Carbon Intensity Of Electricity Research Articles

Load-Shifting Strategies for Cost-Effective Emission Reductions at Wastewater Facilities.

Significant hourly variation in the carbon intensity of electricity supplied to wastewater facilities introduces an opportunity to lower emissions by shifting the timing of their energy demand. This shift could be accomplished by storing wastewater, biogas from sludge digestion, or electricity from on-site biogas generation. However, the life cycle emissions and cost implications of these options are not clear. We present a multiobjective optimization framework for comparing cost- and emission-minimizing load-shifting strategies at a California case study facility with a relatively low carbon intensity grid and high spread in peak and off-peak electricity prices. We evaluate cost and emission trade-offs from the optimal flexible operation of both existing infrastructure and optimally sized energy flexibility upgrades. We estimate energy-related emission reductions of up to 9.0% with flexible operation of existing infrastructure and up to 16.8% with optimally sized storage upgrades. Only a fraction of these potential savings are realized under actual industrial energy tariffs and the EPA's recommended social cost of carbon. Energy flexibility may hold promise as a short-term emission-saving solution for the wastewater sector, but the extent of savings is heavily dependent on the cost of carbon, electricity tariffs, and emission intensity of the regional electricity grid.

Observing the interaction between energy generation carbon emissions and economic conditions could consider generation, intensity, and times of the day.

Management of carbon emissions of regional electricity generation involves resolving much nuanced relationships. However, current studies pertaining to the relationship between energy and the economy utilize only quarterly and annual data and focus on the long-run relationship but are oblivious to temporal associations. This study takes the context of the State of Texas and utilizes per 15min of data between 2007 and 2020 to derive the monthly time series of life-cycle emissions, emissions factor, and energy generation. The study also divides each day into three portions (0:00-8:00, 8:00-16:00, and 16:00-24:00) in order to descend precision down to the hourly level. Impulse-response analysis indicates that (1) employment conditions impact emissions by affecting the amount of electric energy generated, while demographic (population as reflected by property price) tends to impact emissions by affecting the carbon intensity of electricity, and (2) the emissions produced during 0:00-8:00 display different reaction to fluctuation of regional economic conditions compared to emissions produced during other periods, the effect emanates from either energy generation fluctuation or emissions factor shocks. The broader implication of the findings lies in an emphasis on time-interval-specific analysis and concurrent consideration of both energy generation and emissions factors that can lead to optimized policy implementation results.

Assessing the net carbon removal potential by a combination of direct air capture and recycled concrete aggregates carbonation

Removing and storing CO2 from the atmosphere has an important role in combating climate change. This study assessed the CO2 removal potential of combining direct air capture with carbonation of recycled concrete aggregates (RCAs). An industrial-scale RCA carbonation process model quantified key parameters' impacts on carbonation duration and energy consumption. Furthermore, a lifecycle analysis evaluated scenarios of two cases: (i) using pure CO2 with transportation between DAC and carbonation, and (ii) onsite production of low-purity CO2. For 90 % carbonation of 1 tonne of RCA, the performance of case-i scenarios ranged from ∼13 kg net CO2 removal to ∼14 kg net CO2 emission, influenced by DAC technology, transport option, and electricity carbon intensity. In case-ii scenarios, 1 % CO2 feed purity achieved 70 % greater CO2 removal than using pure CO2. This work provides an initial indication of the potential of this scheme while revealing key factors to investigate in future experimental exploration.

Building Electrochemical Roadmaps for Decarbonization in the Specialty Chemical Sector

