Saturday, June 27, 2009
Don't Need No Stinking Biodiesel
Did you know that the carbon intensity (the ratio of carbon dioxide to energy) of natural gas is lower than the average intensity of Brazilian and American soy biodiesel? And that is without counting land displacement impacts (carbon put into the atmosphere by burning a forest to plant soy).
A common argument I hear from biodiesel enthusiasts is that heavy machinery must use diesel engines because of the high torque required. Take a look at that garbage truck above. It is about as heavy as you get and it runs on natural gas. Not only is it producing less GHG than biodiesel, it is producing a tiny fraction of the local air pollution (especially soot, which also contributes to global warming) at the tailpipe. It's also a lot quieter.
Fleets of vehicles with known routes (like buses and garbage trucks) where range is accounted for and where they can all be fueled at their depots are ideally suited for using natural gas. Combine this idea for fleets with today's gasoline hybrid technology for personal transport (that is achieving gas mileage improvements in excess of 100% over average mileage) and one can see how the rush to food-based biofuels is over-hyped.
A recent post by Robert Rapier suggests that America could in theory, replace all gasoline with domestically produced natural gas for roughly the next half-century.
[UPDATE] Here's an interesting article on GAS2.0 claiming that there is enough biomethane (methane from decomposing garbage and manure) to power up to 20% of our diesel fleet. Methane is 20 times worse than CO2 as a GHG. Burning this waste methane instead of letting it escape into the atmosphere would reduce GHG emissions a few orders of magnitude more than running all of our diesel fleet on soy biodiesel.
[ANOTHER UPDATE] Here's an article in the New York Times Green Inc. blog about a company near Seattle called Prometheus Energy that is developing a way to capture waste methane and store it as a liquid. The advantage of this idea is that the methane does not have to be burned at the source of methane production. As a liquid it can be transported and used for other things. You can't do that with the gaseous form because it is too bulky.
[MORE UPDATES] I recently stumbled upon two studies from Australia that were done almost six years ago that show natural gas is worse than diesel on a life cycle basis when it comes to GHG emissions.
The Greet model done by Argonne labs showed a 5 to 25% improvement in GHG over gasoline for natural gas produced in North America but did not compare natural gas to diesel. Natural gas shipped here via tanker is not better than gasoline.
On the other hand, natural gas vehicles produce very little soot, and soot is thought to account for roughly 18% of global warming. Future studies comparing diesel trucks and buses to natural gas versions need to account for soot when evaluating global warming impacts.
(Photo credit Jeff Youngstrom via the Flickr Creative Commons license).
Click here to see a list of my articles and to subscribe to future posts.