Exploring impacts of process technology development and regional factors on life cycle greenhouse gas emissions of corn stover ethanol

This paper examines impacts of regional factors affecting biomass and process input supply chains and ongoing technology development on the life cycle greenhouse gas (GHG) emissions of ethanol production from corn stover in the U.S. Corn stover supply results in GHG emissions from −6 gCO₂eq./MJ ethanol (Macon County, Missouri) to 13 gCO₂eq./MJ ethanol (Hardin County, Iowa), reflecting location-specific soil carbon and N₂O emissions responses to stover removal. Biorefinery emissions based on the 2011 National Renewable Energy Laboratory (NREL) process model are the single greatest emissions source (18 gCO₂eq./MJ ethanol) and are approximately double those assessed for the 2002 NREL design model, due primarily to the inclusion of GHG-intensive inputs (caustic, ammonia, glucose). Energy demands of on-site enzyme production included in the 2011 design contribute to reducing the electricity co-product and associated emissions credit, which is also dependent on the GHG-intensity of regional electricity supply. Life cycle emissions vary between 1.5 and 22 gCO₂eq./MJ ethanol (2011 design) depending on production location (98%–77% reduction vs. gasoline). Using system expansion for co-product allocation, ethanol production in studied locations meet the Energy Independence and Security Act emissions requirements for cellulosic biofuels; however, regional factors and on-going technology developments significantly influence these results.     

Life-cycle greenhouse gas emissions and energy balances of sugarcane ethanol production in Mexico

The purpose of this work was to estimate GHG emissions and energy balances for the future expansion of sugarcane ethanol fuel production in Mexico with one current and four possible future modalities. We used the life cycle methodology that is recommended by the European Renewable Energy Directive (RED), which distinguished the following five system phases: direct Land Use Change (LUC); crop production; biomass transport to industry; industrial processing; and ethanol transport to admixture plants. Key variables affecting total GHG emissions and fossil energy used in ethanol production were LUC emissions, crop fertilization rates, the proportion of sugarcane areas that are burned to facilitate harvest, fossil fuels used in the industrial phase, and the method for allocation of emissions to co-products. The lower emissions and higher energy ratios that were observed in the present Brazilian case were mainly due to the lesser amount of fertilizers applied, also were due to the shorter distance of sugarcane transport, and to the smaller proportion of sugarcane areas that were burned to facilitate manual harvest. The resulting modality with the lowest emissions of equivalent carbon dioxide (CO_2e) was ethanol produced from direct juice and generating surplus electricity with 36.8 kgCO_2e/GJ_ethanol. This was achieved using bagasse as the only fuel source to satisfy industrial phase needs for electricity and steam. Mexican emissions were higher than those calculated for Brazil (27.5 kgCO_2e/GJ_ethanol) among all modalities. The Mexican modality with the highest ratio of renewable/fossil energy was also ethanol from sugarcane juice generating surplus electricity with 4.8 GJ_ethanol/GJ_fossil.     

Life cycle GHG assessment of fossil fuel power plants with carbon capture and storage

The evaluation of life cycle greenhouse gas emissions from power generation with carbon capture and storage (CCS) is a critical factor in energy and policy analysis. The current paper examines life cycle emissions from three types of fossil-fuel-based power plants, namely supercritical pulverized coal (super-PC), natural gas combined cycle (NGCC) and integrated gasification combined cycle (IGCC), with and without CCS. Results show that, for a 90% CO₂ capture efficiency, life cycle GHG emissions are reduced by 75–84% depending on what technology is used. With GHG emissions less than 170 g/kWh, IGCC technology is found to be favorable to NGCC with CCS. Sensitivity analysis reveals that, for coal power plants, varying the CO₂ capture efficiency and the coal transport distance has a more pronounced effect on life cycle GHG emissions than changing the length of CO₂ transport pipeline. Finally, it is concluded from the current study that while the global warming potential is reduced when MEA-based CO₂ capture is employed, the increase in other air pollutants such as NO_x and NH₃ leads to higher eutrophication and acidification potentials.     

