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• Electricity, the most direct and effective use of RES, is in center of energy transition. • An interdisciplinary procedure suitable for the planning of RES is presented. • Key points and procedures for the assessment of large-scale RES installation is presented. • Simulation on Eygiption case shows the technical and economical viability. Due to the environmental impacts brought by current energy schemes, the energy transition, a new paradigm shift from fossil fuels to renewable energy, has been widely accepted and is being realized through collective international, regional, and local efforts. Electricity, as the most direct and effective use of renewable energy sources (RES), plays a key role in the energy transition. In this paper, we first discuss a viable pathway to energy transition through the electricity triangle, highlighting the role of RES in electricity generation. Further, we propose methodologies for the planning of wind and solar PV, as well as how to address their uncertainty in generation expansion problems. Finally, by using a web-based tool, "RES-PLAT" 1 1 https://res-plat.est.polito.it. , we demonstrate the scheme in a case study in Egypt, which evaluates the impacts and benefits of a large-scale RES expansion. 2 2 The short version of the paper was presented at Applied Energy Symposium: MIT A+ B, August 13–14, Boston. This paper is a substantial extension of the short version of the conference paper. [ABSTRACT FROM AUTHOR]

Highlights: [•] Grid capacity problems due to EV integration expected in 2015 in urban areas. [•] A GIS-based simulation assesses risks associated with large scale EV integration. [•] Risks are assessed on neighbourhood level using GIS data. [•] Grid operators can use our method to improve investment planning. [ABSTRACT FROM AUTHOR]

• Earlier phase-out of coal is not the best answer to achieve energy transition. • The 2050 plan and historical RES investments maxima are not enough to reach climate neutrality. • What is the effect of regional RES limits over Nationwide RES limits. • Where will be the states in Germany having major RES deployment. • Myopic optimization reveals new challenges for energy policy. This paper will introduce the open-source model MyPyPSA-Ger, a myopic optimization model developed to represent the German energy system with a detailed mapping of the electricity sector, on a highly disaggregated level, spatially and temporally, with regional differences and investment limitations. Furthermore, this paper will give new outlooks on the German federal government 2050 emissions goals of the electricity sector to become greenhouse gas neutral by proposing new CO 2 allowance strategies. Moreover, the regional differences in Germany will be discussed, their role and impact on the energy transition, and which regions and states will drive the renewable energy utilization forward. Following a scenario-based analysis, the results point out the major keystones of the energy transition path from 2020 to 2050. Solar, onshore wind, and gas-fired power plants will play a fundamental role in the future electricity systems. Biomass, run of river, and offshore wind technologies will be utilized in the system as base-load generation technologies. Solar and onshore wind will be installed almost everywhere in Germany. However, due to the nature of Germany's weather and geographical features, the southern and northern regions will play a more important role in the energy transition. Higher CO 2 allowance costs will help achieve the 1.5-degree-target of the electricity system and will allow for a rapid transition. Moreover, the more expensive, and the earlier the CO 2 tax is applied to the system, the less it will cost for the energy transition, and the more emissions will be saved throughout the transition period. An earlier phase-out of coal power plants is not necessary with high CO 2 taxes, due to the change in power plant's unit commitment, as they prioritize gas before coal power plants. Having moderate to low CO 2 allowance cost or no clear transition policy will be more expensive and the CO 2 budget will be exceeded. Nonetheless, even with no policy, renewables still dominate the energy mix of the future. However, maintaining the maximum historical installation rates of both national and regional levels, with the current emissions reduction strategy, will not be enough to reach the level of climate-neutral electricity system. Therefore, national and regional installation requirements to achieve the federal government emission reduction goals are determined. Energy strategies and decision makers will have to resolve great challenges in order to stay in line with the 1.5-degree-target. [ABSTRACT FROM AUTHOR]

