Dr Marco Raugei

Across West African built environments, patterns of high greenhouse gas emissions are driven by the widespread importation of high embodied carbon building materials by a largely self-built industry and recurring operational carbon costs driven by increased access to fossil-fuel based energy services. Using a whole life cycle assessment (LCA) of major residential typologies in two case-study West African countries, Ghana and Senegal, this paper compares the greenhouse gas emissions of imported building materials with local alternative biogenic and geogenic materials within conventional housing typologies. Results indicated that locally sourced biogenic and geogenic materials may be rendered ineffective in buildings if future typologies do not address the effective space density, passive design strategies and increased renewable energy-use. For the building typology with the highest carbon footprint, the Ghanaian detached house, the substitution of conventional building materials with non-fired earth masonry did not have any significant impact. As shown in the housing typology with the lowest operational to embodied carbon ratio, the Senegalese vertical housing case study, optimizing the thermal mass design of earthen building envelopes can significantly drive down lifetime operational carbon emissions. For tropical low-rise building typologies dominated by high roof area to building volume ratios, roof insulation could drive down operational carbon of the building by a factor of 4 to 5. Although each additional storey results in approximately 10-12% increase in greenhouse gas emissions, the vertical expansion of housing represents an important driver in reducing greenhouse gas emissions per capita.

Extracting, processing, and delivering energy requires energy itself, which reduces the net energy available to society and yields considerable socioeconomic implications. Yet, most mitigation pathways and transition models overlook net energy feedbacks, specifically related to the decline in the quality of fossil fuel deposits, as well as energy requirements of the energy transition. Here, we summarize our position across 8 key points that converge to form a prevailing understanding regarding EROI (Energy Return on Investment), identify areas of investigation for the Net Energy Analysis community, discuss the consequences of net energy in the context of the energy transition, and underline the issues of disregarding it. Particularly, we argue that reductions in net energy can hinder the transition if demand-side measures are not implemented and adopted to limit energy consumption. We also point out the risks posed for the energy transition in the Global South, which, while being the least responsible for climate change, may be amongst the most impacted by both the climate crisis and net energy contraction. Last, we present practical avenues to consider net energy in mitigation pathways and Integrated Assessment Models (IAMs), emphasizing the necessity of fostering collaborative efforts among our different research communities.

Limiting climate heating while meeting basic needs for all necessitates large-scale deployment of renewable energy. Understanding the dynamics of mobilizing materials for the transition requires considering: 1) availability of resources in the environment and technosphere; 2) accessibility depending on resource
quality and available technologies; 3) processability depending on energy availability, processing capacity,
and impacts on planetary boundaries; and 4) operability depending on social acceptance and geopolitical
agreements. Materials can be mobilized through four routes: 1) increasing primary production; 2) diverting
existing primary production; 3) repurposing in-use stocks; and 4) re-mining wastes and emissions. The
interplay of these enabling factors, material efficiency in design, and substitution with materials that are
easier to mobilize determines the maximum possible rate of material mobilization and consequently the
energy transition itself. This paper presents and discusses a framework to explore joint energy-material
transformations, enabling to consider material aspects in transition modelling and guide technological
developments.

As urbanization continues to surge, building materials are poised to become a dominant contributor to global emissions. Traditionally, the building sector has focused on mitigating “operational carbon” linked to a building's day-to-day energy needs, such as heating, cooling, lighting, and equipment usage. However, there has been a paucity of studies on the environmental impacts associated with building materials across a building life cycle. This paper addresses this gap by conducting a life cycle assessment of housing stocks in two diverse case studies: Montreal (Canada) and Lima (Peru). These cities offer a North/South perspective, highlighting the challenges, opportunities, and potential solutions for decarbonizing the housing sector. The study investigates the potential of circular strategies and investigates three scenarios: selective deconstruction (allowing for reuse and recycling), recycling, and landfilling. The results underscore the potential of selective deconstruction in significantly reducing the overall environmental footprint of residential buildings. In Lima, for instance, selective deconstruction, when compared to landfilling, can cut greenhouse gas emissions, water consumption, and fossil resource usage by a substantial 70%, 67%, and 69%, respectively. These findings offer valuable insights for decision-makers in construction materials and waste management, encouraging the adoption of circular economy practices through informed guidelines and recommendations.

There appears to be growing polarization in a large swath of the recent scientific literature on the renewable energy transition, where two opposed “camps” may be identified, i.e. that of the “systemic pessimists”, who champion the broad concepts of carrying capacity and the limits to growth, but often harbour what appears to be pre-conceived scepticism towards renewable energies, and that of the “technological optimists”, who instead typically focus more narrowly on the immediate goal of phasing out fossil fuels, and see great potential for renewable energies to achieve that, but often fail to address other issues of ultimate planetary limits. It is argued here that this is a false dichotomy that is damaging to the reputation of both “camps”, and which risks devaluing and trivializing the most important question of all, namely how to achieve long-term sustainability. This paper calls for the rekindling of a more constructive debate that starts from the recognition that both sets of core arguments (respectively, those centred on the limits to growth and those pointing to the viability of renewable energies) are often simultaneously true, and which moves the goalposts further, to establish to which extent a more sustainable future is indeed possible, and which systemic changes (including, but not limited to, phasing out fossil fuels) will be required to achieve it.

