1 00:00:00,099 --> 00:00:14,930 *34C3 preroll music* 2 00:00:14,930 --> 00:00:23,140 Christoph Sieg: The idea is now to go from space back to earth and try to use drones 3 00:00:23,140 --> 00:00:27,960 – so autonomous flying vehicles – for power generation. So this is the second 4 00:00:27,960 --> 00:00:33,100 part. So the outline here is … *Applause* 5 00:00:33,100 --> 00:00:41,580 Christoph: Thank you very much. *Applause* 6 00:00:41,580 --> 00:00:46,559 Christoph: So the outline is that first I will introduce the source here and 7 00:00:46,559 --> 00:00:52,389 motivate why it is a good idea to harvest high altitude winds and produce energy 8 00:00:52,389 --> 00:00:58,019 from them. The technological part will come in the second part here. This is 9 00:00:58,019 --> 00:01:02,289 about the technology which is called airborne wind energy. And in a third part 10 00:01:02,289 --> 00:01:06,630 I want to show how you can build a wind drone for low cost for yourself and 11 00:01:06,630 --> 00:01:12,630 experiment with this kind of technology. So let's start with the first part. And 12 00:01:12,630 --> 00:01:18,680 here as a reminder is the conventional energy supplier wish list, so probably 13 00:01:18,680 --> 00:01:23,850 what your global players in conventional energy would think about it or tell you: 14 00:01:23,850 --> 00:01:29,380 They would say that is a surely clean- enough resource and, meaning on timescales 15 00:01:29,380 --> 00:01:33,271 here, it is exploitable of the order of one human life expectancy, it's 16 00:01:33,271 --> 00:01:37,670 controllable especially economically and politically, it is depreciable 17 00:01:37,670 --> 00:01:43,909 economically and it leads so to a very high profit for some players. 18 00:01:43,909 --> 00:01:47,359 Unfortunately there's also the technological part and here sometimes it's 19 00:01:47,359 --> 00:01:54,000 driven by hope, saying it will be OK. But, as we know, it might be mostly harmless. 20 00:01:54,000 --> 00:01:58,909 So as we see here for instance there are catastrophes like Chernobyl. This is after 21 00:01:58,909 --> 00:02:03,530 the catastrophe where you have the memorial for the people who died. Then you 22 00:02:03,530 --> 00:02:09,729 have scenarios during the catastrophe here. This is Deepwater Horizon being like 23 00:02:09,729 --> 00:02:15,050 desperately tried to extinguish the fire by the US Coast Guard and Fire Brigades. 24 00:02:15,050 --> 00:02:20,050 And of course – what I don't have to mention here, but in times of fake news 25 00:02:20,050 --> 00:02:25,760 it's important to mention – we are before the catastrophe. So this is here a plot of 26 00:02:25,760 --> 00:02:31,420 the carbon dioxide concentration in the atmosphere taking from ice. And as you see 27 00:02:31,420 --> 00:02:36,750 here the ice ages give this variations over 500,000 years, and now we are at this 28 00:02:36,750 --> 00:02:41,670 spot here that points up. And if you resolve this into the time scale, extent 29 00:02:41,670 --> 00:02:46,310 this time scale from the last thousand to 2,000 years here – so we are here at this 30 00:02:46,310 --> 00:02:51,540 spot at 2000, year 2000 – then you see that this rise has started at the 31 00:02:51,540 --> 00:02:55,590 industrialization. So it's a clear sign that we have to do something. And we have 32 00:02:55,590 --> 00:02:56,787 to do it quickly. 33 00:02:56,790 --> 00:03:05,620 *Applause* 34 00:03:05,620 --> 00:03:10,140 Christoph: So now let's try to propose something which can be part of the 35 00:03:10,140 --> 00:03:15,570 solution, namely sustainable energies. And here's a wish list of what probably you 36 00:03:15,570 --> 00:03:19,590 would think it should be: It should be sustainable, ubiquitous, continous, 37 00:03:19,590 --> 00:03:24,270 accessible and profitable at the very end. So does such a source exist? And first I 38 00:03:24,270 --> 00:03:28,130 should define what it means. So sustainable means it should serve present 39 00:03:28,130 --> 00:03:31,940 needs without compromising the future – and this is clearly not what we are doing 40 00:03:31,940 --> 00:03:38,470 now – so it should be available on timescales which are like the lifetime of 41 00:03:38,470 --> 00:03:43,150 our central star if possible. It should be ubiquitous, meaning that it should be 42 00:03:43,150 --> 00:03:48,780 present almost on any location on earth so that we can without a very complicated 43 00:03:48,780 --> 00:03:54,290 long-range infrastructure have access to the energy. It should be continuous, 44 00:03:54,290 --> 00:03:58,720 meaning it should be present at almost any day time and seasons, so that we can plan 45 00:03:58,720 --> 00:04:02,680 of what we produce. And of course it should be accessible, meaning it can be 46 00:04:02,680 --> 00:04:08,530 tapped by the technology and lead to a significant contribution to our energy 47 00:04:08,530 --> 00:04:14,530 mix. And profitable should of course also be. So does it exist? And the answer is 48 00:04:14,530 --> 00:04:20,620 yes and I want to show that this airborne wind energy can be a big part of it. So 49 00:04:20,620 --> 00:04:27,540 here I have a table of some sustainable energy sources and the wishlist items are 50 00:04:27,540 --> 00:04:33,130 written here and I put some of the sustainable sources. So there is fusion, 51 00:04:33,130 --> 00:04:38,050 there is solar energy – terrestrial and also the spacial energy which was 52 00:04:38,050 --> 00:04:42,820 presented by Anja and by Stefan before – hydro energy, geothermal energy and 53 00:04:42,820 --> 00:04:47,180 conventional wind energy; where