Quadcopter Ditches Batteries; Flies on Solar Power Alone

It seems kind of obvious when you think about it: why not just stick a solar panel on a quadcopter so it can fly on solar power? Unfortunately, physics is a cruel mistress, and it gets a bit more complex when you look at problems like weight to power ratios, panel efficiency, and similar tedious technical details. This group of National University of Singapore students has gone some way to overcome these technical issues, though: they just built a drone that is powered from solar power alone, with no batteries or other power source.

Their creation is a custom-built quadcopter made with carbon fiber that weighs just 2.6kg (about 5.7lbs), but which has about 4 square meters (about 43 square feet) of solar panels. By testing and hand-selecting the panels with the best efficiency, they were able to generate enough power to drive the four rotors, and have managed to achieve altitudes of up to 10 meters. The students have been working on prototypes of this since 2012, when their first version could only generate 45% of the power needed for flight. So, reaching 100% of flight power in the demo shown below is a significant step.

This prototype does look a bit rickety, though: all of that solar panel surface acts as a sail and will catch the wind, so we doubt it will be stable in anything more than a slight breeze. But we’re sure the future holds improvements.

34 thoughts on “Quadcopter Ditches Batteries; Flies on Solar Power Alone

  1. I had pondered about something like this but built entirely on a MEMS level. It would be pretty terrifying to have a fully autonomous assassination quads out to get you, especially if they are difficult to see or hear until they are about to explode a hole in your skull.

    1. A drone that small was envisioned by Arthur C. Clarke in the book Childhood’s End. He described it as a “force multiplier” much more effective than an atomic bomb. What a great thinker.

  2. Holy crap.

    The slow incremental march of solar panels has, over the last thirtysome years, led to abilities far beyond anything I could’ve imagined when I first played with them.

    Fixed-wing flight is one thing; it’s way more efficient and there have been solar fixed-wing drones for some time. But helicopters are another matter entirely! This is a huge milestone and the team and their professor deserve plenty of attention and congratulations for achieving it. It paves the way for some really fascinating applications.

    1. Indeed, this is seriously amazing. If anyone had asked me, I would have said that it’d be impossible to get enough energy from the each solar cell to lift its weight, let alone the extra weight of the motors and frame. I’m glad to be proven wrong!

      I image future improvements in solar cell technology will allow for a sturdier frame and more powerful motors, to let it fly higher and not get blown away or torn apart by wind.

    2. I’d be interested to find out if there’s a diy community for high altitude drones in the way there is for balloons. I read a story last week about a fixed wing solar powered drone that stayed in the air for about 26 days at a time. Apparently it was above the weather and normal airplane traffic. Something like that would be amazing to put a low-power cross-band ham radio repeater on. Or stick a OpenWRT wifi router on it and see how far you can get a wifi link. Maybe that sort of distance would break wifi though. Get something like a LimeSDR and do a DVB modulation?

  3. I wonder how much more efficient it would be in colder air. Solar cell efficiency is strongly temperature-dependent, and Singapore isn’t known for being frigid!

    But then, the sun tends to be lower in the sky in places with chilly climates…. hmmmm…

    The other way to get cold air, even in tropical latitudes, is to gain altitude! If this thing could climb a few km, the air temp falls off rapidly, and it would find itself with a massive boost in power. But then at some point the air gets too thin for blades to push against. I don’t know how to run these numbers but I’m sure someone here can find an ideal hover point for this thing, where its daytime energy budget would be strongly positive and it could afford to run a communications payload…

    1. The bigger issue is winds aloft.
      Even small multirotors get blown around, this thing has gigantic sails and super light weight materials designed to take strain in specific directions. A few hundred meters up (depending on terrain) and you might not be able to control your UAV. Worse it might get torn apart.

  4. I wound if a really light parabolic trough solar concentrator design with high temperature solar cells would be more efficient. High temp solar cells are expensive though and I’m not sure if they’re more efficient… compared to surface area and weight, may be. I also wonder if a lightweight material Fresnel lens layer over the cells would aid in effectiveness if the peak energy isn’t at the max limit of the solar cells.

  5. That’s 172 full on solar cells, or about 700 watts. Amazing! Seems like they could use much smaller motors, etc and get by with only 10 watts or so.
    Imagine how much lighter they will be when structural graphene gets invented (and mass produced). Then, with solid state batteries (also not really invented and mass produced yet), it’ll be flying 24/7…

  6. This was done in 2013:

    , If this should not count, remember that the Kitty Hawk also stayed in the ground effect domain to keep lateral control as their wing warping elevons were not sufficient to keep level. they flew at a height of 20 ft with a wingspan of 40ft.

  7. This is quite impressive, as they are using silicon solar cells, which are still quite heavy. If they had the money(lots and lots), they could go with newer multijunction IMM (inverted metamorphic) cells ment for use in space. They are much lighter, as they are removed from the substrate, and more efficient as well. With those, they could greatly reduce the panel area.

    1. Common solar cells are much thicker than they need to be for generating electricity. The extra thickness makes them more rugged, so that fewer are broken in production, shipping, installation, etc.. If the cells used in this quadcopter are a substantial portion of the total weight, just using thinner cells could make a big difference.
      I’m not an aeronautical engineer, nonetheless I doubt that the aerodynamic design is good – I think the blades should be longer.

  8. Several have pointed out that there’s a lot of wind-catching area and not much mass. What if the cells could be configured on the fly, with some sort of tiny actuators, to turn that into an advantage?

    1. There’s no reason the cells have to remain stationary. The cells themselves could be the blades of large slow-turning propellers, with the motor “flipped” so the coils (and ESC) rotate, and the magnet cup is fixed to the airframe.

      The trick with this approach would be communicating speed commands to each of the whirling ESCs, but that seems like a natural fit for radio.

      1. An electromagnet could subtract from each magnet cup as needed.
        But I also think of the Sopwith Camel and other such WWI aircraft that used the engine block attached to the propeller, and the crankshaft and pistons connected to the fuselage, centrifugal force made turns easy in one direction and difficult in the opposite. (but on a quad copter they would pretty much cancel out.)

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