Post N0. 9, 
Vertical Farms:
Growing food under lights is a bad idea.

In a growing trend, people are building vertical urban "farms" and growing food under artificial lights. Kimbal Musk,  Elon Musk's younger brother, runs Square Roots, an urban farming venture in Brooklyn, that’s into that. Hey. I think urban farming is a great idea, which is why my back yard grows veggies not grass. Well. Lotsa grass, too. I should get a goat. But growing food under artificial lights? Not so much.

Photosynthesis is terribly inefficient: weeds might do 0.2 percent; corn, which is more efficient than most vegetables and grains, utilizes 1 to 2 percent of the light that falls on it, while the most efficient plant, sugar cane, might do 8 percent. [i]  Grow lights, even LEDs, are also less than wonderfully efficient. Blue LEDs might reach 60 percent “wall plug”  efficiency—you might convert 60 percent of the electricity they burn to light, the rest is lost as heat—reds 50 percent, green only 25 percent.[ii]

Potatoes under lights. NASA Marshall Space Flight Center, public domain, Wikipedia Commons

Add in the inefficiencies of all “modern” power generation—3rd Gen coal averages just 33 percent, combined-cycle gas maybe 55 percent, and photovoltaics as currently installed, maybe 18 percent—and line losses, and the energy efficiency of growing produce under lights is abysmal. Obviously people are making a go of it, but the cost of both energy and equipment must be staggering. And if the electricity burned comes from coal- or gas-fired power plants, we’re making climate change worse growing boutique salad.

We’re going to need all of the power we can cleanly generate to electrify transportation and everything else. Growing food under artificial lights will waste power—inefficiency is waste—we will need elsewhere. Sure, use efficient lights of the right spectrum to start tropical plants in late winter in temperate climates: I start 20 peppers and tomatoes under one 3’ high-intensity T-5 fluorescent grow lamp, which also makes an efficient over-the-kitchen-sink task light when I need things bright. It burns 39 watts to produce 2450 lumens; to give you an idea how bright that is, 100 watt incandescents do 1600-1750 lumens, while a 150 might do 2600.

Vegging—vegetating—young plants, letting them gain size for a month or three before putting them outside, doesn’t take a lot of light. Blooming and bearing does. So the kids get a couple of months of  artificial light, early spring, and go outside as soon as it’s warm enough. That’s efficient enough—I get a lot out of 39 watts. But I happen to know, for example, that it takes a kilowatt of HPS, high pressure sodium, to bloom and mature a pound of cannabis indoors. I do an in-depth analysis of the cost of growing cannabis under lights in PTBOCC—around page 200, though that changes a little with every edit. To condense it down, it costs 1,073 kWh and $151 for electricity for lights alone, at 14 cents/kwh, and about 1.5 tons of CO2, to grow a pound. Outdoors, that same plant might give you up to 7 pounds in Portland, 10 a little south of Eugene, or 24 pounds in Happy Camp (why do you think they call it that!?), and you’re not growing over a coal fire.

Growing food under lights isn’t going to be any more efficient.

So for vertical urban gardens/farms, set the sun-facing exterior bearing walls of a high-rise back a few feet from the edges of its floors, and glaze the outer curtain that frames, creating a greenhouse the height of the building. Stack shelves on which to grow produce against the outer bearing wall, and build that wall with windows that open, so the office workers can smell the tomatoes. Make that outer promenade wider, in places, on every floor, or every few floors, and add tables and chairs under fruit trees so the workers have sunny, green, fresh-smelling places to take breaks and buy fresh veggies for lunch or to take home.

Take this one step further, and add shops, cafes, banking, laundries, groceries, a clinic, a gym, day care … to the lower floors of that and nearby buildings. If the people who work in those buildings could get most of what they need every day in the one place they have to be anyway, or within walking distance, without having to drive/bus all over town, their lives would be more convenient and time efficient, and they’d burn a lot less energy on transportation. Some high-rise owners do some of that, now. Most could do more, might coordinate with each other to offer a variety of services in a walkable zone. But let’s start with those vertical farms, grow food in sunlight right where we need it, and avoid the carbon and cost of growing it under lights.

Just because we can doesn’t mean we should. Let’s use the sun, instead of artificial lights, to grow food, please. That’s why it’s there.
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[1] Nicola, “The Photosynthetic Habits of Highly Effective Plants,” Edible Geography, AUG. 18, 2014, https://www.ediblegeography.com/the-photosynthetic-habits-of-highly-effective-plants/
 
[1] LED Grow Light Buyer's Guide, https://chilledgrowlights.com/education/led_buyers_guide#:~:text=It's%20not%20typical%20to%20rate,green%20530nm%20with%2025%25%20WPE

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