This is cool, but at 85% absorptivity it's no better than coatings you can already buy. Absorber plates in glazed solar water heaters you can get in your hardware store today have numbers in the 90s.
Edit: I recommend a look at the original paper instead [0]. The significant feature appears to be the ability to absorb light at a wide range of angles, rather than simply the absolute absorptivity.
What are these other materials' physical characteristics and cost to produce? Apart from absorptivity, a key factor here is the thinness and potential for inexpensive mass production.
In contrast, absorber plates tend to be large and heavy. 1lb per square foot isn't uncommon. They are also often produced with (relatively) expensive copper.
This might not be a breakthrough in terms of new capabilities, but it could allow a scale of use not currently practical.
The thing is a pound of copper has a pretty significant specific heat, and that’s a feature rather than a bug. A thin graphene film may be more conductive, but what is it thermal capacity? If it’s just a thin film that gets blazing hot it’s not necessarily useful in that way.
With copper you have 'heat battery' and can heat additional water by running it through the system without waiting for an equivalent amount of sunlight.
True. It looks like they made a few square centimeters of this stuff. If they make a bit more and slap it on a coffee mug & eliminate the need for a microwave, there could be some very interesting applications.
Though also consider their applications weren't limited to desalination and other "macro" applications, but also electronics, sensors and such. It sounds like this might be significantly cheaper than current monolayer graphene on substrate.
Only if the thermal transfer is one way, otherwise you may find your coffee getting colder quicker as surfaces that capture heat, equally have a penchant to radiate it. For example two metal balls, one painted white, one painted black. Whilst in the sun the black one will heat up more than the white one, at night it will radiate heat much quicker - even if they start at the same temperature.
Though the prospect of sending a coffee mug that only works in the sun to some geeks I know, does bring with it some wry humour opportunities.
As for other uses, agreed, much potential if it has an edge over alternative offerings.
That example sounds wrong. My understanding is that the black ball will heat up more quickly because it's converting a wider range of light frequencies into heat. The color isn't affecting heat conductivity and thus shouldn't affect how quickly it cools down at night.
Light coloured objects are light coloured because they are reflecting most of the photons that hit them back to your eyes. Dark coloured objects are dark because they are absorbing more of the photons. This is why dark coloured objects heat up faster in the sun; they are absorbing more photons. However, generally, the converse is also true, objects that readily absorb photons also readily emit them. So, the dark object will cool down more rapidly in the shade or at night. The wavelength (or colour) emitted depends on the temperature of the object. At room temperature, the emission peaks in the infrared, so the object still appears dark (but will glow brightly in night vision goggles). As it gets hotter, the peak emission moves into the visible spectrum and the object starts to glow (red hot then white hot).
As long as the door opens vertically (vs being the lid on a trunk like a deep freezer) it doesn’t much matter. Refrigerators really need to recover cold air more than focus on absolute perfect insulation.
I’ve always thought that we should just all move to the refrigerator-as-a-bunch-of-independent-drawers design. I think it would be easier to browse efficiently and easier to design a kitchen around.
For insulation, lighting. Key aspect is that the cooling element in a fridge is seperate from the white insulation and is often raw metal.
Now, if you look at the back of the fridge where is expels/radiates the heat - that is black. For me, I've often thought that heat could be utilised. Be is pre warming up water designated for hot water use (which would also aid in cooling fridge and increase its efficiency and life expectancy as well). Or some peltier/sterling type energy recovery.
> For me, I've often thought that heat could be utilised.
It's a specific use case, but this exhaust heat is very useful.
Use the top side of the refrigerator as a delicate drier for damp things that cannot be tumble dried. Soggy umbrellas. Leather gloves (even shoes). Hats made sweaty from work or exercise.
Put them on the top of the fridge overnight and IME by morning they are just about perfectly dried out.
Um, it just happens that I'm sitting behind a brand new fridge (not as awkward as it sounds, this old house doesn't have cabinetry for the fridge yet). It's white.
I don't think it is unusual at all to be honest; the one this fridge replaced was also white, and the neither seems to have a back that is intended to be looked at - there are plenty exposed seams, plumbing, the compressor.
