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Comment by droro | Hacker News Reader

Artificially-lit indoor farming is neato and will be a great technology to bring into space, but makes almost no sense on earth. Basically, it requires expensive infrastructure and way too much electricity (https://gigaom.com/2015/12/29/indoor-farming-good-for-cannab...). Maybe robotically-farmed greenhouses won't have this problem.

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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.

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 :)

Plants are around 2% efficient.

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.

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.

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

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.

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

There was a halfway decent (if simplified) segment on Countryfile [0] about the use of PhytoLux LEDs in the UK.

They've been working with Bristol Uni to investigate the effect of various colours and wavelengths on plant growth (Something Gigaom, linked, is only just experimenting with); they claim energy efficiency [1] as just one advantage when using vertical farming methods.

0: http://www.bbc.co.uk/iplayer/episode/b06z9ph6/countryfile-no...

1: http://resources.phytolux.com/images/phytolux/newsletters/Pr...

But you can't grow multiple levels of crops using sunlight. it might make sense if land is at a premium. A few months back there was an article proposing large farms in downtown Tokyo because you could produce fresh food right where the people are.

Also, I'm wondering if they intend to produce crops more quickly by shortening the day to 23 hours or something like that.

I'm just going to file this one away for 20 years from now when electricity is 10-100x cheaper than today and indoor/underground farming is the most economical due to pest, density, and environmental concerns. Could you also say this technology will never make sense? That would be very helpful.

Currently ~50% of the cost of residential electricity is due to the grid, not generation - and it probably affects commercial electricity.

I would expect this to be economically viable in Iceland, with their short growing season and cheap geothermal power.

Also rich desert nations that normally depend on food imports, like Saudi Arabia. Solar PV + being able to grow food with minimal water waste is sure to make sense.

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