Here’s a lovely little chart that tells a very interesting story.
Every picture tells a thousand words, and this one shows how much of the total land surface of the Earth would be taken up if we used different methods to produce our energy.
For each type of energy there are two bars: one (in red) shows how much land would be needed to supply 10% of the energy we’re using in 2010. And the blue bar shows how much land would be needed if we used this source of energy to provide all the energy we’re using in 2010.
You can click the picture to enlarge it.
The green bars in the middle can be used for comparison. They show the amount of land we currently use for growing crops, and for all human uses.
Clearly (to me, and to the people at Rutgers University who produced the chart) biofuels as currently grown can never be a significant supplier of future energy. Just using them to produce 10% of our energy would require a huge proportion of the land we use for food.
And the other disadvantage of biofuels is the amount of water they use. The consumption of large quantities of water in the production of other alternative fuels is also a constraining factor in the production of other alternative energy sources.
A report from Texas University showed that soybean ethanol required 28 litres of irrigation water to propel an average vehicle 1 kilometre. Corn ethanol from irrigated fields was almost as bad (26 litres/km). Conventional gasoline requires 0.33 litres of water per kilometre, about half the requirement of tar sands fuel (0.78 litres/km) and oil shale fuel (0.59 litres/km).