“Net energy analysis is simple and has great intuitive appeal, but it is also dead wrong and dangerously misleading – net energy must be eliminated from our discourse.”
Net energy is the difference between the energy embodied in a fuel and then subtracting the energy supplied by fossil fuels that was needed to create the new fuel.
The calculation is often carried out in a way that leaves grain ethanol with a net energy of –29%, giving the impression it uses more fossil fuels to produce it that the new fuel supplies. The figure is often used by opponents of biofuels to pour scorn on the new products, but Dale argues it is “likely to be irrelevant and misleading”.
Instead, in a new journal 'Biofuels, Bioproducts and Biorefining,' Dale recommends comparing fuels by assessing how much petroleum fuel each can replace, or by calculating how much CO2 each produces per km driven. The problem with net energy, says Dale, is that it makes an assumption that all sources of energy have equal value.
“This assumption is completely wrong. All energy sources are not equal – one unit of energy from petrol is much more useful than the same amount of energy in coal…and that makes petrol much more valuable,” says Dale.
For evidence, he points to the markets, where a unit of energy from gas, petrol and electricity are worth 3.5, 5 and 12 times as much as a unit of energy from coal, respectively.
“Clear thinking shows that we value the services that energy can perform, not the energy per se, so it would be better to compare fuels by the services that each provides…not on a straight energy basis,” says Dale.
For example, biofuels could be rated on how much petroleum use they can displace or their greenhouse gas production compared with petroleum. His calculations indicate that every MJ of ethanol can displace 28MJ of petroleum, greatly extending our existing supplies of petroleum.
Using corn ethanol provides an 18% reduction in greenhouse gases compared with petrol, while fibre-produced ethanol gives an 88% reduction compared to petrol.
