The Truth About Energy
Petroleum, hydrogen, ethanol, methanol and coal are not sources on energy. They are storage mediums. They are batteries. Although we can convert these materials into energy, they were created by consuming energy. This is pretty clear for hydrogen, ethanol and methanol, all of which are routinely constructed by chemical processes (requiring the consumption of energy). As our major source of petroleum is currently extraction from reserves, it may not be immediately obvious that petroleum is a storage medium. However as petroleum is the result of the decomposition of vegetation over millions of years, the energy that was in the vegetation is transfered into the petroleum. A similar process leads to the production of coal and natural gases.
Where does the energy stored in these materials come from? For the vast majority of the energy on earth the original source is a nuclear reaction. The nuclear reactions taking place in the sun. The plants that became fossil fuels captured their energy from the sun, much as they do today. Wind is largely the result of atmospheric changes caused by the sun heating the earth. Rainfall (which is the source of power for hydroelectric dams) is also powered by the sun. (The only other sources of energy that I could think of are nuclear reactions on earth and tidal).
Given that the primary source of energy for the earth is the sun, it make sense to try and harness that source directly, instead of using multilevel approaches such as creating ethanol from vegetation. Unfortunately for the near term, we don't have particularly efficient ways of capturing the sun's energy directly. In fact it may be more efficient to capture the other effects of the sun (hydro, wind) until the solar energy capture can be made efficient for large scale applications.
In the future we will still need fuels (they can be transported without significant energy loss and (currently) can store energy more densely (less volume and mass) than batteries), however instead of harvesting them (either by converting crops into ethanol or by extracting fossil fuels) we should use the sun's energy to power their manufacture. Hydrogen can be created by just electricity and water and methanol can be created using hydrogen and carbon dioxide. That is, manufacturing methanol consumes carbon dioxide and produces fuel, the exact opposite of our current situation. Of course when these fuels are used, the carbon dioxide and water is released back into the atmosphere where they can be captured and made into methanol once again.
A system like this, using solar energy, water and carbon dioxide to store energy, is carbon neutral. The carbon dioxide released when the fuel is used is the same as was used in the fuel's manufacture. A system like this self-sustaining.