Comparative life cycle assessment of hydrogen and other selected fuels

A streamlined life cycle assessment (LCA) is reported of a nuclear-based copper–chlorine (Cu–Cl) hydrogen production cycle, including estimates of fossil fuel energy use and greenhouse gas (GHG) emissions. Calculations revealed that the process requires 474 kJ of fossil fuel energy per MJ of hydrogen, which is less than for other hydrogen production processes. Moreover, GHG emissions are estimated to be 27 gCO₂e per MJ of hydrogen, which is only slightly higher than the corresponding value for wind-based hydrogen production. A sensitivity analysis demonstrated that the performance of the system could be further improved at higher yields of hydrogen. Although the system significantly outperformed fossil-based gasoline and hydrogen production pathways, the integrated nuclear and thermochemical cycle still requires significant research and development before commercialization is possible.     

Contributing to local policy making on GHG emission reduction through inventorying and attribution: A case study of Shenyang,China

Cities consumed 84% of commercial energy in China, which indicates cities should be the main areas for GHG emissions reduction. Our case study of Shenyang in this paper shows how a clear inventory analysis on GHG emissions at city level can help to identify the major industries and societal sectors for reduction efforts so as to facilitate low-carbon policy-making. The results showed total carbon emission in 2007 was 57 Mt CO₂ equivalents (CO₂e), of which 41 Mt CO₂e was in-boundary emissions and 16 Mt CO₂e was out-of-boundary emissions. The energy sector was dominant in the emission inventory, accounting for 93.1% of total emissions. Within energy sector, emissions from energy production industry, manufacturing and construction industry accounted for 88.4% of this sector. Our analysis showed that comparing with geographical boundary, setting system boundary based on single process standard could provide better information to decision makers for carbon emission reduction. After attributing electricity and heating consumption to final users, the resident and commercial sector became the largest emitter, accounting for 28.5% of total emissions. Spatial analysis of emissions showed that industrial districts such as Shenbei and Tiexi had the large potential to reduce their carbon emissions. Implications of results are finally discussed.     

Life cycle GHG emissions from Malaysian oil palm bioenergy development: The impact on transportation sector's energy security

Malaysia's transportation sector accounts for 41% of the country's total energy use. The country is expected to become a net oil importer by the year 2011. To encourage renewable energy development and relieve the country's emerging oil dependence, in 2006 the government mandated blending 5% palm-oil biodiesel in petroleum diesel. Malaysia produced 16 million tonnes of palm oil in 2007, mainly for food use. This paper addresses maximizing bioenergy use from oil-palm to support Malaysia's energy initiative while minimizing greenhouse-gas emissions from land-use change. When converting primary and secondary forests to oil-palm plantations between 270–530 and 120–190 g CO₂-equivalent per MJ of biodiesel produced, respectively, is released. However, converting degraded lands results in the capture of between 23 and 85 g CO₂-equivalent per MJ of biodiesel produced. Using various combinations of land types, Malaysia could meet the 5% biodiesel target with a net GHG savings of about 1.03 million tonnes (4.9% of the transportation sector's diesel emissions) when accounting for the emissions savings from the diesel fuel displaced. These findings are used to recommend policies for mitigating GHG emissions impacts from the growth of palm oil use in the transportation sector.     

Temporal carbon intensity analysis: renewable versus fossil fuel dominated electricity systems

In order to overcome the negative effects of climate change and ensure a global low-carbon future, decarbonizing the electricity sector has been recognized as an important focus area. Internationally, policymakers use average carbon intensity (in gCO₂-e/kWh) in calculating greenhouse gas (GHG) emissions from the electricity system. However, average carbon intensity is a single rate and a fixed quantity; thus, it does not provide any information about the time-varying nature of carbon intensity. The focus of this paper is to show the usefulness of time-varying carbon intensity estimation, which can provide detailed insights into GHG emissions, and help in identifying potential emission cut opportunities from the electricity sector in order to lessen atmospheric pollution. Time-varying carbon intensity estimation (i) reveals temporal variability of carbon intensity, (ii) explores the interplay between generations and emissions, (iii) identifies peak carbon-intensive hours, and (iv) provides evidence for designing appropriate demand-side management strategies with respect to GHG emission reduction.     