Greenhouse gas emissions from the chemical manufacturing industry are enormous, by some estimates they amount to 5% percent of the global total.1,2 Moreover, chemical manufacturing is widely considered as a “difficult-to-decarbonize” sector due to the deeply entrenched reliance on crude-based hydrocarbons as fuels and feedstocks.3 The ultimate goal of eliminating anthropogenic greenhouse gas emissions, clearly demands a wholesale reconsideration of energy and material flows in chemical manufacturing.One area of research that has gained momentum in the past decade is the use of electrochemistry to perform organic redox reactions. These types of electrosynthetic transformations provide a straightforward means to electrify chemical manufacturing, thereby decreasing the global warming impact as the carbon intensity of grid electricity diminishes with continued adoption of low-carbon power sources. Further improvements are achievable through decarbonization of material inputs, e.g., by replacing problematic redox reagents like methane-derived hydrogen or fuming nitric acid with reactive hydrogen and oxygen intermediates generated at electrodes via water electrolysis.Despite these promising advances, interest in organic electrosynthesis to date has mainly focused on the production of commodity chemicals (e.g., CO2 reuse, ammonia electrosynthesis) at the expense of specialty chemical synthesis. This focus is well justified based on the possible impact of major breakthroughs on global emissions, but it constitutes missed opportunities to drive broad adoption of electrosynthesis across the chemical industry. To address this knowledge gap, our lab has undertaken a collaborative research effort with a global specialty chemical manufacturer to explore opportunities to decarbonize through electrification strategies involving electrosynthetic reaction schemes.This presentation will detail our recent work on a holistic “scoping study” to estimate the potential for reducing the global warming emissions profiles for a representative set of specialty chemicals through the adoption of electrosynthetic methods. First, we mapped the supply chain for 12 specific chemicals (chosen for their relevance to the specialty industry and significant global warming potential from current production methods) in terms of all reactive processes required to generate these compounds from petrochemical feedstocks. Next, we searched for literature reports detailing electrosynthetic pathways to generate each intermediate species along the manufacturing supply chain. The relevant electrochemical reactions were broadly classifiable as (a) generating alternatives to petrochemical feedstocks; (b) direct replacement of an existing chemical redox reaction with an electrochemical reaction; or (c) intensified approaches that use electrochemistry to reduce the total number of reactive process steps required. Finally, we benchmarked the potential for reduced greenhouse gas emissions for electrosynthetic schemes compared to the incumbent technologies based on a set of simplifying assumptions that involve calculating baseline emissions intensities as a function of the thermodynamic minimum energy input and the carbon intensity of the electric power supply, and further applying generic “efficiency factors” to account for all emissions in excess of this thermodynamic minimum. The results of this analysis suggest remarkable opportunities to develop electrosynthetic schemes for a handful of reactions for which global warming emissions could be reduced even in the most conservative scenarios of low process efficiency and high carbon intensity of the input power.This presentation will also cover the hurdles we have identified in the development of modular and continuously operated electrosynthetic reactors, as well as what we have learned in addressing these challenges.References(1) Saygin, D.; Gielen, D. Zero-Emission Pathway for the Global Chemical and Petrochemical Sector. Energies 2021, 14 (13), 3772. https://doi.org/10.3390/en14133772.(2) Gabrielli, P.; Rosa, L.; Gazzani, M.; Meys, R.; Bardow, A.; Mazzotti, M.; Sansavini, G. Net-Zero Emissions Chemical Industry in a World of Limited Resources. One Earth 2023, 6 (6), 682–704. https://doi.org/10.1016/j.oneear.2023.05.006.(3) Gross, S. The Challenge of Decarbonizing Heavy Industry, 2021. https://www.brookings.edu/wp-content/uploads/2021/06/FP_20210623_industrial_gross_v2.pdf.

Reducing CO2 emissions in a peer-to-peer distributed payment network: Does geography matter in the lightning network?

Bitcoin, Ethereum and other blockchain-related globally distributed peer-to-peer networks have become an important payment infrastructure. Because they are naturally decentralized and distributed, they can consume resources unevenly, raising some sustainability concerns. The Lightning Network (LN) is a growing but understudied second layer network built on blockchain infrastructure and designed to make fast and anonymous global multi-pass payments. At a conservative estimate, this infrastructure produces about 1.4 million tons of carbon dioxide (CO2) per year. Thus, in this paper, we aim to justify a general approach to consider topology and the geographical distribution of this type of network in the design and investigate ways to prevent excessive CO2 emissions. While the LN itself shows great promise as a scalable and widely adopted solution, there has been limited research exploring its structure, distribution, and performance from a sustainability perspective. This study contributes to analyzing the LN’s topology, geospatial distribution, and pathfinding algorithms. By examining real-world data snapshots of the LN, we investigate the relationship between payment routes that are produced by native pathfinding algorithms, geographical distribution of the network and the carbon intensity of electricity in the countries involved in the final payment paths. Our analysis highlights the important structural and geospatial characteristics of the LN and reveals a significant correlation between the length of payment paths, geographical distance, carbon intensity of electricity and other features. To tackle sustainability concerns, we propose an original pathfinding heuristic that effectively prevents excessive carbon dioxide emissions in LN infrastructure. Our computational experiments have shown that, under optimal parameters, such a heuristic can prevent the associated CO2 emissions both directly – by limiting path lengths, number of intercountry and intercontinental hops – and indirectly — by giving more weight to channels covering places with lower carbon intensity of electricity. Technically, the highest result it achieves is as follows: the average path length reduced by 28.7%, the average number of intercontinental hops by 28.7%, the average number of intercountry hops by 21.3%, and the average carbon intensity by 9.4%. This solution also maintains a compromise between the average locktimes and fee ratios. In conclusion, we discuss that geographic distribution is a rather important characteristic of decentralized peer-to-peer payment networks, which is usually underestimated at the network design stage.

