A Comparative Analysis of Straw Utilization for Bioethanol and Bioelectricity as Vehicle Power Sources in China

Abstract

Bioethanol and bioelectricity are two main energy conversion processes for straw utilization. Considering the three stages to power a vehicle, namely, energy conversion, distribution, and utilization, a lifecycle comparative analysis was conducted on the two processes according to their energy efficiencies and environmental impacts in China, e.g., CO₂ and NO_x emissions and water consumption. In the base scenario, the net energy output of bioethanol was 1.95 km/kg dry biomass, which was 29.4% of that produced by the bioelectricity process. Comparing the environmental impacts of 1 kg dry biomass, the water consumption and CO₂ and NO_x emissions of bioelectricity were 21.3%, 14.9%, and 53 times higher than those of the bioethanol process, respectively. Using the 1-km vehicle drive as the function unit, water consumption and CO₂ emission of bioelectricity were 53.5% and 58.9% lower than those of bioethanol, respectively, but NO_x emission was about 15 times higher than that of bioethanol. With the possible technology innovation for each process, differences in their energy efficiencies and environmental impacts are expected to be reduced. However, bioelectricity is still more advantageous in most respects except NO_x emission. Conclusions are that straw-based E85 substitution of fossil-dependent fuel should be further expected, especially considering the high water intensity of bioethanol processing and nationwide water scarcity in China. In addition, bioelectric technology improvements in energy conversion efficiency and de-nitrification efficiency should be given priority. Likewise, technology innovation in work performance and construction of supporting service systems for electric vehicles should be prioritized.

Keywords:

• Bioelectricity
• Bioethanol
• Energy output
• CO₂
• Water consumption

ACKNOWLEDGMENTS

This research was supported by Special Research Funding of Ministry of Education titled “Path selection and policy research of bio-ethanol industry development.” The authors thank the referees for their helpful comments on the earlier version of this article.

Notes

¹A PHEV is a hybrid vehicle that utilizes rechargeable batteries, which is restored to full charge by connecting a plug to an external electric power source. PHEVs utilize the combustion engine to work as a backup when the batteries are depleted. In this article, we assumed that PHEV is powered only by battery.