
Scientists Design Solar Cell That Captures Nearly All Energy of Solar Spectrum - 3eto
https://www.rdmag.com/news/2017/07/scientists-design-solar-cell-captures-nearly-all-energy-solar-spectrum
======
sbierwagen
As usual with press releases, this pretends there is no prior art. Of course,
stacking solar cells to increase efficiency has been a thing for five decades:
[https://en.wikipedia.org/wiki/Multi-
junction_solar_cell](https://en.wikipedia.org/wiki/Multi-junction_solar_cell)

~~~
ndonnellan
Yep, see 40% cells used 4 years ago in
[http://www.businesswire.com/news/home/20130426005162/en/Amon...](http://www.businesswire.com/news/home/20130426005162/en/Amonix-
Achieves-World-Record-PV-Module-Efficiency)

(36% eff in practical application due to system losses)

~~~
k__
Nice.

What's the maximum?

What's the current standard?

~~~
hwillis
Max so far is 46%[1], max theoretical is 86.8%[2]

Most solar panels are 15% or better. The best residential cells are 22.2%[3],
the commercial cells are 25.3%. The theoretical maximum efficiency of single-
layer silicon PV cells is ~32%.

[1]: [https://www.nrel.gov/pv/assets/images/efficiency-
chart.png](https://www.nrel.gov/pv/assets/images/efficiency-chart.png)

[2]:
[https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...](https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit)

[3]: [https://us.sunpower.com/sites/sunpower/files/media-
library/d...](https://us.sunpower.com/sites/sunpower/files/media-library/data-
sheets/ds-x22-series-360-residential-solar-panels.pdf)

~~~
deepsun
Curious, what is on spacecrafts. Maybe not really efficient at all, because
weight and reliability is way more important out there, and also abundance of
raw sunlight.

~~~
mlindner
We used triple-junction solar cells on our satellite. If I remember right the
cells ran somewhere around $100-$200 per square inch. I don't remember the
efficiency, but they were left-over dumped cells that were donated to us by
some group at NASA because they "expired" (they're kept under a nitrogen purge
because they oxidize slowly and these had a leak, if memory serves, still
worked great though) and a few were broken as they are more fragile than glass
and are about as thin as a sheet of paper. They glow bright red when you
forward bias them which you can use to visually detect dead portions of the
cell/damage.

------
matt_wulfeck
I just had my panels turned on. I love solar. It's still difficult to justify
it short-term on a cost-basis, but I'm saving about a dollar a day after all
things are said and done.

That being said, I'm generating my own electricity and my panels will run for
a very long time. The best is cranking the AC and still watching the meter run
in reverse during really scorching days.

~~~
fred_is_fred
What the NPV and pay-off time of your system? I've been unable to get one bid
here that's less than 10 years because electricity is fairly cheap here.

~~~
workerIbe
I have built a system that cost just under $2k and should pay off in about 3-4
years (depending on battery lifetime). 2.4 Kw (8 panels) of used panels @
$.32/Watt, Charge controller, 3Kw inverter, transfer switch and 320ah@48v used
Golf Cart Batteries. System is offgrid and supplies all my convenience
outlets, kitchen and 240v circuits are on still on the grid. Panels are on top
of free standing structures and being off grid permits are not required and
only the transfer switch installation needed to be done by an electrician.
Bonus is being offgrid it acts as a big UPS in a power failure.

~~~
matt_wulfeck
This is a great plan. PG&E here in California forces solar customers onto a
more expensive plan. If you can avoid that switch and use solar to
dramatically reduce (but not eliminate) your total kwh load then you'll
definitely come out way ahead, because you'll be on their cheapest tier.

~~~
njarboe
California will be changing dramatically how it charges for electricity in the
next few years[1]. I was talking to a person Tesla today about putting solar
on our house and he mentioned in passing that Time-Of-Use Rates will be the
default for everyone in California in 2019 by law (AB 327 in passed in 2013).
For your net metering you will get credit/pay for power to/from the grid at
the rate for the time it happens. A good up-sell for the powerwall. If the
rates get way out of wack due to high solar input, one could do well charging
your powerwall during the peak solar production hours (see duck curve [2]) and
putting them back on the grid a 3-6 hours later.

[1] [https://cleantechnica.com/2015/06/08/california-rolls-out-
de...](https://cleantechnica.com/2015/06/08/california-rolls-out-default-time-
of-use-rates/) [2] [http://instituteforenergyresearch.org/solar-energys-duck-
cur...](http://instituteforenergyresearch.org/solar-energys-duck-curve/)

------
meri_dian
>"This particular solar cell is very expensive, however researchers believe it
was important to show the upper limit of what is possible in terms of
efficiency. Despite the current costs of the materials involved, the technique
used to create the cells shows much promise. Eventually a similar product may
be brought to market, enabled by cost reductions from very high solar
concentration levels and technology to recycle the expensive growth
substrates."

We will end our reliance on fossil fuels not by forcing masses of people to
change their lifestyles and inconveniencing them, but by developing green
energy tech that is simply more efficient and cost effective than fossil
fuels. Once this happens the transition away from carbon based energy sources
will be swift.

Given the rate of progress, I believe we'll see widespread adoption of
renewable energy far before climactic conditions on earth become dire for
humanity.

