
Rice University researchers propose a way to boost solar efficiency - shry4ns
https://polyarch.co/rice-university-research-heat-into-light/
======
apo
The title is misleading. The full title is:

> 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. ...

~~~
ngold
Maybe speculation should not be presented as a statement of fact in the title.

~~~
colechristensen
"invent" is the key misleading word

~~~
silentrob
perhaps "hypothesize" would fit better.

------
amluto
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.

~~~
TTPrograms
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").

The devices as I am familiar are often called thermophotovoltaic cells:
[https://en.wikipedia.org/wiki/Thermophotovoltaic](https://en.wikipedia.org/wiki/Thermophotovoltaic)

See eg
[http://xlab.me.berkeley.edu/pdf/259.pdf](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](https://www.youtube.com/watch?v=XnVVyTD7CzM)

~~~
amluto
> 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.

~~~
TTPrograms
The absorber/emitter assembly doesn't really resemble a solar cell.
Demonstrated tungsten emitters have exceeded 1500K - it's not really that
wild, it's what's in incandescent light bulbs. You concentrate sunlight
typically.

------
Retric
That really needs some editing, it reads like gibberish.

Just go to the source: [https://news.rice.edu/2019/07/12/rice-device-channels-
heat-i...](https://news.rice.edu/2019/07/12/rice-device-channels-heat-into-
light/)

~~~
Terr_
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.

~~~
elwell
What is the accurate model of infrared light vs. heat?

~~~
dredmorbius
It's a bit complicated, but taking a stab at it:

All physical objects emit electromagnetic radiation corresponding to their
temperature (as opposed to reflected, reaction-induced, or stimulated
radiation, more below), with a corresponding blackbody radiation curve. Note
that blackbody emissions don't have a _specific_ frequency (say, unlike laser
light), though the curve has a _peak_ emission.

Traditional incandescent light bulbs are blackbody emitters, as is a hot coal,
the Sun and other stars, or the glowing elements of an electric radiant
heater. Human eyes see blackbody radiation, in the visible range, as having a
characteristic colour, which paradoxically gets _bluer_ as the temperature
gets _higher_ , so the ruddy tones of low-voltage incandescent lamps are _low_
colour temperature, and the intense white of halogen lamps are _high_ colour
temperatures. Blackbody radiation and colour temperatures are given in Kelvin,
with typical visible light corresponding roughly to ~3,000 - 8,000K. You might
also recognise these values from gamma or colour correction values on monitors
and video equipment.

(Colour temperatures were used to judge processing for ceramics and metal
processing / firing / smelting processes as well. They're also used to
classify stellar temperatures, and in conjunction with brightness and/or
distance estimates can be used to find stellar sizes.)

Infrared light is characteristic of peak blackbody emissions of bodies at or
near "room temperature". So IR is _not_ heat, but is _associated_ with hot
objects. Heat itself is ... thermal energy, which is its own complex thing.

Since _all_ EMR carries energy, all EMR heats objects in which it is absorbed.
A sufficiently intense emission above the IR range will _also_ heat an object.
However hot objects in near proximity transfer a great deal of thermal energy
directly as IR emissions. The _illuminating_ capability of "white" light
(typical solar emissions) allows a small amout of EMR energy to provide a high
degree of visual information without imparting much heat on the illuminated
objects (though it does impart some). Consider that even an (inefficient) 100W
incandescent bulb, whilst hot to the touch, does not significantly heat the
objects it is illuminating, and a far more efficient equivalent LED lamp,
drawing about 15W of electrical power, accomplishes the same illuminating
power with vastly less heat. We _don 't_ have to toast things to be able to
see them, just bounce a small amount of (high-energy) visible light off of
them.

Not all light (or more accurately, EMR) is blackbody radiation. There can be
chemically-emitted light, directly from chemical reactions. The blue glow of
methane (natural gas) combustion is a chemical emission, contrasted with the
yellow-white glow of a candle, actually blackbody emissions of suspended soot
particles in the smoke plume. (There's a blue region of chemical emission at
the base of the flame.)

Chemical emissions are based on specific frequencies of EMR emitted as
electrons transition between energy states, if I understand correctly are a
quantum phenomenon. Fluourescent and LED lamps also work based on chemical /
valance emissions, and operate in far narrower bands than blackbody emissions
-- one of the reasons these lamps can appear harsher than incandescents.
Similarly various chemical lamps, especially high- or low-pressure sodium
vapour, formerly popular as street lighting, which emit in narrow bands (low-
pressure especially).

Some forms of ionizing radiation are also EMR emissions, at far higher energy
levels, triggered by nuclear rather than electron emissions. Typically gamma-
rays.

And stimulated emissions such as lasers and masers are ... another phenomenon
I understand only poorly, but are also tuned to very tight frequencies. Radio
and microwave emitters are somewhat similar.

[https://en.wikipedia.org/wiki/Black-
body_radiation](https://en.wikipedia.org/wiki/Black-body_radiation)

[https://en.wikipedia.org/wiki/Infrared](https://en.wikipedia.org/wiki/Infrared)

[https://en.wikipedia.org/wiki/Heat](https://en.wikipedia.org/wiki/Heat)

~~~
elwell
Thanks, very informative!