Life cycle assessment of the transmission network in Great Britain

Analysis of lower carbon power systems has tended to focus on the operational carbon dioxide (CO₂) emissions from power stations. However, to achieve the large cuts required it is necessary to understand the whole-life contribution of all sectors of the electricity industry. Here, a preliminary assessment of the life cycle carbon emissions of the transmission network in Great Britain is presented. Using a 40-year period and assuming a static generation mix it shows that the carbon equivalent emissions (or global warming potential) of the transmission network are around 11 gCO_2-eq/kWh of electricity transmitted and that almost 19 times more energy is transmitted by the network than is used in its construction and operation. Operational emissions account for 96% of this with transmission losses alone totalling 85% and sulphur hexafluoride (SF₆) emissions featuring significantly. However, the CO₂ embodied within the raw materials of the network infrastructure itself represents a modest 3%. Transmission investment decisions informed by whole-life cycle carbon assessments of network design could balance higher financial and carbon ‘capital’ costs of larger conductors with lower transmission losses and CO₂ emissions over the network lifetime. This will, however, necessitate new regulatory approaches to properly incentivise transmission companies.     

Electricity consumption and CO2 capture potential in Spain

In this paper, different electricity demand scenarios for Spain are presented. Population, income per capita, energy intensity and the contribution of electricity to the total energy demand have been taken into account in the calculations. Technological role of different generation technologies, i.e. coal, nuclear, renewable, combined cycle (CC), combined heat and power (CHP) and carbon capture and storage (CCS), are examined in the form of scenarios up to 2050. Nine future scenarios corresponding to three electrical demands and three options for new capacity: minimum cost of electricity, minimum CO₂ emissions and a criterion with a compromise between CO₂ and cost (CO₂-cost criterion) have been proposed. Calculations show reduction in CO₂ emissions from 2020 to 2030, reaching a maximum CO₂ emission reduction of 90% in 2050 in an efficiency scenario with CCS and renewables. The contribution of CCS from 2030 is important with percentage values of electricity production around 22–28% in 2050. The cost of electricity (COE) increases up to 25% in 2030, and then this value remains approximately constant or decreases slightly.     

Co-benefit analysis of incentives for energy generation and storage systems; a multi-stakeholder perspective

In this work, we are analyzing the advantages of energy incentives for all the stakeholders in an energy system. The stakeholders include the government, the energy hub operator, and the energy consumer. Two streams of energy incentives were compared in this work: incentives for renewable energy generation technologies and incentives for energy storage technologies. The first type aims increasing the share of renewable energies in the electricity system while the second type aims development of systems which use clean electricity to replace fossil fuels in other sectors of an energy system such as the transportation, residential and industrial sector. In this work, we are analyzing the advantages of energy incentives for all the stakeholders in an energy system. The stakeholders include the government, the energy hub operator, and the energy consumer. Two streams of energy incentives were compared in this work: incentives for renewable energy generation technologies and incentives for energy storage technologies. The first type aims to increase the share of renewable energies in the electricity system while the second type aims the development of systems which use clean electricity to replace fossil fuels in other sectors of an energy system such as the transportation, residential and industrial sector. The results of the analysis showed that replacing fossil fuel-based electricity generation with wind and solar power is a less expensive way for the energy consumer to reduce GHG emissions (60 and 92 CAD/ tonne CO_2e for wind and solar, respectively) compared to investing on energy storage technologies (225 and 317 CAD/ tonne CO_2e for Power-to-Gas and battery powered forklifts, respectively). However, considering the current Ontario's electricity mix, incentives for the Power-to-Gas and battery powered technologies are less expensive ways to reduce emissions compared to replacing the grid with wind and solar power technologies (1479 and 2418 CAD/ tonne CO_2e for wind and solar, respectively). Our analysis also shows that battery storage and hydrogen storage are complementary technologies for reducing GHG emissions in Ontario.     

