4 ms·

Say a plant needs 1/10th of actual full sun during the day, could you theoretically remove the electricity step entirely but "just" (putting "just" in quotes be

by Nition 6y ago

Say a plant needs 1/10th of actual full sun during the day, could you theoretically remove the electricity step entirely but "just" (putting "just" in quotes because I'm sure it wouldn't be easy) having some sort of fancy mirror setup on a 10 storey building to send 1/10th of the sunlight hitting the roof to each floor?

macspoofing 6y ago
Mirrors take up space too.
- deleted 6y ago
  [deleted]
- Nition 6y ago
  Might be significantly higher efficiency overall though vs. putting solar panels on the same roof?
  - macspoofing 6y ago
    I guess the devil is in the details but I can't see how mirrors will be positioned to support vertical farming. It's be interesting to see some viable ideas (if those exist).
    - woeh 6y ago
      Thinking aloud here; perhaps we could somehow use optical fibers to bend the light from rooftop to vertical farm?
      - macspoofing 6y ago
        It's beyond my pay grade. I have no idea if 'optical fibers' are an option here. I suspect 'not' only because it hasn't been done already and feels like it if worked for vertical farming, it would also work to supplement office lighting so there is some monetary incentive to get such a system implemented in some way. The other problem is that you still have the same issue. That is, for every square cm of sunlight you collect the best you could do is direct that light to a square cm of a plant. That is, you can't just increase surface area of collected light so to provide sunlight for vertically stacked plants, you need the equivalent horizontal surface area to support those. But I have no idea.
LeifCarrotson 6y ago
Close, it's 1/10th of the spectrum not 1/10th of the intensity. The 'fancy mirrors' required would simply be a prism. You'd separate out the red and blue light and aim it at the plants, and send the green and infrared light to solar cells, to be used for running red and blue LEDs. (Or you could use flourescence if you had something that glowed red or blue when exposed to green or IR light). Check out this spectral plot for chlorophyll-a and -b: http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/ligabs.html http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/ligabs.ht... and compare it to this plot of the solar irradiance at Earth's surface: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/solirrad.html http://hyperphysics.phy-astr.gsu.edu/hbase/vision/solirrad.h... There are peaks in the clorophyl absorption spectrum at 400-500 and 600-700 nm (blue to UV and red), but the sunlight provides energy in an atmosphere-attenuated blackbody curve everywhere from 300-1000nm. In theory, by providing illumination with just 10% the energy of the sunlight's full spectrum in a narrow band from 420-430nm where photosynthesis is most efficient, you could have plants receive the same amount of energy. Unfortunately, solar cells have the exact same problem: Just as the proteins in chlorophyll only use certain spectral energies, so too the semiconductors only make efficient use of certain energies. Multi-bandgap solar cells can help: https://en.wikipedia.org/wiki/Multi-junction_solar_cell#/media/File:StructureMJetspectre.png https://en.wikipedia.org/wiki/Multi-junction_solar_cell#/med... but in both chemical and electrical solar energy extraction, you're working with a particular photon energy and there's going to be waste.
- Nition 6y ago
  Do the plants actually need the full strength of that red and blue light for optimal growth though? I thought the comment above mine was implying that they don't. So my proposition was that if we started with, say, midday sun, maybe we could divide that up (in brightness, not just by spectrum) to cover a larger area (multiple floors in this case).
- frankus 6y ago
  Are there materials that fluoresce at a shorter wavelength than what they absorb? I was under the impression that it was a one-way thing (absorb short wavelength and emit longer wavelength).
cthreepo 6y ago
maybe if the plants are fixed on a very tall pole, and spaced some meters from each other, because of the sunrays inclination, all the plants on the pole can get sunlight. this will not save space in a big farmland setup, because then the poles need to be spaced from each other in proportion to their height, or they will cover the sun from the neighbour pole, bit this can make small isolated empty spaces useful for growing a lot of plants.

by Nition 6y ago

macspoofing 6y ago

Mirrors take up space too.

deleted 6y ago
[deleted]
Nition 6y ago
Might be significantly higher efficiency overall though vs. putting solar panels on the same roof?
- macspoofing 6y ago
  I guess the devil is in the details but I can't see how mirrors will be positioned to support vertical farming. It's be interesting to see some viable ideas (if those exist).
  - woeh 6y ago
    Thinking aloud here; perhaps we could somehow use optical fibers to bend the light from rooftop to vertical farm?
    - macspoofing 6y ago
      It's beyond my pay grade. I have no idea if 'optical fibers' are an option here. I suspect 'not' only because it hasn't been done already and feels like it if worked for vertical farming, it would also work to supplement office lighting so there is some monetary incentive to get such a system implemented in some way. The other problem is that you still have the same issue. That is, for every square cm of sunlight you collect the best you could do is direct that light to a square cm of a plant. That is, you can't just increase surface area of collected light so to provide sunlight for vertically stacked plants, you need the equivalent horizontal surface area to support those. But I have no idea.

LeifCarrotson 6y ago

Close, it's 1/10th of the spectrum not 1/10th of the intensity. The 'fancy mirrors' required would simply be a prism. You'd separate out the red and blue light and aim it at the plants, and send the green and infrared light to solar cells, to be used for running red and blue LEDs. (Or you could use flourescence if you had something that glowed red or blue when exposed to green or IR light). Check out this spectral plot for chlorophyll-a and -b: http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/ligabs.html http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/ligabs.ht... and compare it to this plot of the solar irradiance at Earth's surface: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/solirrad.html http://hyperphysics.phy-astr.gsu.edu/hbase/vision/solirrad.h... There are peaks in the clorophyl absorption spectrum at 400-500 and 600-700 nm (blue to UV and red), but the sunlight provides energy in an atmosphere-attenuated blackbody curve everywhere from 300-1000nm. In theory, by providing illumination with just 10% the energy of the sunlight's full spectrum in a narrow band from 420-430nm where photosynthesis is most efficient, you could have plants receive the same amount of energy. Unfortunately, solar cells have the exact same problem: Just as the proteins in chlorophyll only use certain spectral energies, so too the semiconductors only make efficient use of certain energies. Multi-bandgap solar cells can help: https://en.wikipedia.org/wiki/Multi-junction_solar_cell#/media/File:StructureMJetspectre.png https://en.wikipedia.org/wiki/Multi-junction_solar_cell#/med... but in both chemical and electrical solar energy extraction, you're working with a particular photon energy and there's going to be waste.

Nition 6y ago
Do the plants actually need the full strength of that red and blue light for optimal growth though? I thought the comment above mine was implying that they don't. So my proposition was that if we started with, say, midday sun, maybe we could divide that up (in brightness, not just by spectrum) to cover a larger area (multiple floors in this case).
frankus 6y ago
Are there materials that fluoresce at a shorter wavelength than what they absorb? I was under the impression that it was a one-way thing (absorb short wavelength and emit longer wavelength).

cthreepo 6y ago

maybe if the plants are fixed on a very tall pole, and spaced some meters from each other, because of the sunrays inclination, all the plants on the pole can get sunlight. this will not save space in a big farmland setup, because then the poles need to be spaced from each other in proportion to their height, or they will cover the sun from the neighbour pole, bit this can make small isolated empty spaces useful for growing a lot of plants.