Solar FPV Plane Flies Forever

We love solar power. Not only is it environmentally friendly, but it’s relatively lightweight and involves fragile high technology. Just the sort of thing that we’d want to strap onto the wings of a large model aircraft.

Solar power on a remote-controlled plane would get you unlimited cruising range. Now, a normal land-and-swap-battery process might be good enough for some people, but judging from [Prometreus]’s YouTube channel, he’s a fan of long flights over the Alps, and of pushing long-distance FPV links to the breaking point. For him and his friends, the battery power is definitely the limiting factor in how far / long he can fly.

solar-powered-plane-_-drone-_-fpv-_-built-_-rc-aircraft-rmkpjbf6dnqmkv-shot0012

All of the information we have is in the video, but that’s plenty. [Prometreus] didn’t bother with maximum-power-point tracking, but instead wired up his solar cells to work just about right for the voltage of his batteries and the level of sun that he’s seeing. So it won’t work nearly as well on cloudy days. (Check out this MPPT build that was submitted for the Hackaday Prize.)

He could switch the solar cells in an out remotely, and it’s pretty gratifying to see the consumed current in the battery go down below zero. In the end, he lands with a full battery. How cool is that?

69 thoughts on “Solar FPV Plane Flies Forever

      1. I think we can lock up the thread right here.

        Wow.

        Also, does forever exclude the diminishing capacity of batteries as they age and that motor lubrication does not last forever?

    1. Was gonna say this. Or maybe have them extend below the wing instead of above. It won’t be as efficient for boosting lift, but it will still work just as well in terms of being a rudder.

  1. I feel it’d probably be worth upping the wingspan on this, to aim for more of a glider-type affair, and ride the thermals a bit. On a side note, has anyone ever considered strapping a thermal camera onto an FPV glider? I’m not sure how well thermals would show up, but I feel it’d be interesting.

    1. you’d be better off with a rate of climb indicator, or just watching the altimeter (assuming it has one). if your flying flat and level and your altitude goes up – your in a thermal. start a slow rate turn and ride it all the way up.

    2. The thermal camera will be seeing the surface/sky/ground behind the air, and it will totally eliminate any visual difference in airtemp between. Might work with a special camera tuned to specific narrow spectrums but expensive and wouldnt be worth it with current technology (and probably problems with weight, size and so on). You wouldnt be seeing the temperature of the thermal, more the thermals effect on air or similar. Youre trying to see one coloumn of air moving different from other coloums of air.

        1. That’s interferometry and would only measure an internal volume between mirrors (using really heavy and delicately aligned parts). A variometer is the better choice.

          FWIW there are IR sensors made for gasses but they work on differential absorption of light (so looking for petroleum gasses leaking in air) rather than temperature differences – given the geekery in the “real” glider world, if those worked for finding thermal lift, most of the racers would have them.

          Example videos here: http://www.flir.com/ogi/display/?id=55671

          (I don’t work for FLIR but we use a lot of their stuff)

          1. I think it would be more advantageous to have kind of autopilot mode algorithm that flies in such a way to remain in the same area (GPS), but maximizing orientation for the solar panels and convert the extra energy in height… better not leave in autopilot too long or plane might get out of reach

          1. good idea, use 2 lowpass filters one that reacts more quickly but smooth enough to get accurate readings, and other that reacts much much slower, for the average temperature both inside and outside of thermals

    3. Here’s a video I took of that very subject; the ground is quite visible, and you can identify where thermals *probably* will be, but the air itself has very low emissivity and can’t be easily traced.

  2. This kind of relies on plain ol’ soaring rather than powered flight. There is no way he is running that motor full time and then recharging at a rate enough to power the motor along with charging the batteries. IF you have good thermals to ride, you could get aloft WITHOUT the motor using a slingshot start and use the solar cells to keep your receiver battery topped up, maybe. There is something anti-physics going on here….

    1. Could it stay in the air indefinitely, without using thermals? Just getting a bit of height with the motor, gliding a while, bit more motor, bit more glide, etc?