------
qntty
original article: [https://news.rice.edu/2019/07/12/rice-device-channels-
heat-i...](https://news.rice.edu/2019/07/12/rice-device-channels-heat-into-
light/)

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.”_

------
lifeisstillgood
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.

Some projects have really big ROI

~~~
natermer
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.

~~~
lifeisstillgood
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

[https://en.m.wikipedia.org/wiki/History_of_penicillin](https://en.m.wikipedia.org/wiki/History_of_penicillin)

------
epistasis
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:

[https://www.nrel.gov/docs/fy17osti/68925.pdf](https://www.nrel.gov/docs/fy17osti/68925.pdf)

And that broad category is ~25% of costs.

~~~
teej
We shouldn't discourage progress just because it doesn't fit exactly into
todays model of the world.

~~~
epistasis
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.

~~~
caymanjim
Sure it is. Lower efficiency means you need more panels, larger panels, and
more support infrastructure. It limits where it can be deployed and makes it
less competitive.

~~~
epistasis
And the need for more/larger panels and support structures will only be a win
if overall, the costs decrease.

The cost is what makes the decision for deployment, not the efficiency.
Perhaps this efficiency makes 2-axis tracking economical enough to justify,
and then it gets deployed, but in the end the efficiency wasn't as important
as the improved costs.

~~~
qroshan
To use a Computer Science paradigm. Performance (Efficiency) is not the end
goal, but performance (efficiency) acts like currencies so that you can 'buy'
other things from it.

------
i_am_nomad
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.

~~~
ryanmarsh
This is essentially the same principle behind current night vision tech.

------
xendo
I wonder if the process of changing heat into light can be used for
transferring heat more efficiently than current AC units.

~~~
ryanmarsh
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

~~~
mikepurvis
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?

~~~
mruts
The market should (and has in the past) figured this out. Energy costs money,
tenants want to spend less money. Tenants will pay more money up front to save
themselves money down the line. Therefore landlords should have an incentive
to build energy efficient structures even if they aren’t paying for the
energy.

The problem is when an energy source with an high externality (climate related
or otherwise) isn’t priced in. This isn’t a hard problem for the government’s
perspective though: just price in the externality through some free market
system. Carbon credits are a good example of this.

~~~
rocqua
Part of the reason is that it is hard to gauge what the energy bill of an
apartment will be before you start renting. That is where certification should
come in.

------
Terr_
> turning heat into light

> channel mid-infrared radiation (heat energy) into light energy

> absorbs thermal photons and emits light.

Goddamnit, no! None of this is "heat", it's just one range of light being
converted into another! This is shitty "science"-journalism parroting a common
misconception.

After all, the only reason we associate infrared with "heat" in the first
place is that it's useful for detecting things which happen to be at a range
of temperatures, temperatures which _just happen_ to be slightly warmer than
the operating state of self-reproducing bags-of-mostly-water on a small rocky
planet.

~~~
infogulch
Yeah it seems more like it.. fluoresces (?) around the infrared spectrum.
Fluorescence might actually the right term for what is happening.

------
godelski
On topic of the HN title, there is research being done into carbon nanotube
rectennas. Theoretical efficiency is in the upper 90's%. Problem is that they
have very narrow bandwidth. Also as far as I'm aware, no one has even built
lab samples that do decently.

~~~
PopeDotNinja
> there is research being done into carbon nanotube rectennas. Theoretical
> efficiency is in the upper 90's

I googled optical rectenna.

"An optical rectenna—a device that directly converts free-propagating
electromagnetic waves at optical frequencies to direct current" [1]

[1]
[https://www.nature.com/articles/nnano.2015.220](https://www.nature.com/articles/nnano.2015.220)

------
blunte
This sounds great, but for some years we hear of various discoveries that will
greatly increase solar panel efficiency. Why are we still at 22%-ish?

~~~
ThomPete
The primary issue with everything in this category is that plenty of things
are possible in the lab or in theory which just isn't possible when applied in
reality and at scale.

Blame journalists for hyping this because of the climate change focus.

I am involved in actively looking for better materials and better sources of
energy. The reality is that there are no fundamental breakthroughs since oil
and nuclear.

No matter what you hear we just haven't had anything that fundamentally
changes the game.

So instead of actual breakthroughs in the fundamentals, we get marketing,
branding, and communication. But this is not something that can be fixed with
that, it's physics, not product innovation

We will most likely get fusion (far out) fuel cells (even further out) before
we get any fundamental breakthroughs here.

~~~
anchpop
Why do you consider cheap solar not a breakthrough? If I 30-year mortgaged
some solar cells, I could put them on my house right now and save $20 a month
on net because of reduced electricity costs

~~~
ThomPete
And you can use them to power your watch perfectly fine too.

That doesn't mean it will work at scale for society which is the primary
issue.

The key thing to look for is energy density as that will be more likely to
give society a bang for the buck.

Distributing solar cells out with the capacity factor of solar isn't
economically feasible for society and neither possible as a main source of
energy.

Nuclear and Hydro to some extent Thermal none of them are in vogue.