by conventional wind energy I mean wind 54 00:04:47,180 --> 00:04:53,720 energy up to approximately 100 meter which is the hub height of wind turbines, 55 00:04:53,720 --> 00:05:00,290 approximately. And as you can see some of these items here are not fulfilled by all 56 00:05:00,290 --> 00:05:08,310 these different approaches. So for example the spacial energy is clearly not 57 00:05:08,310 --> 00:05:13,840 ubiquitous, because you have this beam as we heard which is just like basically 58 00:05:13,840 --> 00:05:17,680 hitting a certain spot on the earth and there are transferred into energy, so you 59 00:05:17,680 --> 00:05:23,180 have to distribute this energy. Also it is not yet accessible. On the other hand wind 60 00:05:23,180 --> 00:05:27,270 energy – here conventional wind energy – is not ubiquitous, because you can only 61 00:05:27,270 --> 00:05:32,210 select certain spots. And it is not continuous, because you cannot really plan 62 00:05:32,210 --> 00:05:37,750 when the wind is blowing and when it's not blowing. So let's add to this list what is 63 00:05:37,750 --> 00:05:42,180 called high altitude wind. And high altitude wind is clearly sustainable, 64 00:05:42,180 --> 00:05:46,730 because it's also wind energy – so it's like driven as all the other wind energy 65 00:05:46,730 --> 00:05:53,680 as well. And high altitude here means to go to heights which are above 200 meters 66 00:05:53,680 --> 00:06:04,570 and try to drain energy from these winds. So let me argue why it is a ubiquitous 67 00:06:04,570 --> 00:06:10,250 source. And for this Philip who is also here and part of the team – I'm very happy 68 00:06:10,250 --> 00:06:15,090 he has made this very nice plot here which shows the western part of Europe and it 69 00:06:15,090 --> 00:06:20,800 shows the ratio of wind power which you can extract at an optimal height which 70 00:06:20,800 --> 00:06:24,990 should be below 1,000 meter – so this is just an arbitrary at the moment limit – to 71 00:06:24,990 --> 00:06:31,100 say that we can have a system which can basically get up to thousand meter height 72 00:06:31,100 --> 00:06:38,310 and compare it to the wind energy which is basically available at hundred meter. And 73 00:06:38,310 --> 00:06:43,280 in this plot you can see at the coastline there is a line here and this line is the 74 00:06:43,280 --> 00:06:48,311 line where in the interior you have already a doubling of the wind power. So 75 00:06:48,311 --> 00:06:53,199 meaning at the coast line itself if you go to higher altitude you have the double 76 00:06:53,199 --> 00:06:58,100 wind power available then at hundred meter. Even better, directly at the coast 77 00:06:58,100 --> 00:07:01,880 line there is another line which is a factor of four better. So as soon as you 78 00:07:01,880 --> 00:07:07,990 put your wind turbines on land side, you will be a factor of, you have access to a 79 00:07:07,990 --> 00:07:12,490 factor of four higher wind power. And here, in the region slightly south of 80 00:07:12,490 --> 00:07:17,590 Leipzig, there's another line, this is a factor of eight where you become better in 81 00:07:17,590 --> 00:07:23,780 wind power, in high altitudes wind power. So, seeing that the coastal regions have 82 00:07:23,780 --> 00:07:27,680 already a factor of four in this ratio better and the inland between four and 83 00:07:27,680 --> 00:07:33,320 eight. Oh, the wrong sign. Sorry, they should be reversed of course. So, saying 84 00:07:33,320 --> 00:07:39,900 that here the site of conventional wind- energy harvesting, which are now very 85 00:07:39,900 --> 00:07:44,091 limited, and where you put for instance all the wind turbines in the north, they 86 00:07:44,091 --> 00:07:47,410 become much more accessible if you go to higher heights. Because there you can 87 00:07:47,410 --> 00:07:53,389 basically use all the land sites. So this is where you have more sites available 88 00:07:53,389 --> 00:08:00,479 when you harvest at optimal height. And here, as an example about why it is a 89 00:08:00,479 --> 00:08:06,080 continuous source, you see a time distribution of the wind velocity in 90 00:08:06,080 --> 00:08:15,210 January 2016 in Leipzig. The wind velocity is here increasing from yellow to red, and 91 00:08:15,210 --> 00:08:19,729 the altitude is displayed here, and this is the time scale of the month. And what 92 00:08:19,729 --> 00:08:24,229 you can see is, at hundred meter height you have almost like only in the lower 93 00:08:24,229 --> 00:08:27,770 parts you have winds, whereas, if you go to higher heights you have the reddish 94 00:08:27,770 --> 00:08:33,019 parts where you have high wind velocities. So this shows that continuity is already 95 00:08:33,019 --> 00:08:38,070 improved if you go to higher altitude, especially for land sites. And this is 96 00:08:38,070 --> 00:08:42,458 almost impossible for conventional wind turbines. You would have to build a mast 97 00:08:42,458 --> 00:08:48,959 higher and much, much bigger structures. And also, what is displayed here is the 98 00:08:48,959 --> 00:08:53,160 optimal harvesting height. So this is the height, again below thousand meter, where 99 00:08:53,160 --> 00:08:59,720 it would be optimal to harvest wind at a certain time, displayed over the whole 100 00:08:59,720 --> 00:09:07,389 month. And if one goes from this plot to the histograms, so to the time 101 00:09:07,389 --> 00:09:11,509 distribution of the different wind velocities, you get this picture here. So 102 00:09:11,509 --> 00:09:16,709 this are the spots the histograms of 100, 170, 500, 1000 meter, and of the optimal 103 