[zdragnar]

The original comment suggested putting the farm below apartment buildings ("below grade" means underground).

It's extremely costly to provide sufficient light to grown plants, as photosynthesis isn't terribly efficient. Natural sunlight is significantly stronger than what people tend to expect.

Not only that, but you would need to move massive amounts of air to keep the plants happy, plus the humidity from being underground and all the water they need. Beyond that, you need to go quite a bit underground to feed a sufficient number of people, which isn't always feasible depending on the type of soil and water table, etc

Final note, most plants do better not getting 24 hours of light. They can only grow just so fast and need to photosynthesize just so much.

That's a lot of work (meaning higher prices for people who need to eat) for very little gain.

[jaegerpicker]

Below ground has trade offs, it's easier to use gravity flow designs but you lose all natural sunlight. Most of the time rain catchment systems on roof top vertical farms or free standing green houses are easier to design. There are already a bunch of vertical farms in commercial operation. The Netherlands in particular is leading the science here but in the US a number of farms exist. Vertical farming uses around 90% less water and solar/wind/hydro power for LED's is extremely doable. You are wholly incorrect about the amount of work required and amount of resources. It does take smart design to work however.

[zdragnar]

Where I live, people already struggle with eliminating excess moisture from their basements. Putting growing plants there requires a significant upgrade to air ventilation and dehumidification, as it is the perfect breeding ground for mold.

As for LED grow lights, you typically use about 30-40 watts / square foot. That's a not insignificant added cost compared to growing above ground.

The added challenges to growing underground simply make it irrational.

[jaegerpicker]

Yeah, I'd agree with the underground part. Above ground vertical greenhouse's are absolutely viable but I'm not sure underground would make any sense. LED grow lights I'm using on Tower or aeroponics (Plants grown in towers with a gravy mist based irrigation and feeding) are much less than 30-40 watts / square foot, around 10-20 depending on the time of year but that's above ground in a greenhouse situation with Sun light help.

[crummy]

What's the efficiency loss for light>solar panel>LED>plants vs light>plants?

[imtringued]

jaegerpicker is really uncooperative, even with numbers that should be easy to debunk he is struggling and trying to change the topic to stop you from thinking critically.

https://sustainabledish.com/vertical-farms-thermodynamic-non...

"It turns out it would take about 4.5 acres of solar cells for every one acre of plant growth space" well that implies that the 100x efficiency factor has actually been met for lettuce but jaegerpicker didn't seem too keen on telling you. The obvious problem though is that solar panels are only 20% efficient hence roughly 5 acres of solar per 1 acre of vertical farming grow space.

[jaegerpicker]

Wrong question to ask, PPFD's is the correct measure. It's not a direct energy comparison. Photosynthesis is a chemical reaction of Chlorophyll reacting to certain but not all light wavelength's (Red and Blue being the major ones) plus the distance from the light source. The amount of watts the the sun generates is NOT what grows plants. LED's can produce the same light wavelength's but much closer and with no obstructions. The question isn't about LED's power generation, it's how much power does it take for an LED to cover an area. Obviously a LED can't compare to pure Solar efficiency on a watt by watt basis but it doesn't need to.

[verve_rat]

What's the CO2 output by the concrete used to build the building that houses the farm?

[jaegerpicker]

That's actually a good question, I have no experience with underground systems. Most are free standing greenhouses (about 10x more efficient (water and yield) that traditional farming per square foot). Electric is only a major cost for the pumping of water, LED light coverage is very cheap and we don't need to compete with the power of the sun.