8 ms·

I'm not infuriated, but having teachers and other adults conflate IR with heat certainly added to my confusion about the physical world when I was a child.

p1esk 7y ago
Sorry for a potentially stupid question: why do they need to convert heat into visible light? Why can't we convert heat directly into electricity at the same time as we convert visible light into electricity?
- jfengel 7y ago
  "Light" here is a misnomer. What they're doing is taking the wide array of infrared wavelengths and channeling them into a single wavelength. It's easier to build a solar cell that's tuned to that wavelength. I don't know why they're calling that "light". It's not clear to me if it means visible light. The paper seems to imply that it peaks in the near-infrared. They appear to be using "light" in the general sense of "photons"... but it's all photons. They're talking about very high temperatures, the kind that emit significant visible light as well.
- skosch 7y ago
  You're confused – heat isn't being converted into anything. The article conflates the words "heat" and "infrared radiation", which are not at all the same thing. As a rule, everything around you glows – in other words, it emits photons. Some infrared ones, some visible ones, some ultraviolet (or even higher-frequency) ones. How much of each depends on the temperature of the material. Most things (e.g. you) are too cold to be visibly glowing, but they still emit plenty of infrared radiation. Now, standard solar cells convert visible photons into electricity. Any incoming infrared photons, however, aren't strong enough to kick any electrons loose, so they go to waste. Here, the researchers used carbon nanotubes to absorb the wasted infrared photons. This heats up the nanotubes, which then emit visible photons, which then increase electricity generation. There is no way to convert heat to electricity directly, unfortunately. However, you can get small amounts of electricity out of temperature differences: https://en.wikipedia.org/wiki/Thermoelectric_effect https://en.wikipedia.org/wiki/Thermoelectric_effect
  - reaperducer 7y ago
    This heats up the nanotubes, which then emit visible photons, which then increase electricity generation Once a solar cell is built with this technology, do you think there will be enough light emitted by the nanotubes to make the solar panels appear to glow, themselves? Because that would be pretty interesting.
    - dlivingston 7y ago
      If the solar panels appear glowing, it's because visible light is being dispersed away from the solar panel itself. The consequence of that would be wasted photons that could otherwise be converted into electricity. So, from a pragmatic perspective, I would say that no, they wouldn't glow - proper engineering would ensure these particles are collected.
    - skosch 7y ago
      The idea is to direct all of the nanotube-emitted light onto the PV cells, so hopefully you won't see anything. Citing the Rice article: > Because electrons in nanotubes can only travel in one direction, the aligned films are metallic in that direction while insulating in the perpendicular direction, an effect Naik called hyperbolic dispersion. Thermal photons can strike the film from any direction, but can only leave via one.
  - p1esk 7y ago
    I see, thanks! Why are visible light photons "stronger" than infrared photons?
    - fengazer 7y ago
      Visible light photons have more energy each. The shorter the wavelength, the higher the energy of the photon. Light with a short enough wavelength (UV-B, for example) has enough energy to damage the DNA in our skin and increase our risk of skin cancer.
      - p1esk 7y ago

p1esk 7y ago

Sorry for a potentially stupid question: why do they need to convert heat into visible light? Why can't we convert heat directly into electricity at the same time as we convert visible light into electricity?

jfengel 7y ago
"Light" here is a misnomer. What they're doing is taking the wide array of infrared wavelengths and channeling them into a single wavelength. It's easier to build a solar cell that's tuned to that wavelength. I don't know why they're calling that "light". It's not clear to me if it means visible light. The paper seems to imply that it peaks in the near-infrared. They appear to be using "light" in the general sense of "photons"... but it's all photons. They're talking about very high temperatures, the kind that emit significant visible light as well.
skosch 7y ago
You're confused – heat isn't being converted into anything. The article conflates the words "heat" and "infrared radiation", which are not at all the same thing. As a rule, everything around you glows – in other words, it emits photons. Some infrared ones, some visible ones, some ultraviolet (or even higher-frequency) ones. How much of each depends on the temperature of the material. Most things (e.g. you) are too cold to be visibly glowing, but they still emit plenty of infrared radiation. Now, standard solar cells convert visible photons into electricity. Any incoming infrared photons, however, aren't strong enough to kick any electrons loose, so they go to waste. Here, the researchers used carbon nanotubes to absorb the wasted infrared photons. This heats up the nanotubes, which then emit visible photons, which then increase electricity generation. There is no way to convert heat to electricity directly, unfortunately. However, you can get small amounts of electricity out of temperature differences: https://en.wikipedia.org/wiki/Thermoelectric_effect https://en.wikipedia.org/wiki/Thermoelectric_effect
- reaperducer 7y ago
  This heats up the nanotubes, which then emit visible photons, which then increase electricity generation Once a solar cell is built with this technology, do you think there will be enough light emitted by the nanotubes to make the solar panels appear to glow, themselves? Because that would be pretty interesting.
  - dlivingston 7y ago
    If the solar panels appear glowing, it's because visible light is being dispersed away from the solar panel itself. The consequence of that would be wasted photons that could otherwise be converted into electricity. So, from a pragmatic perspective, I would say that no, they wouldn't glow - proper engineering would ensure these particles are collected.
  - skosch 7y ago
    The idea is to direct all of the nanotube-emitted light onto the PV cells, so hopefully you won't see anything. Citing the Rice article: > Because electrons in nanotubes can only travel in one direction, the aligned films are metallic in that direction while insulating in the perpendicular direction, an effect Naik called hyperbolic dispersion. Thermal photons can strike the film from any direction, but can only leave via one.
- p1esk 7y ago
  I see, thanks! Why are visible light photons "stronger" than infrared photons?
  - fengazer 7y ago
    Visible light photons have more energy each. The shorter the wavelength, the higher the energy of the photon. Light with a short enough wavelength (UV-B, for example) has enough energy to damage the DNA in our skin and increase our risk of skin cancer.
    - p1esk 7y ago