00:09:16,709 --> 00:09:20,790 height, so if you adjust your height. And one of the things that you can see is that 104 00:09:20,790 --> 00:09:26,600 the mean is clearly shifted to higher wind velocities if you increase the height. And 105 00:09:26,600 --> 00:09:31,769 also, if you harvest at optimal altitude you shift the whole probability 106 00:09:31,769 --> 00:09:36,870 distribution to the right. So and what increases there is that the fraction of 107 00:09:36,870 --> 00:09:43,430 time below five meter per second, which is like the the time where the cut in wind 108 00:09:43,430 --> 00:09:47,470 speed for a wind turbine, so you would like starting produce energy, the 109 00:09:47,470 --> 00:09:53,279 probability to have such winds is increased from 76% to 87%, which is quite 110 00:09:53,279 --> 00:09:58,940 a lot of increase. So adjusting to varying optimal harvesting height is not only 111 00:09:58,940 --> 00:10:03,110 almost, but is really impossible for conventional wind turbines. So one has to 112 00:10:03,110 --> 00:10:07,889 find another technology, which is better and can give you access to this higher 113 00:10:07,889 --> 00:10:17,329 altitude winds. So this is the plot again from before. So I have now a little bit 114 00:10:17,329 --> 00:10:22,269 motivated why the source is ubiquitous and continuous. Now the question is, is it 115 00:10:22,269 --> 00:10:26,060 accessible, and how it is accessible. And this is the technological part which is 116 00:10:26,060 --> 00:10:33,050 called airborne wind energy. So how do we access these high altitude winds. So on 117 00:10:33,050 --> 00:10:37,399 for these, let's come back to the design challenges, which would be necessary to go 118 00:10:37,399 --> 00:10:43,050 to higher height. So high altitude means, that you just cannot just increase your 119 00:10:43,050 --> 00:10:48,559 tower, and have more torque on your foundation, and just scale up the system. 120 00:10:48,559 --> 00:10:52,860 So you should avoid proliferation of mass and proliferation of the tower and 121 00:10:52,860 --> 00:10:57,300 foundation. And also, varying altitude means you shouldn't have passive, 122 00:10:57,300 --> 00:11:03,850 stabilizing, static structures, but find something which can vary. So just as an 123 00:11:03,850 --> 00:11:12,459 example here this is the sky walk in the Grand Canyon, and this is already a quite 124 00:11:12,459 --> 00:11:17,120 scary lever arm which you have. And if, in comparison, you take your modern wind 125 00:11:17,120 --> 00:11:21,000 turbine, you rotate it by 90 degrees, and compared it in size to this, you can see 126 00:11:21,000 --> 00:11:27,319 what kind of torque will be, like will act on the foundation. So this is already a 127 00:11:27,319 --> 00:11:34,350 very big piece of technology you have here. So we have to do better, and this is 128 00:11:34,350 --> 00:11:40,920 the second part, namely airborne wind energy, so the technology itself. So the 129 00:11:40,920 --> 00:11:46,420 first slide is probably the most important of this part because it explains the 130 00:11:46,420 --> 00:11:51,769 idea behind this technology. So you take autonomous drones, which are the most 131 00:11:51,769 --> 00:11:56,970 flexible connected to the ground via tethers, and extract wind energy via these 132 00:11:56,970 --> 00:12:02,620 drones. So how does it work? So look at this conventional wind turbine here. You 133 00:12:02,620 --> 00:12:08,079 have most of the energy is produced by the outer part of the wings. They are rotating 134 00:12:08,079 --> 00:12:11,860 with the highest velocity, and at the same time you have the highest the largest 135 00:12:11,860 --> 00:12:15,689 lever arm. So you produce most of the energy in the outer part. The inner part 136 00:12:15,689 --> 00:12:20,399 is more or less passive, stabilizing structure. So you remove that structure 137 00:12:20,399 --> 00:12:25,790 and replace it by something which is flexible, and the first which comes to 138 00:12:25,790 --> 00:12:31,079 mind probably is a tether with which you attach it to the ground. And then you have 139 00:12:31,079 --> 00:12:35,101 just the active part here, which is now an aircraft, moving in this circle, which 140 00:12:35,101 --> 00:12:41,550 before was circulated by the wing tips, to extract your energy. This is the 141 00:12:41,550 --> 00:12:47,970 principle. So how do we bring down the power when circulating this aircraft? So 142 00:12:47,970 --> 00:12:53,510 we have to, in some way, transform it to electric power. So there are, which are 143 00:12:53,510 --> 00:12:57,279 not shown in the picture before, lighter than air systems. So you just basically 144 00:12:57,279 --> 00:13:04,040 take a balloon, you put your wind turbine at high altitude, and extract the power. 145 00:13:04,040 --> 00:13:09,189 And here the tether can clearly serve as the power line. But what we can also do is 146 00:13:09,189 --> 00:13:14,240 crosswind flight, which was shown in the picture before. So here you have a moving 147 00:13:14,240 --> 00:13:19,250 aircraft, which can move in something which is called the drag mode, meaning 148 00:13:19,250 --> 00:13:23,619 that you have onboard generators on the aircraft. So essentially it's a propeller 149 00:13:23,619 --> 00:13:28,829 aircraft, but the propellers are reversed in repeller mode, so that the repellers 150 00:13:28,829 --> 00:13:33,050 produce energy for you. And then the tether serves as power line. So this 151 00:13:33,050 --> 00:13:37,779 principle is shown here. So here you can see the generators and then the power is 152 00:13:37,779 --> 00:13:45,149 brought down by the tether. In the second part, second strategy, is using the so 153 00:13:45,149 --> 00:13:51,259 called lift mode So here you have ground based generators and the tether itself 154 00:13:51,259 --> 00:13:55,360 transmits the power, there are no power lines in the tether. So here you use that 155 00:13:55,360 --> 00:14:00,230 the power is given by the pulling force times the reel out velocity of the tether. 