~~~
pishpash
Climactic conditions will always be a problem. The next headache will be how
to deal with a heat bath from uniformly dissipated waste heat from this energy
rather than natural gradients and storage that drive climactic processes. When
greedy humans get their hands on 'unlimited energy' that is not a panacea, but
a much bigger catastrophe waiting to happen.

~~~
londons_explore
If humans really had "unlimited energy", we could air condition the entire
world, and send the waste heat to space with large infrared (or even visible
light) radiators.

~~~
Thorncorona
Not really. Air conditioning is a heat displacement system, so you'd still
have the same amount of heat. Using infrared radiators would just accelerate
global warming since green house gases mainly absorb infrared light.

Visible light would probably be a hazard. Would be pretty great for "beam in
the sky" special effects though.

~~~
SubiculumCode
I think she was suggesting sending the exchanged heat into space..you know,
up.

------
adamwong246
I always wondered why we did not just use prisms to separate the different
wavelengths, then capturing selections of the spectrum with a variety of
simpler, unstacked panels. Perhaps one could even deflect the infrared into a
more conventional, presumably more efficient, heat collector while the higher
frequencies are directed to true photovoltaics.

~~~
klodolph
Think of how solar is an investment: you pay money up front, use up a certain
chunk of land, and you get energy over the next 25 years. Imagine panel A
which costs $100 and has 22% efficiency, versus panel B which costs $500 and
has 30% efficiency. No point in buying panel B, since you can buy 5x panel A
for the same price.

~~~
jcbrand
But then you'd also need to cover 5 times the area, and land also costs money.

~~~
mikepurvis
I'm doubtful that land area is really a significant cost for most solar
installations. Small ones go on rooftops that people already have, and large
ones go on marginal land in the middle of nowhere that's cheap.

If there's someone with knowledge of the numbers, I'd be interested to be
shown otherwise.

~~~
philipkglass
You are correct. "Small" utility-scale solar projects of 1-20 MW capacity take
7.6 acres of land per megawatt-peak, for fixed-tilt ground mount systems:

[http://www.renewableenergyworld.com/articles/2013/08/calcula...](http://www.renewableenergyworld.com/articles/2013/08/calculating-
solar-energys-land-use-footprint.html)

Fixed-tilt utility scale systems just recently fell to $0.99 per watt-peak in
the US:

[https://www.greentechmedia.com/articles/read/Sunshot-1-Per-W...](https://www.greentechmedia.com/articles/read/Sunshot-1-Per-
Watt-Solar-Cost-Goal-Mission-Accomplished-Years-Ahead-of-S)

You can buy 124 acres of land in California's sunny Imperial County, near
existing solar farms, for $95,000:

[http://www.landwatch.com/Imperial-County-California-Land-
for...](http://www.landwatch.com/Imperial-County-California-Land-for-
sale/pid/3446602)

If you turned that land into a solar farm you could fit about 16 megawatts of
fixed-tilt solar arrays on it. 16 MWp of installed solar equipment would cost
$15.84 million at $0.99/watt and the land is $0.095 million. Land accounts for
only 0.6% of the combined costs. (A 16 MWp farm is small by utility-scale
project standards and probably would not cost only $0.99/watt because of dis-
economies of small scale. I cited $0.99/watt to set a _conservative_ bound on
how much cost the land component represents in a utility scale solar project.)

------
vectorjohn
What is it that makes solar panels cost what they do, ultimately? Not
materials, right? Those are all basically sand and other not so special
things. Labor? Isn't it mostly automated? Upkeep of the factories? Input
energy?

Maybe it's just all those things together. But it sure seems like if we wanted
to it wouldn't be that hard to ramp up production and drive costs down a
couple fold. Not that I know how.

