First-order estimates of the costs, input-output energy analysis, and energy returns on investment of conventional and emerging biofuels feedstocks

Katrina Christiansen,Guiping Hu,Robert Anex,David Raj Raman

doi:10.18331/brj2018.5.4.4

Katrina Christiansen, Guiping Hu + Show 2 more

Open Access

https://doi.org/10.18331/brj2018.5.4.4

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Abstract

Here we report on a static, algebraic, spreadsheet-implemented modeling approach to estimate the costs, energy inputs and outputs, and global warming potential of biomass feedstocks. Inputs to the model included literature sourced data for: environmental factors, crop physiological-parameters such as radiation use efficiency and water use efficiency, and crop cost components. Using an energy-input-output life-cycle-assessment approach, we calculated the energy associated with each cost component, allowing an estimate of the total energy required to produce the crop and fuel alongside the energy return on investment. We did this for crop scenarios in the upper Midwest US and Far West US (for algae). Our results suggested that algae are capable of the highest areal biomass production rates of 120 MG/(ha·a), ten times greater than Maize. Algal fuel systems had the highest costs, ranging from 28 to 65 US $/GJ, compared to 17 US $/GJ for Maize ethanol. Algal fuel systems had the lowest energy returns on investment, nearly 0, compared to 25 for Switchgrass to ethanol. The carbon equivalent emissions associated with the production schemes predictions ranged from 40 (Maize) to 180 (algae PBR) CO2eq/GJnet. The promise of low cost fuel and carbon neutrality from algae is demonstrated here to be extremely challenging for fundamental reasons related to the capital-intensive nature of the cultivation system.

Highlights

Photosynthetically-derived carbon will provide critical material and energy resources for humanity in the 21st century, and beyond
The likelihood is low that these approaches, even collectively, can stave off major climate changes that will severely impact existing global agricultural production (Schuur et al, 2008; Gornall et al, 2010; Jaggard et al, 2010; Lesk et al, 2016), such approaches are still worthy of exploration as they can be part of an effort to reduce the degree of warming that occurs (Pacala, et al, 2004)
In addition to a strong debate on these claims in the scientific literature, some have sought to address the weaknesses of starch-ethanol by developing biofuel production systems that convert into fuel the lignocellulosic portion of Maize, or the lignocellulosic biomass derived from perennial crops, or the oil and lignocellulosic biomass formed by microalgae (Pienkos and Darzins, 2009)

Summary

Introduction

Photosynthetically-derived carbon will provide critical material and energy resources for humanity in the 21st century, and beyond. In addition to a strong debate on these claims in the scientific literature, some have sought to address the weaknesses of starch-ethanol by developing biofuel production systems that convert into fuel the lignocellulosic portion of Maize, or the lignocellulosic biomass derived from perennial crops, or the oil and lignocellulosic biomass formed by microalgae (Pienkos and Darzins, 2009). This plethora of approaches to biofuel production has made it difficult to understand the fundamental performance of and barriers to these different feedstocks. The purpose of this study was to use a generalized modeling approach to provide insight into the strengths and weaknesses of these potential technologies

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