I find it quite annoying that the original papers are not mentioned anywhere in the article. How difficult can it be to include a link/reference/doi to the source? I understand that for many people these scientific articles are too much, and unfortunately most of the times the scientific sources are still behind pay walls, but it is very important if one wants to verify the claims made in the news article.
Agreed. Fortunately there's a media contact details at the end of the article. I'm sure they'd like that feedback as well. Did you email them in addition to posting this comment on HN? :) I just did, expressing similar sentiments.
The advance is not that they "reached 90%", that's absolutely trivial, and nothing to do with a "Solar Power Material". They seem to be claiming that their advance is a black material they can paint onto thermal pipes that is durable at 1000K for an extended period of time in Earth's atmosphere, made out of blends of nanoparticles.
"High temperature black paint created that lasts 5-10 years instead of 1 year, reducing maintenance needs for concentrating solar thermal" would be a more honest title.
A direct comparison with off-the-shelf high-temp black coatings would have been useful. Here's a list of some known values for black coatings for solar collectors. (http://www.solarmirror.com/fom/fom-serve/cache/43.html)
Black chromium plating (absorption 0.87, emission 0.09) is often used for this purpose. It can handle the temperature, tolerates thermal expansion, and, like most hard chrome plating, is a hard plated surface that can be cleaned aggressively, as with pressure washing. There are other black coatings with up to 0.99 absorption, but they aren't as tough.
So what this new work has done is improve performance from 0.87 to 0.90.
(Why are so many "nanotechnology" articles like this? The title and lede sound like it's some earth-shaking development, and then it turns out it's at best a minor improvement.)
it's actually rather surprising, and important, that they were able to get 90 percent solar absorptivity combined with 30 percent infrared emissivity. this is difficult because absorptivity is the same thing as emissivity, but of course you can have different emissivities at different wavelengths; that's why things are different colors. but the vast majority of opaque solid materials have rather pastel colors, which is to say that their absorptivity (and thus emissivity) varies slowly with wavelength. this is undesirable for concentrating solar power, because it makes it hard to transfer the heat energy from the sunlight to the coolant rather than reradiating it as infrared. all the materials you named with albedos of under .1 are also great absorbers of infrared, which means they're also great emitters of infrared, so they wouldn't work very well for this application. (you also happened to pick three that won't withstand kilokelvin temperatures.)
there are a number of 'spectrally selective coatings' already in existence with this unusual combination of emissivities, but they are all very expensive to produce.
the longer lifetime is useful too, but not so useful they bothered to mention it in the abstract of their paper.
the small particles mentioned are made of a silicon-germanium blend, although they claim you can use different semiconductors for this. they picked that blend because its bandgap is about a volt, so it absorbs photons of more than about an electron volt.
Solar power is a bit of a misnomer here because most people reading that will assume it implies eventual conversion into electricity or motive power.
Electricity is like steak, heat energy is more like hamburger. It's useful but not nearly as useful as electricity, so you're going to need another conversion step (steam turbines are best at this right now) to get to a more usable form of power and that conversion step will have losses (radiation losses, mechanical losses, electrical losses).
So 'overall' efficiency is the key, not the efficiency of a single step in the process (they should at a minimum then list their current efficiency next to the previously achieved maximum for that step and how cost effective this new method is).
> The new material can also withstand temperatures greater than 700 degrees Celsius and survive many years outdoors in spite of exposure to air and humidity.
For simplicity, lets assume that it's 723°C (1333°F), and there is a nice summer afternoon and the environment temperature is 23°C (73°F). In Kelvin, we have 1000K and 300K.
By the second law of thermodynamics, we have that Q_in/T_in < Q_out/T_out,
so Q_in/1000K < Q_out/300K
then Q_out > 3/10 Q_in.
At least the 30% of the heat that enters has to be released to the environment in some type of cooler. So the efficiency of the heat to electricity conversion is at most 70%. If we multiply that by the 90% efficiency of the light to heat conversion, we get at most 63%. (65% in a cool winter morning :) ).
The Wikipedia article is not very clear ( http://en.wikipedia.org/wiki/Energy_conversion_efficiency ), but I guess that in a real power plant, we'd get at most a 40% or 60% heat to electricity conversion efficiency instead of the theoretical 70%.
Also, efficiency of solar power isn't even extremely relevant, except perhaps for very space-limited applications like solar vehicles. Since the input to solar power is effectively free, a better measure is dollars per watt.
The heat does not have to be converted to electricity, 60% of a home's energy usage is in the form of heat. 42% for space heating and 18% for water heating.
