BIOFUELS - THE NET ENERGY DEBATE

The question of energy balance is continually raised when discussing the merits of the use of ethanol, and now biodiesel, as a fuel. Does ethanol, produced from corn or cellulosic biomass, have a negative energy balance? In other words, does it take more energy to make a gallon of ethanol than is contained in the ethanol itself? The simple answer is yes since, according to the basic laws of thermodynamics, energy cannot be created but a large portion of the energy utilized in the production comes from the sun and therefore should not be included in the net energy balance calculation. The question is really about whether it takes more fossil fuel derived energy (Fossil Energy Replacement Ratio) to create a gallon of ethanol than is contained in the ethanol itself.

The production of biofuels is one of the only emerging industries where net energy balance has become such a heated controversy. We routinely use more energy to produce a useful form of energy as the quality of the energy is a factor. For example, it takes more fossil energy to produce a kilowatt-hour of electricity than is contained in that electricity, an FER ratio of 0.4. However, electricity is a more useful form of energy than the thermal energy used to produce it because we can store it more easily, transport it more easily and utilize it more easily. We would not consider removing electricity from our life because of the loss of energy in its production.

Other forms of energy both widely used and widely proposed have a low or negative energy balance but are still considered viable. Gasoline has a net energy balance or a FER of only 0.8 and hydrogen fuel has been shown to be negative but it continues to be touted as a fuel solution.

The energy balance issue first arose in the mid 1970's when studies concluded that ethanol was slightly energy negative. Since that time, many studies have been done and the results of these reports showed a large variation. These variations were due to the ranges in assumptions about corn yields, fertilizer manufacture, fertilizer use, ethanol processing technologies and the energy value of the co-products. Some studies even included the energy value of the manufacture of the farm equipment and the fossil fuel usage of the employees.

In recent years, most studies have concluded that the net energy balance of corn ethanol is approximately 1.3, sugar cane ethanol is 8 and cellulosic ethanol has a range of 2-36 depending on the production method. This increase in net energy balance for corn ethanol has occurred due, in part, to improvements in agricultural practices - improved yield of corn per acre from 100 to 140 bushels per acre, reduced use of fertilizers and increased use of conservation tillage. Improvements in the processing and manufacture stage have reduced energy usage by about 20%. Cellulosic ethanol produced from biofuel crops such as switchgrass is anticipated to have a higher net energy balance due to the greater yield per acre.

The debate has recently expanded to include biodiesel and cellulosic ethanol. While all of the studies agree that the net energy ratio of biodiesel is positive, the value of the ratio ranges from .98 to 3.2. Cellulosic ethanol has the potential to have a high net value due to the high yield per acre of cellulosic crops and the use of the lignin portion to generate electricity for the facility.

The thermochemical route for producing ethanol, methanol and other alcohols has not yet come under attack in this debate. This is mainly due to its emerging status and the difference in the feedstocks used. The use of waste materials such as mill residues, agricultural residues and municipal solid waste adds a different twist to the calculation of the net energy balance since these materials are not produced specifically for biofuel production and therefore do not require energy input. Energy use is minimized during the processing stage by utilizing the heat generated in the reaction to dry the feedstock material and using some of the gas produced to fuel the gasification system.

The ongoing debate and the corresponding media coverage regarding the question of the net energy balance of ethanol have distracted the public from the real value of biofuels. Use of biofuels to replace petroleum is being widely subsidized in the US in order to reduce dependency on foreign oil and ultimately wean humankind's reliance on fossil fuels for our liquid fuels.

The ability of the US to produce more of its fuel needs from locally available resources allows the US to rely less on imported oil. As the technologies for biofuels develop and improve, all transportation will eventually be fueled by renewable and sustainable fuels such as ethanol, methanol, butanol and biodiesel. This will result in the dual benefit of independence from foreign oil and reduction of greenhouse gas emissions.

October 2008