
Using carbon nanotubes and rectennas to yield a 90% efficient solar cell - Osiris30
https://pv-magazine-usa.com/2018/11/23/all-i-want-for-christmas-is-a-90-efficient-solar-panel/
======
nkoren
This set off one of those "hey, didn't I read about this a long time ago? Like
quite a few decades ago?" bells.

A quick trip down memory lane, and here's an archive of one of the stories I
was following, back in the day:
[http://rexresearch.com/marks2/marks.htm](http://rexresearch.com/marks2/marks.htm).
Lumeloid was broadly the same as what NovaSolix proposes -- cheap ultra-high-
efficiency PV with optical rectennas -- albeit using polymers rather than
carbon nanotubes. I had high hopes that these would be just around the corner
in the 1990s, but alas the technology seems to have vanished into the mist.
I'm curious to know why: was it a failure of the technology? Financing?
Personalities? Alas its demise seems have been undocumented.

Hopefully NovaSolix will fare better; at least today there is complementary
infrastructure (far better batteries, electric cars, etc.) which makes
investment in any kind of solar tech much more viable than it would have been
in the 1990s.

~~~
agumonkey
There's a 10min interview from 1991

[https://www.youtube.com/watch?v=hMGyob166Cg](https://www.youtube.com/watch?v=hMGyob166Cg)

crazy to think that so many things were already done and fell below the radar

~~~
Retric
Plenty of perpetual motion patents, does not mean they work.

The system is designed to protect ideas, not validate them.

------
jartelt
Just want to post a reminder that solar cells are already efficient enough and
cheap enough to be cost effective for power generation in many regions of the
world. I am all for continued research to improve efficiency or decrease cost,
but sometimes articles like this one lead people to believe that solar cells
are not yet cost effective. They already are!

~~~
brownbat
Just to footstomp this, there are other costs that are already beginning to
dominate the analysis for solar, like customer acquisition costs. Convincing
someone to attach something to their house has significant costs. Like, "over
$2000 per install" significant.[0]

Other soft costs, like land acquisition and taxes, still play dominant roles
in many projects.[1]

The naive assumption is that solar succeeds when there's lots of sun and it's
all just physics.

But these other factors, like, say opportunity costs (the cost of available
substitutes), are why you're often better off installing solar in Alaska than
Florida.[2]

Theoretical physics are great, but at this point I'd be far more excited about
big ideas to deal with the messy economics side of solar generation. An
announcement that some sort of "solar council" was going to pursue a national
marketing campaign to drive solar adoption would be huge news. Or Elon
deciding that strip malls were his new target, to drive installation of solar
on every commercially leased roof, which would reap huge efficiencies of scale
in local installation costs over residential.

Or, the cheesy TED talk clincher would be: the next big solution isn't always
about electrons, sometimes it's about people.

[0] [https://www.solarreviews.com/solar-leads/customer-
acquisitio...](https://www.solarreviews.com/solar-leads/customer-acquisition-
costs-in-the-solar-industry-2017/)

[1]
[https://www.nrel.gov/docs/fy17osti/68925.pdf](https://www.nrel.gov/docs/fy17osti/68925.pdf)

[2] [https://solarpowerrocks.com/solar-basics/how-much-
electricit...](https://solarpowerrocks.com/solar-basics/how-much-electricity-
does-a-solar-panel-produce/)

~~~
newnewpdro
Another issue is theft. I own a remote desert property in many ways ideal for
solar, but the utility electric bill averages < $20/mo.

Nobody is going to try steal the hot copper wires connecting my house to the
grid.

But where there's a substantial PV array on display, there's batteries and an
expensive inverter nearby, and not much to prevent taking them.

~~~
eloff
Also in some parts of the world they will definitely steal your copper wires
(out of the walls of your house if there isn't sufficient security!) But in
those places your solar gear wouldn't last a week.

~~~
pbhjpbhj
In the UK an acquaintance of mine has regular phone outages because the copper
comms lines are pulled. They're shallow ditch laid; the thieves hook one end
to a tow-hitch and drive, I gather.

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isoprophlex
Here's the money shot:

[https://l0dl1j3lc42iebd82042pgl2-wpengine.netdna-
ssl.com/wp-...](https://l0dl1j3lc42iebd82042pgl2-wpengine.netdna-ssl.com/wp-
content/uploads/sites/2/2018/11/antennae-600x300.jpg)

If they can really make that happen cheaply (green shaded areas, meaning
efficient collection of power from near IR photons) this is revolutionary.

Current silicon based tech (blue shaded) is useless for light energies below
red.

~~~
znpy
I am always fascinated by how people that don't waste their time with the
latest data visualization trends can come up with slides so ugly according to
latest trends yet so effective at exposing information.

