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Drones will fly for days with new photovoltaic engine

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Re: Drones will fly for days with new photovoltaic engine

#41

Post by jacobush »

pjc50 wrote: post #35
IanCal wrote: post #23

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.

Exactly. The paper is here: https://www.pnas.org/content/early/2019/07/15/1903001116 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 extract…

I sense a new kind of nuclear power plant?!

Re: Drones will fly for days with new photovoltaic engine

#42

Post by StreamBright »

jacobush wrote: post #41
pjc50 wrote: post #35

Earlier quoted context omitted.

Exactly. The paper is here: https://www.pnas.org/content/early/2019/07/15/1903001116 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 extract…

I sense a new kind of nuclear power plant?!

That would be amazing to get rid of the traditional boiling water part of nuclear power plants. Is this what you are thinking about?

Re: Drones will fly for days with new photovoltaic engine

#43

Post by arijun »

spuz wrote: post #36
IanCal wrote: post #23

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.

> According to Yablonovitch, this finding builds on work that he and students published in 2011, which found that the key to boosting solar cell efficiency was not by absorbing more photons (light) but emitting them. By adding a highly reflective mirror on the back of a photovoltaic cell, they broke efficiency records > "What the mirror does is create a dense infrared luminescent photon gas within the solar cell, a p…

Your quotes seem to very clearly support the idea its a an onboard heat source as claimed by gp. Specifically

>>the mirror can reflect those small photons to reheat the thermal source

I'm pretty sure holding a mirror up to the sun is not going to change the sun's temperature much.

> I am seeing figures for steam turbine efficiency of between 40 and 80%

There's more that goes into choosing an engine for a drone than just efficiency. Particularly important would be power/weight. A Carnot engine would get much higher efficiency for sure, but would not put out nearly enough power per weight for a drone to fly. (It's so low power we don't even use it for cars!)

Re: Drones will fly for days with new photovoltaic engine

#46

Post by jacobush »

StreamBright wrote: post #42
jacobush wrote: post #41

Earlier quoted context omitted.

I sense a new kind of nuclear power plant?!

That would be amazing to get rid of the traditional boiling water part of nuclear power plants. Is this what you are thinking about?

Yes, and especially for my pet daydream nuclear reactor in space, or on Mars, etc.

Re: Drones will fly for days with new photovoltaic engine

#48

Post by wumms »

rebuilder wrote: post #39
wumms wrote: post #28

Earlier quoted context omitted.

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...

The article says "a wide range of applications, from those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle, to 100 megawatts"

I read the 100 watts as referring to lightweight unmanned aerial vehicle.

100 megawatts is followed by "[providing] electricity for 36,000 homes."

The original paper does not mention lightweight aerial vehicles as an application, but a drone is mentioned in the title (and shown in the top image) of the article.

Applications mentioned in the paper are: hybrid cars, unmanned vehicles, deep-space probes, energy storage, enabling efficient cogeneration systems for heat and electricity.

(A less-misleading title might even be: "New thermophotovoltaic engine for deep-space probes")

Re: Drones will fly for days with new photovoltaic engine

#49

Post by macspoofing »

xsace wrote: post #33
asteli wrote: post #7

Earlier quoted context omitted.

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.

The idea behind individual solar energy is not consuming it real time but associating it with a storage solution to allow bigger throughput. You're not going to make toasts all day

>You're not going to make toasts all day

I bet you're doing something throughout the day. Maybe not making toast, but cooking, ironing, heating, cooling, watching TV etc. I'm not sure you can rely on any excess energy being available for storage if you're not connected to the grid.

>The idea behind individual solar energy is not consuming it real time but associating it with a storage solution to allow bigger throughput.

If that's the idea then you are exposing a major issue with solar. Namely: in order to rely solely on solar (+battery), you need a solar deployment that covers your energy needs now + energy to charge battery for when the sun isn't shining (taking into account the associated loss of storing and retrieving power from battery). This means that you need to oversubscribe/over capitalize solar to charge up the battery (which then lowers your total efficiency) in order to bridge daily and seasonal variability in solar output. This means that you need generation capacity that probably exceeds the surface area available to what a typical house or apartment can provide and explodes your costs.

This has major implications for large scale solar+battery deployments because at that scale, there is no grid to fall back on (which is why solar ALWAYS needs reliable backup generation - which is typically gas or biofuels). This is why solar+battery is never going to be cost-effective because you're always going to be forced to over-build infrastructure that will sit idly doing nothing most of the time.

This doesn't even touch on the fact that there is no actual battery technology that keep enough load to power a modern city overnight, much less to bridge seasonal variability at that scale (where the battery would be expected to keep enough energy for weeks at a time).

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