I think a picture is worth a thousand words, when it comes to the asinine arguments of the biofuel lobby:
Biofuels like biodiesel and ethanol represent a carbon neutral energy commodity. The plants they are produced from consume all the Carbon Dioxide liberated in burning them. Because they are hydrocarbons, they are fungible. They are energy dense, can be stored for long periods of time and are easily portable.
The greatest drawback of biofuels is that they cannot replace more than a small fraction of our current oil consumption. There simply isn't enough arable land available in the world to grow the crops that would be needed to fuel our oil habit. Realistically we might be able to replace 5 % of our current oil consumption with biofuels. Therein lies the inane nature of the biodiesel Hummer -- it may be renewable, but it is not sustainable.
My thought is, however, that we should not dismiss biofuels simply because their lobby groups are stupid. Instead, I think they have an important part to play as one component in a multi-faceted approach to the replacement of oil. The key is to exploit the portability of biofuels. In my viewpoint, biofuels and hydrogen are direct competitors as fungible fossil fuel replacements. Neither biofuels or hydrogen reduce our energy consumption.
In sharp contrast, an integrated approach to reduce the amount of energy we consume for personal transportation can increase the role of biofuels. To make biofuels significant we need to do the following:
- Superior well-to-wheel efficiency
- Offset load to electricity
Conservation incorporates a whole variety of factors to reduce consumption. Public transportation is one. Reduced speed limits with photo-radar enforcement is another. Reducing highway speed limits to 90 km/h could increase fuel economy by 15 %. Note that conservation is technology independent.
The biggest gain in conservation to be made is by switching to smaller cars. The current spat of SUVs are oversized beyond our needs. Mandating a switch to smaller vehicles, through something like a feebate, could drastically increase fuel economy. A fleet-wise mileage gain of 25 % from a progressive feebate is quite possible, and the impacts of rising gasoline prices will probably further assist it. Realistically, until GM goes bankrupt, we probably won't see a serious conservation effort in North America. As a huge employer General Motors welds great influence with politicians which allows them to continue their short-sited strategy of pushing giant vehicles. Toyota will pass GM as the world's largest car manufacturer soon enough.
I will assign conservation a 40 % decline in our per capita oil consumption.
The second step is to pick vehicle and energy sources technologies that produce a high well-to-wheel efficiency. The well-to-wheel efficiency of a spark ignition gasoline car is only about 13 %. Gains can be made by incorporating hybrid technologies like regenerative braking, auto-shutdown when stopped at red lights, storing energy from downhill runs for uphill climbs, etc. Switching to compression ignition (Diesel) combustion engines can also increase efficiency by 50 % over spark ignition. Studies have shown that a diesel-hybrid can have 3x the well-to-wheel efficiency of spark ignition engines.
As an aside, fuel cell car powered by electrolysis-produced hydrogen would have a similar well-to-wheel efficiency as gasoline cars. I.e. the hydrogen economy will not reduce our energy consumption.
The third step is to switch transportation load from portable energy sources like gasoline or biodiesel to electricity. This clearly lies in the gradual introduction of the plug-in hybrid (PHEV) with ever increasing all-electric range. A plug-in hybrid with a range of 30 km could easily replace 75 % of hydrocarbon consumption simply because most people don't drive that far in a day.
Electricity can more easily be produced from carbon neutral energy, whether it be renewables, nuclear, or sequestered clean coal. Moreover, the round-trip efficiency of electricity can be extremely high. If we consider power from wind, the electricity may lose 10 % of its energy to transmission losses; Li-ion batteries have a round trip efficiency of 90 %; electric motors can be 95 % efficient. The well-to-wheel efficiency in this case is a staggering 77 %. The plug-in hybrid also can act as grid voltage regulation, mitigating the intermittent aspects of renewable power sources like wind.
So what is the cumulative effect of these three ideas?
Conservation reduces our per capita normalized oil consumption from 1.0 to 0.6. We then replace 75 % of that load with electricity, reducing consumption to 0.15. Now calculate that the switch to the diesel-hybrid increases efficiency by a factor of three, so 0.15 / 3 = 0.05.
Guess what, through these three steps we have reduced our fossil fuel consumption to 5 % of its current value. Remember, how much off our current oil consumption we might be able to replace with biofuels? It's the same number. We can potentially replace all of our fossil fuel consumption for personal transport with biofuels. At the same time, energy consumption would be only 15 - 20 % of its current number, which has great implications for sustainability.
While this may be a simplistic analysis, it does show that biodiesel production could be on the same order of magnitude as consumption. Even if biodiesel and Fischer-Tropsch diesel from biogas can't meet all our oil consumption needs, fossil fuel consumption would be tiny compared to today. Carbon Dioxide emissions would be trivial in comparison, and peak oil would no longer be an issue.
Now, obviously this only addresses personal transportation and not freight transportation. Still, it shows that huge advances can be made in an incremental fashion to our current transportation industry.