In Professor Bugbee's presentation, he describes some drawbacks of vertical farming (VF) versus traditional horizontal agriculture. Most of Bugbee's arguments against VF hinge on grow lamp efficiency. In July of 2015, a step towards a 400lm/W monolithic white laser was announced. Laser lights are several times brighter than LEDs and use much less energy.
He illustrates a compelling argument as follows:
Arrows represent relative inputs and outputs. Sunlight, being large and free, dwarfs fossil fuels (black), water (blue), and crop yield (green).
Bugbee's calculations with respect to his assumptions about photon energy conversion into biomass appear to be correct. Therefore his conclusion also seems to be correct: vertical farms are far less efficient than traditional agriculture (for growing tomatoes). This doesn't necessarily mean they aren't viable.
Given the assumptions above:
- What is the lumens per watt efficiency necessary to allow vertical farming to compete with horizontal agriculture (in terms of energy usage and production)?
- How did you calculate that efficiency?
Basically, barring compact fusion, can can we wholly replace (in time) traditional plant-based agriculture farming by growing indoors using technology? (For example, concentrated solar capture at 85%, batteries with 85% storage efficiency, 95% transmission efficiency, and highly-efficient grow lamps could be in the ballpark. I don't know, hence the question.)