Energy and greenhouse gas balance of the use of forest residues for bioenergy production in the UK

Life cycle analysis is used to assess the energy requirements and greenhouse gas (GHG) emissions associated with extracting UK forest harvesting residues for use as a biomass resource. Three forest harvesting residues were examined (whole tree thinnings, roundwood and brash bales), and each have their own energy and emission profile. The whole forest rotation was examined, including original site establishment, forest road construction, biomass harvesting during thinning and final clear-fell events, chipping and transportation. Generally, higher yielding sites give lower GHG emissions per ‘oven dried tonne’ (ODT) forest residues, but GHG emissions ‘per hectare’ are higher as more biomass is extracted. Greater quantities of biomass, however, ultimately mean greater displacement of conventional fuels and therefore greater potential for GHG emission mitigation. Although forest road construction and site establishment are “one off” events they are highly energy-intensive operations associated with high diesel fuel consumption, when placed in context with the full forest rotation, however, their relative contributions to the overall energy requirements and GHG emissions are small. The lower bulk density of wood chips means that transportation energy requirements and GHG emissions are higher compared with roundwood logs and brash bales, suggesting that chipping should occur near the end-user of application.     

Greenhouse gas reporting for biofuels: A comparison between the RED,RTFO and PAS2050 methodologies

Biofuels have been identified as a potential short-term solution for reducing greenhouse gas (GHG) emissions from road transport. Currently, ‘1st generation’ biofuels are produced from food crops, but there are concerns with the indirect effects of utilising edible crops for fuel. There is increased interest in producing ‘2nd generation’ biofuels from woody crops and straw, as these can be grown on lower grade land or do not compete directly with food. In order to ensure that biofuels actually deliver emission savings, the overall GHG balance of producing them must be calculated accurately, and compared with conventional fossil fuels. The GHG balance can vary significantly however, depending on biomass type, the production processes, the indirect effects, and also by the method by which the GHG emission balance is calculated. Currently, in the UK, there are three main GHG methodologies that potentially affect biofuel producers. Each has a different approach to measure GHG emissions from biofuel production, and each provides a different result, causing difficulties for policy makers. This study performs a partial life cycle assessment for bioethanol production from wheat grain and wheat straw to demonstrate the variability of the results between methodologies.     

Sub-surface soil carbon changes affects biofuel greenhouse gas emissions

Changes in direct soil organic carbon (SOC) can have a major impact on overall greenhouse gas (GHG) emissions from biofuels when using life-cycle assessment (LCA). Estimated changes in SOC, when accounted for in an LCA, are typically derived from near-surface soil depths (<30 cm). Changes in sub-surface soil depths (>30 cm) could have a large positive or negative impact on overall GHG emissions from biofuels that are not always accounted for. Here, we evaluate how sub-surface SOC changes impact biofuel GHG emissions for corn (Zea mays L.) grain, corn stover, and switchgrass (Panicum virgatum L.) using the (Greenhouse Gases, Regulated Emissions, and Energy Use in the Transportation) GREET model. Biofuel GHG emissions showed as much as a 154% difference between using near-surface SOC stocks changes only or when accounting for both near- and sub-surface SOC stock changes. Differences in GHG emissions highlight the importance of accounting for sub-surface SOC changes especially in bioenergy cropping systems with potential for soil C storage to deeper soil depths.     

Economics of herbaceous bioenergy crops for electricity generation: Implications for greenhouse gas mitigation

This paper examines the optimal land allocation for two perennial crops, switchgrass and miscanthus that can be co-fired with coal for electricity generation. Detailed spatial data at county level is used to determine the costs of producing and transporting biomass to power plants in Illinois over a 15-year period. A supply curve for bioenergy is generated at various levels of bioenergy subsidies and the implications of production for farm income and greenhouse gas (GHG) emissions are analyzed. GHG emissions are estimated using lifecycle analysis and include the soil carbon sequestered by perennial grasses and the carbon emissions displaced by these grasses due to both conversion of land from row crops and co-firing the grasses with coal. We find that the conversion of less than 2% of the cropland to bioenergy crops could produce 5.5% of the electricity generated by coal-fired power plants in Illinois and reduce carbon emissions by 11% over the 15-year period. However, the cost of energy from biomass in Illinois is more than twice as high as that of coal. Costly government subsidies for bioenergy or mandates in the form of Renewable Portfolio Standards would be needed to induce the production and use of bioenergy for electricity generation. Alternatively, a modest price for GHG emissions under a cap-and-trade policy could make bioenergy competitive with coal without imposing a fiscal burden on the government.     

