Does the New Solar Cell Violate the Second Law of Thermodynamics?

[Larrymb]

http://tinyurl.com/6fptha

The new solar cell in the link appears to violate the Second Law of Thermodynamics. It extracts energy and cools in a uniform temperature environment according to how I understand the article. Can someone explain why it doesn't? (I have no idea.)

 

[Topher925]

I am not so sure it does violate the second law. It should be noted that these are not actual solar cells but micro antennas which operate on different principles than typical photovoltaics. How they operate, I don't know but I do believe that the same rules do not apply.

 

[uart]

I think this post (from the linked site) sums up the situation nicely.

By rtrski on 8/12/2008 9:29:32 AM , Rating: 2
Look, all they did is come up with an antenna that's resonant in the mid-IR, and produce it on a thin film plastic. That's kind of neat, and a nice first step. But otherwise totally meaningless to all the BS speculation presented in the article and the linked pages.

"Could absorb IR and re-emit at lower wavelengths..." Nothing remotely demonstrated about this. An antenna is simply a coupling mechanism between free-space EM and some form of 'guided' EM mode, antennas are PASSIVE. They don't do frequency multiplication or division. They trap a wave out of the air into a circuit, but it's still at the same frequency, and has to then go somewhere. Otherwise, it comes right back out.

Spiral antennas, square slots, split-ring resonators, etc have all been around forever. Simple wavelength scaling let's you "design" them for almost any frequency range you want. But etching techniques and tolerances might mean you can't get the desired linewidth and spacing for a given application. The only 'new' thing here is that they managed to get a small enough pattern placed on a thin, flexible, and inexpensive material. But without something to connect to, reciprocity says if you receive, you radiate as well. All that mid-IR frequency EM "captured" by the antenna has got to go to a load circuit of some kind, or else it's reflecting right back out as soon as it hits a discontinuity (less some dissipative losses).

If they're just 'block stamping' the antenna pattern, it would be interesting to hear how well they aligned the pattern 'blocks' (certainly they're not stamping each individual spiral, but larger groups thereof). Without the ability to line up your circuitry, you can never realize a larger array. Without the right registration tolerances you're also never connecting any sort of circuitry to these antennas to keep whatever EM they received in the first place.

I'm really becoming more and more disillusioned by the "science" reporting here at Dailytech. Michael still has some pride of authorship, but certain other authors are either ignorant or lazy enough to just parrot whatever grandiose claims anyone else posts (nearly word-for-word, no less) without even performing a basic sniff test.

 

[russ_watters]

It extracts energy and cools in a uniform temperature environment according to how I understand the article. Can someone explain why it doesn't? (I have no idea.)

I would say the wording is just misleading. Here's what it actually says:

The skins could also act as cooling devices by drawing away waste heat, according to the researchers.
[and]
As heat typically is emitted as IR rays from many objects, the antennas could cool objects by collecting these rays and reemitting them at a harmless wavelength.

All that says to me is that it is a good emissivity black-body at those frequencies and only "draws away" heat because it doesn't warm up much when exposed to ir (since it is dissipating the energy). It wouldn't cool anything below ambient.

 

[Larrymb]

I greatly appreciate the responses and can see now that this article was way overhyped. Perhaps the most glaring example is the fifth paragraph:

"The nanoantennas absorb a targeted wavelength range of mid-infrared rays. The Earth continuously emits these rays thanks to the solar energy that it absorbs during the day. This would allow for continuous solar panel operation, in theory. Traditional panels can only absorb visible light and thus are idle at night."

This paragraph clearly implies a violation of the Second Law. It should never have passed review.

 

[russ_watters]

Heh - review? Really? These types of articles are only interesting to the general public because of the hype. Without the hype, there'd be no story to write.