Offhand, it doesn't seem like there would be much thermodynamic advantage in the heated surfaces of a fridge being black. If there were, wouldn't you expect that car radiators and such would be black anodised too? I'd imagine conduction is going to be a much much bigger effect than radiation - other concerns like cost, durability, thermal conductivity of the paint, and aesthetics will likely be more important in deciding what colour paint to use.
I don't understand what you think there is to ponder deeply here.
A fridge body is a pure insulator so the answer has to be white. Also it barely matters because convection will cool the surface anyway. Super straightforward with no math to do or conflict to resolve, unless I'm missing something.
On the inside, even for the cooling elements, it should be irrelevant since the planckian locus at 300k is outside the visible spectrum. The importance of the albedo in the far infrared also depends whether most heat transfer in a fridge is convective or radiative.
Equally it is a good angle in handling racist mentalities, and you get to ask them why do they hate themselves. Science is a wonderful gift in any debate.
The colour of an object we see is based upon light refracted back. So if an object is black it is absorbing most of the light, and the classic grass - which appears green is actually absorbing the red and blue spectrum and reflecting back the green light - appearing green.
"Are dark objects dark just because the light they emit are in an invisible frequency range?" the light they reflect back may well encompass the non visible spectrum, after all that's how radar works and the drive for radar absorbing materials by the military. So not all objects that for us in out limited light spectrum visual senses are equal, even if they look the same - black. May be one reflects back UV, one may absorb it. So for a true picture you would need to see an absorption graph of the full spectrum (visible and non visible).
Crux is - objects we see via refracted light - we are seeing in negative. So whilst we see green grass, it's true colour is everything but green.
>So whilst we see green grass, it's true colour is everything but green.
I've never liked this phrasing. In what sense is the "true" color not green if we perceive green? It is the color it reflects, it's just a little counter-intuitive when you first learn of the physics behind it.
Yes I will conceed it is far from an ideal way of describing how things are and with that, somewhat subjective in perception.
For me, it gets down to physics and how we perceive things. From a human perception aspect - the true colour of grass is green. But when you add the science aspect, it is not that clear cut. Somewhat gets down to context.
For me - if an object emits light - that's it's true colour. Equally how it refracts light is the perceived colour. Objects that emit light have a true and perceived colour the same. Though there is always other factors like whats in between the object and the light (be that refracted or emitted). The sun and sky being good example of that at play. But equally even at a small scale, the air will have an impact, even if we can not perceive it.
But yes, we're all human and with that, you are right in that the true colour from our perception shows grass is green. So I'll try and refer to grass as its true colour of green and it's physics colour as red/blue.
Which feels perhaps a better way of phrasing and one I'll try and run with until something better comes along.
More concerning to me is that I’m unclear how much heat capacity this thin film has. If you can’t layer it, then you’d neee vast sheets of the stuff to be useful as an energy source. Maybe it could be useful, but at the moment it seems more interesting than practical. Of course that could change, but I don’t think applications will be in the realm some here are hoping for.
It could make for a great solar shower lining though...
I don't know the density, but let's say 2g/cm³. That means a 1cm² piece of this film weighs 18 micrograms.
> 30°C to 150°C in 30 seconds
If by "sunlight" they mean 1000 W/m², which is generous, then our 1×1 piece would catch 0.1 W. Over 30 seconds, that makes 3 joules.
3 joules to heat 18 micrograms by 120 degrees – that's a specific heat capacity of 1.388 joules per gram and K (a bit more if the density is lower than 2, a bit less if it's higher). So: a bit more than typical metals, probably, but not by much.
Thanks, why can't this type of information be included in the article. A comparison with a common material would be useful to ok. Like copper or something.
Could you explain why the specific heat capacity is the important metric? It seems like the rate of absorption would be more important. (In other words, the percentage of incident photons absorbed.)
I just wanted to answer the question. The limiting factor is indeed the sunlight and how much of it is absorbed – thus my comment that 85% is nothing special.
