greenhouse gas

Several EU countries import wood pellets from the south-eastern United States. The imported wood pellets are (co-)fired in power plants with the aim of reducing overall greenhouse gas (GHG) emissions from electricity and meeting EU renewable energy targets. To assess whether GHG emissions are reduced and on what timescale, we construct the GHG balance of wood-pellet electricity. This GHG balance consists of supply chain and combustion GHG emissions, carbon sequestration during biomass growth and avoided GHG emissions through replacing fossil electricity. We investigate wood pellets from four softwood feedstock types: small roundwood, commercial thinnings, harvest residues and mill residues. Per feedstock, the GHG balance of wood-pellet electricity is compared against those of alternative scenarios. Alternative scenarios are combinations of alternative fates of the feedstock materials, such as in-forest decomposition, or the production of paper or wood panels like oriented strand board (OSB). Alternative scenario composition depends on feedstock type and local demand for this feedstock. Results indicate that the GHG balance of wood-pellet electricity equals that of alternative scenarios within 0–21 years (the GHG parity time), after which wood-pellet electricity has sustained climate benefits. Parity times increase by a maximum of 12 years when varying key variables (emissions associated with paper and panels, soil carbon increase via feedstock decomposition, wood-pellet electricity supply chain emissions) within maximum plausible ranges. Using commercial thinnings, harvest residues or mill residues as feedstock leads to the shortest GHG parity times (0–6 years) and fastest GHG benefits from wood-pellet electricity. We find shorter GHG parity times than previous studies, for we use a novel approach that differentiates feedstocks and considers alternative scenarios based on (combinations of) alternative feedstock fates, rather than on alternative land uses. This novel approach is relevant for bioenergy derived from low-value feedstocks.

The estimation of greenhouse gas (GHG) emissions from a change in land-use and management resulting from growing biofuel feedstocks has undergone extensive – and often contentious – scientific and policy debate. Emergent renewable fuel policies require life cycle GHG emission accounting that includes biofuel-induced global land-use change (LUC) GHG emissions. However, the science of LUC generally, and biofuels-induced LUC specifically, is nascent and underpinned with great uncertainty. We critically review modeling approaches employed to estimate biofuel-induced LUC and identify major challenges, important research gaps, and limitations of LUC studies for transportation fuels. We found LUC modeling philosophies and model structures and features (e.g. dynamic vs. static model) significantly differ among studies. Variations in estimated GHG emissions from biofuel-induced LUC are also driven by differences in scenarios assessed, varying assumptions, inconsistent definitions (e.g. LUC), subjective selection of reference scenarios against which (marginal) LUC is quantified, and disparities in data availability and quality. The lack of thorough sensitivity and uncertainty analysis hinders the evaluation of plausible ranges of estimates of GHG emissions from LUC. The relatively limited fuel coverage in the literature precludes a complete set of direct comparisons across alternative and conventional fuels sought by regulatory bodies and researchers.

Improved modeling approaches, consistent definitions and classifications, availability of high-resolution data on LUC over time, development of standardized reference and future scenarios, incorporation of non-economic drivers of LUC, and more rigorous treatment of uncertainty can help improve LUC estimates in effectively achieving policy goals.

The U.S. biomass resource can be used several ways that provide domestic, renewable energy to users. Understanding the capacity of the biomass resource, its potential in energy markets, and the most economic utilization of biomass is important in policy development and project selection. This study analyzed the potential for biomass within markets and the competition between them. The study found that biomass has the potential to compete well in the jet fuel and gasoline markets, penetration of biomass in markets is likely to be limited by the size of the resource, and that biomass is most cost effectively used for fuels instead of power in mature markets unless carbon capture and sequestration is available and the cost of carbon is around $80/metric ton CO2e.
 
Biomass Utilization Issues
Biomass is a limited resource with many competing uses. Its allocation for fuel, power, and products depends upon characteristics of each of these markets, their interactions, and policies affecting these markets. In order to better understand competition for biomass among markets and the potential for biofuel as a market-scale alternative to petroleum-based fuels, the Transportation Energy Futures (TEF) study created a unique modeling tool to analyze the impact of these multiple demand areas.
 
