grow crops

In reality that does not happen on its own. Once you figure in the use of land, water and energy to grow crops it's the by far most inefficient way.

Even without the additional costs in farming and just assuming all those plants happily grow on their own, plants are still losing... "Photosynthesis turns roughly 3 percent of incoming sunlight into organic compounds [...] "Artificial photosynthesis"—comprising a PV cell that provides the electricity to split water into hydrogen and oxygen—turns roughly 10 percent of incoming sunlight into usable hydrogen[...]"