> Researchers at Rice University developed a method to convert heat into light that could boost solar efficiency from 22% to 80%
The conditional tense signals that the researchers didn't actually do so, but that the study might enable it. The article re-iterates that this is speculation:
> The implications of their discovery are significant. Research from Chloe Doiron, a Rice graduate student, revealed that 20% of industrial energy consumption is wasted through heat. It could also mean an increase in the efficiency of solar cells, which are currently only 22% efficient at their peak. Recycling the thermal energy from solar cells using carbon nanotube technology could increase the efficiency to 80% according to the researchers. ...
As far as I can tell, this is functionally just a coating with low emittance in the IR outside a narrow band. A matched PV device that is kept cool can, in principle, approach the Carnot efficiency for the temperature difference between the emitter and the PV junction. If the emitter is the sun, then the source temperature is very high and the Carnot efficiency isn’t a major limit. If the source is a solar panel, I’m having a hard time seeing how this is useful.
I can see this being somewhat useful as a no-moving-parts heat engine for something like a solar concentrator, but there’s another relevant thermodynamic limit: even if this magic material has emissivity 1, it won’t radiate at a greater power per unit area than the blackbody spectrum predicts. At non-crazy temperatures, this is not very high, which will limit output for small things like solar concentrator targets.
So I can see this being useful to convert waste industrial heat, or maybe as a bottoming engine for a combined cycle plant, but I am having trouble understanding how it could be useful for solar.
One sketch of such a system is to physically mate an effective high T solar absorber to an effective narrow spectrum photon emitter (as described in this work). Then that can be coupled with a typical solar cell with bandgap matched precisely to the emitter wavelength. So your solar cell is near ideally efficient for the photons it receives. As I understand the emissivity of these materials can exceed blackbody radiation in the near-field but not the far-field (or something like that? Search "Superplanckian emission").
> Then that can be coupled with a typical solar cell with bandgap matched precisely to the emitter wavelength. So your solar cell is near ideally efficient for the photons it receives.
One way or another, once you've converted sunlight to heat, you are limited by the Carnot efficiency. For the 80% efficiency they claim, if all of it comes from thermophotovoltaics, they need a hot side temperature at least 5x ambient, which is over 1000 C. I wish them luck getting anything resembling a solar panel up to 1000 C. (I'm not, in any respect, saying it's impossible -- I'm saying it's very hard. You'd need excellect spectrally or directionally specific absorption to avoid re-radiating all that heat out the top of your panel, and you'd need conventional transparent insulation to stop conduction.)
On top of that, super-Plankian emission or no, if it's limited to the near field, then the PV cell is very, very close to the hot surface. That PV cell needs to be kept near room temperature to get that efficiency.
This whole thing seems extraordinary complex for something that wants to be cost-effective.
For solar, it somehow has to integrate with the solar panel, so that the same square meter is used both for direct photovoltaic generation of electricity, and for this IR capture, so energy is obtained from a wider band.
I understand your point that it can't just be driven by a secondary IR emission from a warmed-up solar panel; that's not hot enough to be that useful.
In a more detailed article, there is talk about the carbon nanotube device being useful because it can withstand high temperatures:
I am especially infuriated by how it repeats a common misconception of infrared light as the epitome of "heat", as if it was some kind of separate particle.
I'm not infuriated, but having teachers and other adults conflate IR with heat certainly added to my confusion about the physical world when I was a child.
Sounds like 80% is a theoretical prediction for this method, not an experimental result:
Naik said adding the emitters to standard solar cells could boost their efficiency from the current peak of about 22%. “By squeezing all the wasted thermal energy into a small spectral region, we can turn it into electricity very efficiently,” he said. “The theoretical prediction is that we can get 80% efficiency.”
I get the maybes and the caveats, the misleading title but the direction seems clear - solar efficiency is a tractable materials science problem - and "we" should see this as a penicillin moment - invest hugely into the research and development until we find the right processes and approach to make cheap ubiquitous solar. Manhattan project levels of finding is what I mean - because the pay off is humans cutting their carbon output.
The penicillin moment happened because penicillin actually came into existence and became widely available pretty rapidly.
Research and speculation is awesome stuff, but the hard part isn't discovering new concepts. It is actually making those concepts into a marketable and affordable good.
The evidence for this is that even though there is essentially a new 'breakthrough' discovery every other week for solar panels, or electric motors, or batteries.. We are still using what amounts to cutting-edge tech from the late 90's.
