Energy system analysis of marginal electricity supply in consequential LCA

Background, aim and scope  

This paper discusses the identification of the environmental consequences of marginal electricity supplies in consequential life cycle assessments (LCA). According to the methodology, environmental characteristics can be examined by identifying affected activities, i.e. often the marginal technology. The present ‘state-of the-art’ method is to identify the long-term change in power plant capacity, known as the long-term marginal technology, and assume that the marginal supply will be fully produced at such capacity. However, the marginal change in capacity will have to operate as an integrated part of the total energy system. Consequently, it does not necessarily represent the marginal change in electricity supply, which is likely to involve a mixture of different production technologies. Especially when planning future sustainable energy systems involving combined heat and power (CHP) and fluctuating renewable energy sources, such issue becomes very important.     

The ecoinvent database version 3 (part I): overview and methodology

Purpose

Good background data are an important requirement in LCA. Practitioners generally make use of LCI databases for such data, and the ecoinvent database is the largest transparent unit-process LCI database worldwide. Since its first release in 2003, it has been continuously updated, and version 3 was published in 2013. The release of version 3 introduced several significant methodological and technological improvements, besides a large number of new and updated datasets. The aim was to expand the content of the database, set the foundation for a truly global database, support regionalized LCIA, offer multiple system models, allow for easier integration of data from different regions, and reduce maintenance efforts. This article describes the methodological developments.

Methods

Modeling choices and raw data were separated in version 3, which enables the application of different sets of modeling choices, or system models, to the same raw data with little effort. This includes one system model for Consequential LCA. Flow properties were added to all exchanges in the database, giving more information on the inventory and allowing a fast calculation of mass and other balances. With version 3.1, the database is generally water-balanced, and water use and consumption can be determined. Consumption mixes called market datasets were consistently added to the database, and global background data was added, often as an extrapolation from regional data.

Results and discussion

In combination with hundreds of new unit processes from regions outside Europe, these changes lead to an improved modeling of global supply chains, and a more realistic distribution of impacts in regionalized LCIA. The new mixes also facilitate further regionalization due to the availability of background data for all regions.

Conclusions

With version 3, the ecoinvent database substantially expands the goals and scopes of LCA studies it can support. The new system models allow new, different studies to be performed. Global supply chains and market datasets significantly increase the relevance of the database outside of Europe, and regionalized LCA is supported by the data. Datasets are more transparent, include more information, and support, e.g., water balances. The developments also support easier collaboration with other database initiatives, as demonstrated by a first successful collaboration with a data project in Québec. Version 3 has set the foundation for expanding ecoinvent from a mostly regional into a truly global database and offers many new insights beyond the thousands of new and updated datasets it also introduced.

     

The ecoinvent database version 3 (part II): analyzing LCA results and comparison to version 2

Purpose

Version 3 of ecoinvent includes more data, new modeling principles, and, for the first time, several system models: the “Allocation, cut-off by classification” (Cut-off) system model, which replicates the modeling principles of version 2, and two newly introduced models called “Allocation at the point of substitution” (APOS) and “Consequential” (Wernet et al. 2016). The aim of this paper is to analyze and explain the differences in life cycle impact assessment (LCIA) results of the v3.1 Cut-off system model in comparison to v2.2 as well as the APOS and Consequential system models.

Methods

In order to do this, functionally equivalent datasets were matched across database versions and LCIA results compared to each other. In addition, the contribution of specific sectors was analyzed. The importance of new and updated data as well as new modeling principles is illustrated through examples.

Results and discussion

Differences were observed in between all database versions using the impact assessment methods Global Warming Potential (GWP100a), ReCiPe Endpoint (H/A), and Ecological Scarcity 2006 (ES’06). The highest differences were found for the comparison of the v3.1 Cut-off and v2.2. At average, LCIA results increased by 6, 8, and 17 % and showed a median dataset deviation of 13, 13, and 21 % for GWP, ReCiPe, and ES’06, respectively. These changes are due to the simultaneous update and addition of new data as well as through the introduction of global coverage and spatially consistent linking of activities throughout the database. As a consequence, supply chains are now globally better represented than in version 2 and lead, e.g., in the electricity sector, to more realistic life cycle inventory (LCI) background data. LCIA results of the Cut-off and APOS models are similar and differ mainly for recycling materials and wastes. In contrast, LCIA results of the Consequential version differ notably from the attributional system models, which is to be expected due to fundamentally different modeling principles. The use of marginal instead of average suppliers in markets, i.e., consumption mixes, is the main driver for result differences.

