Energy and carbon accounting to compare bioenergy crops

To compare the utility of current and future biofuels and biofuel feedstocks in an objective manner can be extremely challenging. This challenge exists because agricultural data are inherently variable, experimental techniques are crop-dependent, and the literatures usually report relative, rather than absolute, values. Here, we discuss the 'PETRO approach', a systematic approach to evaluate new crops. This approach accounts for not only the capture of solar energy but also the capture of atmospheric carbon (as CO₂) to generate a final carbon-based liquid fuel product. The energy yield, per unit area, of biofuel crops grown in different climate zones can thus be benchmarked and quantitatively compared in terms of both carbon gain and solar energy conversion efficiency.