In the modern era this means we generally have to wait till the patents expire and market competition kicks in in order to get the price low enough and the product perfected enough to see widespread usage. If it goes anywhere at all.
It's also worth noting that Florey, the man who is largely responsible in making penicillin practical drug, refused to patent his early innovations to make it widespread as possible.
Penicillin had to undergo decade long R&D to go from Fleming's petria dish to a cheap practical drug - I cannot find the article now but I believe the investment levels from the US Military were compared to Manhattan (obviously poorly compared) but the point is this was not the "gosh what luck" story it is in mass media.
Having made that first breakthrough, world class teams across the globe fought to bring the efficiency up from "froth on the top of a brew" to "gallons of the stuff"
Florey was a big part of the story but so were teams in US and Europe and then the US military scaled it up beyond belief.
We spent money, targeted money, on the best teams globally and then put serious industrial might to it once they found the answers.
That exact approach is what I am calling for again.
And as for patents - if enough global effort is put in, with enough government funds, the pressure to put the results "in public hands" rather than hold out for patents is really strong
If this is the case, then wouldn't "buy a bunch of patents and (with great fanfare) make them open-source" be a relatively low-complexity way for a billionaire who feels like making a name for himself to accelerate progress on fighting climate change?
This is not quite correct. Silicon solar cells have a maximum efficiency of 32%. Various ways, such as using e.g Carbon Nanotubes as Antennas to directly rectify visible light (http://NovaSolix.Com) may eventually yield much higher overall efficiencies.
While this is a very interesting and ingenious development, what's needed for greater deployment are lower costs per unit of energy. Increasing efficiency will reduce the cost of land, but land isn't typically a huge factor in solar deployments. In this NREL analysis, land acquisition gets put into "Other Soft Costs" along with permitting, inspection, interconnection, sales tax, engineering, procurement, construction, developer overhead, and net profit:
If you could multiply the efficiency of a given solar cell by 4, all else being equal, you would also reduce the manufacturing cost by 75%.
From other comments, I am guessing this result doesn't give anything like that but one should keep in mind greater efficiency certainly could give great payoffs.
There are multiple models (markets) even in today's world, and they have different needs and constraints. When you have lots of space but not a lot of money, you probably optimize for least money per unit of energy. When you have money but limited space (skyscraper rooftop, spacecraft), you might want the most energy per unit of area. And there are times when you need a secondary non-grid solution for redundant backup, so reliability matters more than other factors.
Different technologies with different pros/cons could be best for different markets.
I certainly didn't mean to discourage this at all!
But I think it's important to point out that even though people often disparage solar photovoltaic for having low "efficiency," that metric is not an impediment to its broad deployment or great utility to us.
I'd expect most of the costs scales linearly with the number of panels: land, installation, maintenance, interconnect, so this should translate pretty directly to cost savings.
Interesting work - seems like this could also be used to create a thin film that could yield thermal vision, if indeed the nanotubes upshift IR frequencies to visible light. But I’m not a physicist.
This has been discussed in several previous threads on HN. From what I’ve been able to gather, creative ways to reduce the energy consumption of A/C will require a change to building designs, and/or increase the cost and complexity of new buildings. Whereas the cost of running the A/C is up to the future tenant(s).
This is why you see some companies applying eco friendly tech to some new buildings (Apple) but not in general commercial development.
Again this is just what I’ve surmised from reading threads like this. YMMV
Interesting to contemplate what could be done to shift those incentives around. Obviously there are certifications (LEED), and there's straight-up regulation, but would there be a way to mandate that a builder or landlord is responsible for a portion of future HVAC expenses such that they are motivated to get this right upfront?
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> Researchers at Rice University developed a method to convert heat into light that could boost solar efficiency from 22% to 80%
The conditional tense signals that the researchers didn't actually do so, but that the study might enable it. The article re-iterates that this is speculation:
> The implications of their discovery are significant. Research from Chloe Doiron, a Rice graduate student, revealed that 20% of industrial energy consumption is wasted through heat. It could also mean an increase in the efficiency of solar cells, which are currently only 22% efficient at their peak. Recycling the thermal energy from solar cells using carbon nanotube technology could increase the efficiency to 80% according to the researchers. ...
