Thanks for posting that, I just watched the whole thing. One input he does not discuss is cost of land, or rent. This is where vertical farming shines best and helps explain why indoor farms make sense in urban areas.
Under normal circumstances it doesn't come close to redressing the imbalance of costs of indoor vs greenhouse or outdoor production.
He's right about all of this; for example, my water cooled air handlers do pull condensate from the sealed grow space and recycle it. A well sealed space can recycle basically all of the water again and again. This is no free lunch, because the chiller has to provide the energy with which to do it and that's not cheap.
One more thing; he's using a figure of 15% when discussing the efficiency of double ended HPS and LED lighting. This is jarringly different from the 40% number for DE HPS and up to 60% for advanced LED lights. What's going on there? I've seen this discrepancy before and no one has been able to adequately explain it.
Does anyone have any thoughts about the wildly different lighting efficiency numbers?
Again we need to separate 2 things:
Energetic efficiency, and commercial feasibility.
The videos explains quite well in my opinion why it would be both energetically and environmentally better to grow crops outdoors and drive them several hundreds miles in a truck to urban centers for consumption.
But, the video also discusses the fact that market economy and supply and demand, still make it commercially feasible to grow very specific crops in urban farms.
These are crops that are quick to grow and are needed fresh - basil, lettuce etc.
About the numbers and lighting efficiency, the only 15% number I remember that deals with efficiency is the average efficiency of solar panels, compared to direct sunlight on a field of plants. He explains it at 17:46 in the lecture. Basically out of 1000W/m2 of direct sunlight, solar panels capture 150W.
from these 150W of electricity, The best LEDs (of that time, end of 2015) are able to produce 1.74umol/J, which equates to 260umol/m2*s.
He also talks about the big advancements in efficiency in LED and HPS lighting, the numbers he uses are quite recent and are quite accurate still.
My main point is that a system like this one:
Sunlight > Solar panels > electricity > light > plants
Will necessarily, and ALWAYS be energetically less efficient than this system:
Sunlight > plants.
Again, in certain circumstances, and certain scenario this energetic inefficiency can be justified, for example for economical reasons, for fear of being caught by LE for growing illegal crops, for very extreme latitudes/climates, etc. etc.
