good to have a large lift and small drag coefficient so you need something which is like a rigid glider more or less on board you need sensors like accelerometer, gyroscope, GPS, receiver, barometer and a pitot tube to measure the air speed and this is to determine the system state that then is like reacted on by the control surfaces of the in the case of an aircraft by ailerons flaps and the rudder moreover you need of course a microcontroller and algorithms which do the state estimation so from the sensor data they compute the state of the system meaning this position attitude velocity and you have to navigate so and of course you might need something like a propeller for takeoff landing and energy generation and carry case of drag mode the second thing is of course the ground station so here you need the drum for tether windup you need a motor which eventually has to be transformed into generator mode if you have the lift mode you need power converters also microcontrollers and algorithms which synchronize your ground station operation with a drone and you need a runway catapult or something like for takeoff and landing so so far it looks quite easy simple but the devil is in the detail and here I found a nice quote a colleague of mine John Litricica has done in one of his talks and I liked it very much because it displays very well what challenges have to be still overcome so it starts with theory is where nothing works but everyone knows why and to demonstrate this let's have a look at this video here which is one of the flight attempts of one of the companies so the aircraft lifts on off there's no sound yet no there's sound yeah and your desperation of the founder was clearly here at the end and you could see that the tether ruptured and then there was no way to recover that most of the aircraft was lost second sometimes practices when everything works but no one knows why so there are also positive surprises and here is a launch a catapult launch for an aircraft which now uses weight so so a positive surprise for for a test and finally sometimes if you combine theory and practice that nothing works but no one knows why this is where the complication really is the devil is in the detail and here you can see a video from a flight with a crosswind flight everything seems normal and then the prototype is again lost so this is complicated so but there is a lot of progress and so I want to come closely very quickly introduce the current industrial status so I focus on three companies which work on that so one of them is an Akite in Berlin and they have now a system which is basically stationed on such a truck and this is a crosswind system of a passive wing so it's steered via three of three tethers and it produces up to 30 kilowatts of energy then you have Ampix power they have here the launching site in the Netherlands and they are currently producing this aircraft here this type which in crosswind is a crosswind system in lift mode and at the end will produce up to 250 kilowatts of power this is under construction and finally there is Google X Makani in California and they have built a drag mode aircraft here which is flying and I can show you a video that they have on their homepage very nicely where they show a flight so that you can see that the 600 kilowatt system is working here you see the onboard propellers you can see the tether down here this is from the tether attachment point yeah so the things are working there are prototypes um yeah but one of the things which are important is one has to test test test and get experience from tests so experience is what you get when you're expecting something else really so what does it mean so we have to test analyze adapt the systems so because many as you could see from this design variations in the zoo which I've shown many of the concepts are still open so for example the design of the airframe if you use a biplane a flying wing or anything alike or something totally different is still open the tether construction what kind of materials to use is still open the materials in itself is still open for the aircraft etc etc the mode of operation that means takeoff landing and drag versus lift mode is still an open question what is the best thing to realize in for industrial products and then control hardware and software and algorithms have to be tested thoroughly of course it have to be certified by the aerospace agencies of course you want to have it failsafe so what you have to do is you want to even I mean have total losses in experiment you want to do the experimenters with lead to a total loss of your system so here comes the idea that instead you should build a cheap and disposable test platform instead of a largely scaled up system first before you build the expensive prototype and do tests on them and this brought us to the idea to provide a low-cost open-source test platform where everybody at home can build his own wind drone and this is the third part of the talk so the do-it-yourself wind drone yeah what are the ingredients here so first you need a drone so here I want to show the airframe and reinforcement heck which is necessary to prepare your airframe for the additional forces by adding the tether then there's a grouse station and here I want to motivate why the drone is essentially behaving like a fish in this case a barracuda the next thing is navigation on curved manifold is very important because you have like a constraint coming from the tether and finally you need something for your for control which is the autopilot so in this case it's the autopilot open-source project which we adapted so let's come to the airframe reinforcement heck so what you use take your favorite polystyrene airframe so in this case it's an easy star two and glue the wings together this is the lower side of the wings you put in there a carbon rod here in this part and you stabilize it with racks which you glue into the slits we can see here and then you wrap carbon in the in the four in the in the forward part of it where the most of the aerodynamic force is attached attached then you have the carbon wire where you can wind around your tether and you install additional tubes for fixing the the wings on the fuselage so the fuselage is here we cut off the engine blocks included additional carbon rods so you can put these carbon rods on these carbon rods here and fix everything with screws so to show you how that looks like and how what the size of this model is so here here is the original size aircraft with carbon and you can later if you want to pass by the assembly area and look at it and have a look at it and touch it so this is how it looks decomposed into different components so again wings and so on and so on the servos for for the control surfaces the central unit here is the PIXHawk autopilot so the the microcontroller which contains some of the sensors you have a GPS sensor in addition you have a telemetry antenna for data for data transfer to the ground station and you have RC control for manual control when you switch switch switch out of auto mode to have manual control in emergency situations or if you want to make other kind of flight tests yeah so now this is the drone itself so now it's the question what to do with the ground station and here let's look why the the drone behaves as a fish