Prospects for Jatropha biofuels in Tanzania: An analysis with Strategic Niche Management

The paper reports on research in Tanzania about the scope for developing biofuels from an oil-seed bearing plant called Jatropha curcas Linnaeus. The plant is widely seen to have potential to help combat the greenhouse effect, help to stop local soil erosion, create additional income for the rural poor, and provide a major source of energy both locally and internationally. The principal analytic tool is Strategic Niche Management (SNM), an approach rooted in evolutionary innovation theory. We analyse how the scope for an energy transition is influenced by factors at three societal levels: the overarching ‘landscape’; the sectoral setting or ‘regime’; and the ‘niche’ level where the innovation develops and diffuses. Valuable niche processes were found in a few areas, especially in cultivation, but we conclude that there are still many obstacles in Tanzania's prevailing energy regime. The development of Jatropha biofuels is still in an early phase. We list policy recommendations and discuss some methodological issues arising from the use of SNM.     

Change in carbon footprint of canola production in the Canadian Prairies from 1986 to 2006

Accounting for greenhouse gas (GHG) emissions at the production stage of a bioenergy crop is essential for evaluating its eco-efficiency. The objective of this study was to calculate the change in GHG emissions for canola (Brassica napus L.) production on the Canadian Prairies from 1986 to 2006. Net GHG emissions in the sub-humid and semi-arid climatic zones were estimated for fallow-seeded and stubble-seeded canola in intensive-, reduced- and no-tillage systems, with consideration given to emissions associated with synthetic nitrogen (N) fertilizer input, mineralized N from crop residues, N leaching and volatilization, farm operations, the manufacturing and transportation of fertilizer, agrochemicals and farm machinery, and emission and removal of CO₂ associated with changes in land use (LUC) and land management (LMC). The GHG emissions on an area basis were higher in stubble-seeded canola than in fallow-seeded canola but, the opposite was true on a grain dry matter (DM) basis. Nitrous oxide emissions associated with canola production, CO₂ emissions associated with farm energy use and the manufacturing of synthetic N fertilizer and its transportation contributed 49% of the GHG emissions in 1986 which increased to 66% in 2006. Average CO₂ emissions due to LUC decreased from 27% of total GHG emissions in 1986 to 8% in 2006 and soil C sequestration due to LMC increased from 8% to 37%, respectively. These changes caused a reduction in net GHG emission intensities of 40% on an area basis and of 65% on a grain DM basis. Despite the reduction in GHG emission intensities, GHG emissions associated with canola in the Prairies increased from 3.4 Tg CO₂ equiv in 1986 to 3.8 Tg CO₂ equiv in 2006 because of the more than doubling of canola production.     

Utilization of carbon-negative biofuels from low-input high-diversity grassland biomass for energy in China

This paper analyzes utilization of carbon-negative biofuels from low-input high-diversity grassland biomass on degraded lands (LIHD) for energy including energy equivalent to green house gases (GHG) capture and storage. The results show that the energy output of LIHD biomass on degraded soil is nearly equal to that of ethanol from conventional corn grain on fertile soil. It has also been shown that LIHD biofuel is far more economical than the conventional biofuels such as corn ethanol or soybean biodiesel.China is a large agriculturally developing country, with its rural area largely populated and vast land degraded. It is in this respect that we analyzed the utilization of LIHD. The potential of using energy from LIHD biomass on degraded lands in China is estimated. The results show that the potential energy production of LIHD biomass reaches 6350971.32 TJ year^?1, accounting for about 15% of China’s energy consumption in 2002.     