156 00:14:00,230 --> 00:14:05,170 So you circulate in some patterns with your aircraft and you use the lift force 157 00:14:05,170 --> 00:14:10,059 acting on the aircraft to unreal this tether from a drum, and at the drum, on 158 00:14:10,059 --> 00:14:14,899 the base station, there's a generator attached which helps you to get the 159 00:14:14,899 --> 00:14:18,589 energy, to transform the energy into electrical energy. And of course, at some 160 00:14:18,589 --> 00:14:23,629 point the tether is maximally reeled out and then you have to have to go to a reel 161 00:14:23,629 --> 00:14:28,400 in phase, where with minimal energy you reel in the tether again, and start 162 00:14:28,400 --> 00:14:35,560 periodically this phase again. So these are the concepts, and there's a whole zoo 163 00:14:35,560 --> 00:14:39,870 of airborne wind energy devices and proposals, which show that this technology 164 00:14:39,870 --> 00:14:43,819 is still in a very early stage of being developed. So you have people here flying 165 00:14:43,819 --> 00:14:48,709 figure-of-eight patterns with the aircraft. So some things are lighter than 166 00:14:48,709 --> 00:14:53,410 air turbines, which look very exotic like this one, probably this one you have seen 167 00:14:53,410 --> 00:14:58,739 in media already. Proposals like this here. There are quad copters, which 168 00:14:58,739 --> 00:15:05,699 produce the energy by rotating of their, of the propellers here. And all kind of 169 00:15:05,699 --> 00:15:15,649 exotic lever arm and aircrafts which you can use. So let's bring a little bit of 170 00:15:15,649 --> 00:15:21,629 more order into the technology, into the proposals. And one of the things I want to 171 00:15:21,629 --> 00:15:27,209 discuss, which is very promising, is what is called crosswind flight. So here as a 172 00:15:27,209 --> 00:15:32,739 example is a comparison of a conventional, lighter-than-air system with the big wheel 173 00:15:32,739 --> 00:15:40,129 in London. So this is one of the biggest wind turbines. And the harvesting area is, 174 00:15:40,129 --> 00:15:43,689 so the effective area of such a wind turbine is the swept area of your 175 00:15:43,689 --> 00:15:48,589 propellers, essentially. So now let's look what happens if you move an aircraft 176 00:15:48,589 --> 00:15:55,309 instead through the wind. Then the picture of before is like of that size. And if you 177 00:15:55,309 --> 00:16:01,040 take an aircraft, which has the same wing area as the wing areas of the propeller 178 00:16:01,040 --> 00:16:07,170 here, you're harvesting area is of that size. It's much bigger. And the reason for 179 00:16:07,170 --> 00:16:12,970 this is, that the effective area is now given by the wing area times a 180 00:16:12,970 --> 00:16:17,389 coefficient, which is the square fraction of the lift to drag coefficient of the 181 00:16:17,389 --> 00:16:21,529 aircraft times the lift coefficient itself. And this factors of the order of 182 00:16:21,529 --> 00:16:30,689 200. So it increases the efficiency of your of your wings dramatically. This was 183 00:16:30,689 --> 00:16:38,769 already found by Loyd in 1980. And you can now ask "Why does it take 30 years from 184 00:16:38,769 --> 00:16:43,839 this idea to first systems?". And the answers is, in this community for is 185 00:16:43,839 --> 00:16:49,189 probably a very interesting is "Why are these prototypes are appearing only 30 186 00:16:49,189 --> 00:16:52,439 years later?". It's because sufficient computer power. So for the control 187 00:16:52,439 --> 00:17:00,389 algorithms, which allow you to control such flight modes, was not available. So, 188 00:17:00,389 --> 00:17:06,409 as an example, here's an illustration of one of the current leaders in the field 189 00:17:06,409 --> 00:17:11,630 called AMPYX POWER, showing a crosswind airborne wind energy system versus a 190 00:17:11,630 --> 00:17:15,500 conventional system. So here's the conventional wind turbine for two 191 00:17:15,500 --> 00:17:20,010 megawatts. And the conventional this is a conventional system. And the airborne wind 192 00:17:20,010 --> 00:17:26,099 system is, this is the ground station, and this is the aircraft. So one of the things 193 00:17:26,099 --> 00:17:32,070 which are, I mean, visible in this picture is that it has much less like even sight 194 00:17:32,070 --> 00:17:35,710 impact in the environment. So having something like this is much less 195 00:17:35,710 --> 00:17:39,950 disturbing from the even from the aesthetic point of view, than this huge 196 00:17:39,950 --> 00:17:47,980 wind turbine. So now the next step would be to look closer to the technology and 197 00:17:47,980 --> 00:17:53,630 see what are the AWE system components that you need, that you need to build such 198 00:17:53,630 --> 00:17:59,950 a device. So first of all, there is the drone or the fixed-wing aircraft. We have 199 00:17:59,950 --> 00:18:03,929 seen that it's very good to have large lift and small drag coefficients, so you 200 00:18:03,929 --> 00:18:10,090 need something which is like a rigid glider, more or less. On board you need 201 00:18:10,090 --> 00:18:16,940 sensors, like accelerometer, gyroscope, GPS, receiver, barometer, and