Conclusions

LCIA results continue to change as LCI databases evolve, which is confirmed by a historical comparison of v1.3 and v2.2. Version 3 features more up-to-date background data as well as global supply chains and should, therefore, be used instead of previous versions. Continuous efforts will be required to decrease the contribution of Rest-of-the-World (RoW) productions and thereby improve the global coverage of supply chains.

     

Contribution-based prioritization of LCI database improvements: the most important unit processes in ecoinvent

The International Journal of Life Cycle Assessment - Improving the quality and quantity of unit process datasets in Life Cycle Inventory (LCI) databases affects every LCA they are used in. However,...     

Consequential cradle-to-gate carbon footprint of water treatment chemicals using simple and complex marginal technologies for electricity supply

Purpose

Chemicals produced via chlor-alkali electrolysis are widely used throughout the water industry worldwide, with treatment chemicals often the second largest source of environmental impacts from potable water production after electricity use. Population-driven increases in the future demand for potable water will require concomitant increases in the production of water treatment chemicals, with the associated environmental impacts of chemicals production primarily arising from the additional demand for electricity. Due to the dominance of electricity in the environmental performance of chlor-alkali chemicals, assessment of the future environmental impacts of potable water production is largely dependent on proper identification of the marginal source of electricity. In this paper, we present a consequential cradle-to-gate carbon footprint (cCF) for the most widely used chlor-alkali-produced disinfectant (sodium hypochlorite (13 % w/w)) and coagulant (ferric chloride (42 % w/w)) in Australia, with special emphasis placed upon the identification of future marginal electricity supply and the substitution of hydrogen gas and sodium hydroxide during production. While this analysis is presented in an Australian context, commonalities in potable water and chlor-alkali chemical production processes internationally give the findings a broader relevance.

Methods

Consequential models for sodium hypochlorite (13 % w/w) and ferric chloride (42 % w/w) production were developed, and the identification of the marginal source of electricity was modelled using a “simple marginal technology” approach via operationalisation of the Weidema framework and a “complex marginal technology” using a partial equilibrium model. For the simple marginal technology, the levelised cost of electricity was used to select the most competitive energy generation technologies and those most relevant for the Australian market. For the complex marginal technology, the energy sector model was used to simulate the most likely electricity supply mix. Details of the different paths taken in the substitution of hydrogen gas and sodium hydroxide are also presented. To allow for proper incorporation of uncertainties arising from these key factors in the cCF, several scenarios were developed covering fuel and carbon prices for identifying the marginal supply mix of electricity, as well as the likely production routes for sodium carbonate in the context of sodium hydroxide substitution.

Results and discussion

cCF results of sodium hypochlorite (13 % w/w) and ferric chloride (42 % w/w) are presented using simple and complex marginal technologies, and the implications of choosing one marginal technology over the other in the context of water treatment chemicals are presented. For the simple marginal technology approach, the global warming potential (GWP) per megagram of chemical varied from 68 to 429 kg CO₂-eq for sodium hypochlorite (13 % w/w) and 59–1,020 kg CO₂-eq for ferric chloride (42 % w/w). For the complex marginal technology approach, the GWP per megagram of chemical varied from 266 to 332 kg CO₂-eq for sodium hypochlorite (13 % w/w) and 214–629 kg CO₂-eq for ferric chloride (42 % w/w). Insights are given in relation to the impact of the price of fossil fuels, the carbon price, and the different substitution routes.

Conclusions

The use of a partial equilibrium model (PEM) has enabled a better understanding of the variability of the results in this study. For example, the use of PEM for the identification of the complex marginal source of electricity shows that, for the case of Australia, any benefit from a carbon price is lost with high prices of natural gas due to the incentive to use cheaper fuels such as black and brown coal. Likewise, the use of explorative scenarios was decisive to manage the inherent uncertainty of the parameters included in the model. In relation to substitution, the case of ferric chloride (42 % w/w) indicated that using only one substitution route was not enough to fully understand the potential continuum of cCF results. The simple marginal approach, where an exclusive marginal source of electricity or substitution route is considered, presents significant risks for the modelling accuracy of the cCF as shown here for sodium hypochlorite (13 % w/w) and ferric chloride (42 % w/w), therefore, it is not recommended.     

