Printed on paper containing at least 50% wastepaper, including 10% post consumer waste.iii Executive SummaryThe U.S. Department of Energy (DOE) promotes the production of ethanol and other liquid fuels from lignocellulosic biomass feedstocks by funding fundamental and applied research that advances the state of technology in biomass collection, conversion, and sustainability. As part of its involvement in the program, the National Renewable Energy Laboratory (NREL) investigates the production economics of these fuels.This report describes in detail one potential biochemical ethanol conversion process, conceptually based upon core conversion and process integration research at NREL. The overarching process design converts corn stover to ethanol by dilute-acid pretreatment, enzymatic saccharification, and co-fermentation. Ancillary areas-feed handling, product recovery, wastewater treatment, lignin combustion, and utilities-are also included in the design. Detailed material and energy balances and capital and operating costs were developed for the entire process, and they are documented in this report and accompanying process simulation files, which are available to the public.As a benchmark case study, this so-called technoeconomic model provides an absolute production cost for ethanol that can be used to assess its competitiveness and market potential. It can also be used to quantify the economic impact of individual conversion performance targets and prioritize these in terms of their potential to reduce cost. Furthermore, by using the benchmark as a comparison, DOE can make more informed decisions about research proposals claiming to lower ethanol production costs.Building on design reports published in 2002 and 1999, NREL, together with the subcontractor Harris Group Inc., performed a complete review of the process design and economic model for the biomass-to-ethanol process. This update reflects NREL's current vision of the biochemical ethanol process and incorporates recent progress in the conversion areas (pretreatment, conditioning, saccharification, and fermentation), optimizations in product recovery, and an improved understanding of the ethanol plant's back end (wastewater and utilities). The major process updates in this design report are the following:• Feedstock composition is updated to a carbohydrate profile closer to the expected mean.• Pretreatment reactor configuration is revised with significant new detail.• Whole-slurry pH adjustment of the pretreated biomass with ammonia replaced the previous conditioning practice of overliming, eliminating a solid-liquid separation step.

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ForewordThe purpose of this techno-economic analysis is to compare a set of biofuel conversion technologies selected for their promise and near-term technical viability. Every effort has been made to make this comparison on an equivalent basis using common assumptions. The process design and parameter value choices underlying this analysis are based on public domain literature only. For these reasons, the results are not indicative of potential performance. Rather they are meant to represent the most likely performance given the current state of public knowledge.iv List of Acronyms Executive SummaryA techno-economic analysis on the production of cellulosic ethanol by fermentation was conducted to understand the viability of liquid biofuel production processes within the next 5-8 years. Initially, 35 technologies were reviewed and a matrix was prepared considering economics, technological soundness and maturity, environmental aspects, process performance, and technical and economic risks. Then, a two-step down selection was performed to choose scenarios to be evaluated in a more detailed economic analysis. In the first screening, the lignocellulosic ethanol process was selected because it is well studied and portions of the process have been tested at pilot scales. In the second screening, seven scenarios of process variations were selected: four variations involved pretreatment (dilute acid, two-stage dilute acid, hot water, and ammonia fiber explosion) and three variations involved downstream processes (pervaporation, separate 5-carbon and 6-carbon sugar fermentation, and on-site enzyme production). Each of these scenarios was examined in detail. Given the time needed for design, construction, and startup of large process plants, plants operating in the 5-8 year timeframe would likely need to be based on recent experimental data. For this work, process designs were constrained to public data published in 2007 or earlier, without projecting for future process improvements. Economic analysis was performed for an "n th plant" (mature technology) to obtain total investment and product value (PV) (defined as value of the product needed for a net present value of zero with a 10% internal rate of return). The final selection among the scenarios was performed primarily based on the PV. Sensitivity analysis was performed on PV to assess the impact of variations in process and economic parameters. Results show that the modeled dilute acid pretreatment process without any downstream process variation had the lowest PV of $3.40/gal of ethanol (which is $5.15/gallon of gasoline equivalent, GGE) in 2007 dollars. Sensitivity analysis shows that PV is most sensitive to feedstock and enzyme costs.The cellulosic ethanol process is a new technology, for which a pioneer plant is expected to be significantly more expensive than the n th plant. To assess the impact of technology maturity on pioneer plant cost, a cost growth analysis was performed following a method documented in a RAND Corporation report. This methodology attempts ...

