5 ms·

Weather would then affect the production, making schedules unpredictable. Plus, I am no expert but I guess you can't make plants actually use much more than 10

by rini17 7y ago

Weather would then affect the production, making schedules unpredictable. Plus, I am no expert but I guess you can't make plants actually use much more than 100W/m2 for photosynthesis, the rest of sunlight consists of unsuitable wavelengths. It ends up as waste heat that you'd have to cool away. Perhaps if you could efficiently convert green and infrared parts of sunlight to red/blue, that could help.

kragen 7y ago
You mean because sometimes it's cloudy? Couldn't you solve that problem by turning on LEDs just when it's cloudy? Plants are pretty inefficient, it's true, but I don't think they're very efficient even with optimal wavelengths. But, yes, solar cells and LEDs can indeed convert green and infrared sunlight to red and blue, with about 3% efficiency under normal circumstances.
- infogulch 7y ago
  If your plan is "light pipes, but fall back to LEDs" that means you have to build two complete systems. You get double the installation costs, incur the combined complexity of both systems (plus overhead), and box yourself into the limitations of both systems.
  - kragen 7y ago
    That might be true, but I'm not sure it is. It seems to me that you escape the limitations of both systems. Also, I think lightpipe daylighting generally costs orders of magnitude less than sunlight-comparable LED illumination, although I don't have firm numbers on lightpipe costs; so I don't think the installation costs double, just increase slightly. If we're talking about a greenhouse, where a leaky roof is a minor annoyance comparable to a leaky faucet, rather than a life-destroying disaster, lightpipe costs should go down quite a bit compared to their use in office and residential daylighting. The big question for me is, if you're going to build a hothouse, why would you build it with an opaque roof? That just seems perverse, like writing an HTTP server in bash or assembly language or something: http://canonical.org/~kragen/sw/dev3/server.s http://canonical.org/~kragen/sw/dev3/server.s
    - rini17 7y ago
      Efficient light pipes require solar concentration and thus tracking. That will drive costs up. Current residential/office light pipes are using only small fraction of sunlight, so they aren't relevant to this problem at all. Also you haven't said anything about cooling, which the translucent roof inevitably requires in summer.
      - kragen 7y ago
        These are good points. Lightpipes can use non-imaging optics in many cases and thus avoid the need for tracking, but maybe not in this case, and I hadn't thought about that. Cooling, though, is an issue whether your light comes from LEDs or the sun—either way it comes with a lot of extra heat. With the LEDs I'm familiar with, this is a worse problem than with sunlight, but in another thread https://news.ycombinator.com/item?id=20908476 https://news.ycombinator.com/item?id=20908476 I see a report that there are now illumination LEDs that reach an astounding 40–50% efficiency level. If that's true, it would make the LED cooling problem a little smaller than the sunlight cooling problem, instead of much bigger; and of course spectral matching helps.
- tomp 7y ago
  > Couldn't you solve that problem by turning on LEDs just when it's cloudy? Alternatively, every time when it’s not sunny... meaning all night every night. Of course, that would require experimenting if it’s actually more efficient, but AFAIK that’s what a MIT experiment found regarding growing basil (though they were optimising for flavour, not energy efficiency). https://www.technologyreview.com/s/613262/machine-learning-is-making-pesto-even-more-delicious/ https://www.technologyreview.com/s/613262/machine-learning-i...

by rini17 7y ago

kragen 7y ago

You mean because sometimes it's cloudy? Couldn't you solve that problem by turning on LEDs just when it's cloudy? Plants are pretty inefficient, it's true, but I don't think they're very efficient even with optimal wavelengths. But, yes, solar cells and LEDs can indeed convert green and infrared sunlight to red and blue, with about 3% efficiency under normal circumstances.

infogulch 7y ago
If your plan is "light pipes, but fall back to LEDs" that means you have to build two complete systems. You get double the installation costs, incur the combined complexity of both systems (plus overhead), and box yourself into the limitations of both systems.
- kragen 7y ago
  That might be true, but I'm not sure it is. It seems to me that you escape the limitations of both systems. Also, I think lightpipe daylighting generally costs orders of magnitude less than sunlight-comparable LED illumination, although I don't have firm numbers on lightpipe costs; so I don't think the installation costs double, just increase slightly. If we're talking about a greenhouse, where a leaky roof is a minor annoyance comparable to a leaky faucet, rather than a life-destroying disaster, lightpipe costs should go down quite a bit compared to their use in office and residential daylighting. The big question for me is, if you're going to build a hothouse, why would you build it with an opaque roof? That just seems perverse, like writing an HTTP server in bash or assembly language or something: http://canonical.org/~kragen/sw/dev3/server.s http://canonical.org/~kragen/sw/dev3/server.s
  - rini17 7y ago
    Efficient light pipes require solar concentration and thus tracking. That will drive costs up. Current residential/office light pipes are using only small fraction of sunlight, so they aren't relevant to this problem at all. Also you haven't said anything about cooling, which the translucent roof inevitably requires in summer.
    - kragen 7y ago
      These are good points. Lightpipes can use non-imaging optics in many cases and thus avoid the need for tracking, but maybe not in this case, and I hadn't thought about that. Cooling, though, is an issue whether your light comes from LEDs or the sun—either way it comes with a lot of extra heat. With the LEDs I'm familiar with, this is a worse problem than with sunlight, but in another thread https://news.ycombinator.com/item?id=20908476 https://news.ycombinator.com/item?id=20908476 I see a report that there are now illumination LEDs that reach an astounding 40–50% efficiency level. If that's true, it would make the LED cooling problem a little smaller than the sunlight cooling problem, instead of much bigger; and of course spectral matching helps.
tomp 7y ago
> Couldn't you solve that problem by turning on LEDs just when it's cloudy? Alternatively, every time when it’s not sunny... meaning all night every night. Of course, that would require experimenting if it’s actually more efficient, but AFAIK that’s what a MIT experiment found regarding growing basil (though they were optimising for flavour, not energy efficiency). https://www.technologyreview.com/s/613262/machine-learning-is-making-pesto-even-more-delicious/ https://www.technologyreview.com/s/613262/machine-learning-i...