Shift in the marginal supply of vegetable oil

Background, Aims and Scope

The consequential approach to system delimitation in LCA requires that consideration of the technologies and suppliers included are ‘marginal’, i.e. that they are actually affected by a change in demand. Furthermore, coproduct allocation must be avoided by system expansion. Vegetable oils constitute a significant product group included in many LCAs that are intended for use in decision support. This article argues that the vegetable oil market has faced major changes around the turn of the century. The aim of this study is to study the marginal supply of vegetable oil as it has shifted to palm oil and describe the product system of the new supply.

Methods

The methods for identification of marginal technologies and suppliers and for avoiding co-product allocation are based on the work of Weidema (2003). The marginal vegetable oil is identified on the basis of agricultural statistics on production volumes and prices. A co-product from palm oil production is palm kernel meal, which is used for fodder purposes where it has two main properties: protein and energy. When carrying out system expansion, these properties are taken into account.

Results

The major vegetable oils are soy oil, palm oil, rapeseed oil and sun oil. These oils are substitutable within the most common applications. Based on market trends, a shift from rapeseed oil to palm oil as the marginal vegetable oil is identified around the year 2000, when palm oil turns out to be the most competitive oil. It is recommended to regard palm oil and its dependent co-product palm kernel oil as the marginal vegetable oil. The analysis of the product system shows that the demand for 1 kg palm oil requires 4.49 kg FFB (oil palm fruit) and the displacement of 0.035 kg soybeans (marginal source of fodder protein) and 0.066 kg barley (marginal source of fodder energy).

Discussion

The identification of the marginal vegetable oil and the avoidance of co-product allocation by system expansion showed that several commodities may be affected when using the consequential approach. Hence, the product system for vegetable oils is relatively complex compared to traditional LCAs in which average technologies and suppliers are applied and in which co-product allocation is carried out by applying an allocation factor.

Conclusions

This article presents how the marginal vegetable oil can be identified and that co-product allocation between oils and meal can be avoided by system expansion, by considering the energy and protein content in the meal, which displaces a mix of the marginal sources of energy and protein for animal fodder (barley and soy meal, respectively).

Recommendations and Perspectives

The implication of a shift in the marginal vegetable oil is significant. Many LCAs on rapeseed oil have been conducted and are being used as decision support in the bio energy field. Thus, based on consequential LCA methodology, it is argued that these LCAs need to be revised, since they no longer focus on the oil actually affected.

     

The application of the pedigree approach to the distributions foreseen in ecoinvent v3

Purpose

Data used in life cycle inventories are uncertain (Ciroth et al. Int J Life Cycle Assess 9(4):216–226, 2004). The ecoinvent LCI database considers uncertainty on exchange values. The default approach applied to quantify uncertainty in ecoinvent is a semi-quantitative approach based on the use of a pedigree matrix; it considers two types of uncertainties: the basic uncertainty (the epistemic error) and the additional uncertainty (the uncertainty due to using imperfect data). This approach as implemented in ecoinvent v2 has several weaknesses or limitations, one being that uncertainty is always considered as following a lognormal distribution. The aim of this paper is to show how ecoinvent v3 will apply this approach to all types of distributions allowed by the ecoSpold v2 data format.

Methods

A new methodology was developed to apply the semi-quantitative approach to distributions other than the lognormal. This methodology and the consequent formulas were based on (1) how the basic and the additional uncertainties are combined for the lognormal distribution and on (2) the links between the lognormal and the normal distributions. These two points are summarized in four principles. In order to test the robustness of the proposed approach, the resulting parameters for all probability density functions (PDFs) are tested with those obtained through a Monte Carlo simulation. This comparison will validate the proposed approach.

Results and discussion

In order to combine the basic and the additional uncertainties for the considered distributions, the coefficient of variation (CV) is used as a relative measure of dispersion. Formulas to express the definition parameters for each distribution modeling a flow with its total uncertainty are given. The obtained results are illustrated with default values; they agree with the results obtained through the Monte Carlo simulation. Some limitations of the proposed approach are cited.

Conclusions

Providing formulas to apply the semi-quantitative pedigree approach to distributions other than the lognormal will allow the life cycle assessment (LCA) practitioner to select the appropriate distribution to model a datum with its total uncertainty. These data variability definition technique can be applied on all flow exchanges and also on parameters which play an important role in ecoinvent v3.