I am deriving 33% of the energy used for heating our startup headquarters with a solar thermal system we rigged up out of cardboard and black aluminum foil. We are bootstrapping and the electric heat the building has is much more expensive per BTU than oil/gas.
Black aluminum foil will reach 156F in direct sunlight in December in Southeast Connecticut. I have read that black aluminum foil will convert 88% of light to heat. We have 50 square feet of these panels that spend every clear or partly cloudy day between 130-156F, warming the building through convection. On a clear day with an outside temperature of 27F our rig heats two floors to 61F. We are going to add another 50 sq. ft. of panels to attempt to reach 70F+
And the heat mass of the building keeps it warm for four hours after the sun sets. We have some large floor to ceiling windows and we installed the panels so they stand behind the bottom three feet of some of the south-southeast facing windows.
The total cost of our system was $94 and a couple hours of time.
If we owned the building I would install solar hot air panels (basically an insulated rectangular box with a plexiglass top and black aluminum foil tacked into the inside with an intake and exhaust) and run a couple air ducts into the building.
This building already had a solar hot water heating system, with two 4' x 8' water heating panels on the roof. This gives us much of our hot water.
We are awash in solar energy, and heating air with the sun is the cheapest and most efficient way of capturing it. Solar hot air is THE low hanging fruit of solar power.
The only downside with our system is that there is no energy storage. But that could be engineered easily. A concentrated solar trough connected to a buried large cement block or other heat sink could easily store a day or two worth of heat for night time and cloudy days.
55% of the days here are clear or partly cloudy and great for solar heating.
Update:
If you were wondering what we are doing in Southeast CT, we are participating in the first of what we are calling The Winter Startup Challenge, our own laid back, low burn rate version of Y Combinator.
My team rented a waterfront three bedroom house in a beach community for the offseason, October-May. Being the off season we got a great deal.
We have to leave May 31st. We have 8 months to develop the product and reach ramen profitability or get funding. The product challenges have been overcome, the prototype is being built, we have committed buyers waiting for the first production run. Five months left.
The title explicitly mentions conversion into heat, so it's not fair to call it a misnomer. And turning heat into electricity is how most power plants work, not just concentrated solar power ones.
True, but I can picture many uses for the heat as is - such as off-grid heating water for homes/hotels/factories, which would normally burn natural gas or use electricity from the grid.
There are plenty of uses for a temperature difference that don't require arbitrary conversions to and from electricity. Furthermore, if an application desires electricity instead of a heat source, the Stirling cycle generators are tough to beat in terms of cost, reliability and end-to-end efficiency, even with exotic solar cells and lenses.
While what you say is totally true, huge part of the energy budget of humanity is heating stuff. If we remove heating for cooking, heating homes and water ... we will reduce drastically our footprint.
Also my inner steampunk geek will love the sight of huge sterling engines moving around ...
Converting light into heat is by far not as difficult as turning it into electricity. So don't mix this up with the 20-24% efficiency that are achievable in photovoltaics.
What's as useless as the pointed article. I tought the university PR would care to add such things as absorption rate of infrared, and why should I care about this instead of looking at traditional black nickel.
Any random black paint absorbs more than 90% of the light, and lots of black coatings survive 700°C.
What was the previous best conversion rate? This doesn't get us all the way to electricity, so its not really interesting info without a point of reference.
Does this mean that we are closer to replacing fossil fuels? It seems as though for energy we could do it now if we wanted, yet we still obsess about fracking and to a lesser extent middle eastern oil? The cost difference is certainly not the reason we don't dive in and make these changes.
Those in charge still seem to be of a 'secure the oil and the heroin' and you rule the world.
Replacing fossil fuels is not as simple as having high-efficiency solar panels (which these may not be when converting sunlight to electricity instead of heat).
Fossil fuels also have the advantage of having extremely high energy density. They can be transported cheaply and efficiently and they store well. Electricity suffers large losses when being transported long distances directly, and batteries are significantly heavier per kWh. Batteries also degrade over time, are expensive to replace, and often require substances that can be as (or more) destructive to mine than oil is to burn.
We could replace fossil fuels even today everywhere (with enough capital investment) ... except air travel - we are 3 or 4 major breakthroughs away from that.
With an energy source, you can manufacture fossil fuels from atmospheric carbon, giving you carbon-neutral fossil fuels.
The goal is to substantially reduce the CO2 being pumped into the atmosphere, not to just talk about how People Like Us are better than Those Fossil Fuel People, right?
