Friday, July 3, 2009

Renewable, yes, but is it sustainable?

While attending the Apeiron Sustainable Living Festival at the beginning of June, I was introduced to a new concept in alternative power source vehicles. A Dave Nichols of Killingly, CT was demonstrating and speaking about the virtues of a biomass powered Ford F-150 (1989 I believe). While the concept is cool, and a few such vehicles running around the roads certainly wouldn't cause an issue, how much biomass would need to be available in order to power a large deployment of such vehicles? Based on the information given during his presentation, I've set out to try to estimate that. According to Mr. Nichols vehicle can travel about 2 miles per pound of consumed wood or other similar biomass. I've done some back of the envelope type calculations below to figure out what the equivalency to gasoline is and how much wood would be required to power a vehicle exclusively for 1 year. Never mind that it would really only work in a vehicle with a cargo area available to stick the converter such as a pickup truck, at the expense of cargo area. (heck, you need cargo area to haul the fuel...hence why liquid fuels are so desirable and convenient).

  • 1 pound of wood for 1.5 to 2 miles
  • energy content of 1 pound of wood (well dried) = ~8000 BTU
  • energy content of 1 gallon of gasoline = ~125,000 BTU
  • energy content of 1 fl. oz of gasoline = ~968.75
  • 1 pound of wood =~ .069 gallons (8.832 oz)
  • @ 14mpg, 8.8 oz = ~0.96 miles
  • volume of wood per pound = 600kg /cubic meter ( ~ 1 pound per 61 cubic inches or a solid square of wood, 6 x 5 x 2 inches per side, eg: about 6 1/4 inches of a standard US 2x6, or about 4.25" x 1 x 12 [.42 board feet])
Assuming an average miles driver per year of 15,000, that reduces to 7,500 pounds of wood, or, using the 2x6 example, about 3,750 linear feet of 2x6, or 3150 board feet, or about a fourth of the wood required for a 2000 square foot home. Making that number more interesting, about 375 10 foot long 2x6's. Or, more directly, a cube of wood nearly 7 feet high, 10 feet long and 4 feet wide. (for a very non-nonsensical attempt to give that number real world meaning, I calucated this: On 16" centers, that's enough wood to build 1420 feet of standard stick frame wall, enough to enclose a 126 thousand square foot (3 acre) area. )

To realistically implement this would require a huge lumbering industry, and lots of time, or even more wood in order to use the much more common and fast growing pine. At around $4 per board foot, if one were purchasing this form of energy, it's equivalent to about $2 per gallon, ignoring impact of increased demand on prices. The other issue I see, is how many trees and acres of trees are required to yield that volume/energy density of wood, plus processing into small chunks for gasification, and transport to local distribution points. My guess is that on a widespread basis this isn't practical, but if one owns a few acres of trees and were to use such a vehicle, and were willing to harvest and process biomass locally, it could be done, without denuding the land.

To be fair, trees give up a lot of biomass in the form of leaves every year, compressed blocks of dried leaves could work well without cutting trees to supply fuel, and really anything that can be rendered to a syngas at 2200 degrees Fahrenheit could be used (as mentioned, grass clippings, trash (essentially, anything compostable).

While I was watching the demo, I couldn't help thinking of the Mr. Fusion from the end of the first Back the Future movie. I suspect that the energy density of a banana peel is probably not high enough to power a car for more than a few seconds...

For other media coverage, The Norwich Bulletin has a brief article up, and has a video article up, which you can see here:

  1. BTU of wood comes from an article by Sam Foote, P.Eng in a PDF on Masonry Heater Association of North America's web site.
  2. BTU per gallon of gasoline (US) from Wikipedia article on Gasoline.
  3. The 14mpg above comes from for that model and year.
  4. Density to volume conversion based on ash (a soft wood) from Allmeasures.
  5. Wood required for a 2000 square foot home via Realty Times.

Reblog this post [with Zemanta]