     

Comparing functional metabolic effects of marginal and sufficient selenium supply in sheep

This study was performed to characterise key data of long-term ovine Se metabolism and to work out the best biomarker of Se status. An upgrade from marginal (<0.05 mg Se/kg diet, ‘Se?’) to sufficient (0.2 mg Se/kg diet, ‘Se+’) nutritional Se supply using sodium selenite was monitered biweekly by analysing Se concentration, glutathione peroxidase (Gpx) activity and routine biochemistry in blood/serum over 2 years. Se, Cu, Zn, cytosolic Gpx and thioredoxin reductase (TrxR) activity were measured in the liver (biopsies/post-mortem). Se, Gpx, TrxR, glutathione-S-transferase-alpha (aGST) and iodothyronine deiodinase (Dio1) were analysed in the kidney, heart muscle and thyroid. Relative mRNA expression of hepatic aGST1 and Gpx1 was determined.Improvement of Se supply strongly increased serum and liver Se concentration within 10 and 20 days, respectively followed by a plateau. Whereas the achievement of a maximum whole blood Gpx activity was reached after 3 months, serum Gpx3 activity increased with high variations. Hepatic Gpx activity reached a maximum during days 100–200, decreasing thereafter. Distinct group differences in Se and cytosolic Gpx activity were evident in all organs (except Se in kidney). TrxR and Dio1 activity was affected only in the liver. The Se? sheep showed an ongoing decrease in serum Se concentration within 2 years, whereas liver Se remained almost unaffected. High relative Gpx1 mRNA expression in the Se+ group was consensual to high hepatic Gpx activity. Relative mRNA expression of hepatic aGST1 was higher in the Se? sheep. Clinical signs and abnormalities in routine biochemistry were absent.In summary, the best biomarker of Se deprivation and nutritional Se upgrade, respectively was Se in serum. Moreover, hepatic Se concentrations reliably reflected the upgrade of Se supply within days. Whole blood Gpx reacts slowly depending on newly formed erythrocytes restricting its diagnostic use. Vital organs are affected by Se deficiency due to a decrease of cytosolic Gpx activity attenuating the antioxidative system. Cellular up-regulation of aGST1 mRNA expression in the Se? group is assumed to partially compensate for the decreased antioxidant defence due to a loss in Gpx activity. This sheep model appears advantageous for long-term studies on sub-clinical metabolic effects in experimental modifiable nutritional Se supply.     

CO2 emissions related to the electricity consumption in the european primary aluminium production a comparison of electricity supply approaches

The objective of this study is to estimate the specific CO₂ emissions related to the electricity consumption in the European primary aluminium production and to compare different choices of system boundaries of its electricity supply. The study covers all European aluminium smelters, except Russia and the Ukraine. The concepts of single power plant supply, contract mix, national mix and European grid mix are compared as alternative choices of system boundaries of the electricity supply. The calculations of the electricity consumption in the electrolysis are based on plant-specific information on technology, production and electricity supply. Detailed fuel and country-specific data on CO₂ emissions of the relevant types of electricity generation are used with a ‘from cradle to grave’ perspective. The specific emissions calculated for Europe fall into the range of 6-7 kg CO₂/kg Al depending on the choice of system boundaries.     

Quantifying the drivers of long-term prices in materials supply chains

Raw materials costs form an increasingly significant proportion of the total costs of renewable energy technologies that must be adopted at unprecedented rates to combat climate change. As the affordable deployment of these technologies grows vulnerable to materials price changes, effective strategies must be identified to mitigate the risk of higher input costs faced by manufacturers. To better understand potential threats to deployment, a market modeling approach was developed to quantify economic risk factors including material demand, substitutability, recycling, mining productivity, resource quality, and discovery. Results demonstrate that price changes are determined by interactions between demand growth, mining productivity, and resource quality. In the worst cases with high demand and low productivity, development of material substitutes and large recycling rates help reduce the prevalence of price risk from over 90% to under 10%. Investing in these strategies yields significant benefits for manufacturers and governments concerned about costs of materials critical to decarbonization and other advanced technologies.     

