Joe Marriott

Life Cycle Assessment and Grid Electricity: What Do We Know and What Can We Know?

The generation and distribution of electricity comprises nearly 40% of U.S. CO(2), emissions, as well as large shares of SO(2), NO(x), small particulates, and other toxins. Thus, correctly accounting for these electricity-related environmental releases is of great importance in life cycle assessment of products and processes. Unfortunately, there is no agreed-upon protocol for accounting for the environmental emissions associated with electricity, as well as significant uncertainty in the estimates. Here, we explore the limits of current knowledge about grid electricity in LCA and carbon footprinting for the U.S. electrical grid, and show that differences in standards, protocols, and reporting organizations can lead to important differences in estimates of CO(2) SO(2), and NO(x) emissions factors. We find a considerable divergence in published values for grid emissions factor in the U.S. We discuss the implications of this divergence and list recommendations for a standardized approach to accounting for air pollution emissions in life cycle assessment and policy analyses in a world with incomplete and uncertain information.

Evaluating the climate benefits of CO2-enhanced oil recovery using life cycle analysis.

This study uses life cycle analysis (LCA) to evaluate the greenhouse gas (GHG) performance of carbon dioxide (CO2) enhanced oil recovery (EOR) systems. A detailed gate-to-gate LCA model of EOR was developed and incorporated into a cradle-to-grave boundary with a functional unit of 1 MJ of combusted gasoline. The cradle-to-grave model includes two sources of CO2: natural domes and anthropogenic (fossil power equipped with carbon capture). A critical parameter is the crude recovery ratio, which describes how much crude is recovered for a fixed amount of purchased CO2. When CO2 is sourced from a natural dome, increasing the crude recovery ratio decreases emissions, the opposite is true for anthropogenic CO2. When the CO2 is sourced from a power plant, the electricity coproduct is assumed to displace existing power. With anthropogenic CO2, increasing the crude recovery ratio reduces the amount of CO2 required, thereby reducing the amount of power displaced and the corresponding credit. Only the anthropogenic EOR cases result in emissions lower than conventionally produced crude. This is not specific to EOR, rather the fact that carbon-intensive electricity is being displaced with captured electricity, and the fuel produced from that system receives a credit for this displacement.

Preliminary Comparative Life-Cycle Impacts of Streetlight Technology

As part of a streetlight-retrofitting project in Pittsburgh, this study performed a cradle-to-grave life-cycle assessment of four lighting technologies: the widespread high-pressure sodium and metal halide lights, and the newer and more efficient induction and light-emitting-diode technologies. The study used a hybrid life-cycle-assessment approach to build life-cycle models for the various technologies, including manufacturing and installation data for process models and energy supply and input-output data to complete life-cycle models. Three different electricity scenarios were used to examine the sensitivity of the impacts to changes in energy supply: the United States average mix, the regional mix for the ReliabilityFirst Corporation region, and a scenario with 100% wind power. The results show that for all technologies, the impacts of electricity in the use phase dominates the results. Because of their lower wattage, light-emitting diode (LED) and induction technology perform favorably and similarly. With anticipated improvements in technology, however, LEDs are expected to be more efficient than induction in the near future and have lower environmental impacts by the time that Pittsburgh and other cities buy and install lights as part of these streetlight projects, which have the potential to show large cost and emissions savings.

Impact of Power Generation Mix on Life Cycle Assessment and Carbon Footprint Greenhouse Gas Results

Summary The mix of electricity consumed in any stage in the life cycle of a product, process, or industrial sector has a significant effect on the associated inventory of emissions and environmental impacts because of large differences in the power generation method used. Fossil-fuel-fired or nuclear-centralized steam generators; large-scale and small-scale hydroelectric power; and renewable options, such as geothermal, wind, and solar power, each have a unique set of issues that can change the results of a life cycle assessment. This article shows greenhouse gas emissions estimates for electricity purchase for different scenarios using U.S. average electricity mix, state mixes, state mixes including imports, and a sector-specific mix to show how different these results can be. We find that greenhouse gases for certain sectors and scenarios can change by more than 100%. Knowing this, practitioners should exercise caution or at least account for the uncertainty associated with mix choice.

Identifying/Quantifying Environmental Trade-offs Inherent in GHG Reduction Strategies for Coal-Fired Power.

Improvements to coal power plant technology and the cofired combustion of biomass promise direct greenhouse gas (GHG) reductions for existing coal-fired power plants. Questions remain as to what the reduction potentials are from a life cycle perspective and if it will result in unintended increases in impacts to air and water quality and human health. This study provides a unique analysis of the potential environmental impact reductions from upgrading existing subcritical pulverized coal power plants to increase their efficiency, improving environmental controls, cofiring biomass, and exporting steam for industrial use. The climate impacts are examined in both a traditional-100 year GWP-method and a time series analysis that accounts for emission and uptake timing over the life of the power plant. Compared to fleet average pulverized bed boilers (33% efficiency), we find that circulating fluidized bed boilers (39% efficiency) may provide GHG reductions of about 13% when using 100% coal and reductions of about 20-37% when cofiring with 30% biomass. Additional greenhouse gas reductions from combined heat and power are minimal if the steam coproduct displaces steam from an efficient natural gas boiler. These upgrades and cofiring biomass can also reduce other life cycle impacts, although there may be increased impacts to water quality (eutrophication) when using biomass from an intensely cultivated source. Climate change impacts are sensitive to the timing of emissions and carbon sequestration as well as the time horizon over which impacts are considered, particularly for long growth woody biomass.

