
New Solar Power Material Converts 90 Percent of Captured Light into Heat - lelf
http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1589
======
davidovitch
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.

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.2014.06.016)
[http://dx.doi.org/10.1016/j.nanoen.2014.10.018](http://dx.doi.org/10.1016/j.nanoen.2014.10.018)
(behind a pay-wall unfortunately)

~~~
drdiatom
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.

~~~
toddkaufmann
Wouldn't it be great if you could just annotate that article and include the
link? It seems you can now that hypothes.is has launched[1].

[1] [http://hypothes.is/](http://hypothes.is/)

------
mapt
So... black latex paint? Asphalt? Water?

[http://en.wikipedia.org/wiki/File:Albedo-
e_hg.svg](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.

~~~
kragen
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.

~~~
rab_oof
The latter: would that be "structural absorbtion" related to structural color?

~~~
kragen
i don't know! i didn't know about structural coloration,
[https://en.wikipedia.org/wiki/Structural_coloration](https://en.wikipedia.org/wiki/Structural_coloration).
the crude absorption is not structural (it corresponds to a bandgap in the
semiconductor), but clearly they think the structure is important. i didn't
read the paper closely enough to know why.

------
jacquesm
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).

~~~
willholloway
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.

~~~
pbowyer
Can you share some pictures of your setup, and how it works? From your
description, I think the aluminium foil is propped inside your windows, and
absorbs energy from the sun. This then warms the room via convection.

What I don't get is why thin aluminium foil is good for this. Don't you need a
bigger heat absorber? Or is it surface area that's important?

~~~
willholloway
Sure, I'll email you.

The aluminum foil is cheap, and I found some anodized foil that is really dark
for great absorption. Anodized black foil is much better than painting foil
black.

I don't believe the total BTUs would be any higher if one replaced the thin
foil with a 1" sheet of aluminum. An aluminum sheet with fins on the backside
for heat dissipation might help, but I still think the total heat would be the
same because the amount of energy hitting the surface is the same.

It is surface area and temperature of that surface that counts and we don't
need fans because of convection.

If you take an infrared thermometer and take a reading off a baseboard heater
you will see 140-180F temps radiating off the casing and the metal fins inside
that are put there to increase surface area.

These flat panel aluminum foil based collectors work the same way.

When light/heat energy enters a room through the window some of it turns to
heat and some is reflected back out the window. That is why you can see
objects from the other side.

Seeing those objects is how we lose our heat. These collectors let us capture
and convert a much higher percentage of the energy coming into the window
already.

If you look at one of these collectors through the window from the outside it
appears invisible almost, they are hard to see, nothingness from which
precious free energy is harnessed and consumed and not allowed to escape.

~~~
dbdr
If you can make that material/pictures publicly available (e.g. in a
blogpost), I'm sure other people would be interested.

------
jsilence
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.

~~~
lucidstack
40%, since some days. :)

[http://www.livescience.com/49133-super-efficient-solar-
energ...](http://www.livescience.com/49133-super-efficient-solar-energy-
system.html)

~~~
imaginenore
44.7% actually

[http://upload.wikimedia.org/wikipedia/commons/a/a5/PVeff%28r...](http://upload.wikimedia.org/wikipedia/commons/a/a5/PVeff%28rev141208%29.jpg)

[http://en.wikipedia.org/wiki/Solar_cell_efficiency](http://en.wikipedia.org/wiki/Solar_cell_efficiency)

~~~
jsilence
Ah, nice graph! Thanks for posting!

I was unaware about the steady progress. Still far away from the 90+% thermal
efficiency that is possible with solar heating.

My hopes on photovoltaics are on the relatively new contender Perovskite.
Really nice to see the steep progress in efficiency there.

~~~
imaginenore
The theoretical limit for solar cells is much lower than 100%:

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

------
jcr
phys.org is often just regurgitation of press from original sources, typically
university press sites.

Here's a better source URL:

[http://www.jacobsschool.ucsd.edu/news/news_releases/release....](http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1589)

~~~
richmarr
Thanks. It's nice to be able to read the article without the "37 People With
The Worst Eyebrows You'll Ever See".

~~~
dang
That one is a classic. You have a connoisseur's eye. :)

------
Wissmania
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.

~~~
imaginenore
The previous one was 99.965% efficient.

[http://www.iflscience.com/technology/new-super-black-
materia...](http://www.iflscience.com/technology/new-super-black-material-
absorbs-99965-light)

So yeah, this article is bull.

------
rndn
In other words it's a material which has a very low reflectance across a large
range of frequencies (i.e. a black material)?

------
samatman
It's like, how much more black could this be? and the answer is none. None
more black.

[http://en.wikipedia.org/wiki/Black_body](http://en.wikipedia.org/wiki/Black_body)

------
andy_ppp
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.

Oh dear ->
[https://www.youtube.com/watch?v=xW3XeT7qavo](https://www.youtube.com/watch?v=xW3XeT7qavo)

~~~
ajuc
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.

Sorry for wall of text...

~~~
upofadown
From the article (which I suspect you didn't read):

>CSP power plants create the steam needed to turn the turbine by using
sunlight to heat molten salt. The molten salt can also be stored in thermal
storage tanks overnight where it can continue to generate steam and
electricity, 24 hours a day if desired, a significant advantage over
photovoltaic systems that stop producing energy with the sunset.

~~~
ajuc
I skimmed it, but I missed that part, thanks.

------
minthd
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.

[1][http://www.mit.edu/~soljacic/cermet_solar-
thermal_OE.pdf](http://www.mit.edu/~soljacic/cermet_solar-thermal_OE.pdf)

~~~
fche
... or, on the residential scale, a black rubber membrane sandwich known as a
solar pool heater.

------
diltonm
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.

~~~
rab_oof
Exactly. Should open source patent this.

