Invisible Solar Nano Cells Promise Clean Energy

An anonymous reader writes "ZDNet is reporting that Harvard scientists have developed a silicon nanowire 200 hundred times thinner than a human hair that crank out up to 200 picowatts. Charles Leiber from Harvard University, who devised the technology with colleagues, is quoted: "An individual nanoelectronic device will indeed consume very little power, but to do something interesting will require many interconnected devices and thus the power requirement — even for nanosystems — can be a challenge". Conventional sources, he added, are "bulky, non-renewable and expensive" by comparison."

Comments

Localizers

[56]

Anyone ever read Vernor Vinge's 'A Deepness in the Sky'? These things might be a great power source for the localizers he mentions.

I wonder

[Dr. Eggman]

Any biologists out there who wishes to inform me of how this solar cell compares in efficiency and equivalent energy production for photosynthesis. I understand that they're are two very different forms of energy (storage medium may be a better comparison) but I would be interested as I have thought that perhaps natural evolution had already long ago derived the most efficient ways of recovering energy to drive its organisms. I wonder if the real future of small scale generators/batteries lies with organic synthesis of energy through genetically modified organism with some medium transforming the resulting chemical energy into electrical energy (not unlike a battery but with it's own complications necessary for dealing in the organic compounds) rather than straight up developing life-facsimiles.

Then again maybe I'm just rambling on after approaching the 40th consecutive waking hour... It'd be nice to know.

Re:I wonder

[StikyPad]

I have thought that perhaps natural evolution had already long ago derived the most efficient ways of recovering energy to drive its organisms.

Not usually true. Plants and animals have plenty of other concerns, such as the efficient storage thereof, combating predators, reproducing, etc., any one of which could take precedence over obtaining energy. Is fat the most economical storage medium? It's pretty good, but other factors come into play: it's not toxic to the body, it's pliable, which permits relatively free movement, it's a good insulator, and it provides protection to bones and internal organs (any of which may or may not be an evolutionary side effect). Natural selection is about favoring the most competitive in a particular environment, and obtaining the most energy, while ignoring other factors, is not always the best strategy. A design that extracts more energy from sunlight than pine needles might be more prone to wind damage, pests, molds, fungus, etc. Even if an organism is more efficient at extracting energy than its competitors, that's no guarantee that its the *most* efficient possible design, just that it was good enough.

Additionally, what we're primarily concerned with is electromagnetic energy. There are always losses in any conversion, and if we convert the sunlight into chemical energy, then back into electromagnetic energy, we're guaranteeing more losses than if we can harness/store the sunlight directly. That's why it's often more efficient to use net metering rather than off-grid battery storage alone. Many people opt to include batteries in their solar systems, but that's typically for the purpose of grid independence and/or backup power. Of course there are losses inherent in converting DC to AC, so that must be considered as well. Overall, the more directly you can transfer the power from the source to the load, the more efficient that transition will be.

I'm not a biologist, but I did stay at a Holiday Inn last night.

Re:I wonder

[commando_jim]

I had a graduate professor (in bioengineering/nanotechnology) who claimed that the light absorptive complexes in plant cells (chloroplasts) were on the order of 95% efficient(I've forgotten the exact number) in certain wavelengths. (not green since that all gets reflected for you to see the nice green color of the leaf)

Unfortunately comparing the efficiency of plants to this wire thing isn't that simple. Chloroplasts have lots of internal complexes(Thylakoid disks) full of organized protein structures that convert light to electricity as one hugely efficient electron transfer system. To compare a plant leaf to this wire we'd need to know how the wire performs in densities similar to the thylakoid disk density in a plant leaf. We'd also need to know things like whether these wires get more or less efficient with packing, what the peak achievable packing density is, and what kind of alignment restrictions we have regarding the incoming photons.

Simply put: the 0.2nW quoted here is probably not a useful number when considering systems aggregating the production of many of these things.

Disclaimer: although I had relevant class work my degrees focus in biomechanics not biochemistry or nanotechnology.

Re:Definition of PicoWatt

[marcosdumay]

1 pico watt is still 1.6e8 eV/s. See, a huge number. A hypotetical nano-assembly powered by that could ionize near 6.5e7 hydrogen atoms per second, and, while 250nm is a bit big for such application, you could still put 4e6 such machines in a centimeter, leading to 26e13 atoms/(s cm).

Of course, everything depends on how long is the cell. You got 10cm from nowhere, it would even be hard to make it that long. If you are right about the length, it is useless. But if its length is 4 times bigger than the width, you'd get 1e6 such things on a centimeter, getting 26e19 atoms/(s cm^2), what is 26 mols every 10.000 seconds on a square centimeter, or 26 mols every second on a square meter.

As I said, everything depends on the length. But if I had to speculate its length, I'd say that is quite an impressive cell. Not useless.