Forgive me for being skeptical that they can generate more energy than the energy they use + the energy input from solar panels. After all, the entire point to this exercise is to minimize surface area while maximizing volume. At the very least I don't think they'll be able to get enough natural sunlight to all of the crops; thus, they'll need artificial lighting for crop growth. Could you break even, energy-wise, by growing a plant with artificial light and then burning the methane that you generate from the plant? Disregarding all other work involved?

Certainly there are ways to reduce the electrical footprint of the building, but my unsubstantiated gut feeling is that the footprint will still be immense. Has anyone actually run the numbers on this yet?