I hold that solar energy is the optimal solution, and consists of 1/ capture, 2/ storage, 3/ transmission
Focus on (1) is great, but (2) is the breaker of chains. Solving (2) at enough efficiency should largely obviate the need for (3). Store and ship massively efficient solid state "batteries" instead of building (ie, owning) transmission infra
I didn't mean to come across as cynical — it's still a cool discovery, and it might turn out to be useful in some surprising niche context. The researchers do speculate that it might be
> suitable for a wide variety of uses, including desalination of seawater, color displays, photodetectors, and optical components for communication devices.
From the very first sentence of the article: "...a new graphene-based film that can absorb unpolarized incident light striking it over a wide range of angles up to 60 degrees."
'...the device can heat from 300C to 1500C in 30 seconds, he says." Furthermore, the ultrathin property allows easy heat transfer from the metamaterial to the material needed to be heated, such as water, and so could be used to desalinate seawater, for instance'.
If this is accurate that has great value and utility
Remember that temperature does not indicate energy. A graphene layer is a tiny amount of mass per surface area, so a absorbing single (small-c) calorie of energy would be enough to raise a patch of graphene to outrageous temperatures- but, you'd still only be able to get that single calorie back out, which wouldn't do much to a liter of seawater or whatever.
For that matter, it doesn't seem like they specify under what conditions this heating is taking place. Fire a high-powered laser at something and you might see that behavior in a variety of materials.
fun science experiment... fill a large beaker halfway with water and sprinkle a thin layer of powdered, activated charcoal (carbon/graphene) over the surface, cover the top of the beaker with saran wrap and place outside in the sun at midday. the temperature of the charcoal will get much warmer but not much else
yeah, there have been previous papers on creating membranes that wick some of the water up to be heated, and turned into vapor, but not so much that it cools down the carbon layer.
My senior project in college was on Peltier coolers. They're sort of like Cellular Automata of mechanical engineering - cool at first, but the novelty wears off shortly after.
Peltier devices are useless for most applications because of its poor efficiency.
TEGs are rarely over 15% efficient, and usually require 300+°C to operate. At 150C you're probably looking at traditional steam turbine for peak recovery, at this pressure you're looking at about 35% efficiency placing a potential absorber/generator combination a-la-stirling near 29% overall, which is great but for the price and complexity probably not ideal compared to solar at 20%.
This is also important as a consideration for what graphene is not good for or where you have to be careful using it. (A lot of the discussion appears to be around how we could use the heat - which would be great.) For example, if there was a good application in clothing, certain precautions might need to be taken to not burn someone.
Probably due to "It can absorb any wavelength of light from UV to microwaves", playing a factor. I'd speculate that the infrared spectrum as fully encompassed by that range being the primary target for energy transfer and with that, a red bias as seen in the picture would be logical.
Whilst it can absorb energy in the range specified - how efficient it is along that range is another question.
Another aspect, by not being black, I'd expect it to radiate heat less. But then, like many, so many question, so little data.
Not if it absorbs more in one part of the spectrum than other parts. For example an object could absorb red,green and blue light. But absorbs red and blue light more than the green and as such would appear green.
Gets down to if the absorption rate is liner - which it almost definitely is not going to be the case here and as I suspect, an absorption bias in the infrared spectrum is at play.
Look to Carnot vs photoelectric efficiency, modulo fabrication costs, maintenance, and operating life.
Carnot efficiency is dictated by the hot-cold side temperature delta. For internal combustion engines, 20-45% is fairly typical. In electrical generation, thermal energy is generally reckoned at 3x electrical generation.
PV efficiency has a maximum of 37% for single-layer PV, up to a theortical maximum slightly north of 80% for an "infinite" layer cell. (Additional layers provide a diminishing return.) In practice, 40-50% is a likely maximum achievable, and at reasonable costs, 20% is frequently assumed.
Additional considerations are capacity factor, spacing factor, panel angle, and inverter losses.
And PV has a practical effective lifetime of about 20 years, due to numerous degradation mechanisms.
Was useful to know, thanks. I think developing a wide range of highly competitive nano-materials is a serious issue today. There are many good nanomaterials companies but Modern Synthesis Technology company http://mstnano.com/products/graphene/ is one of the best I've worked with. They are known for their reliability, exceptional quality, time and cost efficiency. And they provide international supply of the most up-to-date nanomaterials and cooperate with the leading companies on the global market.
