25 September 2005

A Rational Case for Biofuels

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:

  1. Conservation
  2. Superior well-to-wheel efficiency
  3. 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.


Anonymous said...

The max 5% you give for biofuels is a little bit pessimistic I think. BtL, DME, and biodiesel from semidesert plants like jatropha could satisfy a 20% or even more of global oil consumption.

What I really can't understand is why there are no electric vehicles in the market. Take my father for example. He has a 2500cc diesel pickup truck. It is absurd to use this monster to go to the supermarket 1Km away. That's why he has a small scooter. But a light urban electric vehicle would be even better.

Robert McLeod said...

I think the real answer is no one really knows exactly how much biomass is available. I tend to err on the side of caution. In my case, I'm estimating that 1-2 % of our existing energy consumption (not just for transportation) could be transformed into biodiesel. Moreover, freight traffic will need considerably more biomass since it can't off-load so much consumption to electricity.

On the subject of electric cars, I think the obvious answer is that batteries are expensive. To get a serious range out of an electric car requires a lot of storage. A Prius conversion with a 1.5 km all-electric range will need a smaller battery pack than a converted Smart car with a 10 km range! How much are you willing to pay for a run-about with a 10 km range? Probably not very much; the utility value of the appliance is not high enough.

Robert McLeod said...

Hence the "freight transport" qualifiers. Are you including "light trucks" with "cars"?

Jesse Jenkins said...

A couple of comments:

1) You write that biofuels are carbon neutral in that the co2 they release at combustion is the same co2 that they 'breathed' from the air during growth. This is true. However, there are other carbon inputs to consider such as fertilizers, fuel for farm equipment, transportation of the fuels to end user etc. that go into growing these biofuels. All in all, the EIA estimates in a 1994 report, Alternatives to Traditional Transportation Fuels 1994 Volume 2: Greenhouse Gas Emissions (sorry its old, its the best I've found), that the total greenhouse gas emissions from the entire ethanol from corn fuel cycle yield only a 15% reduction over gasoline. Now, since 1994, incremental gains have been made in the efficiency with which corn feedstocks are utilized for biofuels. However, biofuels will never be entirely carbon neutral until all of the fossil fuel inputs in their life cycle are replaced by carbon-neutral fuels (i.e. biodiesel to power the farm equipment, soy-based fertilizers etc.). [Obviously the life cycle analysis changes completely if you consider cellulosic biomass, which brings me to ...]

2) The claims that there is not enough biomass to supplant our petrol addiction is only true if you dont consider cellusic-biofuel refining processes like those being worked on by Iogen and others. These allow much more efficient utilization of existing feedstocks (corn, soy beans etc) as well as additional feedstocks (many of them currently considered waste feedstocks like forestry waste, corn stover etc). The DOE and USDA estimate in their report, Biomass as Feedstock for a Bioenergy and Bioproducts Industry (google 'Billion Ton Vision' and you'll find it) that a billion dry tons of biomass suitable for energy uses (including combustion and refining to biofuels) or for refining into plastics or other bio-based petroleum replacements could be sustainable harvested in the United States, largely without using dedicated feadstocks. That could be enough to supplant 30% or more of current US petroleum uses. This still isn't 100% but like you get at in your post, if we couple this with increases in efficiency, like utilizing plug-in hybrids, the remaining fossil fuel demand could potentially be supplanted with biofuels. Any way you cut it, with cellulosic biofuel refining and a billion tons of annual supply, biofuels can make up a pretty substaintial part of our energy supply - not all of it, but a good chunk.

Now the only question is, is this the most efficient utilization of our resources or would the biomass better go towards creating carbon-char for a zinc-air process a la Engineer-Poet's pet plan at The Ergosphere... That will take more study.

Fat Man said...

Have you looked at this:

Widescale Biodiesel Production from Algae
Michael Briggs, University of New Hampshire, Physics Department
(revised August 2004)

Anonymous said...

If there is not enough LAND to grow fuel from plants, consider growing the fuel in the ocean. Rather than harvest carbohydrates and require huge investments to convcert them to hydrocarbons, have the PLANT make hydrocarbons directly.

For more on the idea see:


(Not a hot link. Cut & Paste)