Vertical Farming, as its name implies, is where crops are hydroponically grown in skyscrapers so as to use less farmland. There are pros and cons to doing this:
Pros: Less farmland is needed to produce an equivalent amount of crops (allowing more land to return to nature)
Water and nutrients can be used with more precision
An optimal indoor climate can produce crops year-round instead of in seasons
Cons: Buildings are expensive, especially in urban areas
Grow-lights would be needed and would require lots of energy. Using renewable resources would likely negate the benefits as they would need to spread horizontally to harvest the energy.
There is a possibility that PV cells could light the plants since plants only use certain wavelengths of light, and PVs capture more wavelengths. Fossil/bio fuels are an attractive option because the CO2 produced would help plant growth.
I think the idea is exciting, I look forward to seeing where it will go.
_________________ I'm a math evangelist, I believe in theorems and ignore the proofs.