Life cycle assessment of greenhouse gas emissions of feedlot manure management practices: Land application versus gasification

Animal waste is an important source of anthropogenic GHG emissions, and in most cases, manure is managed by land application. Nevertheless, due to the huge amounts of manure produced annually, alternative manure management practices have been proposed, one of which is gasification, aimed to convert manure into clean energy-syngas. Syngas can be utilized to provide energy or power. At the same time, the byproduct of gasification, biochar, can be transported back to fields as a soil amendment. Environmental impacts are crucial in selecting the appropriate manure strategy. Therefore, GHG emissions during manure management systems (land application and gasification) were evaluated and compared by life cycle assessment (LCA) in our study. LCA is a universally accepted tool to determine GHG emissions associated with every stage of a system. Results showed that the net GHG emissions in land application scenario and gasification scenario were 119 and -643 kg CO₂-eq for one tonne of dry feedlot manure, respectively. Moreover, sensitive factors in the gasification scenario were efficiency of the biomass integrated gasification combined cycle (BIGCC) system and energy source of avoided electricity generation. Overall, due to the environmental effects of syngas and biochar, gasification of feedlot manure is a much more promising technique as a way to reduce GHG emissions than is land application.     

Getting ready for carbon capture and storage through a ‘CCS (Carbon Capture and Storage) Ready Hub’: A case study of Shenzhen city in Guangdong province, China

China has been building approximately 1 GW of new coal-fired power plant per week since 2005. Power plants now in construction may continue to operate until 2040. “CCS (Carbon Capture and Storage) Ready” enables and eases the subsequent retrofitting of a plant to be able to capture carbon dioxide later in that plant’s lifetime. Building on the definitions of the IEA GHG (IEA Greenhouse Gas Programme) and GCCSI (Global Carbon Capture and Storage Institute), this study suggests a novel concept ‘CCS Ready Hub’ for implementing CCS Ready. A CCS Ready Hub not only includes a number of new coal-fired power plants but also integrates other existing stationary carbon dioxide emissions sources into the planning for potential infrastructure. We conducted a case study of Guangdong province in China with a detailed engineering and economic assessment in Shenzhen City. The study first reviewed the potential storage sites and analysed the existing stationary emissions sources in Guangdong using a GIS (Geographic Information System) approach. Thereafter, we focused on investigating the economic benefits of a ‘CCS Ready Hub’ at a potential 4 GW new USCPC (ultra-supercritical pulverised coal-fired) power plant in Shenzhen. Using the cost of carbon dioxide avoidance in 2020 as a criterion, we found that the concept of a CCS Ready Hub to finance CCS Ready at a regional planning level rather than at an individual plant is preferred since it significantly reduces the overall cost of building an integrated CCS system to reduce carbon emissions in the future.     

Evaluating the effectiveness of urban energy conservation and GHG mitigation measures: The case of Xiamen city,China

To assess the effectiveness of urban energy conservation and GHG mitigation measures, a detailed Long-range Energy Alternatives Planning (LEAP) model is developed and applied to analyze the future trends of energy demand and GHG emissions in Xiamen city. Two scenarios have been designed to describe the future energy strategies in relation to the development of Xiamen city. The ‘Business as Usual’ scenario assumes that the government will do nothing to influence the long-term trends of urban energy demand. An ‘Integrated’ scenario, on the other hand, is generated to assess the cumulative impact of a series of available reduction measures: clean energy substitution, industrial energy conservation, combined heat and power generation, energy conservation in building, motor vehicle control, and new and renewable energy development and utilization. The reduction potentials in energy consumption and GHG emissions are estimated for a time span of 2007–2020 under these different scenarios. The calculation results in Xiamen show that the clean energy substitution measure is the most effective in terms of energy saving and GHG emissions mitigation, while the industrial sector has the largest abatement potential.     

Primary energy and greenhouse gas implications of increasing biomass production through forest fertilization

