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Updated energy life-cycle assessment of soybean biodiesel finds fossil energy ratio of 5.54; significant improvement from earlier studies

Comparing energy requirements for major biodiesel subsystems and total life-cycle energy requirements between the current study and two earlier assessments: Pradhan et al. (2009), and Sheehan et al. (1998). Pradhan et al. (2011) Click to enlarge.

Researchers from the University of Idaho and the US Department of Agriculture have updated the analysis of the energy life-cycle of soybean biodiesel and found a fossil energy ratio (FER) of 5.54 using 2006 agricultural data. This marks a major improvement over the FER of 3.2 reported in a 1998 NREL study that used 1990 agricultural data and significantly better than the FER of 4.56 later reported using 2002 data.

The FER is the ratio of renewable fuel energy output to the biodiesel share of fossil energy input; only fossil (nonrenewable) energy is included in the input. The improvements are primarily due to improved soybean yields and more energy-efficient soybean crushing and conversion facilities, the team said.

The energy input in soybean agriculture was reduced by 52%; in soybean crushing by 58%; and in transesterification by 33% per unit volume of biodiesel produced. Overall, the energy input reduction was 42% for the same amount of biodiesel produced.

The addition of secondary inputs, such as farm machinery and building materials, did not have a significant effect on the FER—when these inputs were added, the FER decreased to 5.34 (a 3.6% reduction).

They divided their analysis of the life-cycle of biodiesel into four subsystems for the analysis: feedstock production; feed- stock transportation; soybean processing with biodiesel con- version; and product distribution. They then developed an inventory of material and energy that quantifies all fossil energy inputs used in each subsystem.

All direct and indirect sources of energy were included in the inventory, such as the liquid fuel and electricity used to directly power equipment in the system. The energy content of materials that were made from energy resources, such as fertilizers, pesticides, and other petrochemicals, is also included in the inventory. The effect of adding energy used for building biodiesel plants and agricultural machinery was studied separately and not included in the base case to be consistent with.

The soybean crushing and transesterification facilities that have been built in recent times are more energy efficient than older plants. In addition, the continued improvement in soybean yields and reduced overall energy usage on the farm helped increase the energy balance of bio- diesel. The lower chemical uses in recent years can partially be explained by the adoption of GE [genetically engineered] soybeans, which resulted in reduced pesticide use. Five-year average chemical use data showed a general decline in the amount of pesticide use.

...The results from this research suggest a likely improvement of the biodiesel FER over time. All other factors being constant, for every 100 kg/ha (1.5 bu/ac) increase in soybean yield, the FER increases by 0.76%. In addition, the agricultural sector and the biodiesel industry are likely to continue to make energy efficiency gains in order to lower production costs, eventually achieving an even higher FER.

—Pradhan et al.




How can studies with such major results differences can be reliable?

Nick Lyons

"The improvements are primarily due to improved soybean yields and more energy-efficient soybean crushing and conversion facilities, the team said.

According to the article, efficiency has improved over time. Prior studies looked at earlier practices.

Henry Gibson

Oil farms of any type alter the natural ecology of large areas.

The entire crop area of the world, even the US, is not enough to supply any substantial part of the liquid fuel energy supplied by oil, or that produced from other fossil fuels.

Solar energy is more efficiently used by large numbers of concentrating solar collectors-electric generators than it is by plants.

Every person in the world gets thousands of times more nuclear radioactive and UV exposure from the sun and space than they would ever get from multiple small nuclear power plants in every city and town. Such reactors can be buried under many feet of earth so that little radiation will escape with even total failure of cooling systems. Nuclear fuel is so cheap that nuclear power plants do not need to be highly efficient. Rubbia Accelerator Reactors can use very cheap depleted uranium if the preferred much more abundant thorium is too expensive, and the cost of the fuel is only a fraction of a Euro cent per kWh. Large efficient Nuclear reactor power plants are not needed and are wasteful with their expensive high pressure steam pipes and boilers. Coal fired power plants put many times more radioactivity into the air than nuclear power plants and the fuel costs for operating them are usually less than one quarter of the price paid by a home owner for a kilowatt-hour. Natural gas powered power plants also put far more radioactivity into the air and the fuel cost is just a larger fraction of the price paid by consumers.

Even so, generating electricity and heat at the same time in every home or building is the fastest and cheapest way of reducing CO2 build up in the air where natural gas is available or being used. Coal should also not be burned without cogeneration of heat-cooling-power, and even if the cheapest possible gas has to be made from the coal first and delivered to factories and homes and buildings.

Collecting solar heat with small parabolic mirrors or other collectors for lower temperature use should be a principle source of heat for all biofuel production factories. High temperature heat energy can be stored in molten salts or even wax. This is not for efficiency but to demonstrate how expensive solar energy is, including biofuels. ..HG..


Henry, perhaps a Volt type solution using renewable fuels would be practical.. of course fossil oil would last millenia if we all drove Volts.

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