Palm oil from South-East Asia, sugarcane from Brazil and sweet sorghum in China are the most sustainable energy crops at present. Maize from the US and wheat in Europe have a much more negative environmental impact. This conclusion was drawn by the Plant Production Systems chair group, after testing nine energy crops against nine sustainability criteria. The findings will be published soon in Biomass and Bioenergy.
'We only assessed the production ecology of the crops, and not the socio-economic consequences or the impact on biodiversity', explains author Sander de Vries. 'If you have a tract of virgin land for energy production, your best option is to grow oil palms. Sugar cane is very good too.' An advantage of these crops is that their residues produce enough energy to extract the oil and ethanol. In order to process maize into ethanol, the US currently has to use supplementary fossil fuels, as the crop residues are not used to generate energy. It is also important that enough crop residues are left behind in the fields to keep up the level of organic matter in the soils.
We are now waiting for a second generation of energy crops, in which the cellulose in the crop residues can be turned into ethanol. Then Europe and the US will also be able to produce much more energy per hectare with crops such as elephant grass, says De Vries. Until then, the best bet is to mix energy from certified sustainable sugar cane and oil palms, he says, as these crops get the most energy out of each hectare, and do the least environmental damage per litre of fuel.
De Vries conducted a literature study and compiled an overview of earlier research on the environmental impact of various energy crops. 'My way of comparing and ranking is original, he says. He points to his spider diagrams which show the production ecology scores of the energy crops at a glance.
The article in Biomass and Bioenergy.