This is cool, but at 85% absorptivity it's no better than coatings you can already buy. Absorber plates in glazed solar water heaters you can get in your hardware store today have numbers in the 90s.
Edit: I recommend a look at the original paper instead [0]. The significant feature appears to be the ability to absorb light at a wide range of angles, rather than simply the absolute absorptivity.
[0] https://www.nature.com/articles/s41566-019-0389-3
What are these other materials' physical characteristics and cost to produce? Apart from absorptivity, a key factor here is the thinness and potential for inexpensive mass production.
In contrast, absorber plates tend to be large and heavy. 1lb per square foot isn't uncommon. They are also often produced with (relatively) expensive copper.
This might not be a breakthrough in terms of new capabilities, but it could allow a scale of use not currently practical.
The thing is a pound of copper has a pretty significant specific heat, and that’s a feature rather than a bug. A thin graphene film may be more conductive, but what is it thermal capacity? If it’s just a thin film that gets blazing hot it’s not necessarily useful in that way.
Water has a much higher specific heat. If you just want to heat up water anyway, wouldn't you just transfer the energy to it as fast as possible?
Specific heat and thermal conductivity are two different properties.
Sure, but this is a terrible answer to the question "why do we care about specific heat? Wouldn't thermal conductivity be more relevant?"
That question already assumes that specific heat and thermal conductivity are different properties.
With copper you have 'heat battery' and can heat additional water by running it through the system without waiting for an equivalent amount of sunlight.
True. It looks like they made a few square centimeters of this stuff. If they make a bit more and slap it on a coffee mug & eliminate the need for a microwave, there could be some very interesting applications.
Though also consider their applications weren't limited to desalination and other "macro" applications, but also electronics, sensors and such. It sounds like this might be significantly cheaper than current monolayer graphene on substrate.
Only if the thermal transfer is one way, otherwise you may find your coffee getting colder quicker as surfaces that capture heat, equally have a penchant to radiate it. For example two metal balls, one painted white, one painted black. Whilst in the sun the black one will heat up more than the white one, at night it will radiate heat much quicker - even if they start at the same temperature.
Though the prospect of sending a coffee mug that only works in the sun to some geeks I know, does bring with it some wry humour opportunities.
As for other uses, agreed, much potential if it has an edge over alternative offerings.
That example sounds wrong. My understanding is that the black ball will heat up more quickly because it's converting a wider range of light frequencies into heat. The color isn't affecting heat conductivity and thus shouldn't affect how quickly it cools down at night.
Light coloured objects are light coloured because they are reflecting most of the photons that hit them back to your eyes. Dark coloured objects are dark because they are absorbing more of the photons. This is why dark coloured objects heat up faster in the sun; they are absorbing more photons. However, generally, the converse is also true, objects that readily absorb photons also readily emit them. So, the dark object will cool down more rapidly in the shade or at night. The wavelength (or colour) emitted depends on the temperature of the object. At room temperature, the emission peaks in the infrared, so the object still appears dark (but will glow brightly in night vision goggles). As it gets hotter, the peak emission moves into the visible spectrum and the object starts to glow (red hot then white hot).
I have a nice nerd snipe.
Is it better for the inside of a fridge to be black or white?
Discuss.
As long as the door opens vertically (vs being the lid on a trunk like a deep freezer) it doesn’t much matter. Refrigerators really need to recover cold air more than focus on absolute perfect insulation.
I’ve always thought that we should just all move to the refrigerator-as-a-bunch-of-independent-drawers design. I think it would be easier to browse efficiently and easier to design a kitchen around.
My neighbor has this, built directly into the cabinets. Just cold drawers, blew my mind.
IKEA used to sell fridges that were drawers builtin to kitchen units.
For insulation, lighting. Key aspect is that the cooling element in a fridge is seperate from the white insulation and is often raw metal.
Now, if you look at the back of the fridge where is expels/radiates the heat - that is black. For me, I've often thought that heat could be utilised. Be is pre warming up water designated for hot water use (which would also aid in cooling fridge and increase its efficiency and life expectancy as well). Or some peltier/sterling type energy recovery.
