Talk-Polywell.org

http://www.gizmag.com/highly-absorbing- ... lls/14232/

The info is rather sparce, but do I read that correctly?
85% absorbtion and 90% conversion? That would equal ~76% efficiency?
That would be what? Almost twice as good as the best and most expensive cells at the moment? Where is the catch (IMHO the catch is that this is too good to be true and therefore probably is not true, or only partially true)?
Anyway a solar cell like that would make even me reconsider the feasibility of the whole solar thing.

You seem to be reading it correctly. The geometry and the intentional scattering by embedded particles is favorable for increased absorption. The 'catch' is possibly in manufacturabilty or durabilty. The connections to all those silicon nanowires will need to be durable if they want to emphasize the flexibility part, and the polymer needs to be UV-resistant long-term.

This could make a nice power source for the flight deck cooling fan when I park my Polywell SSTO space hopper in the sun.

I wonder if a similar arrangment of depleted uranium nanorods and embedded DU nanospheres might lead to more mass-efficient gamma-ray shields. Maybe stacking several layers of the same.

hmmm....

It all hinges on what is meant by this odd phrasing;

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

So presumably "total collectible sunlight" doesn't mean all wavelengths?

This is beyond anything reasonable as per a regular solar cell, you're right in that. Is it a device that could collect a very high efficiency at a single wavelength, OK, that seems plausible. A vey high efficiency across a whole spectrum. No, I doubt it, more like a little wide-band range around some given frequency.

If it were otherwise, e.g. if it could absorb solar IR, then it could be used as a thermal shield in many applications (by piping off the energy as electrical energy and dissipating it elsewhere).

Sounds interesting, but more specifics required on the phrase "85 percent of total collectible sunlight".

Sounds interesting, but more specifics required on the phrase "85 percent of total collectible sunlight".

Indeed. I was wondering the same thing. I mean in the context, I was tempted to interpret it as "all wavelengths". E.g. they compare it to "black paint". But then what do I know. If it really was 76% of all wavelength, then it would be revolutionary. In that case I would have to wonder though why we have not heard more about it though.

DeltaV wrote: I wonder if a similar arrangment of depleted uranium nanorods and embedded DU nanospheres might lead to more mass-efficient gamma-ray shields. Maybe stacking several layers of the same.

Hmm, if it could absorb Gamma and turn it into electricity it could also do Bremsstrahlung from the polywell since it is suppose to be hard X-ray...

I can send you guys a copy of the paper, if you'd like to see it.

Folks, lets stay real. It says it converts 90ish % of photons into electrons, it does NOT say that it converts 90% of the energy IN the photons into energy in the electrons.

Most solar cells do about the same job with the proper anti-reflective coatings. But they only convert a set amount of the energy per electron, proportional to the band-gap energy. An infrared photon of sufficient energy will deposit the same useful energy as an ultraviolate photon. One electron each at the same voltage. THAT is what makes single junction colar cells as inefficient as they are. It is also how multi-junction cells can be more efficient. This process in no better at it than standard cells, but they appear to be saying they can do the job with 2% of the silicon as standard cells. THAT is interesting and a step beyond the Australian sliver cell.

Ya know... this may lead to a much cheaper way of producing multi-junction cells. Right now, the max junctions I've seen is 3. I wonder if graded fiber growth might allow an "omni-junction cell" that can indeed approach 100% energy harvest. THAT would be even neater!

clonan wrote:

DeltaV wrote: I wonder if a similar arrangment of depleted uranium nanorods and embedded DU nanospheres might lead to more mass-efficient gamma-ray shields. Maybe stacking several layers of the same.

Hmm, if it could absorb Gamma and turn it into electricity it could also do Bremsstrahlung from the polywell since it is suppose to be hard X-ray...

I wasn't thinking of getting electricity from gamma/X-rays, but if you could get DU to do the trick, that would be peachy. If DU doesn't have the right properties, maybe some other dense material would work.

There was a recent multi-layer solar PV design in the news that "channels" photons which hit a dye-coated transparent plate, so that they (mostly) exit at the edges of the plate (i.e., it turns them ~90 deg*). The now-concentrated photons are then collected by thin strips of solar PV along the plate edges. They had 2 or 3 layers tuned for different bands.

To turn gamma/X-rays like that is probably not doable (X-ray telescopes use grazing-incidence mirrors), but maybe something like DU nanostructures could do the trick. If you could get them to mostly exit along the edges of this hypothetical device, then the amount of lead needed to absorb them would be reduced. The nanostructures needed for those wavelengths** are probably non-manufacturable, though.

* Edit- "turns them" is probably naive. Maybe they are absorbed and re-emitted, then reflected within the plate until the edge is reached:MIT_Dye-based_Solar

** Edit - Delete "for those wavelengths". A uranium atom has a diameter of about 350 picometers or about 35,000 gamma wavelengths for lambda=1e-14 m.

Without bothering to look it up, I seem to recall typical solar PV cells are around 12-ish % efficient, exceptional ones maybe 22%. So if we are dealing with apples and apples here the new ones would be a factor of 3 or more over existing types. That would result in a shift in economic viability that would cause a nearly instantaneous shift in the viability of solar.

Just look to the energy markets on Monday. The analysts will have had all weekend to digest the news, and if it is really that good, oil will take a major nose-dive, because a factor of three improvement in solar efficiency would almost certainly make it suddenly viable in a number of areas where it had been uneconomical or marginal before.

Which I doubt.

Laboratory PV efficiency maxes at around 41%, http://www.physorg.com/news137862843.html , so it's more like a factor of 2.

Even 99.9% efficiency only gets you about 1KW/m^2.

Even 99.9% efficiency only gets you about 1KW/m^2.

Which would not be THAT bad. A m^2 is nothing. A typical (single family) residential roof has hundreds of m^2.
That means a lot of KWh. Of course that calculation only applies once you have anything that is even remotely close to a 99% efficient solar cell (which does not exist).

Tom and Delta;

Typical polyXtal PV ~10% efficient.
Typical MonoXtal PV~20%.
Some MultiJunction ~40%.

I suspect this stuff is about 5-10% at present. I'd be happy with 20% and a lower price.

You also need the ability to store the power for use when the sun's not shining. battery tech is still not where it needs to be to make intermittent sources useful.

Tesla built a doodad that got power out of charged particles--atmospheric ions, solar and cosmic rays. I don't think you have nearly the power density available as with pure solar though.

Skipjack wrote:

Even 99.9% efficiency only gets you about 1KW/m^2.

Which would not be THAT bad. A m^2 is nothing. A typical (single family) residential roof has hundreds of m^2. ...

Well, no - in terms of area at least. A large (by UK terms) 5 bedroom house (in the country) has an area of about 100 sq. m. Given the fact that they have pitched roofs the effective area for solar exposure is actually much smaller as a rule (shadow, directionality etc.) assume root 2 as a best case which gives about 70 sq m.

Such a house consumes about 110kWh/day (inclusive of heating, power etc. if built in the last 6-10 years: about double that if built 30 years ago - I have one of each of those). On average either house wouldn't have much of a problem over the year at ~1kW/ sq. m/hr of sunshine (which is what I assume you mean) apart from storage of power from summer to winter.

If you consider one of my flats (apartments for our US friends) in London they consume about 60kWh/day but the effective roof area is only 16 sq. m./flat: I would thus require an average of just under 8 hours/day of sun to get breakeven. We still have the storage problem by the way - summer consumption is around 2kWh/day (fridges, computers and other rubbish) with lots(??) of sun; winter consumption is around 120kWh/day with er.. very little sun.