In this study we analyze the primary energy and greenhouse gas (GHG) implications of increasing biomass production by fertilizing 10% of Swedish forest land. We estimate the primary energy use and GHG emissions from forest management including production and application of N and NPK fertilizers. Based on modelled growth response, we then estimate the net primary energy and GHG benefits of using biomaterials and biofuels obtained from the increased forest biomass production. The results show an increased annual biomass harvest of 7.4 million t dry matter, of which 41% is large-diameter stemwood. About 6.9 PJ/year of additional primary energy input is needed for fertilizer production and forest management. Using the additional biomass for fuel and material substitution can reduce fossil primary energy use by 150 or 164 PJ/year if the reference fossil fuel is fossil gas or coal, respectively. About 22% of the reduced fossil energy use is due to material substitution and the remainder is due to fuel substitution. The net annual primary energy benefit corresponds to about 7% of Sweden's total primary energy use. The resulting annual net GHG emission reduction is 11.9 million or 18.1 million tCO_2equiv if the reference fossil fuel is fossil gas or coal, respectively, corresponding to 18% or 28% of the total Swedish GHG emissions in 2007. A significant one-time carbon stock increase also occurs in wood products and forest tree biomass. These results suggest that forest fertilization is an attractive option for increasing energy security and reducing net GHG emission.     

Good or bad bioethanol from a greenhouse gas perspective – What determines this?

The purpose of this study is to describe how the greenhouse gas (GHG) benefits of ethanol from agricultural crops depend on local conditions and calculation methods. The focus is mainly on the fuels used in the ethanol process and biogenic GHG from the soils cultivated. To ensure that “good” ethanol is produced, with reference to GHG benefits, the following demands must be met: (i) ethanol plants should use biomass and not fossil fuels, (ii) cultivation of annual feedstock crops should be avoided on land rich in carbon (above and below ground), such as peat soils used as permanent grassland, etc., (iii) by-products should be utilised efficiently in order to maximise their energy and GHG benefits and (iv) nitrous oxide emissions should be kept to a minimum by means of efficient fertilisation strategies, and the commercial nitrogen fertiliser utilised should be produced in plants which have nitrous oxide gas cleaning. Several of the current ethanol production systems worldwide fullfill the majority of these demands, whereas some production systems do not. Thus, the findings in this paper helps identifying current “good” systems, how today’s “fairly good” systems could be improved, and which inherent “bad” systems that we should avoid.     

Reduction potentials of energy demand and GHG emissions in China's road transport sector

Rapid growth of road vehicles, private vehicles in particular, has resulted in continuing growth in China's oil demand and imports, which has been widely accepted as a major factor effecting future oil availability and prices, and a major contributor to China's GHG emission increase. This paper is intended to analyze the future trends of energy demand and GHG emissions in China's road transport sector and to assess the effectiveness of possible reduction measures. A detailed model has been developed to derive a reliable historical trend of energy demand and GHG emissions in China's road transport sector between 2000 and 2005 and to project future trends. Two scenarios have been designed to describe the future strategies relating to the development of China's road transport sector. The ‘Business as Usual’ scenario is used as a baseline reference scenario, in which the government is assumed to do nothing to influence the long-term trends of road transport energy demand. The ‘Best Case’ scenario is considered to be the most optimized case where a series of available reduction measures such as private vehicle control, fuel economy regulation, promoting diesel and gas vehicles, fuel tax and biofuel promotion, are assumed to be implemented. Energy demand and GHG emissions in China's road transport sector up to 2030 are estimated in these two scenarios. The total reduction potentials in the ‘Best Case’ scenario and the relative reduction potentials of each measure have been estimated.     

A conceptual lignocellulosic ‘feed+fuel’ biorefinery and its application to the linked biofuel and cattle raising industries in Brazil

It has been argued by some that the substitution of biofuels for gasoline could increase greenhouse gas (GHG) emissions, rather than reduce them. The increase is attributed to the indirect land use change effects of planting new grain and corn crops around the world to replace those progressively being devoted to ethanol production. In this paper, indirect effects are minimised by allowing land to be used for both food and fuel, rather than for one or the other. We present a sugarcane ‘feed+fuel’ biorefinery, which produces bioethanol and yeast biomass, a source of single-cell protein (SCP), that can be used as a high-protein animal feed supplement. The yeast SCP can partially substitute for grass in the feed of cattle grazing on pasture and thereby potentially release land for increased sugarcane production, with minimal land use change effects. Applying the concept conservatively to the Brazilian ethanol and livestock industry our model demonstrates that it would be technically feasible to raise ethanol production threefold from the current level of 27 GL to over 92 GL. The extra ethanol would meet biofuel market mandates in the US without bringing any extra land into agricultural or pastoral use. The analysis demonstrates a viable way to increase biofuel and food production by linking two value chains as called for by industrial ecology studies.     

