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Dynamic and temporal modeling in LCA
Special session coordinator: Annie Levasseur, CIRAIG
The lack of consideration for temporal aspects in LCA is a repeated criticism of the methodology. Inventory phase excludes temporal information, like the dynamics of the different life cycle processes, giving aggregated results. This absence of time resolution in the inventory results implies the use of some assumptions that can decrease the accuracy of impact assessment models. In LCIA, the choice of time horizons for integrating impacts and the distribution of these impacts through time is also an important discussion subject. This session wants to address the problem of temporal aspects in LCA, in inventory and impact assessment, to look at how time could be integrated into LCA to increase its accuracy and application scope.
Presenters:
Annie Levasseur, CIRAIG
How dynamic LCA can bring consistency in assessing global warming mitigation scenarios
Annie Levasseur, CIRAIG
Pascal Lesage, CIRAIG
Manuele Margni, CIRAIG
Louise Deschênes, CIRAIG
Réjean Samson, CIRAIG
presentationWith Kyoto Protocol enforcement in many countries, mitigation mechanisms for GHG like temporary abiotic carbon sequestration scenarios are more and more accepted to meet political targets. To assess the impact of these scenarios, LCA appears to be the preferred tool to avoid burden shifting over whole life cycle. A consensus exists to use GWP (Global Warming Potential) index, developed by the IPCC (Intergovernmental Panel on Climate Change), as characterization factors to assess impacts on climate change. Although many practitioners are aware that GWP index is available for different time horizons, such as 20, 100 and 500 years, only few of them realize that there is often an inconsistency regarding time frame between an aggregated inventory result and the choice of the time horizon used in GWP. In fact, multiplying an inventory result by a set of GWPs for a chosen time horizon assumes that every emission of the aggregated life cycle inventory result is occurring at time zero, which is not true, especially for long-lived products or scenarios.
A new dynamic LCA approach is proposed to overcome this limitation and bring consistency between the inventory and the impact assessment time horizon. This approach consists in i) computing a dynamic inventory to discriminate time dependant emissions over the whole life cycle and ii) calculating dynamic characterization factors for each time step up to the defined time horizon using the AGWP (Absolute Global Warming Potential). A case study for temporary carbon sequestration by afforestation has been developed to illustrate the benefits of this dynamic approach. Dynamic LCA results are showing the change in radiative forcing caused by GHG emissions, at any time t following the beginning of the studied life cycle. The comparison with traditional LCA shows that the dynamic approach gives lower results for a given time horizon, due to the improved consistency in the time frames. Dynamic LCA also brings the temporal resolution necessary for comparing temporary carbon sequestration scenarios.
Capturing the Effects of the Timing of Emissions in Life Cycle Greenhouse Gas Assessments: A Case Study of Photovoltaic Technologies
Alissa Kendall, University of California, Davis
Brenda Chang, University of California, Davis
Benjamin A. Sharpe, University of California, Davis
presentationWith few exceptions [1], studies estimating life cycle greenhouse gas (GHG) emissions for renewable energy systems, such as photovoltaics (PV) report GHG emissions on an emissions intensity basis, such as per-kWh or per-MJ. To calculate emissions intensity, life cycle assessment (LCA) practitioners typically implement a straight-line amortization of the initial emissions, such as emissions from capital investments or manufacturing, over an assumed time horizon [2, 3]. Because the impact of a GHG increases with time in the atmosphere, disregarding when an emission occurs underestimates its climate change effect. This is particula rly true if a large emission occurs at the beginning or in advance of a product’s life cycle.
To address this shortcoming in current LCA practices, we have developed a scaling factor, referred to as a time correction factor (TCF) [4]. To calculate the TCF we use a methodology founded on the same principles as the Intergovernmental Panel on Climate Change’s global warming potentials (GWPs). The TCF is applied to life cycle emissions intensity estimates for various PV technologies. Results show that actual climate change effects are nearly 80% greater than those reported. While this research applies the TCF to better compare climate change effects of alternative PV technologies, the broader concept has a role to play in developing a method to capture the true climate effect of GHG emissions during the impact assessment step of LCA.
[1] O'Hare, M. et. al, 2009. Proper Accounting for Time Increases Crop-Based Biofuels’ GHG Deficit versus Petroleum. Environmental Research Letters 4, 024001.
[2] Fthenakis, V. & E. Alsema, 2006. Photovoltaics Energy Payback Times, Greenhouse Gas Emissions and External Costs: 2004-Early 2005 Stuts. Progress in Photovoltaics: Research and Applications, 14, 275-280.
[3] Raugei, M., S. Bargigle & S. Ulgiati (2007) Life cycle assessment and energy pay-back time of advancedphotovoltaic modules: CdTe and CIS compared to poly-Si. Energy 32, 1310-1318
[4] Kendall, A., B. Chang, & B. A. Sharpe, 2009. Accounting for Time-Dependent Effects in Biofuel Life Cycle Greenhouse Gas Emissions Calculations Environmental Science and Technology, doi: 10.1021/es900529u.
