We can have free unlimited food for everyone today
maybe not free unlimited saffron, but flour(s), legumes and nuts, potatoes could be distributed for free (subject to some rationing, 5000Kcal per person per day). This is not utopian, this is technical possible right now.
It‘s not just about on-farm labour, you need big machines (and lots of diesel!), fertiliser, pesticides… And that‘s before you look at all the rest of the food system, because to put a meal on the table you need the whole supply chain (ag-tech, fertiliser production, food processing, wholesale suppliers, etc.)
In modern agriculture, the farmer only gets a fraction of the money you pay for your loaf of bread, because there are so many other people involved.
Maybe if we can reduce the need for profit we also reduce the need for fertilizers, maybe the relation between fertilizers used and crop productivity is not linear (-20% productivity but -40% fertilizers?). Food processing won't be necessary: why have a factory for chips? or for hummus? _Most_ people can cook.
The thing is, contrary to other things, like fusion, this is possible. Now more so than ever; we have everything we need to start a food UBI.
The rest are just accounting details, like how less rich the 1% should be to fund all this.
Of course it's possible, I'm just saying it's not (and can never be) free. "Free for consumers" simply means somebody else paid for the costs - or more likely, the consumer paid the costs through taxes rather than at the store. You will always have input costs to produce an output, and these will not be negligible.
Just a few points on what you said, and these are not "accounting details": (1) Solar energy is not free - you need to build, install, and maintain panels and a power grid. (2) Of course you can reduce fertiliser, organic farming does so and takes ~20% yield decrease (depending on the crop). But then you have higher labour and machine costs to control weeds, and an overall higher per-hectare price. (3) Food processing matters because you probably don't want to spend most of your day milling your grain ration to make flour that you can then bake into bread. Ditto for other types of staple foods (you want to make your own sausages?). (On a historical side-note, here's a write-up of how ancient food systems worked: https://acoup.blog/2020/08/06/collections-bread-how-did-they...).
Bottom line: Food systems are incredibly complex!
Nuts also take enormous amounts of water, which is a pretty big problem where they're grown.
Big centers, like Costco, could serve as distribution centers; while software can handle the rationing.