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So I asked following question some physicists but they couldn't really help me though:

Right now I read that 1m² of solar cells generates roughly 100Watts of energy. There are really efficient Grow LEDs that use only two spikes in the lightspectrum to make plants grow.

I have seen some graphs like the Quantum Efficiency of Sola Cells that suggest that solar cells can absorb energy in the range of 400nm up to 1200nm (in varying degrees of efficiency).

By my logic (given a high enough overall efficiency of the solar cell), a solar cell can make light that is most of the time reflected by plants in the range of e.g. 500nm-600nm / or 800nm+, into electrical energy, and that electrical energy can be used, in turn, to produce light in the range of 400nm and 700nm that the plants can use again for photosynthesis.

Additionally, i could imagine that the sun sometimes hits the range of diminishing returns in terms of brightness (lux, lumen?) when it's really really bright and hot and shining directly on the plants. Instead it would maybe be more efficient to capture that energy (photon) and convert them only to the wavelength needed in enough brightness that plants can grow (again, given a high enough solar cell efficiency, right now it's 20%, i heard 40% is a theoretical limit?)

You could phrase the question a little bit different: I have 1m² of land and two possibilities:

  1. build a greenhouse and plant 1m² of crops
  2. build a brickhouse as high as I want with as many layers of 1m² levels. But they are only allowed to be lighted with LEDs and no direct sunlight. And the LEDs are only allowed to be powered by 1m² of solar cell on the roof.

What is the needed solar cell efficiency (generated watts/m²) for the solar cell to reach the break even point of total biomass production / timeunit between case 1. and 2.

If there are other environmental conditions that would benefit only one of these cases, assume in favor of case 2 and mention the variable.

I was in a heated discussion about this yesterday and I would love for someone who knows more then me to help me wrap my head around this.

So, to give some extra Information for you guys or to rephrase it again to increase the chance to get an answer: current solar cells operate anywhere from 100W-200W/m² with an upper limit somewhere around 400W to 450W for the way we do it right now. (100W is 10% efficiency, 20% are high quality PVCells right now)

Thanks a lot!

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