The transition to a low-carbon energy future requires large amounts of many raw materials. Some of these materials are deemed critical in terms of their limited availability, concentrated supply chain networks, associated environmental impact, and various social issues. Acknowledging the significant dependency on raw materials for future energy scenarios, this paper presents a systematic review of the existing literature to identify the barriers, solutions proposed and the current research gaps associated with the supply of a range of critical chemical elements. The focus was mainly on evaluating supply risk in light of raw material availability and contemporary extraction technologies. Results indicate that a transition to a low-carbon energy system is possible, but will require efforts to address supply concerns, and strategic planning. A key risk mitigation strategy is increasing material circularity, especially to cope with the growth in demand for cobalt in lithium-ion batteries, platinum used in fuel cells and electrolysers, iridium used in electrolysers and dysprosium used in permanent magnets. Copper was found to be possibly the most concerning critical element due to the expected demand from developing nations in addition to the demand for the energy transition. The geopolitical, social, and environmental risks for lithium, cobalt, rare earth elements and platinum group metals could also hinder future energy security, as demand for these elements continues to grow.

Conventional construction materials which rely on a fossil-based, nonrenewable extractive economy are typically associated with an entrenched linear economic approach to production. Current research indicates the clear interrelationships between the production and use of construction materials and anthropogenic climate change. This paper investigates the potential for emerging high-performance biobased construction materials, produced sustainably and/or using waste byproducts, to enable a more environmentally sustainable approach to the built environment. Life-cycle assessment (LCA) is employed to compare three wall assemblies using local biobased materials in Montreal (Canada), Nairobi (Kenya), and Accra (Ghana) vs. a traditional construction using gypsum boards and rockwool insulation. Global warming potential, nonrenewable cumulative energy demand, acidification potential, eutrophication potential, and freshwater consumption (FWC) are considered. Scenarios include options for design for disassembly (DfD), as well as potential future alternatives for electricity supply in Kenya and Ghana. Results indicate that all biobased alternatives have lower (often significantly so) life-cycle impacts per functional unit, compared to the traditional construction. DfD strategies are also shown to result in −10% to −50% impact reductions. The results for both African countries exhibit a large dependence on the electricity source used for manufacturing, with significant potential for future decarbonization, but also some associated tradeoffs in terms of acidification and eutrophication. 

Passenger vehicles are responsible for significant greenhouse gas (GHG) emissions, which calls for accurate and up-to-date estimates of the comparative emissions of the main types of alternative power trains, to enable evidence-based policy recommendations. This paper provides a systematic review and harmonization of the recent scientific literature on this topic. The results show that battery electric vehicles (BEVs) represent the most promising option to decarbonize the passenger vehicle fleet in all considered world regions, with up to −70% reductions in GHG emissions possible, vs. conventional internal combustion engine vehicles (ICEVs) running on petrol. Hybrid electric vehicles (HEVs and PHEVs) are less effective strategies, but they may be useful in bridging the gap between ICEVs and BEVs, especially in those markets that are harder to electrify quickly. Finally, fuel cell vehicles (FCEVs) may also be a viable option, but only if the hydrogen fuel is produced via water electrolysis using renewable energy.

Research on 100% renewable energy systems is a relatively recent phenomenon. It was initiated in the mid-1970s, catalyzed by skyrocketing oil prices. Since the mid-2000s, it has quickly evolved into a prominent research field encompassing an expansive and growing number of research groups and organizations across the world. The main conclusion of most of these studies is that 100% renewables is feasible worldwide at low cost. Advanced concepts and methods now enable the field to chart realistic as well as cost- or resource-optimized and efficient transition pathways to a future without the use of fossil fuels. Such proposed pathways in turn, have helped spur 100% renewable energy policy targets and actions, leading to more research. In most transition pathways, solar energy and wind power increasingly emerge as the central pillars of a sustainable energy system combined with energy efficiency measures. Cost-optimization modeling and greater resource availability tend to lead to higher solar photovoltaic shares, while emphasis on energy supply diversification tends to point to higher wind power contributions. Recent research has focused on the challenges and opportunities regarding grid congestion, energy storage, sector coupling, electrification of transport and industry implying power-to-X and hydrogen-to-X, and the inclusion of natural and technical carbon dioxide removal (CDR) approaches. The result is a holistic vision of the transition towards a net-negative greenhouse gas emissions economy that can limit global warming to 1.5˚C with a clearly defined carbon budget in a sustainable and cost-effective manner based on 100% renewable energy-industry-CDR systems. Initially, the field encountered very strong skepticism. Therefore, this paper also includes a response to major critiques against 100% renewable energy systems, and also discusses the institutional inertia that hampers adoption by the International Energy Agency and the Intergovernmental Panel on Climate Change, as well as possible negative connections to community acceptance and energy justice. We conclude by discussing how this emergent research field can further progress to the benefit of society.