Spatial variation of emissions impacts due to renewable energy siting decisions in the Western U.S. under high-renewable penetration scenarios

One of the policy goals motivating programs to increase renewable energy investment is that renewable electric generation will help reduce emissions of CO₂ as well as emissions of conventional pollutants (e.g., SO₂ and NO_x). As a policy instrument, Renewable Portfolio Standards (RPS) encourage investments in wind, solar and other generation sources with the goal of reducing air emissions from electricity production. Increased electricity production from wind turbines is expected to displace electricity production from fossil-fired plants, thus reducing overall system emissions. We analyze the emissions impacts of incremental investments in utility-scale wind power, on the order of 1 GW beyond RPS goals, in the Western United States using a utility-scale generation dispatch model that incorporates the impacts of transmission constraints. We find that wind investment in some locations leads to slight increases in overall emissions of CO₂, SO₂ and NO_x. The location of wind farms influences the environmental impact by changing the utilization of transmission assets, which affects the overall utilization of power generation sources and thus system-level emissions. Our results suggest that renewable energy policy beyond RPS targets should be carefully crafted to ensure consistency with environmental goals.     

Green hydrogen-based E-fuels (E-methane,E-methanol,E-ammonia) to support clean energy transition: A literature review

Renewable power-to-fuel (PtF) is a key technology for the transition towards fossil-free energy systems. The production of carbon neutral synthetic fuels is primarily driven by the need to decouple the energy sector from fossil fuels dependance which are the main source of environmental issues. Hydrogen (H₂) produced from water electrolysis powered by renewable electricity and direct carbon dioxide (CO₂) captured from the flue gas generated by power plants, industry, transportation, and biogas production from anaerobic digestion, are used to convert electricity into carbon-neutral synthetic fuels. These fuels function as effective energy carriers that can be stored, transported, and used in other energy sectors (transport and industry). In addition, the PtF concept is an energy transformation that is capable of providing services for the balancing of the electricity grid thanks to its adaptable operation and long-term storage capacities for renewable energy surplus. As a consequence, it helps to potentially decarbonize the energy sector by reducing the carbon footprint and GHG emissions. This paper gives an overview on recent advances of renewable PtF technology for the e-production of three main hydrogen-based synthetic fuels that could substitute fossil fuels such as power-to-methane (PtCH₄), power-to-methanol (PtCH₃OH) and power-to-ammonia (PtNH₃). The first objective is to thoroughly define in a clear manner the framework which includes the PtF technologies. Attention is given to green H₂ production by water electrolysis, carbon capture & storage (CCS), CO₂ hydrogenation, Sabatier, and Haber Bosch processes. The second objective is to gather and classify some existing projects which deal with this technology depending on the e-fuel produced (energy input, conversion process, efficiency, fuel produced, and application). Furthermore, the challenges and future prospects of achieving sustainable large-scale PtF applications are discussed.     

How important are current energy mix choices on future sustainability? Case study: Belgium and Spain—projections towards 2020–2030

Despite recent consumption decrease due to recession, European electricity sector is struggling to reach ambitious targets for reductions of greenhouse gas emissions. Our objective is to carry out a macro analysis of the energy mix in two European countries: Belgium and Spain. Life Cycle Assessments are carried for 2005 as well as for seven possible referenced scenarios to reach EU and also national legal objectives at the horizon 2020 and 2030. Ambitious renewable energy sources’ deployment plans can decrease impacts on the environment significantly as those sources replace polluting traditional sources, such as coal/lignite, oil or gas. When concentrating on projections for the future in Spain, results show that a mix with little coal and oil replaced by up to 54% of RES-E energy sources could bring environmental benefits with CO₂ emissions equivalent around 0.2 kg per kWh produced (compared with 0.54 kg in 2005). In Belgium, all future scenarios presented include more coal and gas with a limited share of RES-E; those mixes present more environmental harmful impacts (up to 0.56 kg CO₂ equivalent). This is why RES-E deployment is crucial as long as it is part of an electricity mix with reduced quantities of traditional fossil fuels.     