a pitot tube 202 00:18:16,940 --> 00:18:25,080 to measure the air the air speed. And this is to determine the system state, that 203 00:18:25,080 --> 00:18:30,200 then is like reacted on by the control surfaces, in the case of an aircraft by 204 00:18:30,200 --> 00:18:34,710 ailerons flaps and the rudder. Moreover, you need of course a microcontroller and 205 00:18:34,710 --> 00:18:40,730 algorithms which do the state estimation. So from the sensor data they compute the 206 00:18:40,730 --> 00:18:46,019 state of the system, meaning it's position, altitude, velocity. And you have 207 00:18:46,019 --> 00:18:51,429 to navigate. So and of course you might need something like a propeller for 208 00:18:51,429 --> 00:18:59,070 takeoff, landing, and energy generation in case of drag mode. The second thing is of 209 00:18:59,070 --> 00:19:03,340 course the ground station. So here you need the drum for tether wind-up. You need 210 00:19:03,340 --> 00:19:08,559 a motor which eventually has to be transformed into generator mode if you 211 00:19:08,559 --> 00:19:12,409 have the lift mode. You need power converters, also microcontrollers and 212 00:19:12,409 --> 00:19:16,510 algorithms which synchronize your ground- station operation with the drone; and you 213 00:19:16,510 --> 00:19:22,299 need a runway, catapult or something alike for takeoff and landing. So far it looks 214 00:19:22,299 --> 00:19:28,320 quite simple, but the devil is in the detail. And here I found a nice quote a 215 00:19:28,320 --> 00:19:33,510 colleague of mine – (uninteligble name) – has done in one of his talks, 216 00:19:33,510 --> 00:19:37,170 and I liked it very much because it displays very well what challenges have to 217 00:19:37,170 --> 00:19:42,600 be still overcome. So it starts with "Theory is when nothing works but everyone 218 00:19:42,600 --> 00:19:48,100 knows why." and to demonstrate this let's have a look at this video here which is 219 00:19:48,100 --> 00:19:56,539 one of the flight attempts of one of the companies: So the aircraft lifts off, 220 00:19:56,539 --> 00:19:58,640 there's no sound … yet. Now there is sound. 221 00:19:58,640 --> 00:20:02,740 *Background music of shown video* 222 00:20:02,740 --> 00:20:05,030 Speaker in shown video: Abort! Abort! Abort! 223 00:20:05,030 --> 00:20:07,898 *Soft laughter* 224 00:20:07,898 --> 00:20:13,110 Christoph: Yeah. And the desperation of the founder was clearly hearable at the 225 00:20:13,110 --> 00:20:16,750 end. And you could see that the tether ruptured. And then there was no way to 226 00:20:16,750 --> 00:20:23,120 recover that most of the aircraft was lost. Second: "Sometimes practice is when 227 00:20:23,120 --> 00:20:27,130 everything works but no one knows why." So there are also positive surprises. And 228 00:20:27,130 --> 00:20:33,330 here is a launch, a catapult launch, for an aircraft which now uses weight. 229 00:20:33,330 --> 00:20:43,290 *Background noise of shown video* *Laughter* 230 00:20:43,290 --> 00:20:48,360 Christoph: So a positive surprise for a test. And finally, sometimes if you 231 00:20:48,360 --> 00:20:52,700 combine theory and practice then "nothing works but no one knows why". This is where 232 00:20:52,700 --> 00:20:57,210 the complication really is: The devil is in the detail. And here you can see a 233 00:20:57,210 --> 00:21:00,649 video from a flight which is crosswind flight: Everything seems normal … 234 00:21:00,649 --> 00:21:14,450 *Dramatic background music of shown video* Christoph: … and then the prototype is 235 00:21:14,450 --> 00:21:23,380 again lost. So this is complicated. So but there is a lot of progress and so I want 236 00:21:23,380 --> 00:21:28,379 to come closely, very quickly introduce the current industrial status. So I focus 237 00:21:28,379 --> 00:21:32,360 on three companies which work on that: So one of them is Enerkite in Berlin, and 238 00:21:32,360 --> 00:21:36,640 they have now a system which is basically stationed on such a truck and this is a 239 00:21:36,640 --> 00:21:41,660 crosswind system of a passive wing. So it steered via three tethers and it produces 240 00:21:41,660 --> 00:21:47,710 up to 30 kilowatts of energy. Then you have Ampyx Power. They have here the 241 00:21:47,710 --> 00:21:51,580 launching site in the Netherlands and they are currently producing this aircraft 242 00:21:51,580 --> 00:21:58,210 here. This type which is a crosswind system in lift mode. And at the end will 243 00:21:58,210 --> 00:22:04,101 produce up to 250 kilowatts of power. This is under construction. And, finally, there 244 00:22:04,101 --> 00:22:10,929 is Google X Makani in California. And they have built a drag-mode aircraft – here – 245 00:22:10,929 --> 00:22:15,750 which is flying. And I can show you a video that they have on their home page – 246 00:22:15,750 --> 00:22:21,799 very nicely. Where they show a flight so that you can see that the 600 kilowatt 247 00:22:21,799 --> 00:22:26,700 system is working. Here you see the onboard propellers. You can see the 248 00:22:26,700 --> 00:22:32,570 tether. Down here this is from the tether attachment point. So the things are 249 00:22:32,570 --> 00:22:42,970 working. There are prototypes. But one of the things which are important is: one has 250 00:22:42,970 --> 00:22:47,300 to "test, test, test" and get experience from tests. So "experience is what you get 251 00:22:47,300 --> 00:22:52,480 when you were expecting something else". You really. So what does it mean? So we 252 00:22:52,480 --> 00:22:57,299 have to test, analyze, adapt the systems. So because many – as