Climate change mitigation strategies are developed at international, national, and local authority levels. Technological solutions such as renewable energies (RE) and electric vehicles (EV) have geographically widespread knock-on effects on raw materials. In this paper, a decision-support and data-visualization tool named “LAYERS” is presented, which applies a material flow analysis to illustrate the complex connections along supply chains for carbon technologies. A case study focuses on cobalt for lithium-ion batteries (LIB) required for EVs. It relates real business data from mining and manufacturing to actual EV registrations in the UK to visualize the intended and unintended consequences of the demand for cobalt. LAYERS integrates a geographic information systems (GIS) architecture, database scheme, and whole series of stored procedures and functions. By means of a 3D visualization based on GIS, LAYERS conveys a clear understanding of the location of raw materials (from reserves, to mining, refining, manufacturing, and use) across the globe. This highlights to decision makers the often hidden but far-reaching geo-political implications of the growing demands for a range of raw materials that are needed to meet long-term carbon-reduction targets.

Net energy, that is, the energy remaining after accounting for the energy “cost” of extraction and processing, is the “profit” energy used to support modern society. Energy Return on Investment (EROI) is a popular metric to assess the profitability of energy extraction processes, with EROI > 1 indicating that more energy is delivered to society than is used in the extraction process. Over the past decade, EROI analysis in particular has grown in popularity, resulting in an increase in publications in recent years. The lack of methodological consistency, however, among these papers has led to a situation where inappropriate comparisons are being made across technologies. In this paper we provide both a literature review and harmonization of EROI values to provide accurate comparisons of EROIs across both thermal fuels and electricity producing technologies. Most importantly, the authors advocate for the use of point-of-use EROIs rather than point-of-extraction EROIs as the energy “cost” of the processes to get most thermal fuels from extraction to point of use drastically lowers their EROI. The main results indicate that PV, wind and hydropower have EROIs at or above ten while the EROIs for thermal fuels vary significantly, with that for petroleum oil notably below ten.

Lithium-ion batteries (LIBs) play a key role in advancing electromobility. With an increasing trend in the demand for LIBs, the sustainability prospect of LIBs lifecycle faces many challenges that require proactive approaches. There are various sustainability challenges and risks across the supply and value chains of LIBs from mining, material supplies to Original Equipment Manufacturers (OEMs), users to final disposal. Risks are for example the increased raw material demands as well as some economic risks due to price increment or political instabilities in some countries within the raw material supply chain. Despite the promising research efforts on the performance metrics of LIBs and advancing the technology, the research on the various aspects of sustainability of LIBs and its life cycle are still in its infancy and require closer attention. As the editorial of the Special Issue on sustainable supply and value chains of EV batteries, this article presents some of the most pressing challenges of EV LIBs across the different stages of its life cycle. It covers issues from supply and demand of the battery raw materials, battery manufacturing, use, and end-of-life treatments. Within this context the reported findings of some 20 different research teams from across the globe, the state-of-the-art, technical or policy gaps in EV LIBs research and development are presented, as well as market instruments such as innovative business models, and governmental interventions like subsidies or regulations. We grouped the materials presented into five main themes (1) EV and LIB materials demand projections (2) EV LIBs international trade risk (3) EV battery regulation and adoption (4) EV LIBs life cycle assessment (5) and EV LIBs reverse logistics. We conclude by discussing some future research challenges such as the need for more reliable and applicable prediction models that use accurate data on EV stock and end-of-life EVs. Finally, we argue that more collaboration between academia, manufactures, OEMs and the battery recycling industry is needed to implement successful circular economy strategies to achieve environmentally friendly, flexible and cost-efficient battery supplies, use and recycling processes.

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This paper exposes the many flaws in the article “Through the Eye of a Needle: An Eco-heterodox Perspective on the Renewable Energy Transition”, authored by Siebert and Rees and recently published in Energies as a Review. Our intention in submitting this critique is to expose and rectify the original article’s non-scientific approach to the review process that includes selective (and hence biased) screening of the literature focusing on the challenges related to renewable energies, without discussing any of the well-documented solutions. In so doing, we also provide a rigorous refutation of several statements made by a Seibert–Rees paper, which often appear to be unsubstantiated personal opinions and not based on a balanced review of the available literature.

Modern intensive agriculture worldwide is generating increasing environmental pressure, which prevents its sustainable development. A number of agricultural sustainability assessment approaches and methodological frameworks have been developed by research worldwide to assess the environmental costs and impacts of resources used in agricultural production. A joint use of Life Cycle Assessment (LCA, to assess a process´ performance and environmental impacts) and Emergy Accounting (EMA, to estimate environmental support to resource generation and provision) is proposed in this study. The goal is not only to ascertain the environmental ‘cost’ of production of selected chemical resources used in agricultural processes, but also to develop a reliable calculation procedure capable to integrate the two approaches (LCA and EMA), while considering their different allocation algebra and space-time scales of application. Specifically, the UEVs of
glyphosate and urea, which are respectively the most used herbicide and nitrogen fertilizer used in worldwide agriculture, are calculated, yielding values of 2.47E+13 sej/kg and 7.07E+12 sej/kg, respectively. In order to do so, UEVs of intermediate process chemicals such as ammonia, acetic anhydride, chlorine gas, formaldehyde, phosphorous chloride, and sodium hydroxide have also been calculated or updated, thus providing at the same time a procedure and a set of values potentially useful for future studies. The LCA impacts of agro-chemicals in China are compared to worldwide averages from the Ecoinvent database, and the UEVs for several chemicals are also compared to previous estimates from published emergy literature.