I can see this being somewhat useful as a no-moving-parts heat engine for something like a solar concentrator, but there’s another relevant thermodynamic limit: even if this magic material has emissivity 1, it won’t radiate at a greater power per unit area than the blackbody spectrum predicts. At non-crazy temperatures, this is not very high, which will limit output for small things like solar concentrator targets.
So I can see this being useful to convert waste industrial heat, or maybe as a bottoming engine for a combined cycle plant, but I am having trouble understanding how it could be useful for solar.
The devices as I am familiar are often called thermophotovoltaic cells: https://en.wikipedia.org/wiki/Thermophotovoltaic
See eg http://xlab.me.berkeley.edu/pdf/259.pdf for a great overview, esp section 3.3.
I saw this video recently that I found accessible from an undergrad physics background and got me interested: https://www.youtube.com/watch?v=XnVVyTD7CzM
One way or another, once you've converted sunlight to heat, you are limited by the Carnot efficiency. For the 80% efficiency they claim, if all of it comes from thermophotovoltaics, they need a hot side temperature at least 5x ambient, which is over 1000 C. I wish them luck getting anything resembling a solar panel up to 1000 C. (I'm not, in any respect, saying it's impossible -- I'm saying it's very hard. You'd need excellect spectrally or directionally specific absorption to avoid re-radiating all that heat out the top of your panel, and you'd need conventional transparent insulation to stop conduction.)
On top of that, super-Plankian emission or no, if it's limited to the near field, then the PV cell is very, very close to the hot surface. That PV cell needs to be kept near room temperature to get that efficiency.
This whole thing seems extraordinary complex for something that wants to be cost-effective.
I understand your point that it can't just be driven by a secondary IR emission from a warmed-up solar panel; that's not hot enough to be that useful.
In a more detailed article, there is talk about the carbon nanotube device being useful because it can withstand high temperatures:
https://news.rice.edu/2019/07/12/rice-device-channels-heat-i...
They of course understand that they need a big temperature differential.
Just go to the source: https://news.rice.edu/2019/07/12/rice-device-channels-heat-i...
Sounds like 80% is a theoretical prediction for this method, not an experimental result:
Naik said adding the emitters to standard solar cells could boost their efficiency from the current peak of about 22%. “By squeezing all the wasted thermal energy into a small spectral region, we can turn it into electricity very efficiently,” he said. “The theoretical prediction is that we can get 80% efficiency.”
Some projects have really big ROI
Research and speculation is awesome stuff, but the hard part isn't discovering new concepts. It is actually making those concepts into a marketable and affordable good.
The evidence for this is that even though there is essentially a new 'breakthrough' discovery every other week for solar panels, or electric motors, or batteries.. We are still using what amounts to cutting-edge tech from the late 90's.
In the modern era this means we generally have to wait till the patents expire and market competition kicks in in order to get the price low enough and the product perfected enough to see widespread usage. If it goes anywhere at all.
It's also worth noting that Florey, the man who is largely responsible in making penicillin practical drug, refused to patent his early innovations to make it widespread as possible.
Having made that first breakthrough, world class teams across the globe fought to bring the efficiency up from "froth on the top of a brew" to "gallons of the stuff"
Florey was a big part of the story but so were teams in US and Europe and then the US military scaled it up beyond belief.
We spent money, targeted money, on the best teams globally and then put serious industrial might to it once they found the answers.
That exact approach is what I am calling for again.
And as for patents - if enough global effort is put in, with enough government funds, the pressure to put the results "in public hands" rather than hold out for patents is really strong
https://en.m.wikipedia.org/wiki/History_of_penicillin
If this is the case, then wouldn't "buy a bunch of patents and (with great fanfare) make them open-source" be a relatively low-complexity way for a billionaire who feels like making a name for himself to accelerate progress on fighting climate change?
Deleted Comment
https://www.nrel.gov/docs/fy17osti/68925.pdf
And that broad category is ~25% of costs.
From other comments, I am guessing this result doesn't give anything like that but one should keep in mind greater efficiency certainly could give great payoffs.
Different technologies with different pros/cons could be best for different markets.
But I think it's important to point out that even though people often disparage solar photovoltaic for having low "efficiency," that metric is not an impediment to its broad deployment or great utility to us.
Fixed size applications like rooftop would see a multiplier.
It's not actually doing that though. It's changing one set of light-frequencies into another.
This is why you see some companies applying eco friendly tech to some new buildings (Apple) but not in general commercial development.
Again this is just what I’ve surmised from reading threads like this. YMMV