31–40 of 99 posts
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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.
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Also, the reported 29.1% efficiency have been reached at a temperature of 1,207 °C. Another 12% and they can compete with a standard steam turbogenerator.
Wouldn't you slap this on top of a steam boiler to get the best of both worlds, though?
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.
People seem to be misinterpreting this a lot. This is not about solar cells. This is about thermophotovoltalics, and the application here is using a burning fuel source to generate electricity. The "drone" the paper talks about seems to be a reference to another paper on unmanned sea vehicles though. Edit - to be fair the flying drone part is from the corresponding author.
There's wasted thermal energy when using solar cells. If you can capture some of it you'd be able to increase the efficiency of the cell.
People seem to be misinterpreting this a lot. This is not about solar cells. This is about thermophotovoltalics, and the application here is using a burning fuel source to generate electricity. The "drone" the paper talks about seems to be a reference to another paper on unmanned sea vehicles though. Edit - to be fair the flying drone part is from the corresponding author.
The context of thermophotovoltalics is very interesting - conventional heat-to-electricity engines are limited by Carnot efficiency, which relies on a "cold side" and generally has low theoretical maximum efficiencies. This approach takes any hot emitter heated by any process - fuel burning, solar concentration, nuclear - and extracts electricity directly from the mostly IR photons it emits.
> Here, we present experimental results on a thermophotovoltaic cell with 29.1 ± 0.4% power conversion efficiency at an emitter temperature of 1,207 °C. This is a record for thermophotovoltaic efficiency.
People seem to be misinterpreting this a lot. This is not about solar cells. This is about thermophotovoltalics, and the application here is using a burning fuel source to generate electricity. The "drone" the paper talks about seems to be a reference to another paper on unmanned sea vehicles though. Edit - to be fair the flying drone part is from the corresponding author.
> "What the mirror does is create a dense infrared luminescent photon gas within the solar cell, a phenomenon that adds voltage," said Yablonovitch
> Recently, his team recognized that this mirror could serve double duty. In fact, it solves one of the biggest challenges in thermophotovoltaics: how to exploit the thermal (heat) photons that have too little energy to produce electricity. It turns out that the mirror can reflect those small photons to reheat the thermal source, providing a second chance for a high energy photon to be created and generate electricity. This phenomenon leads to unprecedented efficiency.
Given these paragraphs and the name "thermophotovoltalics", that this is about solar power seems like a reasonable conclusion to draw. Also, googling around I am seeing figures for steam turbine efficiency of between 40 and 80%. How sure are you this is not about solar cells?
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Wouldn't you slap this on top of a steam boiler to get the best of both worlds, though?
Steam turbines have row after row of blades, each successive blade wheel larger and lower pressure than the last. Exit temperatures from modern turbogenerators are around 120° C, where the steam is about to turn into water, and pressure is usually below atmospheric. Almost all the energy which thermodynamics permits to be extracted has been extracted.
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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.
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.
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.
http://store-en.tmotor.com/goods.php?id=324
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.
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The corresponding author to be fair did say unmanned aerial vehicles.
True, though it is combined (in the article) with a maximum power consumption: "those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle" The original paper says "unmanned vehicles" (no aerial ) and has a reference [0] to "unmanned undersea vehicles". [0] https://www.pnas.org/content/early/2019/07/15/1903001116#ref...
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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...