• Near-optimal low-carbon energy systems with the least spatial conflict are modeled. • Required land for energy infrastructure is quadruple in 2040 at the cost optimum. • Raising 10% costs from the optimum reduces 58% required land area. • Costs of averted land per unit are high compared to land market prices. • Role of nuclear power in lowering area impact depends on flexibility from hydrogen. Long-term power market outlooks suggest a rapid increase in renewable energy deployment as a main solution to greenhouse gas mitigation in the Northern European energy system. However, the consequential area requirement is a non-techno-economic aspect that currently is omitted by many energy system optimization models. This study applies modeling to generate alternatives (MGA) technique to the Balmorel energy system model to address spatial conflicts related to increased renewable energy deployment. The approach searches for alternative solutions that minimize land-use conflicts while meeting the low-carbon target, by allowing a 1% to 15% increase in system costs compared to the least-cost solution. Two alternative objectives are defined to reflect various aspects of spatial impact. The results show that the least-cost solution requires 1.2%–3.6% of the land in the modeled countries in 2040 for onshore wind and solar PV installations. A 10% increase in costs can reduce the required land area by 58% by relying more on offshore wind. Nuclear energy may also be an option if both onshore and offshore areas are to be reduced, or in a less flexible system. Both offshore wind and nuclear energy technologies are associated with higher risks and pose uncertainties in terms of reaching the climate targets in time. The changes in costs and required land areas imply significantly higher annual costs ranging from 200 to 750 kEUR/km2 to avoid land use for energy infrastructure. Overall, this study confirms that the energy transition strategies prioritizing land savings from energy infrastructure are feasible, but high risks and costs of averted land are involved. [ABSTRACT FROM AUTHOR]

• Limited land area complicates renewable energy deployment in archipelagos. • Renewable offshore floating technologies enable energy transition of islands. • Synthetic e-fuels can be imported or self-produced cost-effectively until 2050. • Energy transition in the Maldives until 2030 is possible with minor cost markup. • Floating offshore solar PV and wave power emerge as the major energy sources. Low-lying coastal areas and archipelago countries are particularly threatened by the impacts of climate change. Concurrently, many island states still rely on extensive use of imported fossil fuels, above all diesel for electricity generation, in addition to hydrocarbon-based fuels to supply aviation and marine transportation. Land area is usually scarce and conventional renewable energy solutions cannot be deployed in a sufficient way. This research highlights the possibility of floating offshore technologies being able to fulfil the task of replacing fossil fuels with renewable energy solutions in challenging topographical areas. On the case of the Maldives, floating offshore solar photovoltaics, wave power and offshore wind are modelled on a full hourly resolution in two different scenarios to deal with the need of transportation fuels: By importing the necessary, carbon neutral synthetic e-fuels from the world market, or by setting up local production capacities for e-fuels. Presented results show that a fully renewable energy system is technically feasible in 2030 with a relative cost per final energy of 120.3 €/MWh and 132.1 €/MWh, respectively, for the two scenarios in comparison to 105.7 €/MWh of the reference scenario in 2017. By 2050, cost per final energy can be reduced to 77.6 €/MWh and 92.6 €/MWh, respectively. It is concluded that floating solar photovoltaics and wave energy converters will play an important role in defossilisation of islands and countries with restricted land area. [ABSTRACT FROM AUTHOR]

• We provide an overview of the dynamics between energy transition and COVID-19. • We identify the challenges and opportunities for energy transition under COVID-19. • We investigate the impact of global economic recovery stimulus on energy transition. • We propose a practical roadmap for the post-pandemic energy transition. • We enrich the framework on global low-carbon energy transition. The COVID-19 pandemic has created significant challenges for energy transition. Concerns about the overwhelming emphasis on economic recovery at the cost of energy transition progress have been raised worldwide. More voices are calling for "green" recovery scheme, which recovers the economy while not compromising on the environment. However, limited academic attention has been paid to comprehensively investigating the implications of COVID-19 for global energy transition. This study thus provides a comprehensive analysis of the dynamics between energy transition and COVID-19 around the world and proposes a low-carbon energy transition roadmap in the post-pandemic era. Using energy data from the International Energy Agency (IEA), we first summarized and reviewed the progress of energy transition prior to COVID-19. Building on prior progress, we identified the challenges for energy transition during the pandemic from the perspectives of government support, fossil fuel divestment, renewable energy production capacity, global supply chain, and energy poverty. However, the pandemic also generates opportunities for global energy transition. We hence also identified potential opportunities for energy transition presented by the pandemic from the perspectives of price competitiveness, policy implementation efficiency, and renewable energy strengths. We further provided an in-depth discussion on the impact of current worldwide economic recovery stimulus on energy transition. Based on the identified challenges and opportunities, we proposed the post-pandemic energy transition roadmap in terms of broadening green financing instruments, strengthening international cooperation, and enhancing green recovery plans. Our study sheds light on a global low-carbon energy transition framework and has practical implications for green recovery schemes in post-pandemic times. [ABSTRACT FROM AUTHOR]

