"Plants are self-replicating"? In theory, will corn grow without our help? Sure! In practice? Not if you want it in neat, harvestable rows; not if you don't want it to compete with weeds; not if you want it to have a high per-acre yield; not if you want to control which seeds get to turn into plants next generation; not if you don't want crows to eat it; not if you want it to stick to your property and not take over the neighbor's alfalfa; and not if you take all of the plant's kernels and turn them into car fuel.

We don't settle for the replication rate of wild plants, so it's just not the case that they're "free". There's a legitimate question of whether it's costlier (along any given dimension or overall) to produce ethanol than to produce a solar panel which will generate the same amount of power over its useful life, and I don't know the answer, but please let's not extrapolate from the fact that plants sometimes grow unattended to the mistaken conclusion that corn has a negligible input cost.