California has set two ambitious targets aimed at achieving a high level of decarbonization in the coming decades, namely (i) to generate 60% and 100% of its electricity using renewable energy (RE) technologies, respectively, by 2030 and by 2045, and (ii) introducing at least 5 million zero emission vehicles (ZEVs) by 2030, as a first step towards all new vehicles being ZEVs by 2035. In addition, in California, photovoltaics (PVs) coupled with lithium-ion battery (LIB) storage and battery electric vehicles (BEVs) are, respectively, the most promising candidates for new RE installations and new ZEVs, respectively. However, concerns have been voiced about how meeting both targets at the same time could potentially negatively affect the electricity grid’s stability, and hence also its overall energy and carbon performance. This paper addresses those concerns by presenting a thorough life-cycle carbon emission and energy analysis based on an original grid balancing model that uses a combination of historical hourly dispatch and demand data and future projections of hourly demand for BEV charging. Five different scenarios are assessed, and the results unequivocally indicate that a future 80% RE grid mix in California is not only able to cope with the increased demand caused by BEVs, but it can do so with low carbon emissions (2-eq/kWh) and satisfactory net energy returns (EROIPE-eq = 12–16).

The light duty vehicle fleet in the UK is being electrified aggressively, with an ambitious target to ban the sale of all new internal combustion engine cars by 2030. At the same time, the electricity grid is also undergoing rapid decarbonization, potentially paving the way for a much greener use phase for electric vehicles. The paper presents a holistic prospective life cycle assessment of the environmental implications of these two interrelated transitions, while also considering an alternative scenario characterised by a gradual shift from traditional private vehicle ownership to shared mobility schemes. The results for both scenarios point to clear benefits in terms of reduced demand for non-renewable energy, carbon emissions and local air quality. However, a decisive behavioural shift towards shared mobility is shown to be crucial in order to offset the increased demand for Li, Co, Ni, Mn and Cu for electric vehicle power trains, and to avoid an otherwise potential increase in abiotic resource depletion and human toxicity impacts.

Among existing and emerging technologies to recycle spent Lithium-Ion Batteries (LIBs) from Electric Vehicles (EVs), pyrometallurgical processes are commonly used. However, very little is known about their environmental and energy impacts. In this study, three pyrometallurgical technologies are analyzed and compared in terms of Global Warming Potential (GWP) and Cumulative Energy Demand (CED), namely: an emerging Direct Current (DC) plasma smelting technology (Sc-1), the same DC plasma technology but with an additional pre-treatment stage (Sc-2), and a more commercially mature Ultra-High Temperature (UHT) furnace (Sc-3). The net impacts for the recovered metals are calculated using both ‘open-loop’ and ‘closed-loop’ recycling options. Results reveal that shifting from the UHT furnace technology (Sc-3) to the DC plasma technology could reduce the GWP of the recycling process by up to a factor of 5 (when employing pre-treatment, as is the case with Sc-2). Results also vary across factors e.g. different metal recovery rates, carbon/energy intensity of the electricity grid (in Sc-1 and Sc-2), rates of aluminum recovery (in Sc-2), and sources of coke (in Sc-3). However, the sensitivity analysis showed that these factors do not change the best option which was determined before (as Sc-2) except in a few cases for CED. Overall, the research methodology and application presented by this LCA informs future environmental and energy impact studies that want to assess existing recycling processes of LIB or other emerging technologies.

Most existing life cycle assessment models of waste management have so far underplayed the importance of the waste collection phase, addressing it only in a simplified fashion, either by requesting the total amount of fuel used as a direct user input or by calculating it based on a set of input parameters and fixed diesel consumption factors. However, in certain situations, and especially in the case of source-separated waste fractions, a more detailed analysis of the collection phase is required, lest oversimplified and potentially misleading conclusions are drawn. The new LCA collection model presented here relies on a large number of parameters (number and type of containers, collection frequency, individual distances for the various legs of transport, etc.) and allows the detailed predictive analysis of alternative collection scenarios. The results of applying such newly-developed model to a number of experimental case studies in Portugal are analysed, discussed and compared to those produced by a selection of pre-existing, more simplified models. The new model is confirmed as being the most accurate and, importantly, as the only one capable of predicting the consequences of a range of possible changes in the collection parameters.Bala A. 

