There is some controversy over whether he really got the kinds of yields he reported with the kind of work he said he did. Part of the problem was that he got really famous and people would wander over and help him out for a while so that they could learn his techniques. However, I have a friend who studied with him and I can report that he literally does manage to feed himself and his wife all of their fruit and vegetables and only spend some of his spare time (he is a high school teacher by trade). The biggest piece of labour is cutting the rice, which takes several days (and which he does all by hand).
When I visited his fields (in Japan), it had been a bad year that had been compounded by a typhoon just before harvest. My friend's field was in great shape while you could see that the neighbours had lost at least 20% of their crop. It was also really interesting to see the difference in wildlife diversity between the fields. These fields were very small (about the size of a large house lot in the US) and my friend's lot was full of frogs, snakes and spiders, while the neighbour's had nothing in them but rice. My friend said that his neighbour usually produces more rice than he does, but that his field is always much better in a bad year.
I actually did a 5 year experiment trying to grow food in containers with no inputs other than water. You need fairly big containers (depth is the most important thing), but I was surprised how well it worked. At the end of the 5 years I was getting pretty good yields with virtually no work and no inputs. In the end I had to give up because while the containers grew a lot of food, they also grew a lot of weeds. The neighbours didn't understand and one day I got home to find the gas man spraying herbicide on everything. Everybody thought it was an eyesore and he was delegated to "fix" the problem. :-P
In any case, my experience makes me think that there is room for some research in farming where we don't try to micro-manage everything.
Edit: I should point out in my own defence that I didn't actually realize ahead of time that my planters were a nuisance. I weeded out all noxious weeds and my containers were fairly well isolated with about 10 feet of concrete in every direction. Also, there was a parking lot on one side of my lot and an orchard with about a foot of mulch on the ground on the other. The spread of weeds should not have concerned anyone. I honestly think they thought I had just abandoned the planters. It's too bad, but a lesson for me in the importance of optics when you do hair brained experiments at home ;-)
The question is really can a solar panel + responsible chemical process provide a better product with lower energy and lower environmental impact. This needs to be measured in CO2 output per calorie, m^2/calorie, pesticide/poison introduction etc etc.
Its amazing how quickly you would dismiss this as it seems like an incredibly complex question.
What about using (all kinds of, including human) waste as source material? We're able to genetically engineer bacteria and fungi, these could be used to convert anything biologically degradable (which includes plastics) into raw compounds which can then be re-synthesized into edible "food"... just won't look the same as "the real thing".
Far from "not harming plants or animals," this material extraction comes with huge (but externalized) ecological, social justice, and wealth concentration problems. And of course it's completely unsustainable.
Now compare that to how healthy soil functions: microorganisms leach minerals directly from grains of sand/loam/clay, essentially manufacturing in-situ minerals into bioavailable form right at the root zone. Nitrogen fixation is similar, performed by leguminous plants using otherwise wasted sunlight and ISRU. https://www.youtube.com/watch?v=x2H60ritjag
[1] Since I know someone will bring it up, some do come from plants like soybeans. But mechanized soybean production is primarily either soil mining or (in areas with badly degraded soil) entirely supported by fossil fertilizers.