Reducing life cycle greenhouse gas emissions of corn ethanol by integrating biomass to produce heat and power at ethanol plants

A life-cycle assessment (LCA) of corn ethanol was conducted to determine the reduction in the life-cycle greenhouse gas (GHG) emissions for corn ethanol compared to gasoline by integrating biomass fuels to replace fossil fuels (natural gas and grid electricity) in a U.S. Midwest dry-grind corn ethanol plant producing 0.19 hm³ y⁻¹ of denatured ethanol. The biomass fuels studied are corn stover and ethanol co-products [dried distillers grains with solubles (DDGS), and syrup (solubles portion of DDGS)]. The biomass conversion technologies/systems considered are process heat (PH) only systems, combined heat and power (CHP) systems, and biomass integrated gasification combined cycle (BIGCC) systems. The life-cycle GHG emission reduction for corn ethanol compared to gasoline is 38.9% for PH with natural gas, 57.7% for PH with corn stover, 79.1% for CHP with corn stover, 78.2% for IGCC with natural gas, 119.0% for BIGCC with corn stover, and 111.4% for BIGCC with syrup and stover. These GHG emission estimates do not include indirect land use change effects. GHG emission reductions for CHP, IGCC, and BIGCC include power sent to the grid which replaces electricity from coal. BIGCC results in greater reductions in GHG emissions than IGCC with natural gas because biomass is substituted for fossil fuels. In addition, underground sequestration of CO₂ gas from the ethanol plant’s fermentation tank could further reduce the life-cycle GHG emission for corn ethanol by 32% compared to gasoline.     

Missing carbon reductions? Exploring rebound and backfire effects in UK households

Households are expected to play a pivotal role in reducing the UK's greenhouse gas (GHG) emissions, and the UK Government is encouraging specific household actions to help meet its targets. However, due to the rebound effect, only a portion of the GHG emission reductions estimated by simple engineering calculations are generally achieved in practice. For example, replacing short car journeys by walking or cycling reduces consumption of motor fuels. But this frees up money that may be spent on, for example, purchasing extra clothes or flying on vacation. Alternatively, the money may be put into savings. Since all of these options lead to GHG emissions, total GHG savings may be less than anticipated. Indeed, in some instances, emissions may increase—a phenomenon known as ‘backfire’. We estimate that the rebound effect for a combination of three abatement actions by UK households is approximately 34%. Targeting re-spending on goods and services with a low GHG intensity reduces this to a minimum of around 12%, while re-spending on goods and services with a high GHG intensity leads to backfire. Our study highlights the importance of shifting consumption to lower GHG intensive categories and investing in low carbon investments.     

Does the Gold Standard label hold its promise in delivering higher Sustainable Development benefits? A multi-criteria comparison of CDM projects

The Clean Development Mechanism (CDM) has a twin objective: to help developed countries reduce GHG emissions, and to support developing countries in achieving Sustainable Development (SD). As a response to the widespread criticism of the CDM's unsatisfactory SD record, initiatives have developed premium labels like the Gold Standard, which applies two additional ‘screens’ to filter CDM projects for higher SD benefits. In order to determine whether Gold Standard projects can be associated with higher local SD benefits, this paper evaluates the potential benefits of 48 CDM projects using a multi-criteria method and building on existing work. The 18 evaluated Gold Standard projects are compared to a ‘representative portfolio’ of 30 unlabeled CDM projects in order to capture the ‘full’ effect of the additional Gold Standard requirements, which is further decomposed into the two ‘screen’ effects. The results suggest that Gold Standard Certified Emission Reductions can be associated with higher potential local SD benefits when compared to the ‘representative portfolio’ of unlabeled CDM projects, while the comparison of projects of the same type remains inconclusive. The results support previous findings showing that renewable energy projects may deliver comparatively high SD benefits.     