Climate change is disrupting our environment and business‐as‐usual practices will fail to reverse its impact. This paper focuses on the impact of the building sector and, in particular, it questions the energy and environmental benefits of advanced integrated and more conventional building‐applied photovoltaic (PV) systems, compared to a traditional municipality utility supply. A demonstration project named the ecological living module (ELM) is used to create a comparative life cycle assessment (LCA) of the adoption of these PV systems across three different climatic locations, namely New York City, London, and Nairobi. Findings show that, over the entire life cycle, the solar systems do better than the grid mix in reducing the building's dependence on nonrenewable resources. Unsurprisingly, in comparative terms, these systems do substantially better if the local grid mix is characterized by a predominantly nonrenewable energy profile. When comparing the two solar systems, the environmental impacts of the solar cells are negligible in the advanced system, whereas its structural components result in it being less environmentally friendly than the conventional solar PV. This highlights the possibility of future design iterations of these components to rethink their material ecology in terms of their life cycle—materiality, sourcing, and manufacturing, and so forth. The implications of this work suggest questioning, on a case‐by‐case basis, when and in what contexts integrated solar energy building systems are most plausible. This work also questions the scale at which grid scale distribution should occur.

Limiting human-induced climate change represents a critical challenge for the future, and due to their disproportionate contribution to the problem, the energy and transport sectors are attracting the most attention in terms of emission reduction roadmaps and targets. Energy storage, particularly electrochemical storage, is poised to be a cornerstone in allowing those sectors to become more sustainable. This study presents the results of an integrated dynamic material flow analysis of the cumulative demand for lithium-ion battery metals (Li, Co, Ni and Mn) by the light duty vehicle and electricity generation sectors in the UK over the next three decades. Results have shown that recycling of end-of-life electric vehicle battery packs is very effective in “closing the loop”, and would enable driving the demand for all four metals back down to present levels by 2050, despite having achieved by then a complete shift to 100% electric vehicles. Additionally, repurposing end-of-life vehicle batteries for grid storage (with over 50 GWh of grid storage capacity expected to be in place by 2050) has been found to enable reducing purpose-built grid storage batteries to zero. Finally, an additional scenario analysis has indicated that a widespread behavioural shift from conventional vehicle ownership to shared mobility could even drive the demand for virgin battery metals into negative territory by 2040.

This paper presents a detailed life-cycle assessment of the greenhouse gas emissions, cumulative demand for total and non-renewable primary energy, and energy return on investment (EROI) for the domestic electricity grid mix in the U.S. state of California, using hourly historical data for 2018, and future projections of increased solar photovoltaic (PV) installed capacity with lithium-ion battery energy storage, so as to achieve 80% net renewable electricity generation in 2030, while ensuring the hourly matching of the supply and demand profiles at all times. Specifically—in line with California’s plans that aim to increase the renewable energy share into the electric grid—in this study, PV installed capacity is assumed to reach 43.7 GW in 2030, resulting of 52% of the 2030 domestic electricity generation. In the modelled 2030 scenario, single-cycle gas turbines and nuclear plants are completely phased out, while combined-cycle gas turbine output is reduced by 30% compared to 2018. Results indicate that 25% of renewable electricity ends up being routed into storage, while 2.8% is curtailed. Results also show that such energy transition strategy would be effective at curbing California’s domestic electricity grid mix carbon emissions by 50%, and reducing demand for non-renewable primary energy by 66%, while also achieving a 10% increase in overall EROI (in terms of electricity output per unit of investment).

National Grid, the UK’s largest utility company, has produced a number of energy transition scenarios, among which “2 degrees” is the most aggressive in terms of decarbonization. This paper presents the results of a combined prospective net energy and environmental life cycle assessment of the UK electricity grid, based on such a scenario. The main findings are that the strategy is effective at drastically reducing greenhouse gas emissions (albeit to a reduced degree with respect to the projected share of “zero carbon” generation taken at face value), but it entails a trade-off in terms of depletion of metal resources. The grid’s potential toxicity impacts are also expected to remain substantially undiminished with respect to the present. Overall, the analysis indicates that the “2 degrees” scenario is environmentally sound and that it even leads to a modest increase in the net energy delivered to society by the grid (after accounting for the energy investments required to deploy all technologies).

Renewable electricity generation is intermittent and its large‐scale deployment will require some degree of energy storage. Although best assessed at grid level, the incremental energy and environmental impacts of adding the required energy storage capacity may also be calculated specifically for each individual technology. This paper deals with the latter issue for the case of photovoltaics (PV) complemented by lithium‐ion battery (LIB) storage. A life cycle assessment (LCA) of a 100MW ground‐mounted PV system with 60MW of (lithium‐manganese oxide) LIB, under a range of irradiation and storage scenarios, show that energy pay‐back time and life‐cycle global warming potential increase by 7% to 30% (depending on storage duration scenarios), with respect to those of PV without storage. Thus the benefits of PV when displacing conventional thermal electricity (in terms of carbon emissions and energy renewability) are only marginally affected by the addition of energy storage.

