biofuels

The goal of this repository is to promote transparency and ease-of-access to the U.S. Department of Energy Bioenergy Technologies Office (BETO) supported public studies involving techno-economic analysis (TEA). As such, this database summarizes the economic and technical parameters associated with the modeled biorefinery processes for the production of biofuels and bioproducts, as presented in a range of published reports and papers. The database serves as a quick reference tool by documenting and referencing the results of techno-economic analyses from the national laboratories and in peer-reviewed journals.
 
The analyses presented in this database may be distinguished in several regards, such as cost year, feedstock cost, and financial assumptions (tax rate, percent equity, project lifetime, etc.), and reflect details as they were provided in the original studies. Accordingly, the intent of this database is not to directly compare one technology pathway against another, and caution should be taken in interpreting the outputs as such.

Funding Acknowledgement
This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by  the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

In January 2017, the U.S. Department of Energy’s (DOE’s) Bioenergy Technologies Office (BETO) published a report, titled Biofuels and Bioproducts from Wet and Gaseous Waste Streams: Challenges and Opportunities. The report is the first comprehensive assessment of the resource potential and technology opportunities provided by feedstocks, including wastewater treatment-derived sludge and biosolids, animal manure, food waste, inedible fats and greases, biogas, and carbon dioxide streams. These feedstocks can be converted into renewable natural gas, diesel, and aviation fuels, or into valuable bioproducts.

Complementary to the 2016 Billion-Ton Report, this new resource assessment, conducted by the National Renewable Energy Laboratory and Pacific Northwest National Laboratory, concludes that wet and gaseous organic waste streams represent a substantial and underutilized set of feedstocks for biofuels and biopower. The analysis found that the United States has the potential to use 77 million dry tons of wet waste per year, which would generate about 1,300 trillion British thermal units (Btu) of energy. Also, gaseous feedstocks (which cannot be “dried” and therefore cannot be reported in dry tons) and other feedstocks assessed in the report could produce an additional 1,300 trillion Btu of energy—bringing the total to nearly 2.6 quadrillion Btu annually. For perspective, in 2015, the United States’ total primary energy consumption was about 97.7 quadrillion Btu.

Many waste-to-energy technologies are at an early stage and, therefore, could potentially benefit from DOE’s Small Business Innovation Research (SBIR) program, which increases U.S. private-sector commercialization of innovations to build a strong national economy. Not only are wet and gaseous waste streams available now and unlikely to diminish in the near future, finding a beneficial use for them often helps to address the unique and local challenges of disposing of them. Alternative strategies are increasingly necessary due to decreasing landfill capacity and stringent disposal regulations.

Understanding the complex interactions among food security, bioenergy sustainability, and resource management
requires a focus on specific contextual problems and opportunities. The United Nations’ 2030 Sustainable
Development Goals place a high priority on food and energy security; bioenergy plays an important role in
achieving both goals. Effective food security programs begin by clearly defining the problem and asking, ‘What
can be done to assist people at high risk?’ Simplistic global analyses, headlines, and cartoons that blame biofuels
for food insecurity may reflect good intentions but mislead the public and policymakers because they obscure
the main drivers of local food insecurity and ignore opportunities for bioenergy to contribute to solutions.
Applying sustainability guidelines to bioenergy will help achieve near- and long-term goals to eradicate hunger.
Priorities for achieving successful synergies between bioenergy and food security include the following: (1) clarifying
communications with clear and consistent terms, (2) recognizing that food and bioenergy need not compete
for land and, instead, should be integrated to improve resource management, (3) investing in technology,
rural extension, and innovations to build capacity and infrastructure, (4) promoting stable prices that incentivize
local production, (5) adopting flex crops that can provide food along with other products and services to society,
and (6) engaging stakeholders to identify and assess specific opportunities for biofuels to improve food security.
Systematic monitoring and analysis to support adaptive management and continual improvement are essential
elements to build synergies and help society equitably meet growing demands for both food and energy.