The problem with renewables lies in unpredictability of wind power and photovoltaics, and in transmission infrastructure designed for predictable (and controllable) power sources.
We don't have good storage for electricity at the scale that is needed, not within few orders of magnitude, so at all times energy produced must be equal to energy used (the available storage is insignificant globaly, it is very expansive and is limited by geography - basicaly we can pump water upstream and let it flow back through turbines - this is only possible when you have a lot of water and some place much lower, where it can safely go, and it's still not cheap).
Additionaly each transmission line has maximum capacity and it will destruct itself if you try to send more.
With old-style energy sources we had baseload produced by water dams, coal, gas and nuclear plants, and peak load produced by plants that can be quickly (in less than 30 minutes) switched to produce more or less energy depending on demand - these are usually gas or coal powerplants. So with average demand for X, and peak deamd of Y you need X of stable powerplants and (Y-X) of controllable powerplants. Network is designed around that Y, using assumptions that power is divided into smaller and smaller lines from source to destination.
Only thanks to that, and to accurate predicting of demand by each level of power distribution hierarchy (I know about details of Polish system, but I guess it's similar everywhere) - the system works.
If you just swap 1000 MW of coal/gas/nuclear baseload plants with on-average 1000 MW of photovoltaics or wind turbines - you will literaly destroy your energy network. Half of the time it will produce too much energy (which results in blackouts and costly repairs), the rest of the time you will have blackouts because of not enough energy produced. You need to prepare infrastructure for that.
You need to adjust the whole network to bigger load, and to change the network topology from "connected stars" to peer-to-peer (or at least orders of magnitude more stars, connected orders of mganitude more intimately), and you need to expand the transmission lines a lot, because the only way to provide baseload with renewables is to average out production from a lot of places with different weather.
Right now electric networks aren't designed for that, and upgrading the whole infrastracture is going to be very expansive.
Germany is trying to do that - props to them, but in the meantime they are kinda problematic to their neighbors, because when they cannot deal with excess energy produced by renewables - they dump in on Polish, Czech,etc networks. Germany needs to pay for that (too much power is exactly as bad as not enough power - Polish and Czech controllable powerplants need to adjust production because of that and it costs both ways, also routing the power through the lines need to change because some lines may exceed capacity with that additional energy, and that cascades through the whole network. Energy distribution is organised in such a way, that when somebody predicted demand or production wrong - they pay for the rebalancing of network caused by that.
We already have materials that can achieve 75% efficiency [1] and probably more(it's just a rough search), so the 90% figure is much less impressive . But they also claim low cost and low maintenance over other methods, which are highly valuable.
Checking out some of the Fresnel videos on Youtube really helps one appreciate the power of the Sun. If the new material can withstand 700 C then point a Fresnel at it and hook up the output to a Stirling engine for conversion to electricity.
[+] [-] davidovitch|11 years ago|reply
I believe the following articles are the ones on which this story is based: http://dx.doi.org/10.1016/j.nanoen.2014.06.016 http://dx.doi.org/10.1016/j.nanoen.2014.10.018 (behind a pay-wall unfortunately)
[+] [-] minthd|11 years ago|reply
http://circuit.ucsd.edu/~zhaowei/Journals/Nano_Energy_Dylan_...
[+] [-] drdiatom|11 years ago|reply
[+] [-] mapt|11 years ago|reply
http://en.wikipedia.org/wiki/File:Albedo-e_hg.svg
The advance is not that they "reached 90%", that's absolutely trivial, and nothing to do with a "Solar Power Material". They seem to be claiming that their advance is a black material they can paint onto thermal pipes that is durable at 1000K for an extended period of time in Earth's atmosphere, made out of blends of nanoparticles.
"High temperature black paint created that lasts 5-10 years instead of 1 year, reducing maintenance needs for concentrating solar thermal" would be a more honest title.
[+] [-] Animats|11 years ago|reply
Black chromium plating (absorption 0.87, emission 0.09) is often used for this purpose. It can handle the temperature, tolerates thermal expansion, and, like most hard chrome plating, is a hard plated surface that can be cleaned aggressively, as with pressure washing. There are other black coatings with up to 0.99 absorption, but they aren't as tough.
So what this new work has done is improve performance from 0.87 to 0.90.
(Why are so many "nanotechnology" articles like this? The title and lede sound like it's some earth-shaking development, and then it turns out it's at best a minor improvement.)