New York state is at the forefront in the USA and also high on the list globally in setting ambitious targets for the transition to renewable electricity, with 70% of generation mandated to be renewable by 2030. The consequences of the associated drastic shift from conventional steam generators to a mix of wind, photovoltaic and hydroelectric (supplemented by pumped hydro storage to ensure dispatchability) is analysed here from the joint points of view of life cycle assessment (LCA) and net energy analysis (NEA). Results indicate that not only is the target effective at drastically reducing the grid mix’s carbon emissions and at halving its cumulative demand for imported non-renewable primary energy, but – contrary to often voiced concerns – it is also compatible with sustaining the current level of net energy delivery (after accounting for the energy investments required to deploy and operate all generators).

Solar thermal energy is considered a ‘clean’ form of energy; however, environmental impacts occur during its life-cycle. The present work compares the environmental performance of two scenarios: a solar thermal system for providing domestic hot water (DHW) used in conjunction with a traditional natural gas heating system, and the natural gas heating system on its own. Weak points are found and different eco-design scenarios are evaluated in order to achieve a more circular economy. In addition, the authors explore what would be the national Greenhouse Gas emission reduction potential of a wider use of domestic solar hot water systems (DSHW) in China’s and Spain’s built environment. In this case, five displacement methods are suggested to show how the emissions reduction vary. Through a review of the state of the art and a Life Cycle Assessment of a solar system the two scenarios are assessed. Some impact categories, such as global warming, suggest a markedly better performance of the solar system (-65%). However, weak points in the solar solution have been identified as there is an increase of impacts in cases such as acidification (+6%) and eutrophication (+61%), mostly due to the metals used. The components with higher environmental impact are the collector, the tank, and the copper tubes. The reduction of national emissions by promoting DSHW depends on the actual displaced technology/ies. The consequences on national emissions reduction depending on these choices are assessed. The potential reduction of emissions, if 30% of the DHW were covered with solar sources, would be between 0.38% and 0.50% in the case of Spain and between 0.12% and 0.63% in China.

Energy return on investment (EROI) is a critical measure of the comparative utility of different energy carriers including fossil fuels and renewables. However it must not be used to compare carriers that cannot be put to similar end-use. Additionally, combining carriers to arrive at estimates of ‘average’ or ‘minimum’ EROIs can be problematic.

The transport sector as a whole – and within it passenger cars in particular – is currently responsible for a large share of the total greenhouse gas emissions of many developed and developing countries, and a transition to electric vehicles (EVs) is often seen as a key stepping stone towards the de-carbonization of personal mobility. Research is on-going in the continuous development and improvement of lithium ion (Li-ion) batteries, which may use a range of several different metals in conjunction with lithium itself, such as: lithium manganese oxide (LMO), lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM), and lithium nickel-cobalt-aluminium oxide (NCA). Within the MARS-EV research project, a new cell chemistry has been developed and tested, using a lithium cobalt phosphate (LCP) formulation. This work presents the first life cycle assessment (LCA) for such LCP batteries, including a newly-developed hydrometallurgical battery recycling process which enables the end-of-life recovery of not only the valuable metals, but also of the graphite component, thereby avoiding the associated CO2 emissions.

Electric vehicles (EVs) are increasingly regarded as the way forward to deliver a much-needed improvement in the transport sector's sustainability profile, and the UK is embarking on a major transition towards them. While previous studies focused mainly on greenhouse gas (GHG) emissions, this article assesses the extent to which EVs may contribute to reducing the UK's dependence on (mostly imported) non-renewable primary energy. The study combines a life-cycle model of a compact battery electric vehicle (BEV) with a prospective energy analysis of a range of electricity supply alternatives for the vehicle's use phase. The key metric analysed is the non-renewable cumulative energy demand (nr-CED). Results show that, already under current conditions, the nr-CED of a compact BEV in the UK is lower by approximately 34% with respect to that of an otherwise similar internal combustion engine vehicle (ICEV). Such reduction is then expected to improve further under all future scenarios, indicating that a transition to EVs is indeed a recommendable option to reduce the UK's demand for non-renewable energy, especially if this is accompanied by a shift to a more renewable electric grid.

Chile is one of the fastest-growing economies in Latin America, with a mainly fossil fuelled electricity demand and a population projected to surpass 20 million by 2035. Chile is undergoing a transition to renewable energies due to ambitious national targets, namely to generate 60% of its electricity from local renewable energy by 2035, and to achieve a 45%renewable energy share for all new electric installed capacity. In this work, we present a comprehensive energy analysis of the electricity generation technologies currently deployed in Chile. Then, we analyse potential future scenarios, considering a large deployment of RE, mainly PV and wind, to replace coal-fired electricity. The life cycle assessment (LCA) and net energy analysis (NEA) methods are applied in parallel to provide complementary indicators, respectively nr-CED and EROI, and identify weak spots and future opportunities. Special focus is given to the effect on EROI of transporting fossil fuels to Chile. Results show that a large deployment of PV and wind can significantly improve the overall net energy performance of electricity generation in Chile, while leading to an electricity supply mix that is >60% less reliant on non-renewable energy.