~~~
pjc50
Ah, the good old "I know nothing about this but assume it must be easy"!

It's materials _processing_. They're only "basically sand" in the sense that
glass or microchips are. The key step is purification of silicon, which is
like distillation in the liquid/solid phase. It's very energy-intensive. This
then gives you a solid cylinder of pure silicon.

To make cells, you slice this like a ham. Except it's extremely hard, so you
need a diamond saw: [http://www.asahidia.co.jp/eng/wp-
content/uploads/2015/05/B51...](http://www.asahidia.co.jp/eng/wp-
content/uploads/2015/05/B51.pdf) and, like sawing wood, the material from the
cut ("kerf") is wasted.

A surprising amount of recent cost reductions have been due to making the
cells thinner and making the _cut_ as thin and clean as possible.

They are then run through some annoyingly toxic chemical processes, given an
antireflective coating, have silver wiring attached, and packaged into a glass
or polycarbonate fronted housing.

~~~
rsfern
And the alternative technologies -- e.g. vapor deposition processes for thin
film photovoltaics -- aren't exactly cheap either.

------
Gys
'The new design converts direct sunlight to electricity with 44.5 percent
efficiency, giving it the potential to become the most efficient solar cell in
the world.'

~~~
sbierwagen
Note careful use of "potential" there. Fraunhofer hit 46% two years ago with a
four-junction cell: [https://www.nrel.gov/pv/assets/images/efficiency-
chart.png](https://www.nrel.gov/pv/assets/images/efficiency-chart.png)

~~~
londons_explore
it's sad that nothing more has been published on that architecture for 2+
years...

One would imagine most of the research dollars being into how to make multi-
junction cells cheaply, rather than into other much lower efficiency cells.

~~~
sbierwagen
"The only figure of merit in a PV system is cost per kilowatt-hour installed".
Multijunction cells require concentrating panels and two-axis tracking. In
order for them to make economic sense, both the panels and the tracking have
to have lower lifetime costs than standard untracked panels.

So far, they don't. Plus, concentrating panels don't work under cloudy skies,
so...

~~~
logicallee
>"The only figure of merit in a PV system is cost per kilowatt-hour
installed".

This doesn't make intuitive sense to me. If you could pay $50 for a bucket of
goop you can slather on your roof that would capture 1% of the incident light
energy hitting it forever, would everyone do so?

by your standard "hell yeah" as that means the equivalent of $2.5k per roof (I
multiplied the $50 for 1% by 50 to conpare apples to apples) to capture 50% of
the energy which is far better $ per KWh than offered by anyone else!

The issue is that for many people they would prefer to capture more than 1%
and they are willing to pay more per kwh in exchange for getting more kilowatt
hrs. So they would prefer to pay a large premium, thereby showing that it
really doesn't just come down to cost per KW-hr installed.

there are other factors.

~~~
sbierwagen
I'm a little confused by your argument, so I'll go through it one clause at a
time.

    
    
      If you could pay $50 for a bucket of goop you can slather 
      on your roof that would capture 1% of the incident light 
      energy hitting it forever, would everyone do so?
    

Sure? If you postulate a PV system that has much lower cost per KWh installed
than has ever been achieved, then of course it'll make economic sense.

    
    
      by your standard "hell yeah" as that means the equivalent 
      of $2.5k per roof (I multiplied the $50 for 1% by 50 to 
      conpare apples to apples) to capture 50% of the energy 
      which is far better $ per KWh than offered by anyone else!
    

Sure? You made the fictional system way, way better, so it's an even better
deal now.

    
    
      The issue is that for many people they would prefer to 
      capture more than 1% and they are willing to pay more 
      per kwh in exchange for getting more kilowatt hrs. So 
      they would prefer to pay a large premium, thereby 
      showing that it really doesn't just come down to cost 
      per KW-hr installed.
    

You are now talking about something _completely different._ Homeowners
demonstrably don't care about the power conversion efficiency of their roof--
the penetration rate of rooftop solar is pathetic. People care about how much
their electricity costs, and only install rooftop solar if gives them cheaper
electricity. If grid power costs $0.10/KWh, and solar costs $0.50/KWh, then
they won't buy it. Look out the window! Look at all the solar panels you don't
see.