But good question and in the same spirit:
Why is thermal paste and pads white?
> For me, I've often thought that heat could be utilised.
It's a specific use case, but this exhaust heat is very useful.
Use the top side of the refrigerator as a delicate drier for damp things that cannot be tumble dried. Soggy umbrellas. Leather gloves (even shoes). Hats made sweaty from work or exercise.
Put them on the top of the fridge overnight and IME by morning they are just about perfectly dried out.
Um, it just happens that I'm sitting behind a brand new fridge (not as awkward as it sounds, this old house doesn't have cabinetry for the fridge yet). It's white.
That's unusual - as in never seen one that's not black. Wonder why - aesthetics perhaps.
I don't think it is unusual at all to be honest; the one this fridge replaced was also white, and the neither seems to have a back that is intended to be looked at - there are plenty exposed seams, plumbing, the compressor.
Offhand, it doesn't seem like there would be much thermodynamic advantage in the heated surfaces of a fridge being black. If there were, wouldn't you expect that car radiators and such would be black anodised too? I'd imagine conduction is going to be a much much bigger effect than radiation - other concerns like cost, durability, thermal conductivity of the paint, and aesthetics will likely be more important in deciding what colour paint to use.
Thermal paste isn't designed to radiate heat -- it is intended to conduct it -- so its being black wouldn't make it more effective.
White, because it allows you to clean it effectively.
I don't understand what you think there is to ponder deeply here.
A fridge body is a pure insulator so the answer has to be white. Also it barely matters because convection will cool the surface anyway. Super straightforward with no math to do or conflict to resolve, unless I'm missing something.
On the inside, even for the cooling elements, it should be irrelevant since the planckian locus at 300k is outside the visible spectrum. The importance of the albedo in the far infrared also depends whether most heat transfer in a fridge is convective or radiative.
I like to joke with my daughter that her red shirt is every color BUT red, because that's the only color it doesn't keep.
Equally it is a good angle in handling racist mentalities, and you get to ask them why do they hate themselves. Science is a wonderful gift in any debate.
https://physics.stackexchange.com/questions/159856/why-is-bl...
I used to think that the darker the object, the more light it was turning into heat. Is that idea just plain wrong or is there some correlation?
Are dark objects dark just because the light they emit are in an invisible frequency range?
The colour of an object we see is based upon light refracted back. So if an object is black it is absorbing most of the light, and the classic grass - which appears green is actually absorbing the red and blue spectrum and reflecting back the green light - appearing green.
"Are dark objects dark just because the light they emit are in an invisible frequency range?" the light they reflect back may well encompass the non visible spectrum, after all that's how radar works and the drive for radar absorbing materials by the military. So not all objects that for us in out limited light spectrum visual senses are equal, even if they look the same - black. May be one reflects back UV, one may absorb it. So for a true picture you would need to see an absorption graph of the full spectrum (visible and non visible).
Crux is - objects we see via refracted light - we are seeing in negative. So whilst we see green grass, it's true colour is everything but green.
>So whilst we see green grass, it's true colour is everything but green.
I've never liked this phrasing. In what sense is the "true" color not green if we perceive green? It is the color it reflects, it's just a little counter-intuitive when you first learn of the physics behind it.
Yes I will conceed it is far from an ideal way of describing how things are and with that, somewhat subjective in perception.
For me, it gets down to physics and how we perceive things. From a human perception aspect - the true colour of grass is green. But when you add the science aspect, it is not that clear cut. Somewhat gets down to context.
For me - if an object emits light - that's it's true colour. Equally how it refracts light is the perceived colour. Objects that emit light have a true and perceived colour the same. Though there is always other factors like whats in between the object and the light (be that refracted or emitted). The sun and sky being good example of that at play. But equally even at a small scale, the air will have an impact, even if we can not perceive it.
But yes, we're all human and with that, you are right in that the true colour from our perception shows grass is green. So I'll try and refer to grass as its true colour of green and it's physics colour as red/blue.
Which feels perhaps a better way of phrasing and one I'll try and run with until something better comes along.