• Four environmental indicators suitable for use in energy system models are proposed (85) • The indicators allow direct comparison of decarbonisation potential of renewables (84) • Gearbox double-fed induction generators are the preferred form of wind turbine (80) • Cadmium telluride photovoltaics exhibit best overall raw materials outcomes (78) Raw materials and their related environmental impacts will play a key role in the implementation of renewable energy infrastructures for decarbonization. Despite the growing amount of data quantifying raw materials for energy production technologies, few examples of these data sources are being included in current energy system models. Accordingly, this paper introduces possible pathways for integrating material-specific life cycle assessment outputs and material metabolism indicators into energy system models so that raw material requirements, and their associated impacts, can be accounted for. The paper discusses the availability of life cycle inventories, impact assessment methods and important output indicators. The material metabolism indicators most relevant to the current policy debate surrounding the European Green Deal–namely, material supply risk and contribution of recycled materials to total supply–are also discussed alongside the value of adding this information to energy system models. A methodology for using data from both approaches is offered and operationalised using four sub-technologies of both wind turbines and solar photovoltaic panels as case studies. The results show that considerable variation exists between and within the two groups for all indicators. The technologies with the lowest global warming potential, cumulative energy demand and supply risk are turbines with gearbox double-fed induction generators and cadmium telluride photovoltaics. Furthermore, wind turbines exhibit significantly higher recycling rates than photovoltaics. Ultimately, the integration of such methodologies into energy system models could greatly increase the awareness of raw material issues and guide policies that maximise compatibilities between resource availability and cleaner energy systems. [ABSTRACT FROM AUTHOR]

Abstract: The paper investigates how renewable technologies could promote the transition towards a sustainable energy production in developing nations. Based on two different developing nations in terms of economic, technological and institutional structure: South Africa and Senegal, we implemented scenarios in a bottom-up PowerPlan model in order to analyze the transition toward a sustainable electric production. Two scenarios have been considered: a business-as-usual (BAU) and a hybrid renewable energy (HRE) scenario. In the first scenario (BAU) we assume that the electricity demand is entirely satisfied by an increase of the investment in the current supply structure based on fossil-fuel energy source. Whereas in the renewable energy scenario, we assume 20% and 30% of the electricity supply being generated from renewable resources by 2020 and 2030 respectively. Focusing on wind and solar photovoltaic technologies, our results show the cost-competitiveness of renewable energy deployment in South Africa. In the case of Senegal, our results show that fossil-fuel resource remains the most competitive to generate electricity in the nation during the next coming years as long as environmental advantages of renewable resource are not considered. Our research indicates that in the case of a centralized electricity supply option, both a scale effect and a learning improvement could eventually strengthen the competitiveness of renewable technology deployment in developing nations. [Copyright &y& Elsevier]

• Road-freight TCO compared for 5 drive-technologies in 3 applications, 10 countries. • A database of costs for road-freight TCO parameters is newly compiled. • Low-carbon vehicles largely competitive in light- and medium-duty segments. • Low-carbon vehicles competitive in heavy-duty segments in selected countries. • Findings indicate three important TCO parameters to drive this competitiveness. In light of the Paris Agreement, road-freight represents a critically difficult-to-abate sector. In order to meet the ambitious European transport sector emissions reduction targets, a rapid transition to zero-carbon road-freight is necessary. However, limited policy assessments indicate where and how to appropriately intervene in this sector. To support policy-makers in accelerating the zero-carbon road-freight transition, this paper examines the relative cost competitiveness between commercial vehicles of varying alternative drive-technologies through a total cost of ownership (TCO) assessment. We identify key parameters that, when targeted, enable the uptake of these more sustainable niche technologies. The assessment is based on a newly compiled database of cost parameters which were triangulated through expert interviews. The results show that cost competitiveness for low- or zero-emission niche technologies in certain application segments and European countries is exhibited already today. In particular, we find battery electric vehicles to show great promise in the light- and medium-duty segments, but also in the heavy-duty long-haul segments in countries that have enacted targeted policy measures. Three TCO parameters drive this competitiveness: tolls, fuel costs, and CAPEX subsidies. Based on our analysis, we propose that policy-makers target OPEX before CAPEX parameters as well utilize a mix of policy interventions to ensure greater reach, increased efficiency, and increased policy flexibility. [ABSTRACT FROM AUTHOR]

