Nanopillar Solar May Cost 10x Less Than Silicon

Al writes "A team of researchers from the University of California, Berkeley, have developed a new kind of flexible solar cell that could be far cheaper to make than conventional silicon photovoltaics. The cells consist of an array of 500-nanometer-high cadmium sulfide pillars printed on top of an aluminum foil — the material surrounding the pillars absorbs light and releases electrons, while the pillars themselves transport the electrons to an electrical circuit. The closely packed pillars trap light between them, helping the surrounding material absorb more. This means the electrons also have a very short distance to travel through the pillars, so there are fewer chances of their getting trapped at defects and its possible to use low-quality, less expensive materials. '"You won't know the cost until you do this using a roll-to-roll process," says lead researchers Ali Javey. "But if you can do it, the cost could be 10 times less than what's used to make [crystalline] silicon panels."'"

Re:Based on recent history...

[Marcika]

Don't tell me. It'll be ready for mass production in 3 to 5 years. Somehow, I seem to remember stories like this from more than five years ago, and still, nothing happens and the solar cells are more or less the same as always.

Don't be a universal cynic, inform yourself instead. Look up Nanosolar [wikipedia.org] and First Solar [wikipedia.org] on Wikipedia, and you'll see that they have been already mass-producing panels at one-third of the price of crystalline silicon panels for a year or two.

"Nothing happens" is only true if you close your eyes to all the things that actually do happen.

Re:Based on recent history...

[Spoke]

Surprise, there are already [nanosolar.com] companies [firstsolar.com] that are producing thin-film solar panels for less than $1/watt.

The problem is that demand is so high for these inexpensive cells that at least for Nanosolar, you can't even buy them unless you are buying tons and tons of them. That leaves First Solar and those panels get significantly marked up because of the lack of competition at the low end of the market.

That said, wholesale prices of traditional silicon panels are around $3/watt and as an end user you can get them for slightly above that if you shop around.

But once the system is installed you're looking at a minimum of $6/watt currently. So while the panels are still the most expensive part of the system, pretty soon the other components (inverter, mounting hardware, wiring, labor) will exceed the cost of the panels.

We're getting very close to the point where solar systems make financial sense for just about everyone. It already makes sense for any high electricity users who pay a premium for electricity. We'll probably see solar system pricing continue to drop over the next couple years as manufacturing capacity continues to come online.

Re:Great news!

[JustinOpinion]

For those with access, here's the actual paper:
Fan, Zhiyong, Haleh Razavi, Jae-won Do, Aimee Moriwaki, Onur Ergen, Yu-Lun Chueh, Paul W. Leu, et al. "Three-dimensional nanopillar-array photovoltaics on low-cost and flexible substrates [nature.com]." Nature Materials advanced online publication (July 5, 2009). http://dx.doi.org/10.1038/nmat2493 [doi.org].

One of the cool things is that this new process results in a flexible photovoltaic. In the paper they show that efficiency is maintained even after repeated bending of the material. Even if the energy collection efficiency is lower than conventional silicon photovoltaics, there are tons of applications for flexible photovoltaics, like having tents coated in the material (both for things like camping, but could also be hugely useful for the military, for temporary tents for disaster relief, and so on...), clothing that generates power, and so on... (Maybe even fanciful things like kites that collect solar and wind power?)

It's not a commercial device yet (and oftentimes these kinds of lab devices just don't scale to mass production that well), but it's an encouraging step towards more robust solar cells, which would aid in the more widespread deployments of solar energy.

Re:Low cost until scarcity kicks in....

[TheSync]

How plentiful is cadmium relative to silicon?

Worldwide known reserves of Cadmium are about 490,000 metric tons, and production is about 20,000 metric tons/yr. Cadmium is generally recovered as a byproduct from zinc concentrates. Zinc-to-cadmium ratios in typical zinc ores range from 200:1 to 400:1. Estimated world identified resources of cadmium were about 6 million tons, based on identified zinc resources of 1.9 billion tons containing about 0.3% cadmium. The average annual New York dealer price of cadmium metal in 2007 was $7.61 per kilogram ($3.45 per pound).

The source of the silicon is silica in various natural forms, such as quartzite. Silicon is the second most abundant element (after oxygen) in the crust, making up 25.7% of the crust by mass. Word production of silicon is about 5.7 million metric tons/yr. The price for silicon ranges from $0.66 per pound for 75% ferrosilicon and $1.13 per pound for silicon metal.

Re:That title makes me cringe.

[SlashDotDotDot]

"10x Less"? Is that like "twice as cold"

Maddening, isn't it?

I like to nitpick as much as the next guy, but I didn't blink at that title. A survey of readers would find that everyone one of them knew what the author meant. Consider it as shorthand for "Nanopillar Solar May Cost Less Than Silicon By A Factor Of 10"

Re:Low cost until scarcity kicks in....