Land use change to bioenergy: A meta-analysis of soil carbon and GHG emissions

A systematic review and meta-analysis were used to assess the current state of knowledge and quantify the effects of land use change (LUC) to second generation (2G), non-food bioenergy crops on soil organic carbon (SOC) and greenhouse gas (GHG) emissions of relevance to temperate zone agriculture. Following analysis from 138 original studies, transitions from arable to short rotation coppice (SRC, poplar or willow) or perennial grasses (mostly Miscanthus or switchgrass) resulted in increased SOC (+5.0 ± 7.8% and +25.7 ± 6.7% respectively). Transitions from grassland to SRC were broadly neutral (+3.7 ± 14.6%), whilst grassland to perennial grass transitions and forest to SRC both showed a decrease in SOC (−10.9 ± 4.3% and −11.4 ± 23.4% respectively). There were insufficient paired data to conduct a strict meta-analysis for GHG emissions but summary figures of general trends in GHGs from 188 original studies revealed increased and decreased soil CO₂ emissions following transition from forests and arable to perennial grasses. We demonstrate that significant knowledge gaps exist surrounding the effects of land use change to bioenergy on greenhouse gas balance, particularly for CH₄. There is also large uncertainty in quantifying transitions from grasslands and transitions to short rotation forestry. A striking finding of this review is the lack of empirical studies that are available to validate modelled data. Given that models are extensively use in the development of bioenergy LCA and sustainability criteria, this is an area where further long-term data sets are required.     

Dynamic changes of lignin contents of MT-1 elephant grass and its closely related cultivars

Elephant grass (Pennisetum purpureum Schum.) is a tropical C₄ bunchgrass with high rates of growth and biomass production. It has been considered as a new alternative for energy crop in some countries, and expected to provide abundant and sustainable resources of lignocellulosic biomass for the production of solid biofuels. But in addition to cellulose, plant cell walls contain lignin that hinders the degradation of cell wall polysaccharides to simple sugars destined for fermentation to ethanol and biogas. In this paper, five elephant grass cultivars, such as ‘MT-1’ new line (P. purpureum cv. MT-1), ‘Mott’ (P. purpureum cv. Mott), ‘Huanan’ (P. purpureum cv. Huanan), ‘N51’ (P. purpureum cv. N51) and ‘Guimu-1’ ((Pennisetum americanum × P. purpureum) × P. purpureum cv. Guimu No.1) were tested to determine the lignin content using the acetyl bromide method. The lignin contents increased with the growth development for all five cultivars, but the increasing range was different with the difference of cultivar. In particular, the biggest increasing range was between July and August for ‘Huanan’, ‘N51’, ‘Mott’ and ‘MT-1’. At seedling stage, the contents of five cultivars were not significantly different, but the differences were demonstrated at internode elongation stage. At ripening stage, the upper internode of flowering culm had the lowest lignin content, and the basal internode had the highest content for all the five cultivars. The lignin content was very different at different development stage for different cultivars, indicating the differentiations among the five genotypes. As far as the flowering culm (in December) was concerned, the order of lignin content from the highest to the lowest was ‘Huanan’ (22.04% FW) > ‘N51’ (19.65% FW) > ‘Guimu-1’ (17.45% FW) > ‘Mott’ (15.43% FW) ≥ ‘MT-1’ (14.63% FW). In NJ and UPGMA dendrograms, the five cultivars could be divided into two groups, one for ‘MT-1’, ‘Mott’ and ‘Guimu-1’, one for ‘Huanan’ and ‘N51’. This result is consistent with the pedigree relationships among the five cultivars.     

Greenhouse gas balances and mitigation costs of 70 modern Germany-focused and 4 traditional biomass pathways including land-use change effects

With Germany as the point of energy end-use, 70 current and future modern pathways plus 4 traditional biomass pathways for heat, power and transport have been compiled and examined in one single greenhouse gas (GHG) balancing assessment. This is needed to broaden the narrow focus on biofuels for transport and identify the role of bioenergy in GHG mitigation. Sensitivity analysis for land-use changes and fossil reference systems are included. Co-firing of woody biomass and fermentation of waste biomass are the most cost-efficient and effective biomass applications for GHG emission reduction in modern pathways. Replacing traditional biomass with modern biomass applications offers an underestimated economic potential of GHG emission reduction. The range of maximum CO₂ equivalent GHG reduction potential of bioenergy is identified in a range of 2.5-16 Gt a⁻¹ in 2050 (5-33% of today’s global GHG emissions), and has an economic bioenergy potential of 150 EJ a⁻¹.