[fluoridation]

Does that figure include the cost of manufacturing and installing the photovoltaic cells? Plants may waste sunlight, but they're very cheap to produce. Also, plants produce sugars from sunlight almost directly. Intuitively, producing electricity from sunlight and then using that electricity to produce sugars could not possibly be more efficient. It could very well be that storing energy in carbon-hydrogen bonds is intrinsically inefficient.

[cornholio]

> producing electricity from sunlight and then using that electricity to produce sugars could not possibly be more efficient.

Per photon, no. Per area of sunlit land, yes, orders of magnitude more.

Also, the photosynthesis efficiency generally refers to the entire chemical energy stored in things like the leaves, stem etc., often useless in the food chain. Solar to food efficiency is abysmal.

Then, there is the question of fertilizer and pesticide use, runoffs and accumulation in groundwater and soil, destruction of soils by intensive agriculture, water use, substantial energy required to transport the large masses involved, the subtraction of that land from the natural habitat etc. Modern agriculture is a necessary evil.

[fluoridation]

>Per photon, no. Per area of sunlit land, yes, orders of magnitude more.

That's contradictory. The Solar flux for a given region at a given time is basically constant.

I don't think fertilizer (or something analogous) would be avoidable in such a scenario, since one way or another you need a source of nitrogen.