Eric Williams, Arizona State University
Modeling process, product and usage evolution in LCA: three case studies
Eric Williams, Arizona State University
Liqiu Deng, Arizona State University
Callie W. Babbitt, Arizona State University
Pei Zhai, Arizona State University
presentationLCA was initially designed to produce a static snapshot of materials flows and impacts associated with a supply chain. In many cases the temporal evolution of processes, products and usage patterns can significantly affect LCA results, a challenge which the community has long-recognized and worked to grapple with. This presentation reviews three case studies addressing methods and data to work towards temporal characterization of life cycle inventories. The first case study examine photovoltaic manufacturing and develops a retrospective model of product and process evolution to describe trends in energy and carbon overhead of the supply chain. The inventory method is a variety of hybrid analysis combining process and economic input-output approaches. The second case study of semiconductor manufacturing examines how different definitions of functional unit can affect the temporal evolution of the inventory. In particular, the energy to produce a “typical” microprocessor for a given year is roughly constant (typical product normalization) while the energy per transistor (functionality normalization) decreases rapidly. The third case study addresses the empirical analysis of the temporal evolution of computer usage patterns. Data is gathered describing fifteen years of computer use at Arizona State University. One of the main results is that product lifespan, the time from purchase to disposal, has declined steadily, from around 10.7 years in 1985 to 5.5 years in 2000. This suggests that dynamic modeling of lifespan is needed for LCA of some products.
Dynamic Life Cycle Assessment of biogas production from micro-algae
Collet Pierre, Montpellier SupAgro
Arnaud Hélias, Montpellier SupAgro
Laurent Lardon, INRA
Jean-Philippe Steyer, Montpellier SupAgro
presentationFossil fuel depletion and climate change have lead many research groups and private companies to focus on use of biomass to produce renewable energy and fuel. Because of their high production yield, micro-algae have been pointed as an interesting alternative. A relevant mean to upgrade the energy value of micro-algae with optimal performances is the anaerobic digestion of the algae. It enables achievement of environmental benefits and production of energy from renewable resources. However such processes only exist at lab-scale. In order to assess and optimize its performances and environmental impacts, one has to stimulate its behaviour through dynamical models. In broad outline the two major compartments of the system (micro-algae culture and anaerobic digestion process) are linked by internal flows (micro-algae, digestates…) and receive external flows (light, cosubstrates…). As a consequence, overall behaviour is determined by the interaction of several time-dependent processes. For example, the temporal availability of winery effluents induces a better anaerobic digestion due to the high C/N ratio of this kind of cosubstrate, and consequently a bigger production of biogas. So, due to the close loop operating, the needs of chemical fertilizers are lower, and the emissions caused by their production too. This shows the necessity to realize a dynamic Life Cycle Assessment. In our context, a pertinent Life Cycle Inventory can not be achieved without taking into account the dynamic of several processes; some economic flows are determined according to the temporal evolution of processes. Consequently, we integrate dynamic system modeling of micro-algae growth and anaerobic digestion of biomass in the LCA in order to obtain dynamic flows. This approach allows us to obtain dynamic data for the Life Cycle Inventory. This is a preliminary step to more accurate impact assessment.
Modeling future emissions from Municipal solid waste incineration in Europe
Dominik Saner, ETH Zurich
Daniel Lang, ETH Zurich
Annette Koehler, ETH Zurich
PresentationWith increasing amounts of municipal solid waste being directed to incineration plants the question of future incineration emission loads becomes increasingly important. Emission loads depend on waste amount, waste composition as well as incineration technology, and therefore heavily vary over space and time. A temporal modeling of emissions from municipal solid waste incineration for application in different environmental assessments such as life cycle assessment, substance flow analysis, and pollutant exposure assessment was conducted to address the issue of prospective emission situations.
Applying Formative Scenario Analysis (FSA) future scenarios reflecting socio-economic and demographic developments, technological evolution and different policy settings were generated for municipal solid waste incineration in the coming decades in Europe. Impact variables, which formally describe the driving forces of different scenarios were elaborated. Scenarios were constructed, analyzed for consistency, and used to define input parameters for a probabilistic and spatially-resolved emission model that allows to quantify the incineration emissions into air and water. The waste-input specific, transfer-coefficient based emission model for different waste incineration and flue gas cleaning technologies considers 33 European countries and consists of two databases: one of all existing and planned municipal solid waste incineration plants in Europe, specifying their location and technological installations and a European waste inventory of combustible wastes, including information on current and future national municipal waste quantities, waste types, material compositions and elemental compositions of the waste materials. All input and model parameters are stochastically modeled returning uncertainty ranges for the resulting emission loads. The model thus provides temporally differentiated LCI data for municipal solid waste incineration plants in 33 European countries on a time scale of 4 decades.
