[thescriptkiddie]

If the electricity for the grow lights is produced locally via solar power, it is actually more efficient than using sunlight directly (provided LED grow lights are used). This is because the grow lights provide only the narrow bands of wavelengths that plants absorb most efficiently. Only about 45% of visible sunlight is usable by plants, compared to around 95% for photovoltaics, which more than makes up for conversion losses. You also get the ability to stack the plants vertically, and the lack of windows makes for lower heat loss in the winter.

[vectorjohn]

I don't know if that actually works in practice. Aren't photovoltaics (commercially feasible ones) like 20% efficient? Sure, its 20% of a bigger spectrum, and plants aren't perfectly efficient either, but I don't know if the math quite works as well as you make it sound.

The other benefits are awesome though. And our fusion future will make the photovoltaics issue moot anyway :)

[lhopki01]

Plants are around 2% efficient.

[vectorjohn]

Ok, so they're going to be 2% efficient at using that 20% that was gathered by PV cells. So it still seems like using 2% of all the light would be more efficient than using 2% of a fifth of the light.

I suspect that by 2% efficient, that means they use 2% of the energy of all light. Since they don't use green at all, going through the PV and then generating artificial light of the frequencies they need does seem to improve things. But probably not by so much as to make up for the 20% efficiency of PV.

[lhopki01]

Every plant has a slightly different need but generally speaking you can grow plants very efficiently if you use the entire red spectrum and 10-20% of the blue spectrum. That allows for significant energy savings.

[Joof]

Nobody seems to be pointing out that it is unlikely to be cost efficient as well (sun is free), which is what matters.

[vectorjohn]

Sun is not free. Sun requires land. If (and I don't think we're there yet) you can get to where the sun gathered by PV can be used to grow more plants than direct sunlight, and you're in a space constrained place like Japan, it starts to make sense.

I mean, you can stack farms vertically if artificial light is economical. You can't stack sun-lit farms vertically.

[lololomg]

Solar panels are only about 20% efficient though, you're still losing out.