[+] [-] kragen|11 years ago|reply
there are a number of 'spectrally selective coatings' already in existence with this unusual combination of emissivities, but they are all very expensive to produce.
the longer lifetime is useful too, but not so useful they bothered to mention it in the abstract of their paper.
the small particles mentioned are made of a silicon-germanium blend, although they claim you can use different semiconductors for this. they picked that blend because its bandgap is about a volt, so it absorbs photons of more than about an electron volt.
[+] [-] nv1729|11 years ago|reply
[+] [-] swamp40|11 years ago|reply
[+] [-] jacquesm|11 years ago|reply
Electricity is like steak, heat energy is more like hamburger. It's useful but not nearly as useful as electricity, so you're going to need another conversion step (steam turbines are best at this right now) to get to a more usable form of power and that conversion step will have losses (radiation losses, mechanical losses, electrical losses).
So 'overall' efficiency is the key, not the efficiency of a single step in the process (they should at a minimum then list their current efficiency next to the previously achieved maximum for that step and how cost effective this new method is).
[+] [-] gus_massa|11 years ago|reply
> The new material can also withstand temperatures greater than 700 degrees Celsius and survive many years outdoors in spite of exposure to air and humidity.
For simplicity, lets assume that it's 723°C (1333°F), and there is a nice summer afternoon and the environment temperature is 23°C (73°F). In Kelvin, we have 1000K and 300K.
By the second law of thermodynamics, we have that Q_in/T_in < Q_out/T_out,
so Q_in/1000K < Q_out/300K
then Q_out > 3/10 Q_in.
At least the 30% of the heat that enters has to be released to the environment in some type of cooler. So the efficiency of the heat to electricity conversion is at most 70%. If we multiply that by the 90% efficiency of the light to heat conversion, we get at most 63%. (65% in a cool winter morning :) ).
The Wikipedia article is not very clear ( http://en.wikipedia.org/wiki/Energy_conversion_efficiency ), but I guess that in a real power plant, we'd get at most a 40% or 60% heat to electricity conversion efficiency instead of the theoretical 70%.
[+] [-] baddox|11 years ago|reply
[+] [-] willholloway|11 years ago|reply
I am deriving 33% of the energy used for heating our startup headquarters with a solar thermal system we rigged up out of cardboard and black aluminum foil. We are bootstrapping and the electric heat the building has is much more expensive per BTU than oil/gas.
Black aluminum foil will reach 156F in direct sunlight in December in Southeast Connecticut. I have read that black aluminum foil will convert 88% of light to heat. We have 50 square feet of these panels that spend every clear or partly cloudy day between 130-156F, warming the building through convection. On a clear day with an outside temperature of 27F our rig heats two floors to 61F. We are going to add another 50 sq. ft. of panels to attempt to reach 70F+
And the heat mass of the building keeps it warm for four hours after the sun sets. We have some large floor to ceiling windows and we installed the panels so they stand behind the bottom three feet of some of the south-southeast facing windows.
The total cost of our system was $94 and a couple hours of time.
If we owned the building I would install solar hot air panels (basically an insulated rectangular box with a plexiglass top and black aluminum foil tacked into the inside with an intake and exhaust) and run a couple air ducts into the building.
This building already had a solar hot water heating system, with two 4' x 8' water heating panels on the roof. This gives us much of our hot water.
We are awash in solar energy, and heating air with the sun is the cheapest and most efficient way of capturing it. Solar hot air is THE low hanging fruit of solar power.
The only downside with our system is that there is no energy storage. But that could be engineered easily. A concentrated solar trough connected to a buried large cement block or other heat sink could easily store a day or two worth of heat for night time and cloudy days.
55% of the days here are clear or partly cloudy and great for solar heating.
Update:
If you were wondering what we are doing in Southeast CT, we are participating in the first of what we are calling The Winter Startup Challenge, our own laid back, low burn rate version of Y Combinator.
My team rented a waterfront three bedroom house in a beach community for the offseason, October-May. Being the off season we got a great deal.
We have to leave May 31st. We have 8 months to develop the product and reach ramen profitability or get funding. The product challenges have been overcome, the prototype is being built, we have committed buyers waiting for the first production run. Five months left.
[+] [-] grondilu|11 years ago|reply
[+] [-] binarymax|11 years ago|reply
[+] [-] rab_oof|11 years ago|reply
[+] [-] lotsofmangos|11 years ago|reply
Lonnie Johnson's JTEC is an interesting looking approach for that bit - http://en.wikipedia.org/wiki/Johnson_thermoelectric_energy_c...
[+] [-] venomsnake|11 years ago|reply
Also my inner steampunk geek will love the sight of huge sterling engines moving around ...