[Display omitted] • The presented model can simulate future material and energy demand and carbon emissions. • The model builds upon real individual buildings from GIS data. • Insulation contributes most to carbon reduction for space heating. • Greening electricity mix plays a key role in residential decarbonization. • Nearly 80% of electricity could be met if photovoltaic systems are installed on half of roofs. The building sector plays a key role in energy transition and carbon reduction while capturing the dynamic characteristics (e.g. materials, energy performance, and environmental impact) of building stock is a great challenge during the gradual process. This study presents a bottom-up dynamic building stock model that links dynamic material flow analysis with building energy modeling. The environmental impact of material and energy requirements is assessed by considering future electricity mix. The model is applied to evaluate the pathways to the climate-neutral energy supply of residential building stock in the Netherlands by 2050. Results show that space heating demand decreases by about 2/3 by 2050, while the energy for hot water increases to 92% of space heating demand. 80% of public grid electricity for appliances and lighting can be potentially substituted if rooftop photovoltaic (PV) systems are installed on 50% of renovated buildings and all the new buildings. Greenhouse gas (GHG) emissions of operational energy are reduced by approximately 60–90%, depending on the electricity mix. Annual GHG emissions from material production are not as important as those related to operational energy. Insulation materials account for a large proportion of the carbon footprint of material production. The model has a high spatial and temporal resolution and can be linked with local energy source availability (e.g. buildings or neighborhoods) to provide more accurate support for policymaking. [ABSTRACT FROM AUTHOR]

• To study energy community formation agent-based modelling is proposed. • Institutional conditions influence energy communities' formation greatly. • Trained energy community boards facilitate energy community formation. • Financial considerations alone are insufficient to form energy communities. • Balancing between all relevant decision-making criteria is key to success. Energy communities are key elements for local energy transitions, collectively generating, distributing and consuming energy, using renewable energy technologies. Thermal energy communities, as one type of energy community, are focused on thermal energy applications, such as heating, cooling, bathing, showering and providing hot tap water. As thermal energy applications and systems receive increasing academic and policy attention, there is a need to better understand the formation processes they undergo. In this study, various technical and institutional conditions are explored that influence thermal energy community formation processes by using an agent-based modelling approach. The results show that technology selection is not the most crucial and determining factor for the success of thermal energy communities, yet the surrounding institutional conditions are. Key factors that influence these formation processes pertain to providing training, so that the thermal energy community leaders become more skilled, and allocating subsidies based on the projects' degree of environmental friendliness. For all stakeholders, finding the balance between all of the decision-making criteria is key to success. The results are useful for practitioners - and especially for policy makers - to develop more impactful policies and strategies to support the expansion of local thermal energy communities. [ABSTRACT FROM AUTHOR]

• Energy trilemma objectives are not always conflicting in network design. • Stand-by fossil generators combined with batteries as backup for blackouts. • Required external grid capacity ranges between 43% and 228% of peak load. • Changes in capital expenditure and self-supply could affect business models. • No consensus between 4 multi-objective decision making methods. A significant reduction in greenhouse gas emissions entails complex trade-offs among economic, environmental and security objectives of the energy trilemma. The associated proliferation of distributed energy resources in power distribution networks requires optimized planning to ensure economic efficiency and security, where security is defined as the ability to withstand outages (reliability) and imbalances between generation and load (flexibility). This paper investigates the trade-offs among active distribution network design solutions in the energy trilemma. Storage, renewable and dispatchable generators are installed to minimize cost, interruptions and emissions via epsilon-constraint mixed integer linear program. The ramping capability of distributed energy resources is harnessed to provide flexible capacity to the surrounding grid, and to enable the transition from active distribution networks into microgrids with islanding capability. Decision-making strategies for selecting the best design from a Pareto-optimal set are contrasted based on the economic, sustainability and security of the design and operations. Applying these strategies to a Californian distribution network shows nonlinear trade-offs between the trilemma objectives, reducing both emissions and interruption durations by up to 64%. Remarkably, energy supply is diversified with up to 47% of local generation entailing a strong reduction in operating expenditures. While the increase in local generation can reduce the peak imports from the surrounding grid by 56% compared to a network without distributed energy resources, enforcing strict emission limits can lead to renewable exports that exceed the peak load by 130%. Sensitivity analyses identify the performance indicators which strongly influence the selection of the best design. [ABSTRACT FROM AUTHOR]

