LEDs Are Set to Revolutionize Greenhouse Farming (2014)

This sort of mediated growing environment seems quite interesting as an approach to managing agriculture as environmental changes from global warming progress. In some areas, perhaps conventional greenhouses would suffice alone. But in others, underground agriculture might provide an additional buffer against climate changes. This would allow normalization of growing conditions in regions where the climate has drifted and/or become unpredictable in ways that would severely damage agricultural output.

Apparently at high illuminations you want to be using green too - the issue is that red and blue are absorbed so well that they don't make it past the surface of the leaf and thus the plant quickly maxes out on them, while green light penetrates further and thus reach more tissue.

So when you see pictures of leaf greens being grown under purple light - that's because leaf greens actually need less light than other vegetables, you probably wouldn't want to do that with other crops.

IANAbotanist

High-efficiency solar cells are about 20% efficient across the daylight spectrum.

For some reason, no one gives hard stats on how much energy LEDs waste as heat, but the claims are that incandescents waste about 90% of energy input as heat, and LEDs are about 80% more efficient than that. So let's say LEDs convert about 80% of input power into light at their operating wavelengths as a guess.

So if we put these together, we'll get about 16% of the input daylight back out as light at the wavelengths we want.

According to wikipedia [1], about 47% of light that falls on chlorophyll is wasted because it falls outside the ideal range for plants (400-700nm). Another 3% or so is lost due to wavelength conversion. The rest we can't really do anything about because it has to do with biological limitations. Put another way, our total system has to be about 50% efficient to be better than just putting the plants in the sun. As you can see, we're not even close. In fact, it's not even possible since the theoretical maximum efficiency of solar panels is only about 34% [2].

[1] https://en.wikipedia.org/wiki/Photosynthetic_efficiency [2] https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...

Not an expert so I can't vouch for its veracity, but I'll inline it:

"This can theoretically be more efficient than growing plants under sunlight. Chlorophyll mostly absorbs light in the 400nm to 700nm band which is about half of all the photons that hit lights. Even in that band ~24% (https://en.wikipedia.org/wiki/Photosynthetic_efficiency) of the energy in them in lost due to the higher energy photons (closer to the 400nm side) being converted to lower energy photons.

"So right there plants are only 25% efficient at collecting energy from photons. This is why you see indoor plants grown under red LEDs. Modern commercially available solar panels are about 21% efficient so that is actually getting close to plant can do (I'm not going to include inefficiencies in power conversion right now). Solar panels in the high 40% efficiency range exist, but they are crazy expensive and only used on things like satellites.

"So using current (very advanced) technology we could actually get about double the plant output per area land by using the most advanced solar panels we have to collect light energy to power LEDs."

Building underground is crazy expensive (albeit very cool sci-fi), why not (cheap) above ground.

I think arid regions are kinda cheap for land so why not just a glasshouse? Put solar panels beside it, should they work.

Even if the land is very expensive (And localize food production makes sense), floor one is plants, flood 2+ is for businesses.

Building multifloors underground is the same structurally as above ground.

Exceptions might be places like London where regulations stop you building up.