I must admit that for the latter part of 06, I thought that the whole idea of biodiesel made sense and that it was something that I should invest in. However, after thinking through the various issues on how one get biodiesel and so on, it was obvious to me that the whole scheme is frought with difficulties.
For one, there has to be sufficient space to grow the biomass from which the diesel is to be taken from. That growth means that we have to modify the land use of agricultural land to have plants that can be used for biodiesel generation. While it is true that most of the current cash crops *could* theoretically be candidates for biodiesel generation, the bulk of the favoured source is not.
Close second to the biodiesel scheme is the idea of a hydrogen-based power system (and fuel cells as well). The H system has the issue that you have to have a natural source of H that you do not need to spend energy to extract. If there are underground sources for H, that would be a shoe in. The nature of H is that it is something that needs to be extracted from other sources involving expenditure of energy. I am not sure that the energy balance will be arrived at in that scheme.
Looks like the most likely source for highly efficient energy is via batteries. What we really need is more efficient solar panels that convert sunlight (and perhaps moonlight) into energy that can be stored in highly efficient batteries.
I like some of the discussions here. Batteries are the way to go.