Why this aweful idea is so appealing to some I will never understand.
1) Sunlight is a diffuse form of energy(average irradiance is about 200 W/m^2).
2) Plants are adapted to grow under sunlight(put them under a magnifying glass and they will get burned, not thrive).
Number 1 indicates that farms need to be flat in order to capture a lot of natural lighting.
Vertical farms "solve" this by using artifical lighting. 2000 kcal is a little more than 2 kWh, but close enough for our purposes; 2 kWh is about 0.8 kg of white bread. To provide 2 kWh of food energy, you need to produce about 500-1000 kWh of light(most food-crops are 0.25-0.5% efficient at producing human food from sunlight). In order to produce this light you need ~2500-5000 kWh of electricity(low pressure sodium lamps are ~20% efficient; leaps and bounds ahead of fluorescent lamps and LEDs). That's the yearly electricity consumption for a sizeable house. At 10 cents per kWh, our loaf of white bread would cost $250-$500 just for the electricity.
This gets even sillier if you envision meeting this electrical requirement with solar panels; which would have to cover an area far greater than the area covered by the "horisontal farms" that were replaced with vertical farm.
Number two compounds the problem. You can't cram plants closer toghether and increase crop yields; because plants can't take lighthing that intense. The capital cost of a hectare of "horizontal farm" is fairly low; it's just dirt after all. The capital cost of an acre of floor-space in a vertical farming skyscraper is probably within an order of magnitude of an acre of office space in a skyscraper; really ****ing expensive.
Vertical farming has no redeeming features or attractive qualities. It is an unmitigated disaster.
