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> Drone Question, weight vs solar power
MacFromOK
Posted: February 22, 2018 07:06 am
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Just curious...

Is there a size where a low-power drone can be solar powered with current technology?

Or is the weight to power ratio just too large?


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sherlock ohms
Posted: February 22, 2018 11:09 am
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Not sure. Just wanted to say Hi old friend. 🙌☺


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MacFromOK
Posted: February 22, 2018 08:39 pm
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Heya Sherlock,

Always good to hear from ya. smile.gif


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AwesomeMatt
Posted: February 22, 2018 09:52 pm
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I don't think it's anywhere near possible yet for like, 'copter stuff. Things that are nearly gliders are sort of possible.

RC stuff that's LiPo powered still has run times in single digit minutes (batteries are designed to be discharged at like, 20C) And the power:weight of batteries has gotta be a couple orders of magnitude higher than solar could be.

There are like 1 or 2 solar plane prototypes out in the world which are apparently self-sustaining through a whole day/night cycle. That seems to be the extreme limit. They're 236' across (more than a 747) and a $170 million project. https://en.wikipedia.org/wiki/Solar_Impulse

For drone-sized stuff, not that it's optimized for it (though all drones are already pretty extreme in their optimizing just to be able to exist), let's grab a popular, heavier drone, the Phantom 4 ( https://en.wikipedia.org/wiki/Phantom_(UAV) ). Let's take a poke at the specs: https://www.dji.com/phantom-4/info

- It claims a max flight time of 28 minutes.
- It has an 81.3 Wh battery
- The drone consumes 140 watts max (and, based on flight time of 28 minutes, must be running near it's max all the time
- Drone weighs 1380 grams
- The camera weighs 140 grams
- The battery weighs 462 grams
- Claimed lifting capacity is 200 grams.
- Anecdotal claims for max payload are around 500 grams, (~1 lb), motors get too hot after that and flight time is already reduced to 12 minutes.
- Max anecdotal claims for payload are 2-8 lbs momentarily.

So, base weight is 1380+142+462g = 1984g, which is where it's 28 minute flight time comes from.

You can trim the battery and the camera, so that's 604 grams to play with. The curve probably isn't linear, the lighter the more efficiently it lifts I suspect.

Let's say you trim the battery and camera and replace them with 604g of solar panel. Will that get you 140 watts? That means you'd need a power:weight ratio better than 232 watts/kg for the panels.

The weight of just solar panels typical for residential use (no support system - based on: https://news.energysage.com/average-solar-panel-size-weight/ ), broken down to 604 grams, would be 9.95 watts. Nope, not good enough.

But apparently there are panels that are much more weight efficient? https://space.stackexchange.com/questions/1...ble-solar-array <-- This gives 400w/kg for the best, The ones on the Solar Impulse plane above, are 200w/kg ( http://www.solaripedia.com/13/170/1687/sol..._in_flight.html ). There are claims of up to 4300 W/kg for specialized space stuff in development.

So... for typical residential panels, you're out by an order of magnitude for weight.

For the ones on the Solar Impulse, you're actually not far off (200 w/kg vs. 231 needed). Experimental new ones seem like they'd be okay, if you don't count mounting hardware or wiring.


But on that note...


One of my random dream projects is an autonomous solar blimp. Maybe something beach ball- or perhaps bathtub-sized.

The blimp would be filled with Hydrogen so neutral buoyancy would be free. Then solar panels on top to have enough energy for propulsion, camera, communication.

I'd ideally like a tiny little hydrolysis machine on it, moisture from the air (or a dunk basket?) goes into a little drip collector, solar charged battery runs the cell and splits it into H2 and O2, H2 refills the blimp (which will inevitably leak).

I'd kinda like to just build one and set it loose, float around the world taking pictures and so on without much direction from me.

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MacFromOK
Posted: February 23, 2018 02:10 am
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Oddly enough, just yesterday I was thinking about a small solar powered hot air balloon using mirrors. biggrin.gif

Thanks for the info btw. beer.gif


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