[+] [-] Dirlewanger|11 years ago|reply
[+] [-] JimboOmega|11 years ago|reply
If 90% of the captured energy is turned into heat, what is the other 10% turned into?
[+] [-] at-fates-hands|11 years ago|reply
[+] [-] jsilence|11 years ago|reply
[+] [-] lucidstack|11 years ago|reply
http://www.livescience.com/49133-super-efficient-solar-energ...
[+] [-] jcr|11 years ago|reply
Here's a better source URL:
http://www.jacobsschool.ucsd.edu/news/news_releases/release....
[+] [-] marcosdumay|11 years ago|reply
Any random black paint absorbs more than 90% of the light, and lots of black coatings survive 700°C.
[+] [-] richmarr|11 years ago|reply
[+] [-] sctb|11 years ago|reply
[+] [-] Wissmania|11 years ago|reply
[+] [-] imaginenore|11 years ago|reply
http://www.iflscience.com/technology/new-super-black-materia...
So yeah, this article is bull.
[+] [-] rndn|11 years ago|reply
[+] [-] samatman|11 years ago|reply
http://en.wikipedia.org/wiki/Black_body
[+] [-] andy_ppp|11 years ago|reply
Those in charge still seem to be of a 'secure the oil and the heroin' and you rule the world.
Oh dear -> https://www.youtube.com/watch?v=xW3XeT7qavo
[+] [-] stouset|11 years ago|reply
Fossil fuels also have the advantage of having extremely high energy density. They can be transported cheaply and efficiently and they store well. Electricity suffers large losses when being transported long distances directly, and batteries are significantly heavier per kWh. Batteries also degrade over time, are expensive to replace, and often require substances that can be as (or more) destructive to mine than oil is to burn.
[+] [-] venomsnake|11 years ago|reply
[+] [-] danielweber|11 years ago|reply
The goal is to substantially reduce the CO2 being pumped into the atmosphere, not to just talk about how People Like Us are better than Those Fossil Fuel People, right?
[+] [-] ajuc|11 years ago|reply
We don't have good storage for electricity at the scale that is needed, not within few orders of magnitude, so at all times energy produced must be equal to energy used (the available storage is insignificant globaly, it is very expansive and is limited by geography - basicaly we can pump water upstream and let it flow back through turbines - this is only possible when you have a lot of water and some place much lower, where it can safely go, and it's still not cheap).
Additionaly each transmission line has maximum capacity and it will destruct itself if you try to send more.
With old-style energy sources we had baseload produced by water dams, coal, gas and nuclear plants, and peak load produced by plants that can be quickly (in less than 30 minutes) switched to produce more or less energy depending on demand - these are usually gas or coal powerplants. So with average demand for X, and peak deamd of Y you need X of stable powerplants and (Y-X) of controllable powerplants. Network is designed around that Y, using assumptions that power is divided into smaller and smaller lines from source to destination.
Only thanks to that, and to accurate predicting of demand by each level of power distribution hierarchy (I know about details of Polish system, but I guess it's similar everywhere) - the system works.
If you just swap 1000 MW of coal/gas/nuclear baseload plants with on-average 1000 MW of photovoltaics or wind turbines - you will literaly destroy your energy network. Half of the time it will produce too much energy (which results in blackouts and costly repairs), the rest of the time you will have blackouts because of not enough energy produced. You need to prepare infrastructure for that.
You need to adjust the whole network to bigger load, and to change the network topology from "connected stars" to peer-to-peer (or at least orders of magnitude more stars, connected orders of mganitude more intimately), and you need to expand the transmission lines a lot, because the only way to provide baseload with renewables is to average out production from a lot of places with different weather.
Right now electric networks aren't designed for that, and upgrading the whole infrastracture is going to be very expansive.
Germany is trying to do that - props to them, but in the meantime they are kinda problematic to their neighbors, because when they cannot deal with excess energy produced by renewables - they dump in on Polish, Czech,etc networks. Germany needs to pay for that (too much power is exactly as bad as not enough power - Polish and Czech controllable powerplants need to adjust production because of that and it costs both ways, also routing the power through the lines need to change because some lines may exceed capacity with that additional energy, and that cascades through the whole network. Energy distribution is organised in such a way, that when somebody predicted demand or production wrong - they pay for the rebalancing of network caused by that.
Sorry for wall of text...
[+] [-] minthd|11 years ago|reply
[1]http://www.mit.edu/~soljacic/cermet_solar-thermal_OE.pdf
[+] [-] fche|11 years ago|reply
[+] [-] diltonm|11 years ago|reply
[+] [-] rab_oof|11 years ago|reply