I remember seeing these concept towers where food was grown inside in what was essentially a 40 stories of hydroponic grow rooms co-located inside cities so transporting of food was easy.
I guess I'm insanely naive about growing food at scale and indoors (I've dabbled with produce on a small scale) but why hasn't this approach taken off?
The purchase price of farmland in Ohio is about $5000-6000 per acre.
You're talking about building a skyscraper as if crop production can generate enough revenue to justify that expense and somehow compete with all the other farmers who are just using the land as the found it a couple hundred years ago.
The cost to build a parking garage space is $20,000-$30,000 - and parking garages are just a slab of concrete. You'd still have to add in the costs of irrigation and artificially light the crops.
And then, how do you efficiently harvest vertical farms? Farmers in Ohio drive a giant vehicle over the generally flat and square field. How are you harvesting a vertical farm without huge labor costs in comparison?
There's actually nothing "green" about this vertical farm idea when you think about the extra power, concrete, and construction material requirement needed to realize it.
Hit up the Ohio turnpike around Toledo and notice that at least half of the fields aren't even planted (just an eyeball guess on my part, take that "at least half" with a grain of alt). Rain has been too heavy this year and a lot of wheat and corn either couldn't be planted or the crop looks absolutely pitiful.
(Some people try to quantify the Earth's input into the industrial process of farming in economic terms, an "environmental services" number, to point out that environmental damage may reduce the availability of these free services. Such as pollination - if there aren't enough bees farmers have to rent some.)
But, indoor farming is not well suited for calorie-rich foods (think grains, corn, potatoes, etc). Many of those crops are not suited for hydroponics. They need soil and lots of sunlight. Corn roots grow down to almost 7 feet in the soil. Attempting to grow these crops out of soil and sunlight is incredibly inefficient and expensive.
In order for indoor farms to feed the majority of the world, we believe there needs to be more than one breakthrough than just the indoor farm system itself, including a breakthrough in the production of energy (enough to replace all the solar energy provided by the nuclear reactor in the sky that we use in agriculture today), a breakthrough in the production or collection of water that irrigates the millions of acres of land by rain clouds, and the biological breakthrough of high calorie foods that are adapted to grow hydroponically.
We also believe that the same money spent developing indoor farm systems is better spent developing better adapted crops and researching more efficient and sustainable agriculture practices.
Plants can gather carbon (CO2) from the air. But the Nitrogen cycle requires micro-organisms to capture air and sequester it into the plants roots (or alternatively, nitrogen-based fertilizer).
But C and N are just two of the macro-nutrients needed to grow a plant. You also need Phosphorus, Potassium (NPK == typical fertilizer), Sulfur, Calcium, Magnesium (secondary macronutrients).
Then depending on the plant, you'll need Iron, Molybdenum, Boron, Copper, Manganese... a lot of different micro-nutrients.
You can pump these micronutrients into a hydroponic solution and grow plants in it. Or... you can buy 50+ Acres of land over there for just $10,000 with literally free energy, all the micro-nutrients automatically there from the sun to grow the plants.
The macro-nutrients are used in significant enough numbers you need to sow them into the ground every year. You can get the macro-nutrients from pretty cheap material: worm castings, pee tea, and chicken / horse manure, blood meal, and compost.
There's a reason why people farm in the farmlands. Land is cheap, Chickens are noisy and no one is allowed to keep a coop of chickens in the middle of NYC (you'd keep your neighbors up and people would complain about the smell and noise). Sowing the land with literally animal poop is extremely smelly and no one wants to live next to that.
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If you create an indoor farm, you're competing against farms with literally free solar energy that's roughly 400% more effective than solar panels, as well as macro-nutrient sources that are cheaper than whatever hydroponic chemical solution you can ever hope to batch up. Direct sun is extremely bright.
IIRC, the sun's energy is measured to be around 2000 PAR/m^2 on a typical day. Your typical indoor light is only 200 PAR/m^2, while the more expensive ones may reach 500PAR / m^2.
The common refrain among growers is that the sun on a cloudy day (!!) is still more effective than any LED lamp.
Indoor farms run their weaker ~500 PAR/m^2 lights for 14-hours a day, starting before sunrise and long after the sun has set to maximize their use. That's the only way plants get enough energy from these lower-intensity light sources.
There can be something said about saving on transportation costs + having fresher food inside of cities. But its grossly inefficient from an energy standpoint.
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Whenever I crunch the numbers, it seems like growing any plant in an agricultural zone, then shipping that plant into the city, is the most efficient strategy. Rooftop gardens would be the 2nd most efficient strategy.
Indoor farming conserves land, and maybe rich / expensive cities it makes sense as a source of fresh food for rich people. But indoor farming does NOT scale.