Determining marginal electricity for near-term plug-in and fuel cell vehicle demands in California: Impacts on vehicle greenhouse gas emissions

California has taken steps to reduce greenhouse gas emissions from the transportation sector. One example is the recent adoption of the Low Carbon Fuel Standard, which aims to reduce the carbon intensity of transportation fuels. To effectively implement this and similar policies, it is necessary to understand well-to-wheels emissions associated with distinct vehicle and fuel platforms, including those using electricity. This analysis uses an hourly electricity dispatch model to simulate and investigate operation of the current California grid and its response to added vehicle and fuel-related electricity demands in the near term. The model identifies the “marginal electricity mix” - the mix of power plants that is used to supply the incremental electricity demand from vehicles and fuels - and calculates greenhouse gas emissions from those plants. It also quantifies the contribution from electricity to well-to-wheels greenhouse gas emissions from battery-electric, plug-in hybrid, and fuel cell vehicles and explores sensitivities of electricity supply and emissions to hydro-power availability, timing of electricity demand (including vehicle recharging), and demand location within the state. The results suggest that the near-term marginal electricity mix for vehicles and fuels in California will come from natural gas-fired power plants, including a significant fraction (likely as much as 40%) from relatively inefficient steam- and combustion-turbine plants. The marginal electricity emissions rate will be higher than the average rate from all generation - likely to exceed 600 gCO₂ equiv. kWh⁻¹ during most hours of the day and months of the year - and will likely be more than 60% higher than the value estimated in the Low Carbon Fuel Standard. But despite the relatively high fuel carbon intensity of marginal electricity in California, alternative vehicle and fuel platforms still reduce emissions compared to conventional gasoline vehicles and hybrids, through improved vehicle efficiency.     

Energy consumption and CO2 emissions of potato peel and sugarcane biohydrogen production pathways, applied to Portuguese road transportation

This paper analyses the energy consumption and CO₂ emissions of biological hydrogen production from sugarcane and potato peels using life cycle assessment methodology for the Portuguese scenario. Potato peels are assumed to be produced locally from Portuguese potato cultivation. Sugarcane is assumed to be imported from Brazil and fermented in Portugal. The uncertainty is quantified by a Monte Carlo approach. Biohydrogen was compared with natural gas reforming, electrolysis and other energy resources such as diesel and electricity. Between bioH₂ feedstocks, sugarcane stands out with the lowest values for energy consumption and CO₂ emissions with 0.30–0.34 MJ of consumed energy and 24–31 g of CO₂ emitted per 1 MJ of H₂ produced. However these results do not have a major contribution to the Portuguese energy independency problem. On the other hand potato peels feedstocks are more attractive, presenting values of 0.49–0.61 MJ/MJ_H2 and 60-77 gCO₂/MJ_H2. According to Portuguese production capabilities, it is estimated that biohydrogen will be able to supply 3100 vehicles of a typical Portuguese urban taxi fleet or up to 1.4 million passenger cars with a daily commuting distance of 30 km.     

Study on China's low carbon development in an Economy–Energy–Electricity–Environment framework

Emissions mitigation is a major challenge for China's sustainable development. We summarize China's successful experiences on energy efficiency in past 30 years as the contributions of Energy Usage Management and Integrated Resource Strategic Planning, which are essential for low-carbon economy. In an Economy–Energy–Electricity–Environment (E4) framework, the paper studies the low-carbon development of China and gives an outlook of China's economy growth, energy–electricity demand, renewable power generation and energy conservation and emissions mitigation until 2030. A business-as-usual scenario is projected as baseline for comparison while low carbon energy and electricity development path is studied. It is defined as low carbon energy/electricity when an economy body manages to realize its potential economic growth fueled by less energy/electricity consumption, which can be characterized by indexes of energy/electricity intensity and emissions per-unit of energy consumption (electricity generation). Results show that, with EUM, China, could save energy by 4.38 billion ton oil equivalences (toes) and reduce CO₂ emission by 16.55 billion tons; with IRSP, China, could save energy by 1.5 Btoes and reduce CO₂ emission by 5.7 Btons, during 2010–2030. To realize the massive potential, China has to reshape its economic structure and rely much on technology innovation in the future.     