~~~
pfortuny
Apart from the (ugly) colors, the plot looks like standard R/gnuplot/whatever
tool existing since (I grow old, I grow old) the beginning of time...

------
GeorgeTirebiter
Folks here are missing the fact that the rectifying diodes must operate in the
THz region. The fact that NovaSolix has demonstrated Proof-of-Concept chips
says they are able to build diodes that work at 100s of THz. That, alone,
seems impressive to me. (example: green is 630 nm; f = c / lambda, that is,
476 THz)

~~~
gpm
Just to check my understanding:

A green light would create a AC current at 476 THz. We put this through a
diode to capture the pulses of current that are moving in the right direction?

~~~
std_throwawayay
Yes.

Also, the voltage won't be very high. The diodes have to be efficient in the
millivolt regime.

------
KaiserPro
A carbon nano tube antenna that is capable of working at infra-red frequencies
have been around a few years, thats fairly simple[1]

The hard part was finding a diode/rectifier that was capable of running at
terahertz frequency. I cant see how this rectifies. I assume its to do with
the layout: [https://l0dl1j3lc42iebd82042pgl2-wpengine.netdna-
ssl.com/wp-...](https://l0dl1j3lc42iebd82042pgl2-wpengine.netdna-ssl.com/wp-
content/uploads/sites/2/2018/11/materials.jpg)

If they are not telling porkies, then this is a wondrous breakthrough.
(assuming the nanotubes are UV stable.)

[1] 1/2 wavelength conductor, which is possible with carbon nanotubes

------
aaaaaaaaaab
90%? I thought the theoretical maximum was 86%:
[https://en.m.wikipedia.org/wiki/Thermodynamic_efficiency_lim...](https://en.m.wikipedia.org/wiki/Thermodynamic_efficiency_limit)

~~~
std_throwawayay
I think you are on to something. For non-concentrated solar, what a low-cost
application would use, the limit is given as 43%. The numbers given trigger my
bull-detector hard and I've had some insight into the difficulties that you
face if you actually want to build a rectifying diode. Those things are hard.
Really hard. You're getting nowhere near where you'd have to be to achieve the
limit. To satisfy the claims given, these guys have to be geniuses beyond
imagination.

If something sounds too good to be true, it probably is.

------
sna1l
> And like so many other ideas, if the sales pitch is real, if the scientists
> can deliver, if the hypothesis can move to theory – and the theory become
> applicable in a scalable, manufacturable good – then all the rules change.

------
unchocked
Wow - this is a totally different approach than crystalline silicon, and could
be much cheaper to produce as well as more efficient. Something new is going
to be required to do much better than 35% efficiency, as you can only do so
much lining up the band-gap of semiconductors.

On another note, it's nice to see that crystalline silicon PV is perceived to
be so successful that people are lining up to comment on how a dramatic
improvement in power density and cost wouldn't really matter.

------
narrator
Carbon nanotubes, the wonder material that's only as toxic as asbestos [1].

[1] [https://www.scientificamerican.com/article/carbon-
nanotube-d...](https://www.scientificamerican.com/article/carbon-nanotube-
danger/)

------
Solar19
I assume this won't ever hit the market at the promised performance and cost.
In the past decade or so we've been inundated with hundreds of stories, maybe
thousands, about new solar breakthroughs and they never come to pass. The same
is true of all the battery "breakthroughs". For some reason this stuff is
never commercially viable. I wish I understood why.

------
robomartin
Just a random thought on the idea that there might be a limit function as it
pertains to the desirablility of increased efficiency.

We have a 13 kW array. I make it a point to keep it cleen. However, this isn’t
something one can expect to accomplish daily. At the very least it would waste
a lot of water. As a result of this, my panels, on average, enjoy a
combination of dust, leaves and, yes, bird poo, sometimes lots of it.

If we had 90% efficient panels the combination of dirt, dust and a determined
flock of birds could take out 50% of my energy generation capacity. Having a
less efficient system distributed across a larger area might actually be a
better idea.

~~~
llukas
90% efficient panels would have ~4x smaller area. Wouldn't be that easier to
clean and secure from bird poo etc?

~~~
robomartin
I don’t feel like getting too scientific today. My gut feeling is that the
accelerated loss rate due to greater Watts per square meter will at some point
intersect with the curve denoting cleaning needs. At one point water waste and
man-hours might become a problem.

------
plaidfuji
Their argument that it will be cheaper because of raw materials costs is pure
rubbish. That was supposed to be the point of silicon - it’s just sand! Then
people realized that the structure (crystalline) and energy intensive
processing required to obtain that structure were the real cost drivers, not
to mention the housing, transparent electrode arrays, and installation costs.
Nanotechnology is difficult to manufacture because of the energetic factors
working against the formation of long-range nanostructure.

