I agree with the first part of your comment, though not the second. From 2000-2013, the share of global energy produced by renewables has only grown by 0.8%[0]. (Fun fact; when Germany started their nuclear phase out in 2011, they replaced the mothballed nuclear plants with new coal power plants, not renewables). There's frankly not enough time to rely on the growth of renewables; it looks like we're stuck with fossil fuels until the bitter end.

Edit: Got the dates wrong.

[0] https://en.m.wikipedia.org/wiki/World_energy_consumption

That's not an accurate comparison. You are then using that 20% to power grow lights for photosynthesis. How efficient is photosynthesis using grow lights? Even if it's twice as efficient, you're then looking at 4% of 20% which is 0.8%.

Sure, this can be used used land not suitable for agriculture. I only see this really being helpful in cities that have old industrial buildings that are sitting vacant (reuse existing infrastructure and reduce transportation).