DJI Phantom 3 is 0.3m wide and needs 120W to fly. Solar radiation at surface is 1000W/m2. 0.3m0.3m1000 = 90W at 100% efficiency. They claim 29% eficiency* (compared to regular 23%) which is only 26W out of 120W in ideal circumstances, realistically it would be maybe 1/3 of it. It will not fly.
You can safely ignore ALL articles about breakthroughs in solar cell efficiency and look only at what is sold in shops because that's the only thing that matters. For years this has been 21-23% despite 5 or more articles about solar panel efficiency breakthrough every month for the last 20 years.
I essentially second everything that the person above is saying.
There are an endless number of press releases and public relations bullshit articles put out by people who have some new "breakthrough" in photovoltaics. Whether it's special weird cells, or flower shaped ground mount things, or whatever.
What I believe in, is what I can pull out my visa card and buy right now. And at the moment, here's what that looks like:
One pallet load (22 panels), of high quality 156mm monocrystalline silicon cells, assembled into a 1.99 x 0.99 meter sized panel. Rated at 370W STC (standard test conditions) per panel. Under $0.60/watt.
Everything else is either so high priced that you have to contact a sales person to buy it (weird fresnel lens concentrator and triple junction GaAs cells intended for use on spacecraft), or is not manufactured in sufficient quantity to gain even 1% of market share, and therefore is not stocked by major photovoltaic equipment dealers.
Quadcopter "drones" are much less efficient than winged plane "drones". Additionally, they have the large surface area of the wings to collect more solar energy.
Though the image does show a consumer quadcopter device...
I’ve seen reports of thin film organic solar cells that produce >1 watts per gram of material. A quadcopter motor can generate multiple grams per watt of power. You can today go and buy 100W from a 3.3lb panel, which is like half way there and not even trying. I’m guessing it’s probably possible to make a quadcopter that can hover indefinitely in the sun.
No, not really. The math for watts consumed in total just to hover, for a very large quad, hex or octocopter (with 24 to 28 inch size props, so optimal grams/watt thrust efficiency for something you can fit in a van), doesn't work out.
The weight and size of a 400W solar panel made from the very best cells you can buy commercially today is considerably more than the wattage you would need to hover a 10+ kilogram coaxial octocopter capable of carrying such a large panel on top of it.
For a large octo, a single Tmotor U8 motor with a 28 inch prop requires anywhere from 310W to 850W while in flight, and there's eight motors + eight props on a coaxial medium/heavy lift octo.
I showed this article to a few people in the professional arducopter/ardupilot/arduplane community and it has been quite thoroughly chuckled at.
For reference, here's the datasheet for a prototypical motor, a tmotor u8 170kv with 28 inch prop. You'll see the table for watts consumed and grams/watt efficiency with motor+prop mounted on a thrust stand.
If you wanted to put photovoltaics on a quad/hex/octocopter, you have multiple issues with not enough top deck surface area, not being able to introduce a lot of "sail area" (something big and light that will be grabbed by the wind) sticking out of the top, and the weight of the pv itself.
There is no PV solution anywhere near small enough to fit on the top deck of a really big commercial coaxial octo that is also capable of producing 2000W. Not even 100W in sunlight. Somewhere from 18 to 30 times less watts than is required just to hover in one place.
Hey! I love this problem :) The motor you shared shows >20g/W efficiency at ~40W of power and net lift of 500grams with those 28x9.2 (100g CF props). This implies that we need to produce roughly 40 Watts with under 500grams -- hard to assume negligible structural/electronics mass so more conservatively 40 Watts under 250g or 320Watts under 2kg to make like an octocopter with some power to spare. this is roughly 1 to 4 sq meters of solar area at 32% to 8% efficiency, and the swept area of eight 28" props is about 12 square meters it's might not even look totally ridiculous!
I can find super-light 100Watt panes under 2kg on Amazon (probably actually 60 Watts) but it's definitely more like 2 - 4 times more mass efficiency than what is commercially available and not 18-30.
Silicon mass is under 4 grams per Watt of solar so I think it should be possible to get there with silicon with a focused engineering effort. Organic photo-voltaic materials have shown 6 watts per gram in the lab (imagine for space applications!) -- though they would need even larger area due to lower efficiency and act as more of a sail .... not saying it is a practical machine to make, but again I definitely think it is in the realm of possible.
It doesn't scale down like that. Small motors and small props under 7 inch size have less than 5g/watt thrust efficiency. If you look at the motor and propeller setup that would go on an Armattan Chameleon Ti 7" for instance (a freestyle/gopro hero7 carrying sized FPV quad frame you add your own parts to).
On the large scale you would never actually be applying only 40W to a tmotor u8 with a 28" prop on it, because the total weight of the motors and the whole craft will mean it would just sit on the ground. You'd be moving air around like a fan and not lifting off. Ideally you would design a large octo for a 1:1 thrust ratio (hover) at about 48 to 50% throttle per motor, which is why you see the thrust tables starting from 50% and going upwards to 100% throttle.
Bigger and slower (lower kV) props and motors have higher efficiencies. If you google a bit about the few successful human powered helicopters that have been built in the past ten years you'll see the ultimate extent of using very big, very slow props to maximize lift per watt.
I would dearly love to be proven wrong on my above post. If you can find me a super efficiency triple junction GaAs panel to mount on top of a 20 kilogram sized coaxial filming octo, I'll find a way to get it into the hands of XM2 and see if they want to try flying it.