Not conductivity, but emissivity. In theory anyway, I'm not sure if plain black paint would make a difference.
this makes copper a great heatsink but not a very good solar heater medium
You can't just build desalination equipment out of a thin layer of this material: it has to be bonded with some sturdy substrate.
At that point it's competing with any number of readily-available black coatings that are suitable the use.
Are they water-proof? Could you put them in a pool to heat it up?
Do you mean absorber plates? They may or may not be water proof, but don't need to be to heat a pool. It's a relatively common application [0]
[0]http://www.alternative-energy-tutorials.com/solar-hot-water/...
The kind of system with circulation is overcomplicated. Would be much better to just put the heater into the pool/take it out.
More concerning to me is that I’m unclear how much heat capacity this thin film has. If you can’t layer it, then you’d neee vast sheets of the stuff to be useful as an energy source. Maybe it could be useful, but at the moment it seems more interesting than practical. Of course that could change, but I don’t think applications will be in the realm some here are hoping for.
It could make for a great solar shower lining though...
Back-of-the-napkin:
> 90-nm ultra-thin
I don't know the density, but let's say 2g/cm³. That means a 1cm² piece of this film weighs 18 micrograms.
> 30°C to 150°C in 30 seconds
If by "sunlight" they mean 1000 W/m², which is generous, then our 1×1 piece would catch 0.1 W. Over 30 seconds, that makes 3 joules.
3 joules to heat 18 micrograms by 120 degrees – that's a specific heat capacity of 1.388 joules per gram and K (a bit more if the density is lower than 2, a bit less if it's higher). So: a bit more than typical metals, probably, but not by much.
Thanks, why can't this type of information be included in the article. A comparison with a common material would be useful to ok. Like copper or something.
Could you explain why the specific heat capacity is the important metric? It seems like the rate of absorption would be more important. (In other words, the percentage of incident photons absorbed.)
I just wanted to answer the question. The limiting factor is indeed the sunlight and how much of it is absorbed – thus my comment that 85% is nothing special.
You’re a champion, thanks!
I hold that solar energy is the optimal solution, and consists of 1/ capture, 2/ storage, 3/ transmission
Focus on (1) is great, but (2) is the breaker of chains. Solving (2) at enough efficiency should largely obviate the need for (3). Store and ship massively efficient solid state "batteries" instead of building (ie, owning) transmission infra
So is there anything interesting about this "new" development then?
I didn't mean to come across as cynical — it's still a cool discovery, and it might turn out to be useful in some surprising niche context. The researchers do speculate that it might be
> suitable for a wide variety of uses, including desalination of seawater, color displays, photodetectors, and optical components for communication devices.
So: time will tell!
From the very first sentence of the article: "...a new graphene-based film that can absorb unpolarized incident light striking it over a wide range of angles up to 60 degrees."
'...the device can heat from 300C to 1500C in 30 seconds, he says." Furthermore, the ultrathin property allows easy heat transfer from the metamaterial to the material needed to be heated, such as water, and so could be used to desalinate seawater, for instance'.
If this is accurate that has great value and utility
Remember that temperature does not indicate energy. A graphene layer is a tiny amount of mass per surface area, so a absorbing single (small-c) calorie of energy would be enough to raise a patch of graphene to outrageous temperatures- but, you'd still only be able to get that single calorie back out, which wouldn't do much to a liter of seawater or whatever.
For that matter, it doesn't seem like they specify under what conditions this heating is taking place. Fire a high-powered laser at something and you might see that behavior in a variety of materials.
I was thinking huge areas of graphene but point taken, I was just reading up about graphene after reading the post...
fun science experiment... fill a large beaker halfway with water and sprinkle a thin layer of powdered, activated charcoal (carbon/graphene) over the surface, cover the top of the beaker with saran wrap and place outside in the sun at midday. the temperature of the charcoal will get much warmer but not much else
Isn't that because it is fairly hydrophobic so it doesn't make good contact with the water?
yeah, there have been previous papers on creating membranes that wick some of the water up to be heated, and turned into vapor, but not so much that it cools down the carbon layer.
Are there any real world products utilizing graphene? I hear a lot about how wonderful it is, but don't know any real world usage.