Uncertainty and variability in accounting for grid electricity in life cycle assessment

The generation and distribution of electric power is enormously important in both economic and environmental terms. However, despite the obvious importance of electricity for life cycle assessment and policy analysis, accounting for the environmental emissions associated with electricity remains an uncertain task. In this analysis we examine the different methods available for electricity greenhouse gas emissions accounting, and show that different standards, protocols, and reporting organizations can lead to considerably different estimates of emissions associated with purchased electricity. We discuss the implications of this uncertainty and list recommendations for electricity emissions accounting in the world of incomplete and uncertain information.

The Green Design Apprenticeship

In order to convey the results of our industrial ecology research to broader audiences, the Green Design Institute research group at Carnegie Mellon University offers the Green Design Apprenticeship for local high school students. The Green Design Apprenticeship introduces participants to industrial ecology concepts and how they intersect with engineering. The content of the program has evolved to include the topics of life cycle assessment, energy and water resources, transportation, and the built environment. The program has resulted in exposing a new generation of scholars to industrial ecology and has also benefited the research of graduate students involved with the program. The process of developing the instructional materials for younger, novice students based on complex industrial ecology research was a challenging task requiring thoughtful and iterative planning. Through the development and delivery of the program, we have experienced awareness of where our own research fits into the larger industrial ecology scope, have improved our communication of complex industrial ecology concepts into simple terms, and have gained valuable insight for engaging students in our teaching.

How much electricity do you use? An activity to teach high school students about energy issues

Despite the regular demand for electrical power by common, everyday devices, few people recognize the total electricity consumption levels of household electronics and the associated impacts. To address this problem in an outreach program with high school students, we developed an exercise to have students estimate their personal electricity consumption as a means of introducing basic facts about energy issues. The activity requires students to estimate the annual electricity consumption for their bedroom (not an entire house). Students create a list of electrical devices, recording the rated wattage and estimating the hours the device is used. During the classroom exercise, students use a power meter to measure the actual power consumption of some common items on their lists. After students have calculated their annual electricity consumption, we discuss several points, such as the importance of both the wattage and the time an item is used, rated wattage versus actual wattage, efficiency of various energy sources, and changes students can make to reduce their electricity consumption. After the activity, students have a greater understanding of basic electricity concepts and an awareness of how their behaviors and decisions impact their overall consumption patterns.

Effects of Using Heterogeneous Prices on the Allocation of Impacts from Electricity Use: A Mixed-Unit Input-Output Approach

Summary Economic input-output life cycle assessment (IO-LCA) models allow for quick estimation of economy-wide greenhouse gas (GHG) emissions associated with goods and services. IO-LCA models are usually built using economic accounts and differ from most process-based models in their use of economic transactions, rather than physical flows, as the drivers of supply-chain GHG emissions. GHG emissions estimates associated with input supply chains are influenced by the price paid by consumers when the relative prices between individual consumers are different. We investigate the significance of the allocation of GHG emissions based on monetary versus physical units by carrying out a case study of the U.S. electricity sector. We create parallel monetary and mixed-unit IO-LCA models using the 2007 Benchmark Accounts of the U.S. economy and sector specific prices for different end users of electricity. This approach is well suited for electricity generation because electricity consumption contributes a significant share of emissions for most processes, and the range of prices paid by electricity consumers allows us to explore the effects of price on allocation of emissions. We find that, in general, monetary input-output models assign fewer emissions per kilowatt to electricity used by industrial sectors than to electricity used by households and service sectors, attributable to the relatively higher prices paid by households and service sectors. This fact introduces a challenging question of what is the best basis for allocating the emissions from electricity generation given the different uses of electricity by consumers and the wide variability of electricity pricing.

Updating the U.S. Life Cycle GHG Petroleum Baseline to 2014 with Projections to 2040 Using Open-Source Engineering-Based Models

The National Energy Technology Laboratory produced a well-to-wheels (WTW) life cycle greenhouse gas analysis of petroleum-based fuels consumed in the U.S. in 2005, known as the NETL 2005 Petroleum Baseline. This study uses a set of engineering-based, open-source models combined with publicly available data to calculate baseline results for 2014. An increase between the 2005 baseline and the 2014 results presented here (e.g., 92.4 vs 96.2 g CO2e/MJ gasoline, + 4.1%) are due to changes both in modeling platform and in the U.S. petroleum sector. An updated result for 2005 was calculated to minimize the effect of the change in modeling platform, and emissions for gasoline in 2014 were about 2% lower than in 2005 (98.1 vs 96.2 g CO2e/MJ gasoline). The same methods were utilized to forecast emissions from fuels out to 2040, indicating maximum changes from the 2014 gasoline result between +2.1% and -1.4%. The changing baseline values lead to potential compliance challenges with frameworks such as the Energy Independence and Security Act (EISA) Section 526, which states that Federal agencies should not purchase alternative fuels unless their life cycle GHG emissions are less than those of conventionally produced, petroleum-derived fuels.