Electricity generation is a key contributor to global emissions of greenhouse gases (GHG), NO x and SO 2 and their related environmental impact. A critical review of 167 case studies involving the life cycle assessment (LCA) of electricity generation based on hard coal, lignite, natural gas, oil, nuclear, biomass, hydroelectric, solar photovoltaic (PV) and wind was carried out to identify ranges of emission data for GHG, NO x and SO 2 related to individual technologies. It was shown that GHG emissions could not be used as a single indicator to represent the environmental performance of a system or technology. Emission data were evaluated with respect to three life cycle phases (fuel provision, plant operation, and infrastructure). Direct emissions from plant operation represented the majority of the life cycle emissions for fossil fuel technologies, whereas fuel provision represented the largest contribution for biomass technologies (71% for GHG, 54% for NO x and 61% for SO 2 ) and nuclear power (60% for GHG, 82% for NO x and 92% for SO 2 ); infrastructures provided the highest impact for renewables. These data indicated that all three phases should be included for completeness and to avoid problem shifting. The most critical methodological aspects in relation to LCA studies were identified as follows: definition of the functional unit, the LCA method employed (e.g., IOA, PCA and hybrid), the emission allocation principle and/or system boundary expansion. The most important technological aspects were identified as follows: the energy recovery efficiency and the flue gas cleaning system for fossil fuel technologies; the electricity mix used during both the manufacturing and the construction phases for nuclear and renewable technologies; and the type, quality and origin of feedstock, as well as the amount and type of co-products, for biomass-based systems. This review demonstrates that the variability of existing LCA results for electricity generation can give rise to conflicting decisions regarding the environmental consequences of implementing new technologies.
23Life cycle assessment (LCA) has been used extensively within the recent decade to 24 evaluate the environmental performance of thermal Waste-to-Energy (WtE) 25 technologies: incineration, co-combustion, pyrolysis and gasification. A critical review 26 was carried out involving 250 individual case-studies published in 136 peer-reviewed 27 journal articles within 1995 and 2013. The studies were evaluated with respect to 28 critical aspects such as: i) goal and scope definitions (e.g. functional units, system 29 boundaries, temporal and geographic scopes), ii) detailed technology parameters (e.g. 30 related to waste composition, technology, gas cleaning, energy recovery, residue 31 management, and inventory data), and iii) modeling principles (e.g. energy/mass 32 calculation principles, energy substitution, inclusion of capital goods and uncertainty 33 evaluation). Very few of the published studies provided full and transparent descriptions 34 of all these aspects, in many cases preventing an evaluation of the validity of results, 35 and limiting applicability of data and results in other contexts. The review clearly 36suggests that the quality of LCA studies of WtE technologies and systems including 37 energy recovery can be significantly improved. Based on the review, a detailed 38 overview of assumptions and modeling choices in existing literature is provided in 39 conjunction with practical recommendations for state-of-the-art LCA of waste-to-40 energy. 41 42
In Europe, about 20% of municipal solid waste is incinerated. Large differences can be found between northern and southern Europe regarding energy recovery efficiencies, flue gas cleaning technologies and residue management. Life-cycle assessment (LCA) of waste incineration often provides contradictory results if these local conditions are not properly accounted for. The importance of regional differences and site-specific data, and choice of LCA model itself, was evaluated by assessment of two waste incinerators representing northern and southern Europe (Denmark and Italy) based on two different LCA models (SimaPro and EASEWASTE). The results showed that assumptions and modelling approaches regarding energy recovery/ substitution and direct air emissions were most critical. Differences in model design and model databases mainly had consequences for the toxicity-related impact categories. The overall environmental performance of the Danish system was better than the Italian, mainly because of higher heat recovery at the Danish plant. Flue gas cleaning at the Italian plant was, however, preferable to the Danish, indicating that efficient flue gas cleaning may provide significant benefits. Differences in waste composition between the two countries mainly affected global warming and human toxicity via water. Overall, SimaPro and EASEWASTE provided consistent ranking of the individual scenarios. However, important differences in results from the two models were related to differences in the databases and modelling approaches, in particular the possibility for modelling of waste-specific emissions affected the toxicity-related impact categories. The results clearly showed that the use of site-specific data was essential for the results.
Publication information Applied Energy, 131 : 1-8Publisher ElsevierItem record/more information http://hdl.handle.net/10197/8075 Publisher's statementThis is the author's version of a work that was accepted for publication in Applied Energy. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Applied Energy (VOL 131, ISSUE 2014, (2014 AbstractThe increase of renewable sources in the power sector is an important step towards more sustainable electricity production. However, introducing high shares of variable renewables, such as wind and solar, cause dispatchable power plants to vary their output to fulfill the remaining electrical demand. The environmental impacts relating to potential future energy systems in Ireland for 2025 with high shares of wind power were evaluated using life cycle assessment (LCA), focusing on cycling emissions (due to partload operation and start-ups) from dispatchable generators. Part-load operations significantly affect the average power plant efficiency, with all units seeing an average yearly efficiency noticeably less than optimal. In particular, load following units, on average, saw an 11% reduction. Given that production technologies are typically modeled assuming steady-state operation at full load, as part of LCA of electricity generation, the efficiency reduction would result in large underestimation of emissions, e.g. up to 65% for an oil power plant. Overall, cycling emissions accounted for less than 7% of lifecycle CO 2 , NO x and SO 2 emissions in the five scenarios considered: while not overbalancing the benefits from increasing wind energy, cycling emissions are not negligible and should be systematically included (i.e. by using emission factors per unit of fuel input rather than per unit of power generated). As the ability to cycle is an additional service provided by a power plant, it is also recommended that only units with similar roles (load following, mid merit, or base load) should be compared. The results showed that cycling emissions increased with the installed wind capacity, but decreased with the addition of storage. The latter benefits can, however, only be obtained if base-load electricity production shifts to a cleaner source than coal. Finally, the present study indicates that, in terms of emission reductions, the priority for Ireland is to phase out coal-based power plants. While investing in new storage capacity reduces system operating costs at high wind penetrations and limits cycling, the emissions reductions are somewhat negated when coupled with base load coal. KeywordsLife cycle assessment (LCA), energy modeling, power plant cycling, wind power, renewable energy system, emission factors Highlights Environmental impact of a power system with a high share of wind power assessed Cyc...
To meet climate and sustainability goals a transition of the system of energy supply and use is needed. However, energy transitions are complex long-term processes and require a variety of methodologies to steer their direction. For this purpose, the combination of environmental, social, economic and technical assessments together with prospective energy scenario modelling is very promising but there are several challenges that need to be addressed to fully benefit from these methodologies. This paper presents the discussions held during a conference session on this issue. The solutions proposed facilitate the combination of energy system modelling frameworks and environmental and social assessments aimed at developing comprehensive prospective studies and feeding information to decision making processes for energy transition toward a low-carbon economy.
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