Key words:global warming industrial ecology renewable energy life cycle assessment (LCA) meta-analysis solar Supporting information is available on the JIE Web site SummaryPublished scientific literature contains many studies estimating life cycle greenhouse gas (GHG) emissions of residential and utility-scale solar photovoltaics (PVs). Despite the volume of published work, variability in results hinders generalized conclusions. Most variance between studies can be attributed to differences in methods and assumptions. To clarify the published results for use in decision making and other analyses, we conduct a metaanalysis of existing studies, harmonizing key performance characteristics to produce more comparable and consistently derived results.Screening 397 life cycle assessments (LCAs) relevant to PVs yielded 13 studies on crystalline silicon (c-Si) that met minimum standards of quality, transparency, and relevance. Prior to harmonization, the median of 42 estimates of life cycle GHG emissions from those 13 LCAs was 57 grams carbon dioxide equivalent per kilowatt-hour (g CO 2 -eq/kWh), with an interquartile range (IQR) of 44 to 73. After harmonizing key performance characteristics (irradiation of 1,700 kilowatt-hours per square meter per year (kWh/m 2 /yr); system lifetime of 30 years; module efficiency of 13.2% or 14.0%, depending on module type; and a performance ratio of 0.75 or 0.80, depending on installation, the median estimate decreased to 45 and the IQR tightened to 39 to 49. The median estimate and variability were reduced compared to published estimates mainly because of higher average assumptions for irradiation and system lifetime.For the sample of studies evaluated, harmonization effectively reduced variability, providing a clearer synopsis of the life cycle GHG emissions from c-Si PVs. The literature used in this harmonization neither covers all possible c-Si installations nor represents the distribution of deployed or manufactured c-Si PVs.

Printed on paper containing at least 50% wastepaper, including 10% post consumer waste.iii ForewordThe purpose of this techno-economic analysis is to compare a set of biofuel conversion technologies selected for their promise and near-term technical viability. Every effort is made to make this comparison on an equivalent basis using common assumptions. The process design and parameter value choices underlying this analysis are based on public domain literature only. For these reasons, these results are not indicative of potential performance, but are meant to represent the most likely performance given the current state of public knowledge. iv List of Acronyms Executive SummaryThis study compares capital and production costs of two biomass-to-liquid production plants based on gasification. The goal is to produce liquid transportation fuels via Fischer-Tropsch synthesis with electricity as a co-product. The biorefineries are fed by 2,000 metric tons per day of corn stover. The first biorefinery scenario is an oxygen-fed, low-temperature (870°C), nonslagging, fluidized bed gasifier. The second scenario is an oxygen-fed, high-temperature (1,300°C), slagging, entrained flow gasifier. Both are followed by catalytic Fischer-Tropsch synthesis and hydroprocessing to naphtha-range (gasoline blend stock) and distillate-range (diesel blend stock) liquid fractions. (Hydroprocessing is a set of refinery processes that removes impurities and breaks down large molecules to fractions suitable for use in commercial formulations.)Process modeling software (Aspen Plus) is utilized to organize the mass and energy streams and cost estimation software is used to generate equipment costs. Economic analysis is performed to estimate the capital investment and operating costs. A 20-year discounted cash flow rate of return analysis is developed to estimate a fuel product value (PV) at a net present value of zero with 10% internal rate of return. All costs are adjusted to the year 2007. The technology is limited to commercial technology available for implementation in the next 5-8 years, and as a result, the process design is restricted to available rather than projected data.Results show that the total capital investment required for n th plant scenarios is $610 million and $500 million for high-temperature and low-temperature scenarios, respectively. PV for the hightemperature and low-temperature scenarios is estimated to be $4.30 and $4.80 per gallon of gasoline equivalent (GGE), respectively, based on a feedstock cost of $75 per dry short ton. The main reason for a difference in PV between the scenarios is because of a higher carbon efficiency and subsequent higher fuel yield for the high-temperature scenario. Sensitivity analysis is also performed on process and economic parameters. This analysis shows that total capital investment and feedstock cost are among the most influential parameters affecting the PV, while least influential parameters include per-pass Fischer-Tropsch-reaction-conversion extent, inlet feedstock moisture, and ...

