US farmland occupies 895 million acres (3.6M km^2) [1]. Average solar irradiance on most US farmland is about 200 W/m^2 [2]. By being generous and assuming vertical farming is 100x more efficient than natural photosynthesis, the energy requirements come out to 7.2 terawatts of generating capacity. In contrast, the US currently has 1.1 terawatts of generating capacity. [3] Vertical farming isn't just uneconomical: it's completely absurd.
[1] https://www.statista.com/statistics/196104/total-area-of-lan...
[2] https://en.wikipedia.org/wiki/Solar_irradiance
[3] https://www.eia.gov/energyexplained/electricity/electricity-...