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Drones will fly for days with new photovoltaic engine

techxplore.com

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Re: Drones will fly for days with new photovoltaic engine

#11

Post by sbierwagen »

asteli wrote: post #7
zaarn wrote: post #4

It reads a bit overhyped, considering they claim to power a house with a generator the size of an envelope; that's a hard no since there is a limit on how much energy hits every square meter and it's not THAT much.

To elaborate, solar energy hitting the Earth’s surface is about a kilowatt/m^2 if conditions are perfect. If you were able to convert solar power at the maximum theoretical PV efficiency (the Shockley-Queisser limit, 33.7%), you’d need about 3 square meters to just to make toast.

For those confused by that oddly low theoretical limit: it applies to single junction cells. Panels that achieve higher efficiencies do it by stacking multiple cells.

Re: Drones will fly for days with new photovoltaic engine

#12

Post by walrus01 »

dvh wrote: post #5
EGreg wrote: post #2

So what does this mean, we will be able to have drones flying continuously and getting energy from the sun?

DJI Phantom 3 is 0.3m wide and needs 120W to fly. Solar radiation at surface is 1000W/m2. 0.3m 0.3m 1000 = 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 beca…

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.

STC: https://www.altestore.com/blog/2016/04/how-do-i-read-specifi...

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.

Re: Drones will fly for days with new photovoltaic engine

#13

Post by wyattpeak »

asteli wrote: post #7
zaarn wrote: post #4

It reads a bit overhyped, considering they claim to power a house with a generator the size of an envelope; that's a hard no since there is a limit on how much energy hits every square meter and it's not THAT much.

To elaborate, solar energy hitting the Earth’s surface is about a kilowatt/m^2 if conditions are perfect. If you were able to convert solar power at the maximum theoretical PV efficiency (the Shockley-Queisser limit, 33.7%), you’d need about 3 square meters to just to make toast.

Your broad point is right, but the SQ limit only applies to conventional PV cells, it's not a theoretical limit on PV efficiency and in fact has been exceeded by other cell architectures.

Re: Drones will fly for days with new photovoltaic engine

#14

Post by IanCal »

wumms wrote: post #9
zaarn wrote: post #4

It reads a bit overhyped, considering they claim to power a house with a generator the size of an envelope; that's a hard no since there is a limit on how much energy hits every square meter and it's not THAT much.

Yes, the max. energy from sunlight on earth hitting an envelope should be around 20-30 Watts (at 100% efficiency). Also, the reported 29.1% efficiency have been reached at a temperature of 1,207 °C.

This isn't about sunlight, but about putting this with a furnace or something else generating heat.

Re: Drones will fly for days with new photovoltaic engine

#15

Post by lgats »

dvh wrote: post #5
EGreg wrote: post #2

So what does this mean, we will be able to have drones flying continuously and getting energy from the sun?

DJI Phantom 3 is 0.3m wide and needs 120W to fly. Solar radiation at surface is 1000W/m2. 0.3m 0.3m 1000 = 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 beca…

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...

Re: Drones will fly for days with new photovoltaic engine

#18

Post by numlock86 »

asteli wrote: post #7
zaarn wrote: post #4

It reads a bit overhyped, considering they claim to power a house with a generator the size of an envelope; that's a hard no since there is a limit on how much energy hits every square meter and it's not THAT much.

To elaborate, solar energy hitting the Earth’s surface is about a kilowatt/m^2 if conditions are perfect. If you were able to convert solar power at the maximum theoretical PV efficiency (the Shockley-Queisser limit, 33.7%), you’d need about 3 square meters to just to make toast.

Is this supposed to sound bad or good? Well, 3m² to make toast intuitively sounds bad I guess. Well, consider this: It's enough to run 2 small office PCs with all peripherals. Considering that it sounds much more positive. Really just anything producing heat would sound bad because of power dissipation. A toaster is probably one of the most extreme ... (Imagine putting 1kW into a slice of bread without power dissipation!)

Re: Drones will fly for days with new photovoltaic engine

#19

Post by ajuc »

EGreg wrote: post #2

So what does this mean, we will be able to have drones flying continuously and getting energy from the sun?

We already have drones with wings that are capable of that, or close to it. This would make them more efficient.

https://www.youtube.com/watch?v=8m4_NpTQn0E

For quadcopters and similar I doubt it will be enough.

Re: Drones will fly for days with new photovoltaic engine

#20

Post by IanCal »

zaarn wrote: post #4

It reads a bit overhyped, considering they claim to power a house with a generator the size of an envelope; that's a hard no since there is a limit on how much energy hits every square meter and it's not THAT much.

That is talking about heat and power cogeneration, not solar power if that's what you're thinking. The paper they site [0] says the density can 300-400kW/m^2 and so at 300kW, 50% efficiency and a small C5 envelope you're looking at over 5kW.

[0] https://scholar.google.com/scholar_lookup?author=M.+Bianchi&...

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