• Energy investment of prosumer industrial SMEs is analysed considering costs trends. • A multiple-year methodology is applied with weekly pattern optimisation. • This framework allows to make energy investments with economic evolution awareness. • An automotive industry case willing to invest in new energy equipment is studied. • The results expose the suitability of industrial SMEs for an active energy role. The market is searching for solutions to reduce emissions in the energy sector by increasing the consumer efficiency and flexibility and integrating renewable sources. Prosumers are suited to this role and are increasingly considered crucial to any such solution. Small-and-medium enterprises (SMEs) that need to upgrade their energy infrastructure, due to equipment obsolescence or external pressures to adopt greener technologies, face difficulties in integrating new energy management strategies given the investment required and the payback periods. Industrial SMEs traditionally seek to make on-off investments with fast returns, exploiting the obtained equipment for its whole lifetime. Therefore, this paper presents a novel methodology to determine the optimal sizing and operation of the energy infrastructure for an industrial SME transitioning to a prosumer model to improve its economic perspectives, considering the exploitation of the infrastructure for its complete lifetime. The energy and economic profiles of SMEs are analysed and their energy infrastructure modelled in order to define the sizing and operation optimisation problem. Operation of the equipment is optimised considering weekly cycles along multiple years, obtaining the net present value of the investment. The proposed methodology, which employs direct search and linear programming techniques, enable industrial SMEs to undertake informed energy investment actions. A real manufacturing plant is described, characterized and used as the basis for a case study. The results show the economic feasibility of installing new energy equipment in SMEs, obtaining payback periods less than five years and final investment value of more than ten times the initial expense. [ABSTRACT FROM AUTHOR]

• Early smart grid R&D advancements can indicate future technological developments. • A method for analyzing the evolution of smart grid technologies is proposed. • The Network theory is used to justify the existence of a main path of technologies. • Four innovation trajectories exist around smart energy applications. • The proposed approach complements existing methods of main path analysis. This paper investigates how the strategic decisions of innovative firms to collaborate with other firms in research and development projects shape the early evolution of smart grid technologies as an emerging technological system across Europe. The early innovations and developments in an emerging technological system are crucial for understanding further developments of the system. This early stage is highly influenced by the strategic decisions and lobbying power of the firms experimenting with different technological innovations, and the policies trying to maintain competition and steer the direction of innovative activities. Therefore, it is important to analyze how innovative firms behave in terms of collaborating with other firms and doing research on specific energy solutions, which reflect their strategic priorities. By taking a complex network approach, this paper investigates a network of smart grid R&D projects to analyze the convergence of smart grid research activities towards a stream of innovative solutions, and the variety of innovative activities branching out from these solutions. The results verify the convergence of smart grid activities towards one specific stream of innovations, and reveal the existence of four variations centered around different technological applications. The results can guide strategy development in innovative firms to take part in research collaborations or focus on specific smart energy technologies, and have implications for policy makers aiming to influence the direction of smart grid research programs, as well as for researchers in the field of smart grid innovation and technological innovation systems. [ABSTRACT FROM AUTHOR]