Water consumption and water quality continue to be key factors affecting environmental sustainability in biofuel production. This review covers the findings from biofuel water analyses published over the past 2 years to underscore the progress made, and to highlight advancements in understanding the interactions among increased production and water demand, water resource availability, and potential changes in water quality. We focus on two key areas: water footprint assessment and watershed modeling. Results revealed that miscanthus-, switchgrass-, and forest wood-based biofuels all have promising blue and grey water footprints. Alternative water resources have been explored for algae production, and challenges remain. A most noticeable improvement in the analysis of life-cycle water consumption is the adoption of geospatial analysis and watershed modeling to generate a spatially explicit water footprint at a finer scale (e.g., multi-state region, state, and county scales) to address the impacts of land use change and climate on the water footprint in a landscape with a mixed biofuel feedstock.

The present study experimentally investigates spark-ignited combustion with 87 AKI E0 gasoline in its neat form
and in midlevel alcohol−gasoline blends with 24% vol/vol isobutanol−gasoline (IB24) and 30% vol/vol ethanol−gasoline (E30).
A single-cylinder research engine was used with an 11.85:1 compression ratio, hydraulically actuated valves, laboratory intake air,
and was capable of external exhaust gas recirculation (EGR). Experiments were conducted with all fuels to full-load conditions
with λ = 1, using both 0% and 15% external cooled EGR. Higher octane number biofuel blends exhibited increased
stoichiometric torque capability at this compression ratio, where the unique properties of ethanol enabled a doubling of the
stoichiometric torque capability with E30 as compared to 87 AKI, up to 20 bar IMEPg (indicated mean effective pressure gross)
at λ = 1. EGR provided thermodynamic advantages and was a key enabler for increasing engine efficiency for all fuel types.
However, with E30, EGR was less useful for knock mitigation than gasoline or IB24. Torque densities with E30 with 15% EGR at
λ = 1 operation were similar or better than a modern EURO IV calibration turbo-diesel engine. The results of the present study
suggest that it could be possible to implement a 40% downsize + downspeed configuration (1.2 L engine) into a representative
midsize sedan. For example, for a midsize sedan at a 65 miles/h cruise, an estimated fuel consumption of 43.9 miles per gallon
(MPG) (engine out 102 g-CO2/km) could be achieved with similar reserve power to a 2.0 L engine with 87AKI (38.6 MPG,
engine out 135 g-CO2/km). Data suggest that, with midlevel alcohol−gasoline blends, engine and vehicle optimization can offset
the reduced fuel energy content of alcohol−gasoline blends and likely reduce vehicle fuel consumption and tailpipe CO2 emissions.

The present study experimentally investigates spark-ignited combustion with 87 AKI E0 gasoline in its neat form
and in midlevel alcohol−gasoline blends with 24% vol/vol isobutanol−gasoline (IB24) and 30% vol/vol ethanol−gasoline (E30).
A single-cylinder research engine is used with an 11.85:1 compression ratio, hydraulically actuated valves, laboratory intake air,
and was capable of external exhaust gas recirculation (EGR). Experiments were conducted with all fuels to full-load conditions
with λ = 1, using both 0% and 15% external-cooled EGR. Higher octane number biofuel blends exhibited increased
stoichiometric torque capability at this compression ratio, where the unique properties of ethanol enabled a doubling of the
stoichiometric torque capability with E30 as compared to that of 87AKI, up to 20 bar IMEPg (indicating mean effective pressure
gross) at λ = 1. The results demonstrate that for all fuels, EGR is a key enabler for increasing engine efficiency but is less useful
for knock mitigation with E30 than for 87AKI gasoline or IB24. Under knocking conditions, 15% EGR is found to offer 1°CA of
CA50 timing advance with E30, whereas up to 5°CA of CA50 advance is possible with knock-limited 87AKI gasoline. Compared
to 87AKI, both E30 and IB24 are found to have reduced adiabatic flame temperature and shorter combustion durations, which
reduce knocking propensity beyond that indicated by the octane number. However, E30+0% EGR is found to exhibit the better
antiknock properties than either 87AKI+15% EGR or IB24+15% EGR, expanding the knock limited operating range and engine
stoichiometric torque capability at high compression ratio. Furthermore, the fuel sensitivity (S) of E30 was attributed to reduced
speed sensitivity of E30, expanding the low-speed stoichiometric torque capability at high compression ratio. The results illustrate
that intermediate alcohol−gasoline blends exhibit exceptional antiknock properties and performance beyond that indicated by
the octane number tests, particularly E30.

