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?
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