you could see from 253 00:22:57,299 --> 00:23:01,429 this design variations in the zoo which I've shown – many of the concepts are 254 00:23:01,429 --> 00:23:06,559 still open. So for example the design of the airframe. If you use a biplane, a 255 00:23:06,559 --> 00:23:10,190 flying wing or anything alike – or something totally different – is still 256 00:23:10,190 --> 00:23:14,860 open. The tether construction – what kind of materials to use – is still open. The 257 00:23:14,860 --> 00:23:20,590 materials in itself is still open for the aircraft etc. etc.. The mode of operation 258 00:23:20,590 --> 00:23:25,070 – that means takeoff, landing and direct versus lift mode – is still an open 259 00:23:25,070 --> 00:23:30,299 question. What is the best thing to realize for industrial products? And then 260 00:23:30,299 --> 00:23:34,649 control hardware and software algorithms have to be tested thoroughly. Of course 261 00:23:34,649 --> 00:23:40,720 it'd have to be certified by the aerospace agencies, of course. You want to have a 262 00:23:40,720 --> 00:23:46,119 failsafe. So what you have to do is you want to even, I mean, have total losses in 263 00:23:46,119 --> 00:23:49,979 experiment. You want to do the experiments wich would lead to a total loss of your 264 00:23:49,979 --> 00:23:56,210 system. So here comes the idea that instead you should build a cheap and 265 00:23:56,210 --> 00:24:01,949 disposable test platform instead of a largely scaled-up system first, before you 266 00:24:01,949 --> 00:24:05,860 build the expensive prototype and do tests on them. And this brought us to the idea 267 00:24:05,860 --> 00:24:10,559 to provide a low-cost open-source test platform where everybody at home can build 268 00:24:10,559 --> 00:24:15,890 his own wind drone. And this is the third part of the talk. So the do-it-yourself 269 00:24:15,890 --> 00:24:24,340 wind drone. What are the ingredients here? So first you need a drone, so here I want 270 00:24:24,340 --> 00:24:29,120 to show the airframe and reinforcement hack which is necessary to prepare your 271 00:24:29,120 --> 00:24:33,330 airframe for the additional forces by adding the tether. Then there's a ground 272 00:24:33,330 --> 00:24:37,740 station and here I want to motivate why the drone is essentially behaving like a 273 00:24:37,740 --> 00:24:44,110 fish – in this case a barracuda. The next thing is navigation on curved manifold is 274 00:24:44,110 --> 00:24:48,680 very important because you have like a constraint coming from the tether. And 275 00:24:48,680 --> 00:24:54,100 finally you need something for control which is the autopilot. So in this case 276 00:24:54,100 --> 00:25:01,120 it's the ardupilot open-source project which we adapted. So let's come to the 277 00:25:01,120 --> 00:25:05,890 airframe-reinforcement-hack. So what you use: Take your favourite polystyrene 278 00:25:05,890 --> 00:25:11,289 airframe – so in this case it's an Easy Star II – and glue the wings together. 279 00:25:11,289 --> 00:25:15,580 This is the lower side of the wings. You put in there a carbon rod – here in this 280 00:25:15,580 --> 00:25:21,139 part – and you stabilize it with racks which you glue into the slits we can see 281 00:25:21,139 --> 00:25:29,179 here. And then you wrap carbon in the forward part of it where the most of the 282 00:25:29,179 --> 00:25:35,789 aerodynamic force is attached. Then you have the carbon ???? ???? wind around your 283 00:25:35,789 --> 00:25:44,320 tether. And you install additional tubes for fixing the wings on the fuselage. So 284 00:25:44,320 --> 00:25:48,610 the fuselage is here. We cut off the engine blocks, included additional carbon 285 00:25:48,610 --> 00:25:52,639 rods. So you can put these carbon rods on these carbon rods here, and fix everything 286 00:25:52,639 --> 00:25:59,570 with screws. So to show you how that looks like and what are the size of this model 287 00:25:59,570 --> 00:26:05,799 is: So here is the original-size aircraft with carbon. And you can later – if you 288 00:26:05,799 --> 00:26:15,330 want – pass by the assembly area and look at it and have a look at it and touch it. 289 00:26:15,330 --> 00:26:20,580 So this is how it looks decomposed into different components: So again wings and 290 00:26:20,580 --> 00:26:27,269 so on and so on, the servos for the control surfaces. The central unit here is 291 00:26:27,269 --> 00:26:33,150 the Pixhawk autopilot. So there's a microcontroller which contains some of the 292 00:26:33,150 --> 00:26:37,340 sensors: You have a GPS sensor, in addition you have a telemetry antenna for 293 00:26:37,340 --> 00:26:45,830 data – for data transfer to the ground station. And you have RC control for 294 00:26:45,830 --> 00:26:51,580 manual control when you switch out of auto mode to have manual control in emergency 295 00:26:51,580 --> 00:26:58,740 situations – or if you want to make other kind of flight tests. So now this is the 296 00:26:58,740 --> 00:27:02,560 drone itself. So now is the question what to do with the ground station. And here 297 00:27:02,560 --> 00:27:09,250 let's look why the drone behaves as a fish: Because what it does is, like in 298 00:27:09,250 --> 00:27:13,059 fishing, you would need a free-moving tether; it has to be fast and fail-safe 299 00:27:13,059 --> 00:27:16,889 reeled in and reeled out; and it should remain twist free so that it doesn't give 300 00:27:16,889 --> 00:27:21,490 any knots if it is not under tension. And the thing which we came up with wich best 301 00:27:21,490 --> 00:27:27,559 serves for our needs at the moment is an off-shore fishing reel. 302 00:27:27,559 --> 00:27:33,769 *Applause* Christoph: So and you need offshore here 303 00:27:33,769 --> 00:27:37,889 because the drum has to be perpendicular to the rod: This guarantees you like 304 00:27:37,889 --> 00:27:42,750 reload phases twist free on the tether. Other fishing rods have the drum 305 00:27:42,750 --> 00:27:47,549 aligned with the rod, and then you accumulate twist on the tether which can 306 00:27:47,549 --> 00:27:52,769 lead to knots, lead to knots and then … it's not a good idea. It will destroy your 307 00:27:52,769 --> 00:27:56,950 tether. So and this is the first flight test. So we were very enthusiastic and 308 00:27:56,950 --> 00:28:02,650 started the first flight test. And here it is. 309 00:28:02,650 --> 00:28:13,149 *Indistinct voice in shown video* Voice in shown video: OK. … Hinterher? 