We performed a comprehensive and internally consistent assessment of the energy performance of the full range of electricity production technologies in the United Kingdom, integrating the viewpoints offered by net energy analysis (NEA) and life cycle assessment (LCA). Specifically, the energy return on investment (EROI), net-to-gross energy output ratio (NTG) and non-renewable cumulative energy demand (nr-CED) indicators were calculated for coal, oil, gas, biomass, nuclear, hydro, wind and PV electricity. Results point to wind, and to a lesser extent PV, as the most recommendable technologies overall in order to foster a transition towards an improved electricity grid mix in the UK, from both points of view of short-term effectiveness at providing a net energy gain to support the multiple societal energy consumption patterns, and long-term energy sustainability (the latter being inversely proportional to the reliance on non-renewable primary energy sources). The importance to maintain a sufficient installed capacity of readily-dispatchable gas-fired electricity is also recognized.

Purpose As a class of environmental metrics, footprints have been poorly defined, have shared an unclear relationship to Life Cycle Assessment (LCA), and the variety of approaches to quantification have sometimes resulted in confusing and contradictory messages in the marketplace. In response, a task force operating under the auspices of the UNEP/SETAC Life Cycle Initiative project on environmental Life Cycle Impact Assessment (LCIA) has been working to develop generic guidance for developers of footprint metrics. The purpose of this paper is to introduce a universal footprint definition and related terminology as well as to discuss modelling implications.

Methods The task force has worked from the perspective that footprints should be underpinned by the same data systems and models as used in LCA. However, there are important differences in purpose and orientation relative to LCA impact category indicators. Footprints have a primary orientation toward society and nontechnical stakeholders. They are also typically of narrow scope, having the purpose of reporting only in relation to specific topics. In comparison, LCA has a primary orientation toward stakeholders interested in comprehensive evaluation of overall environmental performance and trade-offs among impact categories. These differences create tension between footprints, the existing LCIA framework based on the Area of Protection paradigm, and the core LCA standards ISO14040/44.

Results In parallel to Area of Protection, we introduce Area of Concern as the basis for a universal footprint definition. In the same way that LCA uses impact category indicators to assess impacts that follow a common cause-effect pathway toward Areas of Protection, footprint metrics address Areas of Concern. The critical difference is that Areas of Concern are defined by the interests of stakeholders in society rather than the LCA community. In addition, Areas of Concern are stand-alone and not necessarily part of a framework intended for comprehensive environmental performance assessment. The Area of Concern paradigm is needed to support the development of footprints in a way that fulfils their distinctly different purpose. It is also needed as a

mechanism to extricate footprints from some of the provisions of ISO 14040/44 which are not considered relevant. Specific issues are identified in relation to double counting, aggregation, and the selection of relevant indicators.

Conclusions The universal footprint definition and related terminology introduced in this paper create a foundation that will support the development of footprint metrics in parallel with LCA.

A complete and fully consistent LCA-based comparison of a range of lightweighting options for compact passenger vehicles is presented and discussed, using advanced lightweight materials (Al, Mg and carbon fibre composites), and including all life cycle stages and a number of alternative end-of-life scenarios. Results underline the importance of expanding the analysis beyond the use phase, and point to maximum achievable reductions of environmental impact of approximately 7% in most impact categories. In particular, lightweighting strategies based on the use of aluminium were found to be the most robust and consistent in terms of reducing the environmental impacts (with the notable exception of a relatively high potential toxicity). The benefits of using magnesium instead appear to be less clear-cut, and strongly depend on achieving the complete phase-out of SF6 in the metal production process, as well as the establishment of a separate close-loop recycling scheme. Finally, the use of carbon fibre composites leads to similar environmental benefits to those achieved by using Al, albeit generally at a higher economic cost.

This paper considers the different approaches taken in dealing with waste products and flows in Life Cycle Assessment (LCA) and Emergy Accounting (EMA), from a methodological point of view, and aims to develop more standardized and synergistic procedures. LCA deals with the waste issue from the point of view of the impact of their disposal, as well as the potential benefit (‘environmental credit’) afforded by the avoided extraction and processing of additional primary resources when waste is recycled or its energy content recovered. The ‘environmental burden’ associated to the entire production and consumption chain leading to the waste item is generally not included in LCAs of waste management systems, due to the boundary being placed – consistently with the intended goal – around the actual disposal processes (including recycling alternatives and associated environmental credits). Instead, Emergy Accounting, a donor-side approach with its implicit boundary set at the biosphere level, in principle keeps track of the entire supply-chain at all times, considering even waste flows as products (or co-products), and calculating their intensity factors and assessing their role within the ecosystem's web and hierarchy. However, when the focus is limited to evaluating processes under human control, within the narrower space and time boundary of human-dominated production and consumption processes, waste products can arguably be regarded as something to be recycled or disposed of to minimize the environmental burden. When this is the case, and particularly in comparative analyses, the emergy perspective thus becomes closer to the LCA perspective and interesting methodological synergies may emerge. A clearly defined set of emergy algebra rules for waste products and flows, and specifically for recycling, was found to be still lacking in the available emergy literature. We propose here that a better and more consistent methodological solution may be arrived at by leveraging the work done in LCA.