Techno-Economic Comparison of Low-Carbon Energy Carriers Based on Electricity for Air Mobility

The decarbonization of air mobility requires the decarbonization of its energy. While biofuels will play an important role, other low-carbon energy carriers based on electricity are considered, such as battery electrification and liquid hydrogen (LH2) or eFuel, a hydrogen-based energy carrier. Each energy carrier has its own conversion steps and losses and its own integration effects with aircraft. These combinations lead to different energy requirements and must be understood in order to compare their cost and CO2 emissions. Since they are all electricity-based, this study compares these energy carriers using the well-to-rotor methodology when applied to a standard vertical take-off and landing (VTOL) air mobility mission. This novel approach allows one to understand that the choice of energy carrier dictates the propulsive system architecture, leading to integration effects with aircraft, which can significantly change the energy required for the same mission, increasing it from 400 to 2665 kWh. These deviations led to significant differences in CO2 emissions and costs. Battery electrification is impacted by battery manufacturing but has the lowest electricity consumption. This is an optimum solution, but only until the battery weight can be lifted. In all scenarios, eFuel is more efficient than LH2. We conclude that using the most efficient molecule in an aircraft can compensate for the extra energy cost spent on the ground. Finally, we found that, for each of these energy carriers, it is the electricity carbon intensity and price which will dictate the cost and CO2 emissions of an air mobility mission.

Reliance on fossil fuels increases during extreme temperature events in the continental United States

Increasing extreme climate events driven by climate change raise the question of their impacts on the power production system, and implications for renewable versus fossil power supply. Here, using climate reanalysis data and daily electricity generation (2018–2023), we systematically quantify the impact of extreme climate events, specifically extreme cold events and extreme hot events on United States state-level carbon emissions and on the carbon intensity of electricity. We find that extreme climate events increase the carbon intensity of the energy production, increasing the reliance on fossil-based sources of energy and reducing the capacity of renewables. The states with more renewable electricity generation were also more affected by extreme temperatures. Our results reveal the extent to which the reliability and resilience of the current United States electricity system depends on fossil energy during extreme climate events, and suggest a need for adaptation measures as the country will transition to higher shares of renewable energy while extreme events will become more frequent.

The Use of Biomethane in Internal Combustion Engines for Public Transport Decarbonization: A Case Study

Public transport can play a central role in representing a viable and sustainable mobility solution, especially in urban areas. Average energy consumption and emissions per passenger are much lower than for private cars. At the same time, current buses often mostly rely on diesel, and there are different solutions that can contribute to public transport decarbonization. Biomethane is among the options to exploit local low-carbon resources to decrease the emissions of public transport in urban environments. This paper presents the analysis of a real case study considering real data on the fuel consumption and mileage of the existing bus fleet in the city of Turin, Italy, composed by diesel and natural gas buses. The aim of this study is to estimate the effect of different penetration levels of biomethane in substitution of the current fuels. The results show that the use of biomethane in urban buses could save to up to 71% of emissions compared to the current situation, and savings would increase to 75% when deploying biomethane and electric buses together. Average emissions per pkm could decrease from a current level of 85.5 gCO2/pkm to 21.3–63.4 gCO2/pkm depending on the penetration of biomethane and electric buses. The sensitivity analysis shows even higher savings when accounting for the future decrease of the electricity carbon intensity in Italy and for the additional benefits related to avoided emissions from manure disposal. The results of the analysis demonstrate the potential contribution of biomethane in decarbonizing urban buses, and the findings presented for this case study can be of use for policy makers and researchers that deal with a similar situation in other cities and countries.