• Electricity, hydrogen and methane system will be more integrated in the future. • The developed integrated model considers their interactions and interdependencies. • As proof-of-concept, the model is applied to the Dutch Infrastructure Outlook 2050. • Interweaving electricity, hydrogen and methane system will provide much needed flexibility. The future energy system is widely expected to show increasing levels of integration across differing energy carriers. Electricity, hydrogen, methane and heat systems may become increasingly interdependent due to coupling through conversion and hybrid energy technologies. Market parties, network operators, policy makers and regulators require tools to capture implications of possible techno-economic and institutional developments in one system for the operation of others. In this article, we provide an integrated electricity, hydrogen and methane systems modelling framework focusing on interdependencies between them. The proposed integrated electricity and (renewable) gas system model is a market equilibrium model with hourly price and volume interactions, considering ramp rates of conventional units, variability of intermittent renewables, conversion, transport as well as storage of electricity, hydrogen and methane. The integrated model is formulated as a linear program under the assumption of perfect competition. As proof-of-concept, the model has been applied to a test case consisting of 34 electricity nodes, 19 hydrogen nodes and 22 methane nodes, reflecting the regional governance scenario in the Dutch Infrastructure Outlook 2050 study. The case study also includes different sensitivity analyses with regard to variable renewable capacity, energy demand and biomass prices to illustrate model response to perturbations of its main drivers. This article demonstrates that the interweaving of electricity, hydrogen and methane systems can provide the required flexibility in the future energy system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Clean energy transitions based on the circular economy (CE) are analysed for a town in China. • This could reduce energy use, CO 2 emissions and PM 2.5 emissions compared to the BAU scenario. • COVID pandemic is a new opportunity to introduce circular economy measures. • Circular economy measures could accelerate clean energy transitions. This paper models the energy and emissions scenarios for a circular economy based clean energy transitions in a 140,000-population town in China, taking into account the new situation encountered by the COVID-19 pandemic. The modelled scenarios propose new clean energy transition roadmaps towards a sustainable urban system through the implementation of circular economy strategies. This is represented by the cascading use of industrial excess heat to form symbiosis between factories and to cover the growing building heat demand, as well as by the electrification of the transport sector and reusing the batteries for a second life as energy storage devices. The results show that for a circular economy scenario, during 2020–2040, an accumulated saving of 7.1 Mtoe final energy use (34%), a decline in 14.5 Mt CO 2 emissions (40%) and 592 t PM 2.5 emissions (43%) could be achieved compared with the business-as-usual scenario. The outcomes of the circular economy strategies are at least 7% better than the new policy scenario which simply has energy efficiency improvements. The outbreak of the COVID-19 tremendously impacts the socio-economic activities in the town. If taking the pandemic as an opportunity to enhance the circular economy, by 2040, compared with the scenario without introducing circular economy measures, the extra avoided final energy use, CO 2 emissions and PM 2.5 emissions could be 1.6 Mtoe (8%), 3.8 Mt (11%) and 229 t (17%) respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Open model-based analysis for 100% renewable and sector-coupled energy systems. • Cost-optimization tool based on Oemof to investigate Germany's energy system in 2050. • Renewable energy is sufficient for electricity and building heat in Germany in 2050. • Investment cost (bn €/yr): 17.6–26.6 (Volatile), 23.7–28.8 (Heat), 2.7–3.9 (Storage). • Energy mix and LCOE comparison validate the developed tool's effectiveness. The ambitious energy target to achieve climate-neutrality in the European Union (EU) energy system raises the feasibility question of using only renewables across all energy sectors. As one of the EU's leading industrialized countries, Germany has adopted several climate-action plans for the realistic implementation and maximum utilization of renewable energies in its energy system. The literature review shows a clear gap in comprehensive techniques describing an open modeling approach for analyzing fully renewable and sector-coupled energy systems. This paper outlines a method for analyzing the 100% renewable-based and sector-coupled energy system's feasibility in Germany. Based on the open energy modeling framework, an hourly optimization tool 'OSeEM-DE' is developed to investigate the German energy system. The model results show that a 100% renewable-based and sector-coupled system for electricity and building heat is feasible in Germany. The investment capacities and component costs depend on the parametric variations of the developed scenarios. The annual investment costs vary between 17.6 and 26.6 bn €/yr for volatile generators and between 23.7 and 28.8 bn €/yr for heat generators. The model suggests an investment of a minimum of 2.7–3.9 bn €/yr for electricity and heat storage. Comparison of OSeEM-DE results with recent studies validates the percentage-wise energy mix composition and the calculated Levelized Cost of Electricity (LCOE) values from the model. Sensitivity analyses indicate that storage and grid expansion maximize the system's flexibility and decrease the investment cost. The study concludes by showing how the tool can analyze different energy systems in the EU context. [ABSTRACT FROM AUTHOR]

