“Just add solar panels to the wings” is a popular suggestion for improving the flight times of fixed-wing drones. However, the reality is not so simple, and it’s easy to hurt rather than help flight times with the added weight and complexity. The team at [Bearospace Industries] has been working on the challenge for the while, and their Solar Dragon aircraft recently had a very successful test flight, producing about 50% more power than it was consuming.
Instead of just trying to slap solar panels to an existing plane, an airframe should ideally be designed from the ground up as a balancing act between a range of factors. These include weight, efficiency, flight envelope, structural integrity, and maximum surface area for solar panels. All the considerations are discussed by [Bearospace] in an excellent in-depth video, which is an indispensable resource for anyone planning to build a solar plane.
[Bearospace] put all the theory into practice on Solar Dragon, which incorporates over 250 W of high-efficiency Maxeon C60 solar cells on the wing, tail, and triangular fuselage. The cells were wired to match their maximum power point voltage as closely as possible to the plane’s 3S lithium-ion battery pack, enabling the solar cells to charge the battery directly. To prevent overcharging, a solid state relay was used to disconnect the solar cells from the battery as required.
The batteries maintained the same average state of charge during the entire one-hour late morning flight, even though the panels were only connected 65% of the time. The team expects they might be able to get even better performance from the cells with a good MPPT charger, which will be required for less than ideal solar conditions.
Solar Dragon has a much larger payload capacity than was used during the test flight, more than enough for an MPPT charger and a significantly larger battery. With this and a long list of other planned improvements, it might be possible for the Solar Dragon to charge up during the day and fly throughout the night on battery power alone. One interesting potential approach mentioned is to also store energy in the form of altitude during the day, and use the aircraft’s slow sink rate to minimize battery usage at night.
Solar planes come up every few months on Hackaday, with [rctestflight] being one of the usual suspects. You also don’t need solar panels for long flight times, as [Matthew Heiskell] proved with a 10-hour 45 minute flight on battery power alone.
I always enjoy seeing the variety of deigns such challenges promote – like the Human powered aircraft there is still some divergence in design choices and build methods to meet the goal so some pretty serious variations pop up. Though this one seems to be along the more common lines of build a mostly normal glider with solar on the wings.
What really burns me up is that nobody seems to bother with amorphous solar cells! Basically, you sputter some silicon onto a thin sheet of steel and voila (or viola for the musically inclined)! The big advantages are being extremely light weight, can fit any shape or size, doesn’t have to be facing any particular direction to get maximum power. They are much better for mobile systems because they don’t need to be positioned correctly though this reduces the maximum efficiency to 22% which is sooo much higher than what you get with normal cells not being perfectly positioned!
And, if you sputter the cells onto structural parts, you can save even more weight. Probably beyond the budget of this project though.
How many aeroplanes do you know with a steel skin and exposed structural parts?
“extremely light weight,” or extremely heavy vs the aluminium/composite that was there before.
From flying gliders: the minimum sink rate speed is usually just a couple of knots above stall speed. When just trying to keep airborne for as long as possible that’s what you want. However, the more efficient flight happens somewhat faster at what is called L/Dmax (lift / drag). That gets you the farthest over the ground with the least amount of sink. The sink rate there at L/Dmax is actually faster by quite a bit more than the minimum possible sink rate. Juggling these factors in your head as the goals of your flight change dynamically is what makes gliders super fun to fly. Designing this solar aircraft with the design goal “stay aloft overnight” must involve some really fun challenges. If they go in a straight line at minimum sink, headed East, daytime (and thus sun charging) won’t come as quickly as if they fly at L/D max because they would cover much more ground, but also sink faster.
I thought Maximum Sink was a nose dive.
I was hoping it was an action movie set entirely in a kitchen.
That is best avoided. Hahah. Although you may be interested to know that the spoilers (or dive brakes) on most modern gliders have the charming name “terminal dive brakes” because they are so effective you can indeed point the nose straight to the ground, deploy the brakes and not exceed the maximum rated speed of the aircraft. Under what circumstance you would ever want, or need, to do that is best left to the imagination.
“SOLAR PLANE MIGHT BE ABLE TO LAST THROUGH THE NIGHT”
already been done a few years ago…
They’re targeting multi-day now https://skydweller.aero/ Still. interesting project
Yep impressive nonetheless…. just surprised to never see a mention of a manned solar plane that flew almost 5days a few year ago.
grumble at edit button…
actually skydweller just bought an already multi-day solar plane to study it and improve over it…
this is what I was talking about:
https://en.wikipedia.org/wiki/Solar_Impulse
To impress me, you’ve got to stay up longer than a plane without a motor at all.. https://rc-soar.com/wr_duration/
thing people dont realize is the plane itself, while in flight, is an energy storage device. gain altitude to store potential energy. you can turn that into kinetic energy simply by dropping the nose. by maintaining airspeed, you regulate the conversion. so given a good enough glide slope and enough altitude, you can in theory fly for a long time in glide. i think the record glider flight is something like 70 hours, though that likely involved catching thermals. a battery also buys time as it can re-boost altitude a couple times in the night.
The Airbus Zephyr-S solar powered drone (a.k.a. High Altitude Platform Station or HAPS) has been flying in the stratosphere (~67,000 feet) non-stop for with the U.S. Army for more than 50 days breaking numerous world flight records. In this run Zephyr crossed International boundaries (flew over Belize in C. America) and spent record time over International waters.
* More about Zephyr.
https://en.wikipedia.org/wiki/Airbus_Zephyr
https://www.airbus.com/en/products-services/defence/uas/uas-solutions/zephyr
* Watch Zephyr’s Flight in Real Time via ADSB. This link does not require log-in and does not time-out. This flight tracks as Callisign: ZULU82, ICAO ID: AE1313. Once the ADSB tracker page loads, zoom in with the center mouse wheel or the on-screen the +/- buttons to see the ground track live.
https://globe.adsbexchange.com/?icao=ae1313
* Currently Zephyr is running loiter patterns over the Kofa National Wildlife Refuge and Yuma Proving Ground in South Central Arizona (approx: 33°16′N 114°00′W).
https://en.wikipedia.org/wiki/Kofa_National_Wildlife_Refuge
https://en.wikipedia.org/wiki/Yuma_Proving_Ground