Assessing the CO2 capture potential for waste-fired CHP plants

The integration of CO2 capture with biomass-fired power plants has attracted much attention due to its ability to achieve negative emissions. Waste-fired combined heat and power (CHP) plants with CO2 capture, on the other hand, has received little attention, and their potential remains unclear. This study aims to identify the possible range of the amount of captured CO2 and investigate the impact of CO2 capture on the performance of waste-fired CHP plants. Since heat is the primary product of CHP plants, it is important to maintain heat production unchanged when CO2 capture is integrated. Based on this prerequisite, two operating strategies (OS) were investigated, which correspond to the upper and lower boundaries of CO2 capture: OS1 was to maximize the amount of captured CO2 while keeping the heat supplied to the district heating (DH) network unchanged; and OS2 was to maximize CO2 capture while keeping both supplied heat and generated electricity unchanged. To obtain more accurate results regarding the CO2 capture, a dynamic model developed in Aspen Hysys™ was utilized to simulate monoethanolamine (MEA) based chemical absorption for CO2 capture. By using real dynamic data from a waste-fired CHP plant, dynamic simulation results showed that the highest amount of captured CO2, which was achieved in OS1, was 401 kton/year, corresponding to a CO2 capture ratio of 82%; while the lowest amount of captured CO2, which was achieved in OS2, was 99 kton/year, corresponding to a CO2 capture ratio of 20%. For OS1, the electricity generation was substantially decreased by 61%. When determining the negative emission, the emission resulted from the share of fossil fuel in the waste needs to be excluded. For the studied CHP plant, the fossil share was around 45%. As a result, only OS1 can achieve the negative emission, which was 181 kton/year; while OS2 still led to positive emissions. Compared to the plant without CO2 capture, the carbon intensity of heat was reduced from 0.405 ton/MWh to 0.091 ton/MWh in OS1 and 0.351 ton/MWh in OS2, while the carbon intensity of electricity was reduced from 0.409 ton/MWh to 0.072 ton/MWh in OS1 and 0.343 ton/MWh in OS2.

Life cycle climate performance evaluation (LCCP) of electric vehicle heat pumps using low-GWP refrigerants towards China's carbon neutrality

The environmental-friendly heat pump with low global warming potential (GWP), such as R1234yf, CO2, R290, and several potentially promising refrigerant mixtures, is increasingly essential for the electric vehicle (EV) to save energy consumption and extend the driving range. It is beneficial to achieve carbon neutrality by reducing both direct and indirect carbon emissions. Previously, the life cycle climate performance (LCCP) was a widely accepted metric to evaluate the carbon footprint of mobile air conditioning systems “from cradle to grave” for the internal combustion engine vehicle (ICEV), however, such LCCP analyses about EV heat pumps can hardly be found. To facilitate the EV industry and policymakers' better understanding of the environmental impacts of those low-GWP refrigerants, this study provided a comprehensive LCCP analysis for the EV heat pumps based on the system bench test results, local climates, local power supply characteristics, real-world driving patterns, vehicle cabin thermal sensation, and climate control load. Five low-GWP refrigerants, i.e., R1234yf, CO2, R290, binary blends of CO2 and R41 (with GWP values of 49), M2(R410A substitute with GWP values of 137), were compared against R134a and R410A in 31 provinces of mainland China. We also considered the impacts of electric vehicle adoption rates and the carbon intensity of electricity from 2020 to 2060. Results show that the total life-cycle emissions per vehicle are highly related to climate conditions in different provinces, while R290 shows the lowest emission on the national average. The national mean life-cycle emissions per vehicle are projected to decrease 14% by 2030 and 45.4% by 2060 under the current technological trajectory of electricity generation. By using low-GWP heat pump systems in EVs, the cumulative emissions counting all vehicles can be saved up to 1450 Mt. CO2e from 2020 to 2060.