~~~
Brakenshire
These are arbitrary metrics, why does energy density matter for anywhere which
has the space? Even in Northern latitudes and high density countries you can
generate a lot of electricity with a nominal amount of land. All the more if
they can be fitted on rooftops. For sunny places near deserts it can
absolutely provide a big percentage, even a dominant percentage of power. The
main issue is matching demand to supply, production density is a distant
concern.

~~~
ThomPete
Energy density isn't arbitrary. It normally means something can be used in
compact form (batteries, oil, gasoline, coal, uranium) and deliver energy at
will.

Look at the capacity factor of wind and solar, add to that the huge areas they
need and the fact that they are intermittent and you start to get a glimpse of
the problem.

This is neither economically nor technically feasible. You can't generate as
much as you think and you can't do it at a cost that makes it feasible
generally for society not even with lowered cost.

Currently, we are talking 1% of world energy consumption not expected to be
much more than 3-4% in 2040 and that's despite huge investments and all the
political goodwill you can ask for [1] Keep in mind that the numbers you
normally see displayed is for electricity not for energy. Electricity is only
a subset of energy.

Furthermore, investments in solar and wind is decreasing especially when you
take china out of the equation. [2]

And again. Lab results or theoretically possible advantages most of the times
aren't feasible in reality and at scale.

[1]
[https://www.iea.org/weo/?fbclid=IwAR3eH1AFcRSPSEit8JINLCMvE_...](https://www.iea.org/weo/?fbclid=IwAR3eH1AFcRSPSEit8JINLCMvE_UmZAsNNdxRRpIepIGqCz_rILNEHHwLtNw)

[2] [https://www.globalresearch.ca/growth-renewables-stalled-
inve...](https://www.globalresearch.ca/growth-renewables-stalled-investment-
falling/5678889?fbclid=IwAR0Sd3mRotIjpUDmwO-6M1t9lQ4buvB8BW8ceQBlJesRA5b4rgUW23Af7FU)

~~~
Brakenshire
Those IEA renewable projections are comically wrong every year:

[https://pbs.twimg.com/media/DsX2rpPW0AIVORG?format=jpg&name=...](https://pbs.twimg.com/media/DsX2rpPW0AIVORG?format=jpg&name=large)

~~~
ThomPete
Ate they wrong about the current situation?

------
michaelcampbell
Is solar efficiency the new "battery breakthrough" that will transform our
lives "in 10 years", for 25 years straight now?

------
m3kw9
Nano tubes are super expensive

~~~
pacala
They have no use at scale yet. Expect prices to drop exponentially once a use
at scale is found.

------
ejz
Very cool! Let's see if it reproduces experimentally, and then let's see if it
scales.

------
darksaints
I'm really curious as to what this will do for waste heat from other
processes.

------
elif
I hope this means that my computer fans will be replaced by a laser show

------
anewguy9000
ive always wondered why leaves all generally evolved to be green instead of
black. wouldnt black be more efficient?

~~~
outside1234
The short answer is that absorbing a narrow band of energies is more efficient
than a wide band.

See:
[http://scienceline.ucsb.edu/getkey.php?key=4979](http://scienceline.ucsb.edu/getkey.php?key=4979)

------
sovnade
For anyone curious: Carbon Nanotubes, so this will likely not see the outside
of a lab any time soon.

~~~
clouddrover
Why not? Nawa's ultracapacitors are based on carbon nanotubes and they're
going in to production:

[https://newatlas.com/nawa-nanotube-ultracapacitor-
production...](https://newatlas.com/nawa-nanotube-ultracapacitor-
production/59684/)

Vantablack is based on carbon nanotubes and you can buy it now:

[https://www.surreynanosystems.com/vantablack/science-of-
vant...](https://www.surreynanosystems.com/vantablack/science-of-vantablack)

------
dreamcompiler
"This light can then be used as electricity."

No. One cannot use light as electricity. One can use light _to make_
electricity. This is not just a minor typo; it's flat-out wrong.

~~~
marshray
If you want to get pedantic, you can't "make electricity" either because
'electricity' isn't a defined concept. Usually when people use words such as
"make electricity", they actually mean to refer to energy or power transferred
using electromagnetic fields interacting with a conductor. But a purely
chemical reaction that charges a battery could be said to "make electricity"
without even involving that.

More info:
[http://amasci.com/miscon/elect.html](http://amasci.com/miscon/elect.html)

~~~
dreamcompiler
I was going for a simpler idea: Light is photons, electricity is moving
electrons. And yeah, if you're talking about electromagnetic fields we're back
to photons again. It just struck me as a sentence that was very misleading to
lay people.

~~~
marshray
It's only simpler because "electricity is moving electrons" is not a
meaningful claim.

What is the physical unit of 'electricity'? There's not one, because it's not
a thing.

------
chovy
This is what we need before we're all fucked.

~~~
pstuart
probably too late but we should never give up.

~~~
kevin_thibedeau
Best that we prepare a smooth transition for our robot overlords.

