Energy content of biodiesel is about 10% lower than for ordinary diesel. Energy efficiency is difficult to assess in the case of alternative fuels since there is no reasonable point of reference. An energy balance of biodiesel has to take into account the energy input needed to produce the rape and process it to obtain RME. This is best be done by a CO₂ balance.

CO₂ balance

A CO₂ comparison between RME and fossil diesel has to take into account CO₂ emissions from the whole energy chain (i.e. caused by the production and processing and transport of the respective fuel). A very thorough environmental balance by the German IFEU institute revealed a specific CO₂ advantage of RME over diesel between 30 and 80 % per kilogram of fuel (depending on the energetic use of the by-products). However, the total possible savings in CO₂ are seen as very modest due to the limited agricultural capacity to grow rape.

Toxic emissions

Toxic emissions from the combustion of RME as compared to diesel:

• CO: reduced (- 10-12%)
• HC: reduced (- 10-35%)
• NOx: increased ( 8-12%)
• Particulate: reduced (- 24-36%)
• Soot: reduced (- 50-52%)
• SO2: reduced (almost no emission)

Pollution effects of rape cultivation

The cultivation of rape causes the emission of N2O (laughing-gas) which is also a greenhouse gas. Furthermore the large extent of land use and the extensive utilization of fertilizers and pesticides are negative from an environmental point of view.

Eco-balance

A thorough study by the German IFEU institute concluded that RME “holds no distinct advantages for the environment” (Umweltbundesamt 2001).