Purpose This paper aims to provide an alternative method for calculating the environmental credits associated with material recycling in life cycle assessment (LCA) of waste management systems. The method proposed here is more consistent with the general attributional approach in LCA than the hitherto common practice of simply assuming a 1:1 substitution of primary material production.

Methods The formula proposed for estimating the environmental credit is applicable for the recovered materials that are reintroduced into the market (outputs of the recycling facilities), after all process losses in the various stages of the waste management system have been accounted for. It considers the displacement of materials by using the mix of virgin and recycled materials for each individual material that is used in the market for the production of goods. Moreover, it also considers the changes in the inherent properties of the materials undergoing a recycling process (‘down-cycling’), by introducing a quality (Q) factor, affecting the proportion of virgin material that is accounted for.

Results and discussion Example applications of the proposed formula to a number of different materials (aluminium, steel, paper and cardboard and plastics) illustrate the range of possible results obtained.. The environmental credit calculated using the proposed formula can be interpreted as an indication of the remaining margin for improvement, since it depends on the existing mix of virgin and recycled materials already on the market, and on the potential of the recycled material to actually replace the primary one on a functional basis. We also discuss the possible use of a material’s Q factor to estimate the maximum allowable % of recycled material in a product consistent with the quality demands of selected applications.

Conclusions and recommendations We have introduced here a consistent and unified formula for the evaluation of the credits associated with material recovery of all waste materials in waste management systems (paper, glass, plastics, metals, etc.). Such a formula requires the knowledge of the current average market consumption mixes of primary and secondary materials (or the application-specific average mixes when the final application of the recovered materials is known), and of suitable Q factors for the material(s) that are recycled. As the latter are often not readily available, more research is called for to arrive at a ready-to-use Q factors database.

In recent years, footprint indicators have emerged as a popular mode of reporting environmental performance. The prospect is that these simplified metrics will guide investors, businesses, public sector policymakers and even consumers of everyday goods and services in making decisions which lead to better environmental outcomes. However, without a common “DNA”, the ever expanding lexicon of footprints lacks coherence and may even report contradictory results for the same subject matter.(1) The danger is that this will ultimately lead to policy confusion and general mistrust of all environmental disclosures.

Footprints are especially interesting metrics because they seek to express the environmental performance of products and organizations from a life cycle perspective. The life cycle perspective is important to avoid misleading claims based only on a selected life cycle stage. For example, the water used to manufacture beverages may be important, but if a beverage includes sugar, irrigation water used to cultivate sugar cane could be a greater concern. The focus on environmental performance distinguishes footprints from technical efficiency measures, such as energy use efficiency or water use efficiency, which typically only make sense when applied to a single life cycle stage as they lack local environmental context.

However, unlike technical efficiency, which can usually be accurately measured and verified, footprint indicators, with their wider view of environmental performance, are usually calculated using models which can differ in scope, complexity and model parameter settings. Despite the noble intention of using footprints to evaluate and report environmental performance, the potential inconsistency between different approaches acts as a deterrent to use in many public policymaking and business contexts and can lead to confusing and contradictory messages in the marketplace.

In a recent Point of View piece, William Pickard made an excellent case for the importance of energy return on investment (EROI) as a useful metric for assessing longterm viability of energy-dependent systems from bands of hunter-gatherers, to modern society and, finally to the specific case of a solar electricity generating project. The author then highlighted a seeming disparity between a number of different research groups
1) Fthenakis group at Brookhaven,
2) Prieto group in Madrid,
3) Weißbach group in Berlin, and
4) Brandt group at Stanford
all of whom have recently published values for the EROI (or similar metric) for solar photovoltaic (PV) technologies.

Unfortunately, in so doing, the author directly compares results calculated using different system boundaries, methodologies, and assumptions.

It is the purpose of this response to (1) adjust the results for the four groups to better compare like systems and (2) outline details of two methodological issues common in the EROI literature. The objective of these two activities is to explain much of the apparent disparity between the different EROI values produced by the different research groups.

This work centres on one block built in 1983 in which temperatures have been monitored which show that the optimum temperature conditions are not reached for long periods during the year. The current state of the building is referred to as scenario one.

Energy consumption is evaluated considering the lifecycle of the components necessary for the refurbishment, their subsequent operation and disposal.

All scenarios address the suitability of passive measures or the implementation of active systems in temperate climates under the assumption that comfort in dwellings is achieved.

Scenarios two and three are assessed applying insulation and changing the windows. The fourth and fifth implement an alternative solution, a controlled mechanical ventilation based on a typical mild climate cross ventilation.

Evaluation uses two environmental indicators, gross energy requirement (GER) and global warming potential (GWP).

It is concluded that scenarios four and five reduce the GER in 4.4 and 9%, respectively, and the GWP in 2.6 and 4.3% compared to the current state.