Quote Originally Posted by Frozen_Feet View Post
By the way, any time you have the question "how cost effective something is?" or "can we build this?", think of the biggest building or piece of infrastructure you know. We already build humongous towers of steel and glass and keep them electrically lit through day and night, and have thousands of kilometers of cabling and pipelines to sustain them.
We typically keep them lit with poor efficiency flourescent bulbs rather than highly efficient LED's. And for some bizarre reason we light those buildings even when vacant at night time. If we can do that, a 3D farm is already feasible given what amount of energy we are already wasting.

Also, because people have a tendancy to get a bit hung up on the implied scale, let me clarify that something the size of a 4 storey apartment building is plenty high enough, let alone something half the height of modern business towers.