because what it does is like a like in fishing you would need a free moving tether it has to be fast and failsafe real in and reeled out and it should remain twist free so that it doesn't give any knots if it is not an attention and the thing which we came up with was best served for our needs at the moment is an offshore fishing reel so you need offshore here because the drum has to be perpendicular to the rod this guarantees you that real out phases twist free on the tether other fishing rods have the drum aligned with the rod and then you accumulate twist on the tether which is can give to not lead to knots and then it's it's not a good idea it's destroy your tether so and this is the first flight test so we were very into the stick and started the first flight test and here it is okay so unfortunately it didn't work so what happens this was the result the tail was broken and because the tether apparently wrapped around the back of the aircraft and then it became uncontrollable so we come up with what do we do if you don't know any further any better use carbon so we put some carbon on the lower part of the of the fuselage to reinforce it yeah and then of course you have to think about writing your navigation code to navigate on if you are under tethered flight so here is the the recipe for how to do it so first you take one git clone of autopilot this autumn open source software you take one curve two dimensional manifold which is essentially given as a hypersurface embedded in three-dimensional euclidean space in case of constant tether length this is just a sim hemisphere s2 which is centered around your ground station then you take a planar curve which you want to fly along or curve segments and a pinch of differential geometry to wrap it on the sphere to make this curve appearing on the sphere you take a little bit of classical mechanics for the for the flight control to transfer the curve accelerations into actually control surface motions and then you need of course a dozen coffee for doing so you put everything together into of course not the coffee into the computer algebra system and steer well and let the CPU bake it at 100 degrees and then you come up with a smooth at least c1 curve so the curve is shown here so it's this is one part of a figure eight pattern so the other part would be behind here it's composed of two geodesic segments and one turning segments and they are c1 glued together here and these are the equations so you can find in the paper I don't want to go into detail so now you have to modify the source code of this autopilot project so here they are highlighted the patterns which you basically have to where you have to do modifications you have to implement new flight modes and change some of the control algorithms and then you come up with the next flight test and here is the next attempt so yeah the whistling sound you have heard at the end is the tether being dragged through the air so there was really tension on the tether and you can also see this if you do a data analysis on the flight data later so here's for example multiple possibilities you have a lot of data which is possible to analyze so the autopilot this was very very it's very very nicely done in this open source project so they have a data file with all primary and secondary data you can use for your analysis so for instance this is the flight curve with different flight modes which we used you have the attitude of the aircraft you can look to deviations in radial and transverse directions you can look to tether tension or like a measure for tether tension by looking to the length variation of the tether and you can of course do time series analysis of how your figure eight pattern is flown along and yeah that is what you can do with this very very nice autopilot open source software which is available um written by many many people um on the internet so the question which remains is after all of this is will it be fail safe to 100% and the answer is nope it will not uh it will there will be of course accidents happen but the thing is nothing is fail safe and um so here's a standard winter bin and look for yourself um let's see there is no 100% guarantee but we have to try very hard to get it as fail safe as possible so yeah this is essentially it that was the talk so um uh what i want to say is that the current status of uh air and wind energy uh can be uh seen here by a nice book uh in the stringer on the springer uh page which you can download here and uh we are very very happy to have any kind of critical remarks input to help in uh developing the system further so please if you want look to this web page there's a lot of information including a paper and we'll be very happy for any kind of help and uh yeah and finally i would uh again stress that we could rely on this tremendous work of the open source community working on this autopilot project that has helped us to realize this project in very short time so very happy about this and i want to thank of course um Philipp Bechtliu is here and Thomas Germann and Maximilian Schultzerberg the students and Udo Zellmann who cannot be here for uh working on this project and putting so much work also into it thank you very much for your attention we can uh put some on the microphone here and here one and five so two questions the first one please so you talk so you talked a lot about powered and not powered about controlled flight how does it compare energy wise to uncontrolled flight basically putting a propeller on a kite um so the thing is the propeller on the kite you with kite you need uh you mean i guess um non-rigid structures so meaning that the first question is how do you want to put a propeller on a kite if it's non-rigid so um that is a question which goes back to you so um because that is uh something is not clear to me but in any case um uh rigid air flame is harder to control than a kite so there are people who work with a kite and by kite surfing or if you do uh like a steer normal kites from the ground you know it's like moving not that fast in the um in the wind field so it's easier to control this is a big benefit of kites and also the weight is a big benefit but uh the power output because of the bad worst lift to drag coefficient is unfortunately not that efficient as the rigid aircraft so you want to go to the rigid aircraft if you leave the room now please be quiet because we have questions and answers here number three please and that is the last question i'm afraid but you can ask questions after the talk um i want to go back to the space part um i was wondering there are some ideas about bootstrapping like a solar station on the moon and then like shipping i don't know hydrogen or like pre-charged lithium batteries back to earth and back and forth is it like realistic or not really i think it's it also this approach would be quite expensive and you have to you have to install this infrastructure on the moon first and you have to establish the the flight basis back and forward um yeah realistic as a thing you know at the at the end that's a question of money and investment and i'm not sure whether this will would pay out but i'm we haven't uh analyzed this kind of approaches yet thank you so thank you very very much Stefan, Anja and Christoph give them a warm applause again please thank you