Exploring carbon dioxide emissions forecasting in China: A policy-oriented perspective using projection pursuit regression and machine learning models

Achieving a balance between future greenhouse gas reduction and sustained economic growth is of utmost importance. This study leverages machine learning (ML), specifically projection pursuit regression (PPR), to evaluate the key factors that influence CO2 emission predictions in China. The analysis notably identifies the escalating electricity consumption as a primary influencing factor. Based on empirical findings, it is evident that building electricity consumption will continue to rise steadily until 2050 unless new restrictions or technological advancements are implemented. Relying solely on the reduced carbon intensity of electricity will not enable China to achieve carbon neutrality. Therefore, there is a pressing need for more energy-efficient building retrofits and technologies to reduce power consumption in both residential and commercial properties. This policy-oriented study underscores its practical implications, offering valuable insights to policymakers for developing targeted CO2 reduction strategies that align with sustainable development and climate goals.

Evaluation of the environmental sustainability of SOFC-based cogeneration systems in commercial buildings

In order to achieve the European Union (EU)’s climate targets, efficient and sustainable solutions must be developed. In this context, the building sector has a key role to play in the transition to a decarbonized society. Cogeneration is considered an efficient solution that enables better use of fuel energy to supply buildings with heat and electricity. In particular, fuel cell-based cogeneration systems have shown promising performance, thus attracting considerable attention in recent years. The main goal of this study is to analyze the environmental impact of Solid Oxide Fuel Cell (SOFC) cogeneration systems, focusing on commercial buildings. The analysis was performed in the framework of the H2020 Comsos project, whose aim is to investigate the techno-economic and environmental feasibility of SOFC-based systems in non-residential buildings. An MILP-based optimization framework was developed to address the optimal design and operation of energy systems with the inclusion of SOFC-based cogeneration solutions. Electrical and thermal efficiency curves, derived from real SOFC operation, were used to improve the accuracy of the SOFC performance simulation. A sensitivity analysis on the carbon intensity of electricity was carried out to explore the role of the SOFC technology under different levels of electrical grid decarbonization. It was found that natural gas-fed SOFC systems become environmentally advantageous (in terms of CO2 emissions) when the carbon intensity of electricity is higher than ∼ 300 gCO2/kWh.

Evaluating energy flexibility requirements for high shares of variable renewable energy: A heuristic approach

Efforts to reduce carbon intensity of electricity involve increasing shares of variable renewable energy (VRE), including a trend towards decentralized generation. Ensuring their high utilization necessitates addressing generation variability at different spatial and temporal scales, likely involving a coordination of multiple systems (e.g. flexible loads, storage, dispatchable generation). This paper presents a methodology for estimating the energy flexibility required from such a synchronized system. The simple data-based approach uses local load and VRE production patterns, and provides a regional assessment considering (1) indicators to evaluate energy flexibility requirements based on VRE self-consumption (2) visualization methods to observe consumption and production patterns’ impact on flexibility requirements across day/week/year and (3) simple algorithms to estimate the energy flexibility requirements at different timescales. The approach is demonstrated for three Swiss distribution system operators, for both current and increased shares of VRE generation. The largest benefits for optimal self-consumption are realized for the energy flexibility timescale of 6–12 h. Medium- and long-term (seasonal) storage appears beneficial at VRE penetration levels beyond 40%. The proposed framework can be readily utilized to assess energy flexibility requirements of different regions, and serve as a basis for identifying a suitable mix of strategies needed to address them.

Estimating the Dominant Life Phase Concerning the Effects of Battery Degradation on CO2 Emissions by Repetitive Cycle Applications: Case Study of an Industrial Battery System Installed in an Electric Bus

Many studies have evaluated CO2 emission from batteries. However, the impact of Li-ion battery (LiB) degradation on the CO2 emissions from the material through operation phases has not been sufficiently examined. This study aims to clarify the dominant CO2 emission phase and the impact of the degradation of general industrial LiBs from repetitive cycle applications. We developed a model common to general LiB composition and calculated CO2 emissions by the LCA method using the IDEA database. Our model simplifies the degradation process, including capacity decrease and internal resistance increase. We used it in a sensitivity analysis of the carbon intensity of electricity charged to a LiB. The loss mechanism was determined by experimental data for an electric bus with an industrial LiB. The results illustrate that the carbon intensity of electricity affects CO2 emissions dominance, the operation phase for mix (71.3%), and the material phase for renewables (70.9%), and that battery degradation over six years increases the total amount of CO2 emissions by 11.8% for mix and 3.9% for renewables equivalent. Although there are limitations regarding the assumed conditions, the present results will contribute to building a method for monitoring emissions and to standardizing degradation calculations.