      If it can, then this “counts”, it’s valid. If the solar power is the only power input, and is necessary for flight. Also makes it OK to be autonomous.

      If it flew 224KM, then I dunno if it needed thermals. Can you even spot thermals from the ground, for a remote controlled model plane? I think glider pilots keep an eye out for circling birds, also exploiting thermals, as well as other signs. Unless the 224KM was round in circles over the same bit of land. Or a factory chimney.

      If it has a good glide ratio (if that’s the right term), then it won’t need to keep the motor running just to stay in the air.
      All with standard physics, unless I’ve missed a point you’re making.

      1. It folds back while not rotating, becoming more streamlined and reducing drag. Centrifugal force pulls it outward when the motor is running, so that it engages with the airstream. They sometimes do get caught in each other when folded back, which can cause a motor to shake loose when it’s started up, but that’s easily solved with a prop-stop.

    1. At the 1:05 mark in the video, is that a tracking helical antenna, or does it just look like it? (That doesn’t answer the question…just an observation.) I’d like to hear more information on this myself!

  3. Until recently, back-of-the-envelope calculations showed that the solar cells would not be able to power the /added/ energy consumption of the plane due to the weight of the solar cells. Apparently these guys JUST managed it. Wow!

  4. Few advises from the personal experience:
    1) Order a bigger batch of cells and test each-one individually – their performance differs by +-20%. Pick only the best-ones.
    2) You can overcome random shadows passively with “active solar bypass diodes”

    that should enable you pushing for 8hrs. flight

  5. Possibly the designers can follow the Swiss doing the same thing with manned-solar-powered-flight as late as last month (April 2016) in USA. It’s called the Solar Impulse (website: http://www.solarimpulse.com/).

    One innovation neither Solar Impulse nor this team have thought of is “reducing solar cell payload weight”. That would minimize payload and balance if some sort of solar paint could be used. Some may know the fate of Nanosolar who actually invented such a paint. Now only being used by the USG. However, another entity has emerged that uses Quantum Dots embedded in some sore of lightweight paint.

    The company is Nano Werk (http://www.nanowerk.com/) Berlin Germany and Honolulu Hawaii (USA).

    Imagine spray painting on the solar cells over two contacts on the wings. It’s cheaper and more efficient than normal photovoltaics.

    Quantum Dots

    1. Key word here is “imagine.” The technology doesn’t very well, and the efficiency is in the 0.5% to 3% range – on a good day.

      Intel didn’t ask us to imagine how fast our computers would be with magical 7nm technology, they simply built it and showed us.

    2. I’ll let you in on a secret…. Every solar power flying project is VERY aware of “solar cell weight”.
      If you have developed a spray-on solar cell with reasonable efficiency, then everybody would like to hear about it. Occasionally speculative research that MIGHT lead to say spray-on-solar cells gets in to the news. The researchers involved in that sort of research need to do this to generate interest and funding for their projects. However no serious results are available at this moment.

      If we assume that of the total flying weight 50% is “solar cells” then a 100% reduction in weight sounds good, but only tolerates a 50% loss in efficiency. The spray on solar cells are not at that level yet.

      For example: https://www.sciencedaily.com/releases/2015/09/150928083119.htm At the end they mention efficiency: at 5% that is about 4 times lower than what these guys used. If you can spray-paint the parking lot at wallmart, that’s an interesting level of efficiency. However for flying a rough estimate shows at least 10% (at zero weight) is required for sustained flight.

    3. I guess I should have been much more clear here; this is the invention of NANO WERK’s NOT me! Here is the SOLAR PAINT 2014 article on their website I thought an average HaD’r knew how to drill down to: their website above and path = /nanotechnology-news/newsid=34636.php. True the efficiency is only 1% and regular solar cells are up to 15%. But the very low cost price differential outweighs that.True you might have to paint on a lot or even expand UAV wingspan to accommodate. But you won’t go broke purchasing the required paint or making it yourself. And maybe the smaller amounts could accommodate trickle-charging the battery. Here is a YouTube video explaining it:

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