Biodiesel is way better than fossil diesel: a 1998 life-cycle analysis

After 15 years of burning B100 in our 2003 VW Jetta TDI, it’s nice to have happened upon the helpful insights within this 1998 study by the National Renewable Energy Laboratory:

Reductions in Petroleum and Fossil Energy Consumption

As one component of a strategy for reducing petroleum oil dependence and minimizing fossil fuel consumption, the use of biodiesel offers tremendous potential. Substituting 100% biodiesel (B100) for petroleum diesel in buses reduces the life cycle consumption of petroleum by 95%. This benefit is proportionate with the blend level of biodiesel used. When a 20% blend of biodiesel and petroleum diesel (B20) is used as a substitute for petroleum diesel in urban buses, the life cycle consumption of petroleum drops 19%.

In our study, we found that the production processes for biodiesel and petroleum diesel are almost identical in their efficiency of converting a raw energy source (in this case, petroleum and soybean oil) into a fuel product. The difference between these two fuels is in the ability of biodiesel to utilize a renewable energy source.

Biodiesel yields 3.2 units of fuel product energy for every unit of fossil energy consumed in its life cycle. The production of B20 yields 0.98 units of fuel product energy for every unit of fossil energy consumed. By contrast, petroleum diesel’s life cycle yields only 0.83 units of fuel product energy per unit of fossil energy consumed. Such measures confirm the “renewable” nature of biodiesel.

Reductions in CO2 Emissions

Given the low demand for fossil energy associated with biodiesel, it is not surprising that biodiesel’s life cycle emissions of CO2 are substantially lower than those of petroleum diesel. Biodiesel reduces net emissions of CO2 by 78.45% compared to petroleum diesel. For B20, CO2 emissions from urban buses drop 15.66%.

In addition, biodiesel provides modest reductions in total methane emissions, compared to petroleum diesel. Methane is another, even more potent, greenhouse gas. Thus, use of biodiesel to displace petroleum diesel in urban buses is an extremely effective strategy for reducing CO2 emissions.

It’s refreshing to see a clear flux diagram showing how soybean carbon cycles!

Other interesting bits:

  • A barrel of typical (1995) crude provides about 100 kg of liquid fuel. Upon combustion each kg of fuel generates 3.15 kg of CO2. (ref)
  • Union of Concerned Scientists: “Oil is Changing” site

U Mich makes algal crude in minutes

A Wired article (thanks Mike!) that got me thinking about how much of crude oil’s energy is geologic, rather than photosynthetic.  Upon deposition of biogenic sediments, there is tectonic transport, geothermal heating, and compression in subduction zones or beneath additional deposits.  How to account for these energetic contributions?

Also, the researchers’ general approach seems sort of sloppy.  A good terrestrial farmer would harvest a crop (of plants), mechanically process it into products, and compost/recycle the “waste.”  Here the crop of algae appears to be simply cooked en mass (including with water) into crude with little analysis of how distillation or cracking would generate products from the resultant soup.  Given that we have the option of processing the crop before cooking it (which was long-missed for fossil fuels), is it more efficient to process before attempting thermo-baro-chemical transformations, or to crack apart the goo once cooked?