~~~
whatshisface
Energetic? It sounds like it would be entropic. Every crystal or polymer is a
long-range nanostructure.

~~~
plaidfuji
Sorry, you’re right- but entropy is a part of the thermodynamic free energy of
a structure, I was glibly rolling all that into “energy”..

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

------
mabbo
I think scientists and inventors often do themselves no favors by making
claims like "90% efficient". That's the theoretical maximum. Now if they hit
80%, we'll all say they failed despite it being an incredible achievement.

They should claim "75% or more", and then hit 80% and blow our minds. The
Scotty Factor[0] should be liberally applied when possible[0].

[0][http://wiki.c2.com/?ScottyFactor](http://wiki.c2.com/?ScottyFactor)

~~~
Dylan16807
I don't think that's an issue at all. If the panel actually comes out and it's
60% at comparable prices to existing ones I'll still be overjoyed.

------
WheelsAtLarge
The highest cost of Solar installations these days is the installation cost
itself and the batteries -- if you're willing to spend the cost for the
batteries. 90% efficient is great but the real value for most would be in
reducing the cost in the additionals to the solar cells.

Less than 40% of the installation costs are the actual solar panels.

If someone came out with a DIY solar installation, that would be a major
advance.

~~~
codingdave
I've done numerous DIY solar installs, to power outbuildings on my property,
as off-grid battery-powered systems. I hired professional help for our system
that powers the main house, as the scale was larger and the grid-tie was
beyond my expertise. But an experienced electrician could surely do that part
as well. So the lack of DIY installs is less about the solar tech, and more
about where any given individual's DIY skills fall.

------
driverdan
There's a speculative solar announcement like this every week. Until they
actually produce results don't get your hopes up.

------
nabla9
Any technology that surpasses 50% efficiency will never double its efficiency
again.

We are already very close to 50% with 40-46% efficient solar cells. The
installation cost, scaffolding cost, maintenance and the cell price start to
dominate. Solar panel tilt can improve efficiency up to 30 percent (flat panel
versus sun following 2-axis panel).

~~~
unchocked
If you double efficiency you halve the size, roughly halving the installation,
scaffolding, & etc. costs you mention.

Also those 40-46% efficient cells are expensive, requiring 3 different layers
of semiconductors each tuned to a different band-gap. The panels we all buy
for ~$1/watt are about 20% efficient, single-layer designs.

------
headgasket
I this is actually true and feasible, this has immense implications. Imagine
mirror powered airplanes.

------
baybal2
>yield a 90% efficient solar cell

Yield a 90% efficient solace cell _for a single wavelength_

~~~
darkmighty
edit: actually, I'm wrong, see below

You're right, I believe. I don't have time to investigate, but if the claim is
90% efficiency w.r.t. total radiation input, it's certainly wrong. Doing so
would violate the 2nd law. For example, room temperature thermal radiation has
significant emmitance in the radio range of the spectrum. Needless to say
nobody can build radio antennas to turn this energy into work.

If it is 90% of the thermodynamic limit, then maybe. But then I think
multijunction cells are already significantly close to the thermodynamic limit
(much better than 22% claimed).

[https://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodyna...](https://en.wikipedia.org/wiki/Carnot%27s_theorem_\(thermodynamics\))

(obs1: substituting Tsun as Th and Tearth as Tc left as an exercise to the
reader ;) )

(obs2: try changing Tc to CMB temperature! )

~~~
Dylan16807
Those "significant" amounts of radio are an extremely small amount compared to
the visible and near infrared output of the sun.

> substituting Tsun as Th and Tearth as Tc left as an exercise to the reader

Left to the reader because doing the math reveals that it's only a 6%
difference and undermines your point? ;)

~~~
darkmighty
Oh thanks. I hadn't actually plugged in the numbers, shame on me :P

It seems the maximum efficiency in this case is ~94.8%, so the claim does seem
plausible at least.

------
samstave
ELI5: What is a 'rectenna'

~~~
tim333
[https://en.wikipedia.org/wiki/Rectenna](https://en.wikipedia.org/wiki/Rectenna)

Radio waves jiggle the electrons back and forth in your chunk of metal. Stick
in a diode so they can only go one way and you have power.

------
djrogers
> hopes to use carbon nanotubes to...

> a process they hope will yield...

Yawn. I hope to get a new truck for Christmas- let me know when Santa Claus is
real.

------
smaddox
Nice in theory. Very difficult to get anywhere near that efficiency in
practice. Best of luck to them, but I'm not holding my breath.