Assessment of the role of hydrogen to produce high-temperature heat in the steel industry

The iron and steel industry is a major source of industrial greenhouse gas emissions, accounting for 7–9% of global energy-related CO2 emissions. Current steel production routes are therefore expected to undergo a profound decarbonisation process in the coming decades.This work aims to shed light on the role of hydrogen in decarbonising the supply of high-temperature heat in the steel sector by means of an optimisation framework. The model includes on-site hydrogen production using a low-temperature electrolyser integrated with a compression and storage system and gas burners, which can be fed with hydrogen and/or natural gas to cover the process heat demand. The assessment also takes advantage of real thermal load profiles of a scrap-based electric arc furnace steel plant.A sensitivity analysis is conducted on the electricity, natural gas and carbon prices. Cost-optimal maps are then derived to unveil the combination of energy and carbon prices at which hydrogen becomes convenient for heat production in the steel industry. A general relationship to define the cost-effectiveness of hydrogen is also given.The results show that, at current carbon prices (about 100 €/tCO2), the use of hydrogen becomes economically convenient when the electricity price is less than 0.4–0.6 times the natural gas price. In scenarios with electricity prices lower than about 0.10 €/kWh, as could occur with on-site renewable electricity generation, hydrogen cost falls below 6.5 €/kgH2, leading to cost savings of up to 60–70% compared to a natural gas-based configuration. Finally, when total CO2 emissions (direct + indirect) are considered, hydrogen becomes environmentally beneficial if the electricity carbon intensity is below 123 gCO2/kWh.

Decarbonizing regional multi-model transportation system with shared electric charging hubs

In light of the growing concerns of global climate change, the pace of transportation electrification has greatly accelerated in recent years as an effort towards net-zero greenhouse gas (GHG) emissions. However, it remains unclear how to effectively deploy and operate public charging infrastructure to best serve an electrified transportation system within a multi-modal context while maximizing the benefits of decarbonization. This is especially true when considering the GHG emitted by generating one kWh of electricity, i.e. the electricity carbon intensity, varies across a day due the change of generation mix between renewable and fossil fueled resources. To address this question, we propose a mechanism of shared charging hubs that can provide holistic energy management for both electric buses (EBs) and passenger electric vehicles (EVs). The deployment and operation of shared charging hubs is determined by a new spatio-temporal optimization model which aims to minimize GHG emission given a budget limit while avoiding the occurrence of massive spikes in peak power demand. This is achieved by coherently accommodating the charging demand of EBs and EVs, and explicitly integrating the time-varying electricity carbon intensity and vehicle-to-grid (V2G) technology. To demonstrate its effectiveness, the model is applied to the bus fleets operated by seven transit agencies and the park-and-ride facilities (for EVs) near twelve rail transit stations in Contra Costa County, California, USA. The results show that the shared charging hubs can lead to significant GHG emission reduction while mitigating the peak electricity demand. This research will help policymakers and transportation agencies make more informed decisions regarding the planning and design of charging infrastructure.

Benchmarking marine renewable energy technologies through LCA: Wave energy converters in the Mediterranean

The present work evaluates the environmental performance of three wave energy converters including on-shore oscillating water columns and oscillating floaters embedded in piers, and near-shore seabed-based buoys in the Mediterranean Basin. The life cycle assessment methodology was used to account for their potential environmental impact, in terms of carbon footprint (t CO2eq), considering four main phases, i.e., manufacturing of material components, assembling and installation on site, maintenance in time, and decommission end of life. Results show the greenhouse gas emission from different lifecycle processes, based on the inventory of main energy inputs and materials, highlighting the major impact of the manufacture of the structural components (52 %), especially due to the limited durability of materials. In order to compare the performances of the three different wave energy converters, the carbon intensity of electricity was evaluated considering a range of electricity production per technology based on data available in scientific literature. The results obtained for a single device (203–270 g CO2eq‧kWh−1 for the oscillating water column system; 94–374 g CO2eq‧kWh−1 for oscillating floater and 105–158 g CO2eq‧kWh−1 for the seabed-based buoy) highlight that wave energy converters are promising solutions to harvest wave energy, showing lower carbon intensity of electricity values compared to fossil energy sources; nevertheless, technological improvements are needed to increase efficiency and achieve the performances of other renewable energy sources. Moreover, the combination of wave energy converters with other solutions, such as offshore wind turbines, represents a valuable option in the future to increase productivity and foster energy transition of the Mediterranean regions.

