3 ms·

One sketch of such a system is to physically mate an effective high T solar absorber to an effective narrow spectrum photon emitter (as described in this work).

One sketch of such a system is to physically mate an effective high T solar absorber to an effective narrow spectrum photon emitter (as described in this work). Then that can be coupled with a typical solar cell with bandgap matched precisely to the emitter wavelength. So your solar cell is near ideally efficient for the photons it receives. As I understand the emissivity of these materials can exceed blackbody radiation in the near-field but not the far-field (or something like that? Search "Superplanckian emission"). The devices as I am familiar are often called thermophotovoltaic cells: https://en.wikipedia.org/wiki/Thermophotovoltaic https://en.wikipedia.org/wiki/Thermophotovoltaic See eg http://xlab.me.berkeley.edu/pdf/259.pdf http://xlab.me.berkeley.edu/pdf/259.pdf for a great overview, esp section 3.3. I saw this video recently that I found accessible from an undergrad physics background and got me interested: https://www.youtube.com/watch?v=XnVVyTD7CzM https://www.youtube.com/watch?v=XnVVyTD7CzM

amluto 7y ago
> Then that can be coupled with a typical solar cell with bandgap matched precisely to the emitter wavelength. So your solar cell is near ideally efficient for the photons it receives. One way or another, once you've converted sunlight to heat, you are limited by the Carnot efficiency. For the 80% efficiency they claim, if all of it comes from thermophotovoltaics, they need a hot side temperature at least 5x ambient, which is over 1000 C. I wish them luck getting anything resembling a solar panel up to 1000 C. (I'm not, in any respect, saying it's impossible -- I'm saying it's very hard. You'd need excellect spectrally or directionally specific absorption to avoid re-radiating all that heat out the top of your panel, and you'd need conventional transparent insulation to stop conduction.) On top of that, super-Plankian emission or no, if it's limited to the near field, then the PV cell is very, very close to the hot surface. That PV cell needs to be kept near room temperature to get that efficiency. This whole thing seems extraordinary complex for something that wants to be cost-effective.
- TTPrograms 7y ago
  The absorber/emitter assembly doesn't really resemble a solar cell. Demonstrated tungsten emitters have exceeded 1500K - it's not really that wild, it's what's in incandescent light bulbs. You concentrate sunlight typically.

amluto 7y ago

> Then that can be coupled with a typical solar cell with bandgap matched precisely to the emitter wavelength. So your solar cell is near ideally efficient for the photons it receives. One way or another, once you've converted sunlight to heat, you are limited by the Carnot efficiency. For the 80% efficiency they claim, if all of it comes from thermophotovoltaics, they need a hot side temperature at least 5x ambient, which is over 1000 C. I wish them luck getting anything resembling a solar panel up to 1000 C. (I'm not, in any respect, saying it's impossible -- I'm saying it's very hard. You'd need excellect spectrally or directionally specific absorption to avoid re-radiating all that heat out the top of your panel, and you'd need conventional transparent insulation to stop conduction.) On top of that, super-Plankian emission or no, if it's limited to the near field, then the PV cell is very, very close to the hot surface. That PV cell needs to be kept near room temperature to get that efficiency. This whole thing seems extraordinary complex for something that wants to be cost-effective.

TTPrograms 7y ago
The absorber/emitter assembly doesn't really resemble a solar cell. Demonstrated tungsten emitters have exceeded 1500K - it's not really that wild, it's what's in incandescent light bulbs. You concentrate sunlight typically.