310 00:28:13,149 --> 00:28:15,139 *Laughter* Visv: Versuch mal rauszugehen. Manual? 311 00:28:15,139 --> 00:28:17,789 Achtung, Achtung! Versuch ihn zu fangen. Na gut. 312 00:28:17,789 --> 00:28:19,779 *Beeping in shown video* Christoph: OK. 313 00:28:19,779 --> 00:28:23,259 *Laughter* Christoph: So unfortunately it did not 314 00:28:23,259 --> 00:28:27,620 work. *Applause* 315 00:28:27,620 --> 00:28:34,720 Christoph: So what happens? This was the result: The tail was broken. And because 316 00:28:34,720 --> 00:28:38,749 the tether apparently wrapped around the back of the aircraft and then it became 317 00:28:38,749 --> 00:28:42,700 uncontrollable. So we came up with what do we do: If you don't know any further, any 318 00:28:42,700 --> 00:28:47,700 better, use carbon! So we put some carbon on the lower part of the of the fuselage 319 00:28:47,700 --> 00:28:53,499 to reinforce it. And then of course you have to think about writing your 320 00:28:53,499 --> 00:29:00,019 navigation code, to navigate if you are under tethered flight. So here is the 321 00:29:00,019 --> 00:29:05,360 receipe for how to do it: So first you take one git clone of ardupilot – this 322 00:29:05,360 --> 00:29:09,019 autumn open-source software. You take one curved 2-dimensional manifold – 323 00:29:09,019 --> 00:29:13,700 it's essentially giving us a hypersurface embedded in 3-dimensional Euclidean space. 324 00:29:13,700 --> 00:29:18,220 In case of constant tether length this is just a semi-hemisphere as to which is 325 00:29:18,220 --> 00:29:22,160 centered around your ground station. Then you take a planar curve which you want to 326 00:29:22,160 --> 00:29:28,070 fly along – or curved segments – and a pinch of Differential Geometry to wrap it 327 00:29:28,070 --> 00:29:32,230 on the sphere, to make this curve appearing on the sphere. You take a little 328 00:29:32,230 --> 00:29:38,279 bit of Classical Mechanics for the flight control to transfer the curve 329 00:29:38,279 --> 00:29:45,549 accelerations into actually control- surface motions. And then you need, of 330 00:29:45,549 --> 00:29:51,559 course, 12 dozen coffee for doing so. You put everything together into – of course 331 00:29:51,559 --> 00:29:55,620 not the coffee – into the computer algebra system and stir well, and let the CPU bake 332 00:29:55,620 --> 00:30:03,559 it at 100 degrees, and then you come up with a smooth – at least C¹ – curve. 333 00:30:03,559 --> 00:30:09,350 *Applause* Christoph: So the curve is shown here. So 334 00:30:09,350 --> 00:30:13,820 it's … this is one part of a figure-8 pattern. So the other part would be behind 335 00:30:13,820 --> 00:30:17,949 here. It's composed of two geodesic segments and one turning segment and they 336 00:30:17,949 --> 00:30:21,720 are C¹ glued together here. And these are the equations: So you can find in the 337 00:30:21,720 --> 00:30:26,899 paper – I don't want to go into detail. So now you have to modify the source code of 338 00:30:26,899 --> 00:30:31,450 this ardupilot project. So here there are highlighted the patterns which you 339 00:30:31,450 --> 00:30:35,289 basically have to … where you have to do modifications: You have to implement new 340 00:30:35,289 --> 00:30:42,139 flight modes and change some of the control algorithms. And then you come up 341 00:30:42,139 --> 00:30:49,499 with the next flight test. And here is the next attempt. 342 00:30:49,499 --> 00:31:11,389 *Music and propellor sounds* Voice in shown video: Beim Auswerten 343 00:31:11,389 --> 00:31:28,909 müssen wir sehen, ob wir dann verschiedene wählen. 344 00:31:28,909 --> 00:31:35,480 *Music ends* *Applause* 345 00:31:35,480 --> 00:31:41,160 Christoph: The whistling sound you have heard at the end is the tether being 346 00:31:41,160 --> 00:31:45,259 dragged through the air. So there was really tension on the tether. And you can 347 00:31:45,259 --> 00:31:50,019 also see this if you do a data analysis on the flight data later. So yes for example 348 00:31:50,019 --> 00:31:54,539 multiple possibilities. You have a lot of data which is possible to analyze. So the 349 00:31:54,539 --> 00:31:59,610 autopilot this was very very it's very very nicely done in this open-source 350 00:31:59,610 --> 00:32:04,210 project: So they have a data file with all primary and secondary data you can use for 351 00:32:04,210 --> 00:32:08,049 your analysis. So for instance this is the flight curve of different flight modes 352 00:32:08,049 --> 00:32:11,919 which we used. You have the altitude of the aircraft, you can look to deviations 353 00:32:11,919 --> 00:32:16,440 in radial and transverse directions. You can look to tether tension – or like a 354 00:32:16,440 --> 00:32:20,621 measure for tether tension – by looking to the length variation of the tether. And 355 00:32:20,621 --> 00:32:26,519 you can of course do time series analysis of how your figure-8 pattern has flown 356 00:32:26,519 --> 00:32:33,620 along. And that is what you can do with this very very nice autopilot open-source 357 00:32:33,620 --> 00:32:40,359 software which is available when … written by many many people on the internet. So 358 00:32:40,359 --> 00:32:44,019 the question which remains is: After all of this is, will it be a fail-safe to 359 00:32:44,019 --> 00:32:49,929 100%? And the answer is nope, it will not! It will … there will be of course 360 00:32:49,929 --> 00:32:56,850 accidents happen. But the thing is: Nothing is failsafe. And so here's a 361 00:32:56,850 --> 00:33:00,960 standard wind turbine and look for yourself. 