Projected life cycle greenhouse gas (GHG) emissions and net energy value (NEV) of high-ethanol blend fuel (E85) used to propel a passenger car in the United States are evaluated using attributional life cycle assessment. Input data represent national-average conditions projected to 2022 for ethanol produced from corn grain, corn stover, wheat straw, switchgrass, and forest residues. Three conversion technologies are assessed: advanced dry mill (corn grain), biochemical (switchgrass, corn stover, wheat straw), and thermochemical (forest residues). A reference case is compared against results from Monte Carlo uncertainty analysis. For this case, one kilometer traveled on E85 from the feedstock-to-ethanol pathways evaluated has 43%-57% lower GHG emissions than a car operated on conventional U.S. gasoline (base year 2005). Differences in NEV cluster by conversion technology rather than by feedstock. The reference case estimates of GHG and NEV skew to the tails of the estimated frequency distributions. Though not as optimistic as the reference case, the projected median GHG and NEV for all feedstock-to-E85 pathways evaluated offer significant improvement over conventional U.S. gasoline. Sensitivity analysis suggests that inputs to the feedstock production phase are the most influential parameters for GHG and NEV. Results from this study can be used to help focus research and development efforts.

Executive SummaryPyrolysis of biomass followed by hydroprocessing may provide infrastructure-compatible transportation fuels that present an advantage over bioethanol, which must be blended with gasoline for use in vehicles and does not address diesel demand. Recent studies analyzed the economics of pyrolysis-derived biofuels and suggested that these biofuels can be cost competitive with gasoline under "n th plant" assumptions. With these advantages, pyrolysis has garnered greater research attention. Despite this, there have been few life cycle assessments (LCA) estimating greenhouse gas (GHG) emissions and net energy value (NEV) of a pyrolysis process.In this work, an LCA of the production of gasoline and diesel from forest residues via fast pyrolysis and hydroprocessing, from production of the feedstock to end use of the fuel in a vehicle, is performed. The fast pyrolysis and subsequent hydrotreating and hydrocracking processes are based on a Pacific Northwest National Laboratory (PNNL) design report. Stages other than biofuels conversion, including forest residue production and harvesting, preprocessing, feedstock transportation, fuel distribution, and vehicle operation, are based on previous work. Probability distribution functions (PDFs) are assumed for key parameters involved in the pyrolysis process. These PDFs, along with PDFs previously used in other supply chain stages, are used as inputs for Monte Carlo uncertainty analysis.This preliminary LCA for the production of gasoline and diesel via pyrolysis and upgrading assumes grid electricity is used and supplemental natural gas is supplied to the hydrogen plant. Monte Carlo uncertainty analysis shows a range of results, with all values besting conventional gasoline in 2005. Grid electricity accounts for 27% of the net GHG emissions in the base case. A sensitivity using biomass-derived electricity shows significant improvement in GHG emissions. Further research to achieve the target fuel yields is needed to reduce the uncertainty of the GHG and NEV results. In addition, other sensitivities, such as biomass-derived hydrogen and reduction in electricity demand through process optimization, should be explored in tandem with their associated technoeconomics. . Ethanol also has a lower energy density than gasoline, which means that a vehicle travels fewer miles on a gallon of ethanol than on a gallon of gasoline. An infrastructure-compatible biofuel that substitutes for conventional gasoline or diesel would overcome these shortcomings.One way to produce infrastructure-compatible biofuels is through fast pyrolysis followed by hydrotreating and hydrocracking. In fast pyrolysis, biomass is rapidly heated to temperatures around 400°C to 500°C in the absence of oxygen, causing thermal decomposition of the biomass and ultimately resulting in a bio-oil. This bio-oil resembles crude oil in appearance but has higher oxygen content and is more acidic. To convert bio-oil to usable transportation fuels, the bio-oil is upgraded through hydrotreating and hydrocracking. In h...