There are compelling reasons for use of biomass in each of these three markets:
• Fuel: Biomass is the primary renewable resource that can be used to generate liquid fuels for today’s vehicles and infrastructure.
• Power: Technology is currently available to enable co-firing with coal, reducing the carbon intensity of baseload electricity and providing one of the few renewable dispatchable options.
• Products: Mixtures of chemicals with carbon-hydrogen-oxygen bonds such as those found in biomass are too valuable to burn.
 
Federal policy and activities have supported both biofuels and biopower. Relevant policies include the renewable fuels standard, the renewables portfolio standard, the clean energy standard, and many state and regional greenhouse gas (GHG) policies. Goals for biofuel policies include reduction in petroleum and, especially, petroleum imports to increase energy security. Other goals for biofuel policies focus on environmental and economic concerns, GHG emissions reduction, and diversification of agricultural products. Goals for biopower policies include displacement of coal for environmental concerns and GHG reduction. In the past two decades, the U.S. Department of Energy’s research and development (R&D)

The petroleum-based transportation fuel system is complex and highly developed, in contrast to the nascent low-petroleum, low-carbon alternative fuel system. This report examines how expansion of the low-carbon transportation fuel infrastructure could contribute to deep reductions in petroleum use and greenhouse gas (GHG) emissions across the U.S. transportation sector. Three low-carbon scenarios, each using a different combination of low-carbon fuels, were developed to explore infrastructure expansion trends consistent with a study goal of reducing transportation sector GHG emissions to 80% less than 2005 levels by 2050.1 This goal was for analytic purposes only. These scenarios were compared to a business-as-usual (BAU) scenario and were evaluated with respect to four criteria: fuel cost estimates, resource availability, fuel production capacity expansion, and retail infrastructure expansion.
 
Initial evaluations of these four criteria enable consideration of screening-level questions about fuel infrastructure in the low-petroleum, low-carbon scenarios:
1. How do alternative fuel costs compare to conventional fuel costs?
2. Are low-carbon resources sufficient?
3. How does expansion of alternative fuel production capacity compare to conventional production capacity replacements, upgrades, and expansion?
4. How do costs of providing alternative fuel retail infrastructure compare to conventional retail infrastructure?
 
Although definitive comparisons are not possible in this screening study, results suggest that expansion of the retail infrastructure for alternative fuels may pose greater issues than fuel costs, resources, or production capacity. The study does not address market barriers and transition costs associated with the development of new advanced vehicle and low-carbon fuel markets, so fuel cost estimates do not reflect investment risks or projected fuel prices. However, an evaluation of each scenario suggests that the goal of a reduction of 80% in GHGs can be reached while maintaining total fuel costs that are ultimately lower than BAU fuel cost projections without imposing excessive demands on energy resources such as biomass, natural gas, or renewable electricity systems.
 
The amount of new fuel production capacity required [e.g., billions of gallons of gasoline equivalent energy (BGGE) per year] in the low-carbon scenarios is comparable to those for conventional fuels in the BAU scenario, despite the transition to different fuels, because fuel demand in the low-carbon scenarios is lower. Expansion of retail infrastructure, on the other hand, may prove challenging in terms of spatial coverage and sustainable business models for retail outlets. Suggestions in the study for further analysis call for improved cost estimates, an improved understanding of the influence of refueling infrastructure on consumer vehicle purchase decisions, exploration of the potential role of public-private partnerships in infrastructure planning and expansion, and spatial and temporal market and infrastructure expansion trends.

Land-use change (LUC) is a contentious policy issue because of its uncertain, yet potentially substantial, impact on bioenergy climate change benefits. Currently, the share of global GHG emissions from biofuels-induced LUC is small compared to that from LUC associated with food and feed production and other human-induced causes. However, increasing demand for biofuels derived from feedstocks grown on agricultural land could increase this contribution. No consensus has emerged on how to appropriately isolate and quantify LUC impacts of bioenergy from those of other LUC drivers. We reviewed the literature and illustrate some strategies to minimize bioenergy-related LUC, including ways to increase land’s total productivity and the design and implementation of effective land use policies. The best strategies to reduce LUC risk will vary geographically, requiring a balancing of the advantages and limitations of potential options within the local context together with other goals (social, environmental, economic, energy security, and diversification).