> I've read a bunch on this, and haven't been able to find an authoritative source for what the efficiency conversion is -- how many acres of solar panels power how many acres of vegetables, and is it greater or less than 1:1? -- but it's certainly not as simplistic as "solar would need 3x more land because they are 30% efficient."
I own a townhome, so my only real ability to grow plants is through a grow-light connected to electricity.
As such, I've spent some time calculating the PAR values of a decent grow-light, as well as the amount of PAR that natural sunlight gives. Plants need a ludicrous amount of PAR (basically blue + red lights, green not needed cause green just bounces off of plants).
Sunlight is mostly broad spectrum: broader than plants need and therefore a source of inefficiency (green light is wasted) that LEDs can somewhat replace.
Grow-lights have a benefit that they can be placed very close to the plant (maybe just 1-foot away) to "focus" the energy a bit better. Nonetheless, the amount of PAR / PPFD from a typical day sun (or even a cloudy day) far exceeds what you'd get from 500W or even 2000W grow lights.
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Its just a hobby of mine, and I'm not growing anything especially hard (just Basil, which is really easy to grow... but Basil is a summer plant that really wants sunlight).
Still, once you start calculating PAR and actually mapping out how much electricity your "emulated sunlight" needs, you'll realize how grossly inefficient that "solar panel -> electricity -> LED" plan really is.
EDIT: Natural sun is like 2000 PPFD or something FAR in excess of what most plants need. Still, a good growlight solution might hit ~1000 PPFD constantly. Lets take this 650W LED and think about it: https://allgreenhydroponics.com/collections/american-made-le...
You'll get ~500 to ~1000 PPFD across a 4'x4' or 16-square foot area from that 650W LED (and most of that light is focused on the center: you'll want to overlap your lights a bit for more consistency).
Then think about how much solar panels you need to power a 650W LED for the 16-hours / day your typical plant would want (to account for the lesser PPFD indoor plants get, you run the lights for a bit longer than sunrise-sunset).
Just some napkin math. Nothing serious here: just guestimating the area in my head.
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EDIT: Now it should be noted: I've heard of good hydroponic greenhouses that have the "do both" approach: glass roofs to let the sun in most of the time, and LEDs to augment the natural sun (cloudy / rainy days, as well as winter-settings when you have fewer hours of sun). The sun isn't nearly as consistent as we'd like, but... that means that you need something aside from solar power powering those LEDs.
But the concept of building a all-LED underground (or "inside a building") without any natural light just... seems grossly inefficient to me. Such a setup only seems useful to those growing contraband IMO.