Global and regional potential for bioelectricity with carbon capture and storage

Among technological options to mitigate greenhouse gas (GHG) emissions, biomass energy with carbon capture and storage technology (BECCS) is gaining increasing attention. This alternative offers a unique opportunity for a net removal of atmospheric CO₂ while fulfilling energy needs. Empirical studies using bottom-up energy models show that BECCS has an important role to play in the future energy mix. Most of these studies focus on global BECCS potential, whereas it is of interest to understand where this mitigation option will be deployed. This key issue will strongly depend on regions’ biomass resources and possession of storage sites. The aim of this study is to assess the global and regional potential of BECCS up to 2050 in power generation. This analysis is conducted using the multiregional TIAM-FR optimization model. The climate policy scenarios investigated lead to a considerable expansion of renewable energy and CCS and BECCS technologies in the power sector. CCS from fossil fuel is mainly deployed in fast developing countries (India and China) and BECCS is highly distributed in developing countries, even though biomass resources are widely available in all regions.     

Comparative study of a hybrid research vessel utilizing batteries or hydrogen fuel cells

The Scripps Institution of Oceanography (SIO) current coastal/local research vessel, the R/V Robert Gordon Sproul, is nearing the end of its service life and will soon require replacement. This study compares three potential variants for an R/V Sproul replacement vessel (SRV): a Baseline SRV consisting of a traditional diesel-electric powertrain, a Battery Hybrid SRV (battery/diesel-electric) and a Hydrogen Hybrid SRV (hydrogen fuel cell/diesel-electric). All three variants meet the science mission requirements of the SRV but with varying levels of zero-emission runtime, energy efficiency and emissions. The Battery Hybrid SRV can provide 2.5 h of zero emissions (battery only) operation, but could not complete any of the identified SRV science missions without also engaging the diesel generators. In contrast, the Hydrogen Hybrid SRV can provide 23.4 h of zero emission (hydrogen only) runtime, and can complete 74% of the SRV science missions solely with zero-emission operation. The superior performance of the Hydrogen Hybrid SRV is attributable to the higher volumetric energy storage density of the LH₂/fuel cell combination. The capital costs of these vessels are estimated to be: ∼ $21.4 M for the diesel-electric Baseline SRV, ∼ $26.0 M for the Battery Hybrid SRV vessel and ∼ $34.4 M for the Hydrogen Hybrid SRV. The “well-to-waves” (WTW) greenhouse gas (GHG) and criteria pollutant emissions were estimated using various sourcings for the diesel fuel, electricity and hydrogen fuel. The lowest emission levels are achieved with the Hydrogen Hybrid variant using 100% renewable hydrogen. The annual WTW GHG emissions from the Hydrogen Hybrid using renewable LH₂ in combination with fossil diesel in the hybrid arrangement yields a 26.7% GHG emissions reduction from the Baseline vessel using fossil-derived diesel fuel. The Battery Hybrid vessel with 100% renewable electricity combined with diesel fuel provides a 6.9% reduction in GHG emissions. Similar results are seen for the criteria pollutant emissions. The hybrid vessels are also compared with regard to operational safety. The study reveals that hydrogen fuel-cell technology provides an effective hybrid supplement to diesel power for a coastal/local research vessel.     

Energy demand and greenhouse gas emissions during the production of a passenger car in China

Rapidly-rising oil demand and associated greenhouse gas (GHG) emissions from road vehicles in China, passenger cars in particular, have attracted worldwide attention. As most studies to date were focused on the vehicle operation stage, the present study attempts to evaluate the energy demand and GHG emissions during the vehicle production process, which usually consists of two major stages—material production and vehicle assembly. Energy demand and GHG emissions in the material production stage are estimated using the following data: the mass of the vehicle, the distribution of material used by mass, and energy demand and GHG emissions associated with the production of each material. Energy demand in the vehicle assembly stage is estimated as a linear function of the vehicle mass, while the associated GHG emission is estimated according to the primary energy sources. It is concluded that the primary energy demand, petroleum demand and GHG emissions during the production of a medium-sized passenger car in China are 69,108 MJ, 14,545 MJ and 6575 kg carbon dioxide equivalent (CO₂-eq). Primary energy demand, petroleum demand and GHG emissions in China’s passenger car fleets in 2005 would be increased by 22%, 5% and 30%, respectively, if the vehicle production stage were included.