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Are Solar Carpets The Future Of Solar Tech?

Alternative energy sources always seem to be in the news lately.

No need to wonder why with all the turmoil in the blood-and-oil-soaked Middle East, all the downsides to fossil fuels, fears of oil running out and on and on.

We do seem to be tackling our energy problems with a sense of urgency of late. I wish the US and other countries had more of  this sense of urgency a few decades ago in the wake of that wake-up-call oil crisis of the 70′s.

As usual, I think this is one of those areas of research that really needs billions more dollars poured on it. This is too important to wait a few more decades to finally see which technologies will be the immediate successors oil. I don’t think the government should pick a horse like hydrogen and run with it though. Let the scientists and the markets figure out what’s best.

As far as sources of energy goes, my personal third-favorite is probably solar energy. Numbers one and two are of course antimatter and fusion.

Antimatter may take quite a while to iron out but fusion and solar seem poised for something big soon. I recently blogged about recent advances in fusion energy but I’ve been waiting for news in solar that really piqued my interest. Color me piqued.

This latest advance is being called silicon whiskers or rods or even micro carpets.


These refer to a new type of solar cell researchers have recently announced involving the creation of  a new flexible nanowire-based technology that is at least as efficient as currently available silicon solar tech but uses only one percent of the silicon.

This was announced in the journal Nature Materials by scientists at the California Institute of Technology (Caltech)

Harry Atwater, Howard Hughes Professor, professor of applied physics and materials science, and director of Caltech’s Resnick Institute said
“These solar cells have, for the first time, surpassed the conventional light-trapping limit for absorbing materials,”

The “light-trapping limit” is the amount of light a specific material can absorb. According to Atwater, these arays can absorb 96% at a specific wavelength and 85% of all the collectible light. :

“We’ve surpassed previous optical microstructures developed to trap light,” he said.

Absorption is only part of the equation. Black paint absorbs a lot of light too; but you can’t convert that to electricity because no charge carriers are created. This new material absorbs a lot of light but also is efficient at making electricity as well. That’s a winning perfecta in Solar Cell Tech.

So how does this work?

Imagine a tiny forest of minuscule wires or rods sticking up. These silicon wires intercept light causing it to bounce around inside until it hits the side at the proper angle to absorb it and produce flowing electrons. The biggest problem was that when the light source was directly overhead, only the ends of the wires could get the light. Imagine a solar cell that works at dusk but not at noon…..not good.

To resolve this, they tweaked the transparent polymer that surrounds the wires. They did this by doping it with nano-particles of aluminum oxide so the light that didn’t hit the wires would bounce around within the polymer until it hit one of them.

It’s important to note that this is basically a proof of concept, a lab demonstration.
Their next step is to increase the size and make a fully functioning solar cell. They claim that they are close to doing this and demonstrating the big cells work just as well as the smaller ones.

Keith Barnham of the Quantum Photovoltaics Group at Imperial College London says that it’s not a forgone conclusion that they will work when scaled up. Material defects can wreak havoc with cell performance.

He ends hopefully saying that: “By demonstrating that they can get an efficient current, the group are halfway there though, and that’s great.”

I’m not sure about these efficiencies though.

On the one hand Atwater says:
“We have shown the optical absorption efficiency and charge carrier collection efficiency of a silicon wire array cell is comparable to a conventional silicon cell”

Other claims include the following:

“The silicon-wire arrays absorb up to 96 percent of incident sunlight at a single wavelength and 85 percent of total collectible sunlight”

My confusion aside, this looks like a promising advance for a few reasons.
If they already broken through the “light-trapping limit”, perhaps they could go even a bit further.

The ever-important issue of scalability looks promising as well because the tools needed to create the wires and these solar cells are commercially available.

Silicon is a great semi-conducting material for solar cells but its expense and brittleness has limited its use.  Achieving similar efficiencies while using 100th the silicon not only makes it cheaper and flexible but also makes it more dependable and increases its life-expectancy.

You’ll be able to roll these up like plastic sheets. People are also talking about putting this stuff in clothes as well. Imagine doing that with conventional hard-silicon solar panels.

Who knows if this will work out. There are many potential obstacles. The more solar irons we have in the fire though, the greater the odds we’ll eventually see the sun powering everything from homes to businesses and even cities…at least until antimatter power sources are developed.

5 comments to Are Solar Carpets The Future Of Solar Tech?

  • I’d think we are where scientists and markets have led when it comes to energy. No one has yet come up with a replacement for coal, gas and oil. Isn’t it government subsidy that is driving much of what is happening in the alternative energy field?

    I wonder if the energy storage problem isn’t a bigger problem when considering solar powered cities. Doesn’t seem like batteries would ever do the job. Are there any promising storage ideas?

  • Thanks for the comments DS,

    I guess I don’t mind the government energy subsidies too much especially considering that no energy sector of our economy evolved without them.

    As long as the govt’s input is scientifically and not politically motivated. Their goal should be to offer broad support for research and may the best tech win.

    Storing solar energy could be achieved using various methods including thermal storage. This uses an inexpensive material that has a high specific heat capacity like water, stone, molten salts etc. Another possibility is using excess daytime energy to move water to a higher elevation. At night, the water can flow back down through a hydroelectric power generator.

    MIT was working on a solar storage technology that looked promising. The idea is to use solar energy during the day to split water into hydrogen and oxygen. At night, they recombine the gases inside a fuel cell to produce carbon-free electricity.

    Here’s an article on this.
    http://web.mit.edu/newsoffice/2008/oxygen-0731.html

  • I think non-politically motivated government input might be an oxymoron.

    I read the article you linked to, and while I hope the research does pan out, it seems a little over optimistic to hope that this or any other type of solar energy will be used on a large scale within 8 1/2 years.

    Another thing I wonder about is the idea of not having a central power source. Are people really going to want to be their own power supplier with all the problems that might entail? It seems more realistic to plan that there will be some sort of centralized source for most people.

    It’s certainly interesting research though, and I appreciate the info.

  • I agree, 8 1/2 years is not enough time.

    I kind of like the idea of supplying my own power or a least a sizable chunk of it. My buddy is installing solar right now that will produce 1/3 of his electricity in the summer. This would never see large-scale implementation unless maintenance was manageable and reliability was very high. I’m sure companies would sprout all over the place for maintenance and repairs. Like the guy that comes occasionally to help with your pool or furnace.

    I think we’ll see a good mix of different types of less centralized energy production. Some will be produced at the house level and some will be produced at the town or city level.

  • I think you hit the nail on the head about maintenance and reliability. My brother, like me, is not the type to want to install or maintain solar panels, so when he considered getting them he found that there is a company here in California that leases the panels. This seemed ideal except his projections showed him losing money, so he didn’t do it. We both still thought there was potential for this here in California in terms of the summer power issues.

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