Why graphene hasn’t taken over the world...yet https://www.youtube.com/watch?v=IesIsKMjB4Y
Ugh I hate it when they say "A sheet of graphene could support X". It's utter bullshit because you can't ever have a sheet of defect-free graphene.
It's like how defect-free glass is 2-4 times stronger than steel. Actual glass is obviously nowhere near that strong and nobody pretends it is.
Can we put a moratorium on articles about graphene until it can be produced at scale?
Even at laboratory-scale, almost all manufacturers are lying about their purity: http://blogs.sciencemag.org/pipeline/archives/2018/10/11/gra...
Didn’t that just start happening?
Edit: https://phys.org/news/2019-03-cambridge-spin-out-graphene-co...
What about fusion? Or self driving cars? Or .... ?
So... any else thinking Sterling Engine?
*Stirling
That and peltiers.
My senior project in college was on Peltier coolers. They're sort of like Cellular Automata of mechanical engineering - cool at first, but the novelty wears off shortly after.
Peltier devices are useless for most applications because of its poor efficiency.
TEGs are rarely over 15% efficient, and usually require 300+°C to operate. At 150C you're probably looking at traditional steam turbine for peak recovery, at this pressure you're looking at about 35% efficiency placing a potential absorber/generator combination a-la-stirling near 29% overall, which is great but for the price and complexity probably not ideal compared to solar at 20%.
Sorry to be that guy but no one gave it a meaningful name!
Vampire skin!
This is also important as a consideration for what graphene is not good for or where you have to be careful using it. (A lot of the discussion appears to be around how we could use the heat - which would be great.) For example, if there was a good application in clothing, certain precautions might need to be taken to not burn someone.
If it could boil water, could one use it for generating electricity or even as a part of a steam engine of sorts?
I mean, it doesn't take a lot of energy to heat something that is 90nm thick. This is so misleading.
Can this be used for indoor Ag or a new kind of greenhouse membrane?
Why isn't it black?
Probably due to "It can absorb any wavelength of light from UV to microwaves", playing a factor. I'd speculate that the infrared spectrum as fully encompassed by that range being the primary target for energy transfer and with that, a red bias as seen in the picture would be logical.
Whilst it can absorb energy in the range specified - how efficient it is along that range is another question.
Another aspect, by not being black, I'd expect it to radiate heat less. But then, like many, so many question, so little data.
if it's absorbing all wavelengths of light then it should appear black, because it is not reflecting any light
Not if it absorbs more in one part of the spectrum than other parts. For example an object could absorb red,green and blue light. But absorbs red and blue light more than the green and as such would appear green.
Gets down to if the absorption rate is liner - which it almost definitely is not going to be the case here and as I suspect, an absorption bias in the infrared spectrum is at play.
How would a heat engine using this compare to photoelectric cells for energy generation?
Look to Carnot vs photoelectric efficiency, modulo fabrication costs, maintenance, and operating life.
Carnot efficiency is dictated by the hot-cold side temperature delta. For internal combustion engines, 20-45% is fairly typical. In electrical generation, thermal energy is generally reckoned at 3x electrical generation.
PV efficiency has a maximum of 37% for single-layer PV, up to a theortical maximum slightly north of 80% for an "infinite" layer cell. (Additional layers provide a diminishing return.) In practice, 40-50% is a likely maximum achievable, and at reasonable costs, 20% is frequently assumed.
Additional considerations are capacity factor, spacing factor, panel angle, and inverter losses.
And PV has a practical effective lifetime of about 20 years, due to numerous degradation mechanisms.
See:
https://old.reddit.com/r/dredmorbius/comments/28cvgv/calcula...
Thermal materials such as this are likely best suited to thermal capture and direct-heating systems, as low-grade space or water (pre)heating.
Was useful to know, thanks. I think developing a wide range of highly competitive nano-materials is a serious issue today. There are many good nanomaterials companies but Modern Synthesis Technology company http://mstnano.com/products/graphene/ is one of the best I've worked with. They are known for their reliability, exceptional quality, time and cost efficiency. And they provide international supply of the most up-to-date nanomaterials and cooperate with the leading companies on the global market.
Amazing.