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> This cell achieved an efficiency of 41.1% operating at a power density of 2.39 W cm–2 and an emitter temperature of 2,400 C. At those temperatures, this is n

by _hypx_ 3y ago

> This cell achieved an efficiency of 41.1% operating at a power density of 2.39 W cm–2 and an emitter temperature of 2,400 C. At those temperatures, this is not very impressive.

RobLach 3y ago
For those of us unfamiliar with the properties of these materials, what would be considered impressive? Are there examples that are better?
- mnw21cam 3y ago
  If you have a heat source with a temperature of 2500C, then the theoretical maximum efficiency of conversion is around 89% assuming you have a heat sink available that can stay below 30C. (1.0 - (30+273)/(2500+273) = 0.89). All heat engines will be worse than this because of practicalities, but a real steam turbine system can be around 47% efficient and a combined cycle can be 60% efficient, using a cooler "hot" end than 2500C. https://en.wikipedia.org/wiki/Thermal_efficiency https://en.wikipedia.org/wiki/Thermal_efficiency
  - magicalhippo 3y ago
    For photovoltaic cells there are other factors which limits this further. For a single p-n junction the limit is around 33% for normal sunlight[1], though it's too early in the morning for me to calculate it at the proposed ~2700K temperature. By stacking junctions you can get higher but then other things kick in[2]. [1]: https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi... [2]: https://en.wikipedia.org/wiki/Solar-cell_efficiency#Factors_affecting_energy_conversion_efficiency https://en.wikipedia.org/wiki/Solar-cell_efficiency#Factors_...
  - _hypx_ 3y ago
    Which is the problem of the idea. Any kind of thermal engine, such as a stirling engine, would beat this idea in efficiency with those kinds of temperatures.
throwbadubadu 3y ago
> not very impressive vs "a higher performance than conventional solar cells, and produce 100 times more power than similarly sized devices” You have some numbers against that to understand the buzz? Because it sounds pretty impressive? Is it comparing the wrong technology, or are the numbers off for prior performance (in this use case) or how?
- adrian_b 3y ago
  The performance is very impressive in comparison with devices of the same type that have been produced in the past. The performance is not impressive in comparison with the existing alternative for converting heat into electricity, i.e. with electric generators powered by closed-cycle gas turbines or by steam turbines, which can reach a higher efficiency already at much lower temperatures and without using so expensive materials. Therefore it is not clear whether this direction of research is worth pursuing. Moreover, triple-junction (very expensive) solar cells with an efficiency of around 45% for the direct conversion of solar light, without passing through heat, have already been demonstrated some time ago. Due to their high cost, they must also be used with solar concentrators, but the concentrators can be much cheaper than those needed to heat something over 2000 Celsius degrees (which requires very precise focusing).
konstantinua00 3y ago
it's the temperature of light emitter, not of the panel it's pretty much saying "efficient (for a photovoltaic) electricity from powerful infrared" Sun is 6000 degrees, so most of its emergy is in different frequency Instead, this panel is planned to be used in thermal batteries, I think the article says. I guess main competition is steam turbine or smth?
- bestouff 3y ago
  FWIW when we say "a light at 6000 K" it means "a light with the same color as a black body heated to 6000 Kelvin", so it has nothing to do with temperature, it's only a (veery rough) way of characterizing color.
  - jddj 3y ago
    And we also say that it's a "cooler" colour temperature than a black body only heated to 3500K. Go figure.
  - gruturo 3y ago
    Except that in the case of the Sun, it has all to do with temperature: its surface temperature indeed matches the emitted light temperature. The sun indeed qualifies as a black body (I know, it's pretty bright... but black body just means it doesn't reflect light coming from somewhere else)

by _hypx_ 3y ago

> This cell achieved an efficiency of 41.1% operating at a power density of 2.39 W cm–2 and an emitter temperature of 2,400 C. At those temperatures, this is not very impressive.

RobLach 3y ago

For those of us unfamiliar with the properties of these materials, what would be considered impressive? Are there examples that are better?

mnw21cam 3y ago
If you have a heat source with a temperature of 2500C, then the theoretical maximum efficiency of conversion is around 89% assuming you have a heat sink available that can stay below 30C. (1.0 - (30+273)/(2500+273) = 0.89). All heat engines will be worse than this because of practicalities, but a real steam turbine system can be around 47% efficient and a combined cycle can be 60% efficient, using a cooler "hot" end than 2500C. https://en.wikipedia.org/wiki/Thermal_efficiency https://en.wikipedia.org/wiki/Thermal_efficiency
- magicalhippo 3y ago
  For photovoltaic cells there are other factors which limits this further. For a single p-n junction the limit is around 33% for normal sunlight[1], though it's too early in the morning for me to calculate it at the proposed ~2700K temperature. By stacking junctions you can get higher but then other things kick in[2]. [1]: https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi... [2]: https://en.wikipedia.org/wiki/Solar-cell_efficiency#Factors_affecting_energy_conversion_efficiency https://en.wikipedia.org/wiki/Solar-cell_efficiency#Factors_...
- _hypx_ 3y ago
  Which is the problem of the idea. Any kind of thermal engine, such as a stirling engine, would beat this idea in efficiency with those kinds of temperatures.

throwbadubadu 3y ago

> not very impressive vs "a higher performance than conventional solar cells, and produce 100 times more power than similarly sized devices” You have some numbers against that to understand the buzz? Because it sounds pretty impressive? Is it comparing the wrong technology, or are the numbers off for prior performance (in this use case) or how?

adrian_b 3y ago
The performance is very impressive in comparison with devices of the same type that have been produced in the past. The performance is not impressive in comparison with the existing alternative for converting heat into electricity, i.e. with electric generators powered by closed-cycle gas turbines or by steam turbines, which can reach a higher efficiency already at much lower temperatures and without using so expensive materials. Therefore it is not clear whether this direction of research is worth pursuing. Moreover, triple-junction (very expensive) solar cells with an efficiency of around 45% for the direct conversion of solar light, without passing through heat, have already been demonstrated some time ago. Due to their high cost, they must also be used with solar concentrators, but the concentrators can be much cheaper than those needed to heat something over 2000 Celsius degrees (which requires very precise focusing).

konstantinua00 3y ago

it's the temperature of light emitter, not of the panel it's pretty much saying "efficient (for a photovoltaic) electricity from powerful infrared" Sun is 6000 degrees, so most of its emergy is in different frequency Instead, this panel is planned to be used in thermal batteries, I think the article says. I guess main competition is steam turbine or smth?

bestouff 3y ago
FWIW when we say "a light at 6000 K" it means "a light with the same color as a black body heated to 6000 Kelvin", so it has nothing to do with temperature, it's only a (veery rough) way of characterizing color.
- jddj 3y ago
  And we also say that it's a "cooler" colour temperature than a black body only heated to 3500K. Go figure.
- gruturo 3y ago
  Except that in the case of the Sun, it has all to do with temperature: its surface temperature indeed matches the emitted light temperature. The sun indeed qualifies as a black body (I know, it's pretty bright... but black body just means it doesn't reflect light coming from somewhere else)