In the presentation, the set-up of future scenarios and their temporally varying impact variables will be elaborated. The crucial step of translating scenarios into temporal input parameters of the incineration model will be discussed and the trade-offs between scenario-based (temporal) and stochastically modeled future emission loads analyzed. The results for the pollutant loads show that batteries now and in the future are a main source of heavy metals and that N and S inputs from biodegradable waste into incineration become increasingly important due to prohibited landfilling of biowaste.
LCA of Waste Prevention Options for the Residential Construction Sector in Oregon
Jon Dettling, Quantis
Dominic Pietro, Quantis
Jordan Palmeri, Oregon Department of Environmental Quality
Bill Jones, Earth Advantage, Inc.
Johnathan Balkema, Oregon Home Builders Association
Bruce Sullivan, Earth Advantage, Inc.
David Allaway, Oregon Department of Environmental Quality
Sebastien Humbert, Quantis
Olivier Jolliet, Quantis
presentationWithin Oregon, the residential construction sector is responsible for a significant portion of the waste generated. While the Oregon DEQ recognizes the importance of waste prevention actions in this sector, it is also recognized that the residential housing sector is an extremely important contributor to other environmental impact areas through its material demands and energy use: a classic case of the potential for shifting burdens. There is therefore a need to ensure that the waste prevention actions that the state government may take are optimized to achieve maximal benefit (and avoid net impacts) in multiple environmental impact categories.
A life cycle assessment has been undertaken to identify the residential construction waste prevention practices that provide the greatest overall environmental benefit. Supporting information for the study has been compiled with the help of the Oregon Home Builders Association (OHBA), Earth Advantage Inc. (EAI, the leading building energy certifier in the state), and the Oregon DEQ in addition to a wide range of subject-matter experts on the building practices. A whole-building LCA framework has been established that integrates detailed data on building materials and energy use (supplied by OHBA and EAI, respectively) with detailed information about the context of residential buildings in Oregon.
More than two dozen possible waste prevention practices have been identified. In a first screening-level phase, these practices were evaluated to narrow the list to those practices showing the most promise. The best performing practices are being evaluated in a second phase in which the level of detail was greatly enhanced and the study was expanded to consider the practices within the framework of a state-wide residential building stock.
In both phases of the project, temporal considerations are highly important. The choice of a lifetime for the modeled residential structures, as well as replacement schedules, highly influences the relative contributions of various aspects the home. When considering state-wide building stock, both the longevity of structures and the chosen time horizon are important.
This presentation will discuss the context of the project, the methodologies used, discuss the findings of the first phase and provide some preliminary results of the second phase.
Meeting the NEEDS of European environmental sustainability assessment
Rolf Frischknecht, ESU-services Ltd.
Krewitt Wolfram, German Aerospace Centre
presentationMixing LCI data from databases representing today’s situation with LCI data for energy systems and technologies that will only be realised in some decades from now leads to results that do not well represent the environmental impact of the intended future situation. This is the more true for technologies with low or zero direct emissions such as wind, or photovoltaic. Within the recently completed European NEEDS project, the environmental efficiency of the production of selected relevant commodities are adapted to a 2025 and 2050 situation, differentiating three possible scenarios of economic developments and energy policies. Using background data based on unit processes a change in selected datasets propagates into every dataset. This substantially improves accuracy and consistency of the resulting product systems. In the NEEDS project the future energy mix including a share of these new technologies is taken into account as well as changes in the mining, materials and transport sectors. It is shown that a consistent modification leads to results that are significantly different from those using unmodified data.
Exploring Leverage in Responsible Purchasing - A recursive life-cycle simulation to explore green purchasing and life-cycle simulation
Evan Andrews, Sylvatica
presentationResponsible purchasing among institutions is growing. Green procurement, one such example of this, proliferates as companies increasingly seek to manage risks and opportunities in their supply chains. While great progress has been made, one question is often deferred because it is either not understood, or deemed too difficult to address: How deep should green purchasing efforts go into the supply chain? Should suppliers be judged solely on their environmental impacts, or should they also be judged on their purchasing decisions as well? Is it worth the effort to request data from deep in the supply chain? If the goal is to make the world a better place, just how much leverage do purchasers have towards this end? How much faster does the economy green if purchasers take a life-cycle perspective, rather than “one-tier green”, when making buying decisions?
The presentation will tackle these topics through the lens of a life-cycle simulation. The model allows for dynamic interplay of companies, and uses market information to simulate how the economy might change in response to green purchasing decisions. The market features includes pricing, competition, and constrained production among other variables. For example, a supplier that would otherwise be the best candidate to furnish a good might not bid because the job would put her over capacity. Similarly, purchasers make procurement decisions based on the context in which they find themselves, such as whether their company has committed to green purchasing.
The results of the study will be presented. Scenarios will be compared where green purchasers do, and don’t, dig into their supply chains. There will also be discussion of insights gained and future work.