True, but the systems that do this most effectively require a lot of other limited resources besides solar power - most notably arable soil, fresh water, time, and usually also some additional processing to render that glucose ingestible for one of those people.

So maybe the Earth could supply 1 trillion people with food if it was turned into a farm planet devoid of any other biodiversity but those required to support human life, assuming those 1 trillion people were living and doing all their non-agricultural industry somewhere else.