The map shows the centroids (geometric centres) of the local gas distribution zones (dotted circles), the offshore pipeline network connecting the potential hydrogen storage sites to the UK gas terminals. The scaling of the circles is logarithmic base ten, hence the energy storage need of LDZ is generally one or two orders of magnitude smaller than the storage capacity of individual storage sites. The LDZ are indicated in italic next to their matching centroid. Their storage need in TWh is also indicated. SC: Scotland, NO: Northern England, NE: North East England, NW: North West, EM: East Midlands, WM: West Midlands, WN: Wales North, WS: Wales South, SW: South West, SO: Southern England, SE: South East, NT: North Thames, EA: East Anglia. • A new method comparing geological storage capacity to storage need is presented. • Geological hydrogen storage capacity exceeds UK heating seasonal storage needs. • Offshore UK gas fields can potentially store 2661.9 terawatt-hour of hydrogen. • Hydrogen storage is unlikely to compete with other subsurface uses. • Stores used with hydrogen, instead of natural gas, can store up to 75% less energy. Hydrogen is considered as a low-carbon substitute for natural gas in the otherwise difficult to decarbonise domestic heating sector. This study presents for the first time, a globally applicable source to sink methodology and analysis that matches geological storage capacity with energy demand. As a case study, it is applied to the domestic heating system in the UK, with a focus on maintaining the existing gas distribution network. To balance the significant annual cyclicity in energy demand for heating, hydrogen could be stored in gas fields offshore and transported via offshore pipelines to the existing gas terminals into the gas network. The hydrogen energy storage demand in the UK is estimated to be ~77.9 terawatt-hour (TWh), which is approximately 25% of the total energy from natural gas used for domestic heating. The total estimated storage capacity of the gas fields included in this study is 2661.9 TWh. The study reveals that only a few offshore gas fields are required to store enough energy as hydrogen to balance the entire seasonal demand for UK domestic heating. It also demonstrates that as so few fields are required, hydrogen storage will not compete for the subsurface space required for other low-carbon subsurface applications, such as carbon storage or compressed air energy storage. [ABSTRACT FROM AUTHOR]

During the necessary transition to sustainable power systems, fossil generators are used to complement generation from renewable energies. Yet not all fossil technologies can be operated flexibly enough to balance the fluctuating output of renewables. I study how the efficient transition to renewables is influenced by the endowment with flexible and inflexible generators. To this end, I develop a parsimonious analytical model that incorporates a variable renewable energy (VRE) technology with stochastic generation availability as well as flexible and inflexible fossil generators with rigid capacities. I find that early in the transition, VRE generation replaces generation from flexible capacities. Only later is the output of inflexible generation reduced and substituted by increasing flexible and renewable generation. The early deployment of VRE is hampered by high inflexible capacities. However, deployment speed surges once VRE generation begins to substitute inflexible generation. The more excess capacities exist in the initial endowment, the higher the sudden increase in deployment is. The decreasing use of inflexible fossil generation is usually accompanied by an increasing utilization of flexible generators. Nevertheless, constructing additional flexible capacities is only cost-efficient if a cost threshold is not exceeded. By contributing to a better understanding of the impact of flexibility on efficient VRE deployment, this work aims to facilitate an efficient transition to renewable energies. • New analytical model to analyze power system transitions under limited flexibility. • Renewables first replace flexible generation and later inflexible generation. • Instant increase of renewables is efficient once use of inflexible plants decreases. • Benefits of flexible generation peak when inflexible plants are no longer used. • Excess capacity endowments induce fluctuations in renewable deployment. [ABSTRACT FROM AUTHOR]

• Sector coupling leads to lower cost of energy supply in a RE-based system. • Power sector becomes the backbone of the entire energy system. • Integration impact depends on demand profiles, flexibility and storage cost. • Electrolysers are an important source of flexibility in an integrated system. • All sector defossilisation is achieved even for severe conditions as of Kazakhstan. Transition towards long-term sustainable energy systems is one of the biggest challenges faced by the global society. By 2050, not only greenhouse gas emissions have to be eliminated in all energy sectors: power, heat, transport and industry but also these sectors should be closely coupled allowing maximum synergy effects and efficiency. A tool allowing modelling of complex energy system transition for power, heat, transport and industry sectors, responsible for over 75% of the CO 2eq emissions, in full hourly resolution, is presented in this research and tested for the case of Kazakhstan. The results show that transition towards a 100% sustainable and renewable energy based system by 2050 is possible even for the case of severe climate conditions and an energy intensive industry, observed in Kazakhstan. The power sector becomes backbone of the entire energy system, due to more intense electrification induced sector coupling. The results show that electrification and integration of sectors enables additional flexibility, leading to more efficient systems and lower energy supply cost, even though integration effect varies from sector to sector. The levelised cost of electricity can be reduced from 62 €/MWh in 2015 to 46 €/MWh in 2050 in a fully integrated system, while the cost of heat stays on a comparable level within the range of 30–35 €/MWh, leading to an energy system cost on a level of 40–45 €/MWh. Transition towards 100% renewable energy supply shrinks CO 2eq emissions from these sectors to zero in 2050 with 90% of the reduction achieved by 2040. [ABSTRACT FROM AUTHOR]

