In vertical farms you need to use LEDs to make plants grow, which in turn have to be powered e.g. by solar panels. If solar panels had the same efficiency as plants, then you would need the same amount of solar panels as you had plants before, if your LEDs had perfect efficiency. So the claim that vertical farms would use less surface area seems strange at first.
But it appears that solar panels are more efficient than plants. Although the accepted (at the time of writing) answer focused on creating electricity (burning biofuels), which is advantageous to solar panels as there are no further conversion steps.
So the question is, does it make sense to go the (Sunlight -> solarpanel -> electricity -> light -> plant) detour?
As you probably lose efficiency in every step this seems wrong intuitively, but reasons this might make sense are:
- plants might be able to convert a smaller percentage of the light spectrum into energy, if solar panels can capture the entire spectrum and LEDs produce only that spectrum, you gain some efficiency
- plants might only be able to use energy up to a certain point and "throw the rest away". If solar panels can capture all the energy you could split it up to multiple plants with dimmer lights
So the question is: To grow one square meter of crop plants, how many square meters of solar panels do you need?
(This might depend on the latitude)