Defossilisation assessment of biodiesel life cycle production using the ExROI indicator

Ensuring the sustainability of biofuels is a mandatory requisite for the EU Member States. The EU Renewables Directive focuses on the reduction of greenhouse gas emissions and the protection of high biodiversity and carbon stock lands. The current framework does not consider the consumption of non-renewable resources. Starting from the paper "Assessment of biodiesel energy sustainability using the ExROI concept" published in Energy [4], which defined the ExROI (Exergy Return on Investment) indicator and applied it to well-to-tank biodiesel production from rapeseed, sunflower and palm, this paper proposes extending the use of ExROI, which involves exergy cost accounting, to the life cycle; extending the calculations to soybean and used cooking oil; and assessing ways to "defossilise" the cycles. This paper demonstrates that the ExROI is a better indicator than the EROI (Energy Return on Investment) which only considers energy flows. Also, it shows that biodiesel life cycles have positive ExROI values and that the ExROI value can be improved up to 26.51; i.e. for one unit of non-renewable sources invested in the process more than 26 units of biodiesel are obtained. This means that biodiesel can be around five times more sustainable than fossil diesel, from the viewpoint of non-renewable resources consumption.