lca

Review of the sustainability aspects and issues covered within various bioenergy initatives inclusing social, economic, and environmental aspects.

Provides a summary of the key findings of the IPCC Special Report on Renewable Energy Sources (SRREN) and Climate Change Mitigation.

EXECUTIVE SUMMARY: Life cycle assessment (LCA) is a powerful tool that may be used to quantify the environmental impacts of products and services. It includes all processes, from cradle-to-grave, along the supply chain of the product. When analysing energy systems, greenhouse gas (GHG) emissions (primarily CO2, CH4 and N2O) are the impact of primary concern. In using LCA to determine the climate change mitigation benefits of bioenergy, the life cycle emissions of the bioenergy system are compared with the emissions for a reference energy system. The selection of reference energy system can strongly affect the outcome.
 
When reviewing the literature one finds large ranges of GHG emissions per unit of energy from LCA studies of similar bioenergy systems. The differences occur for a multitude of reasons including differences in technologies, system boundaries, and reference systems. Some studies may be incomplete in that the bioenergy system and reference system provide different services. Others may omit some sources of emissions (e.g. land use change).
 
This paper discusses key criteria for comprehensive LCAs based on IEA Bioenergy Task 38 case studies. LCAs of the GHG balance of four different bioenergy systems and their counterpart reference system are highlighted using the case study examples.
 
The first example investigates heat production from woody biomass and grasses. This study shows that the emissions saved for the same type of service can vary due to the source of the biomass. The bioenergy systems studied reduce GHG emissions by 75-85% as compared to the counterpart reference systems.
 
In the second example, electricity is produced from woody biomass using two different technologies with different efficiencies. Depending on the technology, the biomass must
be transported different distances. The example illustrates the importance of the efficiency of the system and the small impact of soil organic carbon (SOC) decline in comparison
with emissions saved. Since the bioenergy systems include carbon sequestration, they reduce GHG emissions by 108-128% as compared to the counterpart reference systems.
 
A biogas plant providing combined heat and power is analysed in the third example, which illustrates the importance of finding a beneficial use for the heat produced, and of controlling fugitive emissions. In the optimal configuration of closed storage and maximised use of heat, the biogas system reduces emissions by 71% as compared to the counterpart reference system. This reduction decreases to 44% when the heat is not fully used and to only 27% if fugitive emissions are not controlled.
 
In the final example the bioenergy system provides biodiesel for transport. This example demonstrates the importance of the use of co-products, as the same bioenergy chain produces very different emissions savings per kilometre depending on whether the co-product is used as a material or combusted for energy. Compared to the reference system, the bioenergy system reduce GHG emissions by 18% and 42% when the co-products are used for energy or materials respectively.
 
Similar to the case studies presented here, published studies find that GHG mitigation is greater where biomass is used for heat and electricity applications rather than for liquid transport fuels. Overall, the emissions savings from bioenergy systems tend to be similar to that of other renewable energy sources.

This review on research on life cycle carbon accounting examines the complexities in accounting for carbon emissions given the many different ways that wood is used. Recent objectives to increase the use of renewable fuels have raised policy questions, with respect to the sustainability of managing our forests as well as the impacts of how best to use wood from our forests. There has been general support for the benefits of sustainably managing forests for carbon mitigation as expressed by the Intergovernmental Panel on Climate Change in 2007. However, there are many integrated carbon pools involved, which have led to conflicting implications for best practices and policy. In particular, sustainable management of forests for products produces substantially different impacts than a focus on a single stand or on specific carbon pools with each contributing to different policy implications. In this article, we review many recent research findings on carbon impacts across all stages of processing from cradle-to-grave, based on life cycle accounting, which is necessary to understand the carbon interactions across many different carbon pools. The focus is on where findings are robust and where uncertainties may be large enough to question key assumptions that impact carbon in the forest and its many uses. Many opportunities for reducing carbon emissions are identified along with unintended consequences of proposed policies.
http://www.corrim.org/pubs/articles/2011/FSG_Review_Carbon_Synthesis.pdf
 

The IPCC SRREN report addresses information needs of policymakers, the private sector and civil society on the potential of renewable energy sources for the mitigation of climate change, providing a comprehensive assessment of renewable energy technologies and related policy and financial instruments. The IPCC report was a multinational collaboration and synthesis of peer reviewed information: Reviewed, analyzed, coordinated, and integrated current high quality information. The OBP International Sustainability activities contributed to the Bioenergy chapter, technology cost annex as well as lifecycle assessments and sustainability information.

We assessed the life-cycle energy and greenhouse gas (GHG) emission impacts of the following three soybean-derived fuels by expanding, updating, and using Argonne National Laboratory’s Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model: (1) biodiesel produced from soy oil transesterification, (2) renewable diesel produced from hydrogenation of soy oil by using two processes (renewable diesel I and II), and (3) renewable gasoline produced from catalytic cracking of soy oil.

This study focuses on the simulation of a complete process for producing butanol via
acetone, butanol, and ethanol corn fermentation.

The aim of this study is to show the impact of different assumptions and methodological choices on the life-cycle greenhouse gas (GHG) performance of biofuels by providing the results for different key parameters on a consistent basis. These include co-products allocation or system expansion, N2O emissions from crop cultivation, conversion systems and co-product applications and direct land-use change emissions. The results show that the GHG performance of biofuels varies depending on the method applied and the system boundaries selected. Key factors include selected allocation procedures and the location of production and related yields, reference land and soil N2O emissions.

Governments worldwide are promoting the development of biofuels in order to mitigate the climate impact of using fuels. In this article, I discuss the impacts of biofuels on climate change, water use, and land use. I discuss the overall metric by which these impacts have been measured and then present and discuss estimates of the impacts. In spite of the complexities of the environmental and technological systems that affect climate change, land use, and water use, and the difficulties of constructing useful metrics, it is possible to make some qualitative overall assessments. It is likely that biofuels produced from crops using conventional agricultural practices will not mitigate the impacts of climate change and will exacerbate stresses on water supplies, water quality, and land use, compared with petroleum fuels. Policies should promote the development of sustainable biofuel programs that have very low inputs of fossil fuels and chemicals that rely on rainfall or abundant groundwater, and that use land with little or no economic or ecological value in alternative uses.

Negative environmental consequences of fossil fuels and concerns about petroleum supplies have spurred the search for renewable transportation biofuels. To be a viable alternative, a biofuel should provide a net energy gain, have environmental benefits, be economically competitive, and be producible in large quantities without reducing food supplies. We use these criteria to evaluate, through life-cycle accounting, ethanol from corn grain and biodiesel from soybeans. Ethanol yields 25% more energy than the energy invested in its production, whereas biodiesel yields 93% more. Compared with ethanol, biodiesel releases just 1.0%, 8.3%, and 13% of the agricultural nitrogen, phosphorus, and pesticide pollutants, respectively, per net energy gain. Relative to the fossil fuels they displace, greenhouse gas emissions are reduced 12% by the production and combustion of ethanol and 41% by biodiesel. Biodiesel also releases less air pollutants per net energy gain than ethanol. These advantages of biodiesel over ethanol come from lower agricultural inputs and more efficient conversion of feedstocks to fuel. Neither biofuel can replace much petroleum without impacting food supplies. Even dedicating all U.S. corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand. Until recent increases in petroleum prices, high production costs made biofuels unprofitable without subsidies. Biodiesel provides sufficient environmental advantages to merit subsidy. Transportation biofuels such as synfuel hydrocarbons or cellulosic ethanol, if produced from low-input biomass grown on agriculturally marginal land or from waste biomass, could provide much greater supplies and environmental benefits than food-based biofuels.