Elon Musk:

Ethanol (a.k.a. alcohol) will certainly grow as a business and serve as a partial solution to our energy problem, particularly given that it is now taking the place of the gasoline additive MTBE. However, even if large-scale cellulosic ethanol technology is perfected, I don’t believe it can become the primary solution to the world’s energy needs.

The often-used example of Brazil does not apply to most parts of the world and may not even apply to Brazil if they see high economic growth with its attendant energy demands. Brazil is in the tropics with an all year round growing season and an enormous amount of arable land relative to its population food requirements and the number of cars on the road.

In contrast, domestic ethanol as the primary solution will definitely not work for the world’s most populous countries, such as Japan, China, India, Pakistan, Indonesia, etc. Those countries are either breaking even on domestic food production or are net importers. If you argue that ethanol is to be grown elsewhere and shipped, where are the vast tracts of unused arable land? And, bear in mind, the calories burned by two ton cars are much greater than those burned by 170 pound humans.