Benchmarking Marine Energy Technologies Through LCA: Offshore Floating Wind Farms in the Mediterranean

Floating wind turbines are a valid option for offshore wind farms in the Mediterranean, where the sea-floor falls off rapidly with distance from the coastline. The present study concerns a Life Cycle Assessment of the environmental performance of two types of floating wind turbine. Greenhouse gas emissions of two standard models (raft-buoy and spar-buoy, 154 m rotor diameter, 6 MW installed power) were estimated in terms of Global Warming Potential (t CO2eq) with the aim of determining a benchmark for evaluating the performance of similar offshore wind farms. Thus, the aim of the paper was to create a benchmark for the design of innovative technologies, such as those developed by specialist companies, and to verify the validity of new designs and technologies in terms of avoided greenhouse gas emissions. The results show that the Carbon Intensity of Electricity of a single floating wind turbine varies in the range 26–79 g CO2eq·kWh−1, averaging 49 g CO2eq·kWh−1, in line with other studies of offshore wind turbines and other renewable energy sources (such as onshore wind and photovoltaic). Extension of our study to the whole life cycle, including manufacturing, assembly and installation, maintenance and material replacement and a hypothetical decommissioning and end-of-life, showed that wind farms are among the most promising marine renewable energy technologies for the Mediterranean.

Can heat‐pumps provide routes to decarbonization of building thermal control in the US Midwest?

AbstractClimate change mitigation demands rapid decarbonization; in cold regions such as the US Midwest, building thermal control (BTC) presents a potential for significant cuts in emissions by combining renewable energy with heat pumps. Trends in natural gas and electricity pricing over the period 2007–2020 have significantly upended economic feasibility of this decarbonization approach. Heat pump‐based BTC has moved from being cost advantageous in operations but higher GHG emitting (in 2007), to the exact opposite—higher cost but lower emitting (in 2020). Due to energy price fluctuations, the coefficient of performance required of a heat pump to breakeven on operational cost with high efficiency natural gas heating has doubled, changing from 2.25 to 4.5 over the period 2007–2019. The value of 4.5 is infeasible for all available cold‐climate heat pump systems. Thus, while electrification via both air‐source and ground‐source heat pumps is a commonly identified component of decarbonization plans in the region, actual implementation has declined. Improvements in heat pump performance, overcoming adoption barriers, and adopting policies that buffer long‐term climate solutions against short‐term price fluctuations are all needed. In part due to continuing decreases in carbon intensity of electricity, heat pump climate benefits can be substantial over project life cycles; however, there is no current policy mechanism to enable this benefit to be considered relative to short‐run economic considerations.

From Food to Foot: The Energy and Carbon Flows of the Human Body at Walking and Cycling

The carbon footprint of motorized transport modes per unit length traveled encompasses the unit share of the vehicle lifetime emissions, that of the transport infrastructure, and those of the motor energy, considered both from “well to tank” and from “tank to wheel”. In the active modes of transport, i.e., walking and cycling, the counterpart of motor energy is human energy, which is associated with two kinds of carbon flows: the carbon footprint of food intake, – which we call the Food to Body component – and the carbon dioxide emissions of respiration – say the Body to Foot component. In this article, we provide a model in simple mathematical form to assess those carbon flows per unit length. It involves the modal speed in (i) the Metabolic Equivalent of the Task (MET) which gives rise to the energy and carbon flows, and (ii) the ratio of time spent to length travelled. The two influences of speed onto a modal carbon footprint combine in the net MET per unit length, with some compensation. The carbon footprint of food intake varies widely depending on the food diet of individuals. In a numerical study, the Food to Foot carbon emission of walking, cycling, e-scooter riding, and driving a car are estimated and compared to the rest of modal carbon footprint. Under conditions typical of France in the 2010s based on the average food diet and low carbon intensity of electricity, the inclusion of F2F in modal footprints changes the ranking of the modes according to the carbon footprint per unit length.