I can't listen to your podcast right now, but solar panels are more efficient than photosynthesis, and you can produce the wavelength of light needed for plants by LEDs using a fraction of that power, so what makes you say that the solar farm that powers a vertical farm will always take up more space than the vertical farm saves?
You're right, I was generalising a bit in my above comment. The wavelength - focusing argument actually comes up in the podcast and we agree it might possibly offer a way out of the energy trap.