[mcgrew]

Cadmium is used for red and yellow paints for artists, both oil and acrylic based paints. They're really bright yellows and reds, so the bright orange and yellow jackets road crews wear probably have cadmium pigments.

I wonder what color these cells are? Will everyone's roof be red in the future?

Re:Great news!

[JustinOpinion]

I don't think the pillars are acting as antennas in the way you're thinking. It's simpler than that. The pillars are just providing a higher surface area of interface between the light-absorbing material and the conducting material, and creating a shorter path for the electron-hole-pairs (EHP) to reach their respective conducting materials. Basically one of the main limitations in photovoltaics of this type is the short lifetime of the EHP before it recombines... having the pillars penetrate into the absorbing layers means the EHP have a shorter path to travel. From the paper:

Conventional thin-film photovoltaics rely on the optical generation and separation of electron-hole pairs (EHPs) with an internal electric field, as shown in Fig. 1a. Among different factors, the absorption efficiency of the material and the minority carrier lifetime often determine the energy conversion efficiency15. In this regard, simulation studies have previously shown the advantages of three-dimensional (3D) cell structures, such as those using coaxially doped vertical nanopillar arrays, in improving the photocarrier separation and collection by orthogonalizing the direction of light absorption and EHPs separation (Fig. 1b)16.

Later in the paper they discuss the light-absorbing properties of these kinds of pillar arrays:

In addition, 3D nanopillar or nanowire arrays, similar to the ones used in this work, have been demonstrated in the past to exhibit unique optical absorption properties13,18. Similarly, we have observed reduced reflectivity from CdS nanopillar arrays especially when the inter-pillar distance is small (see Supplementary Fig. S6). This observation suggests that 3D nanopillar-based cell modules can potentially improve the light absorption while enhancing the carrier collection.

References 13,18 are:
L. Tsakalakos, J. Balch, J. Fronheiser, B. A. Korevaar, O. Sulima and J. Rand "Silicon nanowire solar cells [aip.org]". Appl. Phys. Lett. 91, 233117 (2007). doi 10.1063/1.2821113 [doi.org]
Hu, L. and Chen, G. "Analysis of optical absorption in silicon nanowire arrays for photovoltaic applications [acs.org]". Nano Lett. 7, 3249-3252 (2007). doi 10.1021/nl071018b [doi.org]

Quoting from that second paper:

We found that, in comparison to thin films, nanowire array based solar cells have an intrinsic antireflection effect that increases absorption in short wavelength range.

Essentially the nanowire arrays are acting as anti-reflection coatings and allowing the light to instead be absorbed.

Re:Photovoltaics are for rich dummies

[Ironica]

For cooling look at evaporative cooling or simply pumping the heat into a local river or ocean... Most of California's cities are sited near the Pacific... Yet air conditioning is the single largest consumer of electricity, by far.

Well, yes, our cities are near the Pacific... but Downtown Los Angeles is some 15-20 miles from the ocean, and the LA River, while it is recovering its riparian habitat these days, is hardly up to taking on any significant amount of waste heat. You're talking about *maybe* being able to cool a few beach hotels this way... and that would probably have a detrimental effect on near-shore habitats.

Re:I am f tired reading about cheap solar panals

[mcrbids]

for last 5 years same shit gets posted over and over again - Cheap solar panals
5 years later - in some cases panels went up in price

Whine whine whine. It's been going on for much longer than 5 years. When I was in 5th grade, I did a report on PV electricity, and I read numerous reports that PV panels could be much cheaper soon.

Truth is, all those funky predictions were right. Solar power HAS been dropping very steadily and very predictably all along [frozennorth.org] in its own version of Moore's law - PV prices drop about 6% per year per watt, cutting in half every 10.5 years. It's not dropping like a stone, but it's very predictable and very steady.

What's been going on the last 5 years? Simple: supply and demand. For many reasons, people have become wary of using fossil fuels and are willing to invest more into solar, causing a sudden, worldwide deficiency in production capacity. Low-cost production companies like Nano-Solar [nanosolar.com] are ramping up production literally as fast as they are physically able.

For example, Nano-Solar has, for all intents and purposes, unlimited funding, and has already sold out several years worth of production, even that which is not actually happening yet. They are buying huge rafts of warehouse space in the Bay Area, in what used to be automotive manufacturing areas.

So the laws of supply and demand are working their magic, even though the response isn't instant. Your children will bask in a society powered by cheap solar electricity that you are funding right now, just as you benefit from the electrical power infrastructure built by your parents.

Re:That title makes me cringe.

[dontmakemethink]

Even better is how the cells "create electrons". All we need now are cells to create protons and neutrons, and solar powered replicators will be on the market in no time!

(TFA reads "creates free electrons", also a misnomer, should read "frees electrons")

Re:That title makes me cringe.

[mbenzi]

Arrrrgh NO! "10x Less" is the important phrase because it renders the sentence meaningless.

If something costs $1, then "10x Less" is $-9.

I am pretty sure they are not going to pay people to take these devices.