The global indirect land use change (ILUC) implications of biofuel use in the United States of America (USA) from 2001 to 2010 are evaluated with a dynamic general equilibrium model.  The effects of biofuels production on agricultural land area vary by year; from a net expansion of 0.17ha per 1000 gallons produced (2002) to a net contraction of 0.13ha per 1000 gallons (2018) in Case 1 of our simulation.  In accordance with the general narrative about the implications of biofuel policy, agricultural land area increased in many regions of the world.  However, oil-export dependent economies experienced agricultural land contraction because of reductions in their revenues.  Reducing crude oil imports is a major goal of biofuel policy, but the land use change implications have received little attention in the literature.  Simulations evaluating the effects of doubling supply elasticities for land and fossil resources show that these parameters can significantly influence the land use change estimates.  Therefore, research that provides empirically-based and spatially-detailed agricultural land-supply curves and capability to project future fossil energy prices is critical for improving estimates of the effects of biofuel policy on land use.

This paper connects the science of sustainability theory with applied aspects of sustainability deployment. A suite of 35 sustainability indicators spanning six environmental, three economic, and three social categories has been proposed for comparing the sustainability of bioenergy production systems across different feedstock types and locations.   A recent demonstration-scale switchgrass-to-ethanol production system located in East Tennessee is used to assess the availability of sustainability indicator data and associated measurements for the feedstock production and logistics portions of the biofuel supply chain.  Knowledge pertaining to the available indicators is distributed within a hierarchical decision tree framework to generate an assessment of the overall sustainability of this no-till switchgrass production system relative to two alternative business-as-usual scenarios of unmanaged pasture and tilled corn production.  The relative contributions of the social, economic and environmental information are determined for the overall trajectory of this bioenergy system’s sustainability under each scenario.  Within this East Tennessee context, switchgrass production shows potential for improving environmental and social sustainability trajectories without adverse economic impacts, thereby leading to potential for overall enhancement in sustainability within this local agricultural system.  Given the early stages of cellulosic ethanol production, it is currently difficult to determine quantitative values for all 35 sustainability indicators across the entire biofuel supply chain.  This case study demonstrates that integration of qualitative sustainability indicator ratings may increase holistic understanding of a bioenergy system in the absence of complete information.

Developing scientific criteria and indicators should play a critical role in charting a sustainable path for the rapidly developing biofuel industry. The challenge ahead in developing such criteria and indicators is to address the limitations on data and modeling.

Defining and measuring sustainability of bioenergy systems are difficult because the systems are complex, the science is in early stages of development, and there is a need to generalize what are inherently contextspecific enterprises. These challenges, and the fact that decisions are being made now, create a need for improved communications among scientists as well as between scientists and decision makers. In order for scientists to provide information that is useful to decision makers, they need to come to an agreement on how to measure and report potential risks and benefits of diverse energy alternatives in a way that allows decision makers to compare options. Scientists also need to develop approaches that contribute information about problems and opportunities relevant to policy and decision making. The need for clear communication is especially important at this time when there is a plethora of scientific papers and reports and it is difficult for the public or decision makers to assess the merits of each analysis. We propose three communication guidelines for scientists whose work can contribute to decision making: (1) relationships between the question and the analytical approach should be clearly defined and make common sense; (2) the information should be presented in a manner that non-scientists can understand; and (3) the implications of methods, assumptions, and limitations should be clear. The scientists’ job is to analyze information to build a better understanding of environmental, cultural, and socioeconomic aspects of the sustainability of energy alternatives. The scientific process requires transparency, debate, review, and collaboration across disciplines and time. This paper serves as an introduction to the papers in the special issue on ‘‘Sustainability of Bioenergy Systems: Cradle to Grave’’ because scientific communication is essential to developing more sustainable energy systems. Together these four papers provide a framework under which the effects of bioenergy can be assessed and compared to other energy alternatives to foster sustainability.