The response of ectomycorrhizal fungal inoculum to long-term increases in nitrogen supply

The inoculum of ectomycorrhizal (EM) fungi was examined in a 16 y long nitrogen fertilization experiment maintained in a temperate oak savanna. To measure EM fungal inoculum, bur oak seedlings were grown in three types of bioassays: (i) intact soil cores that measure inoculum such as spores, mycelia and mycorrhizal roots; (ii) resistant propagule bioassays that measure inoculum types resistant to soil drying; and (iii) previously mycorrhizal root bioassays that measure the ability of EM fungi to colonize new roots from mycorrhizal roots. Colonization of bur oak seedlings was characterized by morphotyping and where necessary by restriction analysis and internal transcribed spacer (ITS) sequencing. Fourteen morphotypes were found in intact soil core bioassays with species of Cortinarius, Cenococcum and Russula abundant. Five morphotypes were found in resistant propagule bioassays with Cenococcum, a thelephoroid morphotype and a Wilcoxina-like ascomycete abundant and frequent. In intact soil core bioassays total percent root colonization and number of morphotypes were not affected by N supply in 2000 and 2001. However the composition of EM fungi colonizing oak seedling roots was different with increased N supply such that Russula spp. (primarily Russula aff. amoenolens) were most abundant at the highest level of N supply. Dominant Russula spp. did not colonize any roots in resistant propagule bioassays but did colonize oak seedling roots from previously mycorrhizal roots. Results suggest that in this savanna N supply can influence the kinds of inoculum propagules present and thereby might affect the dynamics of ectomycorrhizal communities by differentially influencing reproductive and colonization strategies.     

Immunofluorescence examination of beta tubulin expression and marginal band formation in developing chicken erythroblasts

Chicken erythrocyte beta tubulin, a tubulin variant with unique biochemical and assembly properties, is found to be specifically contained in two chicken blood cell types--erythrocytes and thrombocytes. The beta tubulin variant is absent or present in low amounts in a variety of white blood cell types and other body tissues, as determined by immunofluorescence microscopy and a semi-quantitative immunoblotting procedure. During differentiation in the marrow the beta tubulin variant appears suddenly in mid-stage erythroblasts at the onset of hemoglobin synthesis, and forming marginal bands are seen in all subsequent polychromatophilic erythroblast stages. The developmental sequence of events in marginal band formation entails microtubule nucleation at the centrosome, followed by microtubule elongation, consolidation of loose parallel microtubules into a compact bundle, and microtubule association with the cell membrane.     

The marginal zone and marginal sinus in the spleen of the gerbil. A light and electron microscopy study

The spleen of the adult gerbil (M. unguiculatus) is characterized by the absence of venous sinuses and ellipsoid sheaths. The follicle (white pulp) is separated from the surrounding red pulp by a distinct marginal zone. The cell types in the marginal zone are common to both the follicle and red pulp. Separating the marginal zone from the follicle is a vascular channel of capillary dimension, the marginal sinus. A number of terminal segments of the arterial vessels within the follicle were observed to form a direct connection with the marginal sinus. Ultrastructurally, discontinuities were evident within the walls of the marginal sinus that would permit passage of both cellular and plasma components from the marginal sinus to either marginal zone or the follicle.     

Cellular modeling of cancer invasion: integration of in silico and in vitro approaches

Cancer invasion is one of the hallmarks of cancer and a prerequisite for cancer metastasis. However, the invasive process is very complex, depending on multiple correlated intrinsic and environmental factors, and thus is difficult to study experimentally in a fully controlled way. Therefore, there is an increased demand for interdisciplinary integrated approaches combining laboratory experiments with multiscale in silico modeling. In this review, we will summarize current computational techniques applicable to model cancer invasion in silico, with a special focus on a class of individual-cell-based models developed in our laboratories. We also discuss their integration with traditional and novel in vitro experimentation, including new invasion assays whose design was inspired by computational modeling.     

生物多样性管理最小有效面积选取模型与GIS的耦合

人口的增长和自然资源的有限性决定了很难把更多的土地用于生物多样性的保护。通过BMAS(生物多样性管理面积选取)模型与GIS(地理信息系统)的结合,可以用尽可能少的土地资源实现一定水平的生物多样性的保护。该方法初步在西双版纳的勐拉县进行了应用。与现实自然保护区面积的对比,用模型选区自然保护区有显著效果。该方法在保护与发展矛盾尖锐的发展中国家非常适用。