That's the argument from economics. The argument from product availability:
regular planar unconcentrated multijunction cells for terrestrial use don't
exist. You can't buy them, because there's no market for a $10,000 500 watt
cell when $200 300 watt cells are sold. [https://www.wholesalesolar.com/solar-
panels](https://www.wholesalesolar.com/solar-panels)

You can get them for space applications, presumably at incredible expense:
[http://www.spectrolab.com/DataSheets/Panel/panels.pdf](http://www.spectrolab.com/DataSheets/Panel/panels.pdf)

Concentrated multijunction panels for terrestrial use exist, but are only used
in utility-scale installations, since you don't do two-axis tracking with
rooftop solar. (Dual tracked solar panels cast shadows on each other, so they
have to be spaced much farther apart, and consequently have bad space
utilization)

 _The only figure of merit in a PV system is cost per kilowatt-hour
installed._ Right now, all rooftop solar installations are single-junction. If
multijunction cells resulted in a lower cost per kilowatt-hour installed, then
they would be used, but they don't, so they aren't.

~~~
logicallee
I'm really confused why you don't follow my argument. Suppose instead of $50
for a 1% efficient goop, my goop only cost $1 but was only 0.1% efficient.
That is five times more efficient _per dollar_ but reduces your yield by 10x!

Do you see why nobody who wanted any appreciable amount of solar energy would
put my "$1 for a roof's worth of 0.1% efficient solar collection" on their
roof? They would naturally choose the "$50 for a roof's worth of 1% efficient
solar collection" goop over that one (if those two were the only two choices),
even though it's 5x worse per kilowatt-hour?

I hope this explains what I'm talking about. A lot of people want more than
0.1% efficiency because they'd like to collect more energy than that...

~~~
sbierwagen
I follow your argument, I just don't think it matches reality.

In any system analysis, you have to consider all the relevant factors. If you
wave away important factors for the sake of argument, you get the wrong
answers, and end up in long arguments on internet forums, repeating yourself a
lot.

Let's game out some scenarios using your numbers. The choices are between a $1
array that gives 100 watt-hours, ($0.01/Wh) or a $50 array that gives 1000
watt-hours. ($0.05/Wh)

Rooftop solar, grid power is $0.001/Wh: You don't buy either array, since
neither is cheaper than grid. This is true for most of the industrialized
world.

Rooftop solar, grid power is $0.025/Wh: You buy the 100 watt-hour array, since
the power it produces is cheaper than grid power. You _don 't care_ about
total wattage, since you can get all the watts you want from the grid. This is
true of places where either electricity is expensive, or PV is subsidized.
(Hawaii, Germany, etc)

Rooftop solar, grid power is $0.1/Wh: You do buy the 1000 watt-hour array,
since it saves you from having to buy expensive grid watt-hours. There is no
place on Earth where grid power is more expensive than both single-crystal and
multijunction PV.

Rooftop solar, offgrid: Here you do strongly care about array output... but
you're only offgrid in very rural locations, where land is cheap. In practice,
off grid solar is never limited to just rooftops! If you need more watt-hours,
you build bigger arrays, rather than paying five times as much per panel.

