5 ms·

With an solar cell with an infinite number of layers the maximum efficiency for normal sunlight is 68.7% to go from light->electricity[1]. Real cells don't have

With an solar cell with an infinite number of layers the maximum efficiency for normal sunlight is 68.7% to go from light->electricity[1]. Real cells don't have infinite numbers of layers, so conversion efficiency is around 25% for single-layer monocrystalline silicon cells. Those have a maximum possible efficiency of 32%. Current LEDs are around 40-50% efficient. So 45% efficient LED * 25% efficient solar = about 12% total efficiency. [1] A. De Vos & H. Pauwels (1981). "On the Thermodynamic Limit of Photovoltaic Energy Conversion". Appl. Phys. 25 (2): 119–125. Bibcode:1981ApPhy..25..119D. doi:10.1007/BF00901283. S2CID 119693148.

londons_explore 4y ago
However, you also get the uplift in efficiency from the fact plants prefer certain wavelengths of light, and have nearly no use for others (eg. green). And LED's are good at producing certain wavelengths of light. Not sure how to calculate that...
- neatze 4y ago
  This seems to be not the case, most recent LED's grow lights are full spectrum.
  - londons_explore 4y ago
    I think that's just because full spectrum LED's are cheaper because they're made in massive quantities for lighting homes and offices. If you were designing a set of LED's purely for plant growth, and making them in sufficient quantities that you can design your own dopant concentrations etc, then you probably wouldn't end up with full spectrum LED's.
    - neatze 4y ago
      This are LED's designed[0] for horticulture, doubt it is basic LED for indoor lighting. [0]https://www.samsung.com/led/lighting/applications/horticulture-lighting/ https://www.samsung.com/led/lighting/applications/horticultu...
hommelix 4y ago
Thanks for the numbers on LED lighting. As a comparison, photosynthesis efficiency is about 5% [1]. One could at first think that 12% is better than 5%, but the plant still need to grow even with LED lighting. The first step in the photosynthesis is the light absorption. The loss there is due to the limited light absorption (range 400 - 700nm). So maybe this step could be improved by using LED lighting dialled in to the range of the plant. The rest of the loss chain would remain mostly the same. Doing the math with the wikipedia numbers Plant growing in open field =========================== 0.53*0.7*0.76*0.32*0.6 = 0.05413632 ==> 5.4% Plant growing with LED lighting =============================== Considering 100 % LED light absorption by the plant (which is an exaggerated hypothesis) and the 12% LED lighting efficiency 0.12*1.0*0.7*0.76*0.32*0.6 = 0.01225728 ==> 1.2% efficiency [1] https://en.wikipedia.org/wiki/Photosynthetic_efficiency https://en.wikipedia.org/wiki/Photosynthetic_efficiency
- dredmorbius 4y ago
  Efficiency of photosynthesis applies after delivering light to the plant. So take your 12% delivered Solar PV -> LED light to the plant ... and then apply 5% photosynthetic efficiency to that. The efficiency of naturally-delivered sunlight to plants is of course 100%. (I believe that's what you're actually calculating here, though your "As a comparison..." statement confuses the message.)
deleted 4y ago
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londons_explore 4y ago

However, you also get the uplift in efficiency from the fact plants prefer certain wavelengths of light, and have nearly no use for others (eg. green). And LED's are good at producing certain wavelengths of light. Not sure how to calculate that...

neatze 4y ago
This seems to be not the case, most recent LED's grow lights are full spectrum.
- londons_explore 4y ago
  I think that's just because full spectrum LED's are cheaper because they're made in massive quantities for lighting homes and offices. If you were designing a set of LED's purely for plant growth, and making them in sufficient quantities that you can design your own dopant concentrations etc, then you probably wouldn't end up with full spectrum LED's.
  - neatze 4y ago
    This are LED's designed[0] for horticulture, doubt it is basic LED for indoor lighting. [0]https://www.samsung.com/led/lighting/applications/horticulture-lighting/ https://www.samsung.com/led/lighting/applications/horticultu...

hommelix 4y ago

Thanks for the numbers on LED lighting. As a comparison, photosynthesis efficiency is about 5% [1]. One could at first think that 12% is better than 5%, but the plant still need to grow even with LED lighting. The first step in the photosynthesis is the light absorption. The loss there is due to the limited light absorption (range 400 - 700nm). So maybe this step could be improved by using LED lighting dialled in to the range of the plant. The rest of the loss chain would remain mostly the same. Doing the math with the wikipedia numbers Plant growing in open field =========================== 0.53*0.7*0.76*0.32*0.6 = 0.05413632 ==> 5.4% Plant growing with LED lighting =============================== Considering 100 % LED light absorption by the plant (which is an exaggerated hypothesis) and the 12% LED lighting efficiency 0.12*1.0*0.7*0.76*0.32*0.6 = 0.01225728 ==> 1.2% efficiency [1] https://en.wikipedia.org/wiki/Photosynthetic_efficiency https://en.wikipedia.org/wiki/Photosynthetic_efficiency

dredmorbius 4y ago
Efficiency of photosynthesis applies after delivering light to the plant. So take your 12% delivered Solar PV -> LED light to the plant ... and then apply 5% photosynthetic efficiency to that. The efficiency of naturally-delivered sunlight to plants is of course 100%. (I believe that's what you're actually calculating here, though your "As a comparison..." statement confuses the message.)

deleted 4y ago

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