362 00:33:00,960 --> 00:33:06,070 *Laughter* Christoph: You see there is no 100% 363 00:33:06,070 --> 00:33:15,480 guarantee, but we have to try very hard to get it as failsave as possible. So yeah 364 00:33:15,480 --> 00:33:20,220 this is essentially it. That was the talk. So what I want to say is that the current 365 00:33:20,220 --> 00:33:28,919 status of airborne wind energy can be seen here by a nice book on the Springer page 366 00:33:28,919 --> 00:33:33,499 which you can download here. And we are very very happy to have any kind of 367 00:33:33,499 --> 00:33:38,280 critical remarks, input to help in developing the system further. So please 368 00:33:38,280 --> 00:33:41,860 if you want, look to this web page, there's a lot of information including a 369 00:33:41,860 --> 00:33:48,450 paper and we will be very happy for any kind of help. And finally I would again 370 00:33:48,450 --> 00:33:52,279 stress that we could rely on this tremendous work of the open-source 371 00:33:52,279 --> 00:33:56,710 community working on this autopilot project that has helped us to realize this 372 00:33:56,710 --> 00:34:02,029 project in very short time; so very happy about this. And I want to thank of course 373 00:34:02,029 --> 00:34:07,040 Phillip Bechtle, who is here, and Thomas Gehrmann and Maximillian Schulz-Herberg, 374 00:34:07,040 --> 00:34:11,250 the students, and Udo Zillmann, who can not be here, for working on this project 375 00:34:11,250 --> 00:34:14,980 and putting so much work also into it. Thank you very much for your attention! 376 00:34:14,980 --> 00:34:17,230 *Applause* 377 00:34:17,230 --> 00:34:27,670 H: We can have two more on the microphones 378 00:34:27,670 --> 00:34:32,900 here and here – one and five – so two questions. The first one, please! 379 00:34:32,900 --> 00:34:37,380 Question: So you talk, so you talked a lot about powered – and not powered –, but 380 00:34:37,380 --> 00:34:41,590 controlled flight. How does it compare – energy wise – to uncontrolled flight? 381 00:34:41,590 --> 00:34:46,400 Basically putting a propellor on a kite? Answer: So the thing is the propellor on 382 00:34:46,400 --> 00:34:53,909 the kite … with kite you mean, I guess, non-rigid structures. So meaning that the 383 00:34:53,909 --> 00:35:00,080 first question is how do you want to put a propeller on a kite if it's non rigid. So 384 00:35:00,080 --> 00:35:07,030 that is a question which goes back to you. So because that is something is not clear 385 00:35:07,030 --> 00:35:12,170 to me. But in any case rigid air frame is harder to control than a 386 00:35:12,170 --> 00:35:17,160 kite. So there are people who work with a kite. And by kite surfing or if you do 387 00:35:17,160 --> 00:35:21,740 like steer normal kites from the ground. You know it's like moving not that fast in 388 00:35:21,740 --> 00:35:27,130 the wind field, so it's easier to control. This is a big benefit of kites. And also 389 00:35:27,130 --> 00:35:32,410 the weight is a big benefit. But the power output – because of the bad or worse lift- 390 00:35:32,410 --> 00:35:37,600 to-drag coefficient – is unfortunately not that efficient as a rigid aircraft. So you 391 00:35:37,600 --> 00:35:42,280 want to go to the rigid air craft. H: If you leave the room now, please be 392 00:35:42,280 --> 00:35:45,810 quiet because we have questions and answers here! Number three please, and 393 00:35:45,810 --> 00:35:50,400 that is the last question I'm afraid. But you can ask questions after the talk. 394 00:35:50,400 --> 00:35:57,890 Q: I want to go back to the space part. I was wondering … there are some ideas about 395 00:35:57,890 --> 00:36:03,040 bootstrapping like a solar station on the moon and then like shipping, I don't know, 396 00:36:03,040 --> 00:36:08,480 hydrogen or like pre-charged lithium batteries back to earth and back and 397 00:36:08,480 --> 00:36:14,360 forth. Is it like realistic or not really? A by Anja Kohfeldt (previous talk): I 398 00:36:14,360 --> 00:36:19,280 think also this approach would be quite expensive. And you have to install this 399 00:36:19,280 --> 00:36:25,630 infrastructure on the moon first, and you have to establish the flight base back and 400 00:36:25,630 --> 00:36:30,840 forward. Realistic is a thing, you know. At the end that's a question of money and 401 00:36:30,840 --> 00:36:38,010 investment. And I'm not sure whether this would pay out, but we haven't analyzed 402 00:36:38,010 --> 00:36:44,500 this kind of approaches, yet. H: Thank you! So thank you very very much 403 00:36:44,500 --> 00:36:53,100 Stefan, Anja and Christoph! Give them a warm applause again please! 404 00:36:53,100 --> 00:36:57,210 *Applause* Stefan: Thank you! 405 00:36:57,210 --> 00:37:01,750 *Outro music* 406 00:37:01,750 --> 00:37:14,236 subtitles created by c3subtitles.de in the year 2019. Join, and help us!