3-4x yield for which crops exactly? They are only used for growing leafy greens and low volume high cost fruits such as strawberries. Do they produce 4x corn and soy? 4x potatoes?

The capital investment required to grow corn indoors would be enormous relative to the per bushel cost. I reckon the operational cost would even outweigh the revenue.

Average corn yields in Iowa were 205 bushels per acre in 2021. Let's say corn is $10 a bushel (trading around $7 on the spot market right now). So $2050 per acre for conventional ag.

Let's assume 4x yield for indoor production, so roughly 1000 bushels/acre. Or $10k per acre at $10.

I had trouble finding any good information on energy consumption in an indoor cropping system, but I'd bet lighting energy consumption would eat up the additional revenue from higher yields.

Edit: Please let me know if anyone has access to scientific literature/experience on indoor farming energy use, I'm genuinely interested to know

Perhaps you can collect light vertically as well? And deliver it to crops either via the conversion to electricity and back, or even by some sort of optical/waveguide/handwave thing?

There's only so much sunlight that reaches any point on the Earth throughout the day. You could build something really tall to collect more light from the sun at more angles, but that will cast a shadow and reduce what's available for other collectors. So you end up with a lot of collectors receiving little sunlight or fewer collectors spread far apart.