Space: You need every milliwatthour, and each gram of spacecraft costs
hundreds of dollars anyway, so multijunction PV suddenly becomes price
competitive.

~~~
logicallee
your own third scenario analysis shows (grid power $0.1/Wh), if all rooftop
options are cheaper than grid, a worse $/KWh would be chosen as long as it
saved reliance on the grid.

You left something out of your analysis: people can have an ethical reason to
assign a cost of $0.1/Wh to grid power, because they consider environmental
externalities they're not paying for, to be something they actually _are_
paying for. If forced to, they may use the grid, but they might treat its cost
higher than the listed cost.

You've summarized things well in your second sentence: "In any system
analysis, you have to consider all the relevant factors."

As both your and my analysis show, it is not simply the dollar per kilowatt-
hour that informs purchase decisions.

If a certain cheap solar array manufacturing process was extremely toxic to
the environment, the environmentalist might not buy it at any price.

it's a complicated, not simple analysis.

------
philipkglass
The abstract is more informative than the press coverage:

[http://onlinelibrary.wiley.com/doi/10.1002/aenm.201700345/ab...](http://onlinelibrary.wiley.com/doi/10.1002/aenm.201700345/abstract)

 _The cell is assembled in a mini-module with a geometric concentration ratio
of 744 suns on a two-axis tracking system and demonstrated a combined module
efficiency of 41.2%, measured outdoors in Durham, NC. Taking into account the
measured transmission of the optics gives an implied cell efficiency of
44.5%._

Since this is a concentrating cell, compare to the concentrator cell records
tracked on NREL's PV efficiency records chart:

[https://www.nrel.gov/pv/assets/images/efficiency-
chart.png](https://www.nrel.gov/pv/assets/images/efficiency-chart.png)

The current record for 4-junction-or-more concentrator cells is 46.0%. This
isn't a record-setting cell even if the implied efficiency holds up under
standardized test conditions.

This cell like all high-concentration cells is unlikely to see mass market
acceptance on Earth. The module needs precise two-axis sun tracking to work
effectively even under perfect clear-sky conditions. That's significantly more
expensive than fixed arrays or single-axis sun tracking as used by
conventional large scale PV. And there's a vicious feedback loop: since two-
axis tracking is significantly more expensive, it doesn't get
developed/scaled, so the cost gap gets even wider over time WRT its
competitors.

But that's not actually the worst problem of high-concentration PV for
terrestrial use. The worst problem is that HCPV can use only direct normal
irradiance. Ordinary non-concentrating PV cells produce very nearly 25% of its
rated output if it receives 25% of test-condition illumination under non-ideal
conditions (due to some combination of clouds, air pollution haze, dusty
glass, etc.) Concentrating cells will produce close to 0% of rated output
under the same non-ideal conditions. Few regions have clear enough skies to
work with HCPV, but those same regions tend to be dusty, which the
concentrating optics cannot tolerate. Mechanical and optical complications
make HCPV higher-maintenance than ordinary flat PV _and_ more expensive to
install initially.

That's why there were a dozen+ companies working on concentrating PV in 2008
and all of them are now bankrupt or have exited HCPV manufacturing. Eking out
another cell-level improvement wouldn't have rescued the value proposition of
their complete systems. The refined polysilicon price spike that made exotic
technologies look briefly promising only lasted a few years and then it became
clear again that crystalline silicon is very hard to beat.

~~~
mark-r
I wonder if it wouldn't have more luck in outer space applications? Perhaps
not if the optics add much weight for the amount of power produced.

~~~
philipkglass
In orbit you wouldn't have to worry about dust or clouds, to be sure. But
keeping pointed exactly at the sun could still be a pain. As far as I know
there are no spacecraft using concentrating PV for power, though spacecraft do
commonly use multi-junction cells similar to these _without_ concentration.
Space applications are very conservative due to the high cost of hardware and
the small fraction of the total budget represented by the PV power system.
Cutting another 30% from PV system cost is outstanding if you're building
utility-scale PV projects on Earth, but down in the noise if you're building
communication satellites.

------
grandalf
Would these panels capture energy from the signal being radiated by my mobile
phone? What about gamma rays?

In other words, is a solar cell something that captures energy from photons
and converts it into usable electricity? Or from some subset of photons?

~~~
tim333
These panels would not. The capture a subset.

~~~
grandalf
Is this a limit of photovoltaics or a design optimization? Or other?

~~~
tim333
Most photovoltaics capture a narrow range which is why they stack different
ones in this design.

------
afeezaziz
If the process to make this kind of solar cell can be lowered enough through
scale then they should communicate this process to Chinese solar companies. I
am sorry for my poor understanding of chemical process; if the materials of
the solar cell are roughly the same then it would be quite easy for the
existing manufacturers to actually switch to this solar cell production.

I cannot wait for the era of super cheap electricity!

~~~
wavefunction
Why should research funded by American taxpayers be transferred to Chinese
solar cell producers, and by whom?

I hope an American firm implements the underlying science into a manufacturing
process, and any Chinese firms that want to use the process pay a fair and
equitable license for the technology.

~~~
zAy0LfpBZLC8mAC
> Why should research funded by American taxpayers be transferred to Chinese
> solar cell producers, and by whom?

Because Americans live in the atmosphere that Chinese CO2 emissions go to?

Not saying they should, but that would obviously be the reason?

~~~
wavefunction
Well, I'm in favor of technological spread across the world, especially when
it's beneficial to the environment or society at large.

However, Chinese solar cell firms have been dumping cheap and sub-standard
solar panels on America for years in an attempt to destroy the American
industry, so I am less excited about specifically Chinese solar panel firms
gaining access to this technology.

I suppose it marks me as a bit of a chauvinist in this case but I would prefer
if those who conduct themselves as adversaries do not also enjoy the benefits
accorded a friend.

~~~
eeZah7Ux
> dumping cheap and sub-standard solar panels on America

The country receiving the goods can refuse to buy if the quality is poor, or
there are safety risks, or the workers are being exploited or the
manufacturing process is environmentally unsustainable.

Poor countries have little freedom to turn down wealthy customers.

