Maybe there are too many people.
You don’t get something for nothing. Corn varieties historically yielded 26 bu/acre. Granted, their land was probably tired out from overcropping. The only way to cheat nature on this was to breed race cars of the corn world, varieties which would draw in greater amounts of resources. Bigger carbs, higher test fuels. Of course we are talking about adding nitrogen fertilizer, granular, or anhydrous ammonia. Plus phosphate, a critically limited resource we will soon be very sad trying to cope without. Typical grain yields are in the 30 - maybe 60 or 80 bu/ acre in an exceptional year. But you won’t repeat that steadily.
So Carl is correct in his figuring. His grapes are taking about the sustainable maximum from the environment. Maybe plant breeders could develop a highly input responsive grape, then Carl could get multiples of his yields by applying anhydrous till the land smokes, the way corn farmers do.
That’s the natural limit we have to get our heads around. Do the math on how many people can be comfortably sustained under those limits. And then figure how many cars. As cited earlier, more than double, perhaps triple the arable land mass of the US would have to be sacrificed to perpetuate the automobile vision. And that’s just fueling, never mind manufactiring, lubricant oils, replacement tires, etc.
I would rather focus on human beings than cars. At least the car culture, it was a product of limitless oil, and will not be a part of the future aside from for an elite, or serious jobs. If we have a future, if we get our act together.
As for conversion efficiencies of solar panels, we can’t eat the electricity, or guaranteed make food from it, or fuel with a higher efficiency than photosynthesis. Steps in the photosynthesis pathway are quantum, zero losses. And if nature has been tweaking that looking for breakthroughs for 3 billion years, with no better results than current state of the art, I think its safe to say us hairless chimps aren’t going to better it.
I consider the ethanol fuel issue about debated out. Keep ethanol for drinking. We might want to have a few stiff drinks in the future that’s coming. Or, recognize that ethanol is no panacea, it comes at a significant expense, you can certainly make shaft power with it, but in reality syngas is far more efficient, and syngas itself is more work than refined fossil fuels.