In power systems, flexibility can be defined as the ability to cope with variability and uncertainty in generation and demand. The ongoing energy transition is affecting how much flexibility is required, but also who should provide it: some existing solutions are being phased out, while new solutions' entire business models are based on providing flexibility (e.g. storage or demand response). With the intention of condensing information and rationalising debates, a significant number of methods have been proposed to quantify various facets of flexibility; this paper reviews and classifies them depending on the question they attempt to address. We propose a pair of novel tools to quantify a comparatively unexplored aspect of flexibility: who is providing it. These frequency spectrum analysis based tools separately quantify flexibility provision on the annual, weekly and daily timescales. The tools' effectiveness and versatility is demonstrated through several example applications, analysing both historical and prospective power systems, in several geographical locations with contrasting characteristics. The proposed tools are of particular value to the capacity expansion planner, allowing them to quantify changes in flexibility provision as new solutions are introduced, or as carbon taxes, generation and interconnector capacities evolve. • Historical analysis shows evolutions in definitions of power system flexibility. • Flexibility quantification methods are classified depending on the question addressed. • Method quantifies flexibility provision over annual, weekly and daily timescales. • Applications show future flexibility contribution of electric vehicle smart charging. • Applications show contribution of cross-border trade in highly interconnected systems. [ABSTRACT FROM AUTHOR]

• Electricity and electrification is a viable solution for the energy transition. • Electricity triangle assures a consistent framework for the energy transition. • Multifaceted benefits: energetic, environmental and socio-economic. • Conceptualization of a set of metrics for impact assessment. • A real case study (Italy) considering its evolution up to 2050. Greenhouse gases along with pollution generated by the present energy paradigm widely based on fossil fuels are providing large impacts in terms of climate change and the health of human and biological systems at large. A shift in the energy paradigm, from fossil fuels to renewable energy, is urgently needed for nature and society. This is what we refer to as the energy transition. An old commodity – electricity – can play a new key role in the energy transition. That can happen through what we call the electricity triangle involving electricity generation from Renewable Energy Sources, exploitation of electricity as the main energy vector, and electrification of the final energy uses in all sectors. The possible deployment of the electricity triangle must be carefully assessed in all its possible implications, from technological, economic, societal and environmental perspectives. In this paper, we conceptualize the electricity triangle as a viable approach to the energy transition, and we propose a set of holistic metrics to assess its possible impacts. We apply the electricity triangle framework to the case of Italy based on sectorial studies on RES generation and electrification in building, industry and transport sectors. Our results indicate that Italy in 2050 has the potential to achieve 85.6% penetration of RES in its electricity supply, while 41%, 53% and 42% of the energy consumptions in transport, residential, and industry sectors will be electrified. Ultimately, this would lead to a 68% reduction in CO 2 emissions compared to current levels. [ABSTRACT FROM AUTHOR]

• Rationale behind multi-objective design of low-carbon hydrogen supply chains. • Competition of several solutions for low-carbon hydrogen production. • Competition and interplay between hydrogen, biomass and CO 2 networks. • Impact of CO 2 value chain features on optimal design of hydrogen supply chains. • Impact of biomass availability on optimal design of hydrogen supply chains. This study investigates the optimal design of low-carbon hydrogen supply chains on a national scale. We consider hydrogen production based on several feedstocks and energy sources, namely water with electricity, natural gas and biomass. When using natural gas, we couple hydrogen production with carbon capture and storage. The design of the hydrogen, biomass and carbon dioxide (CO 2) infrastructure is performed by solving an optimization problem that determines the optimal selection, size and location of the hydrogen production technologies, and the optimal structure of the hydrogen, biomass and CO 2 networks. First, we investigate the rationale behind the optimal design of low-carbon hydrogen supply chains by referring to an idealized system configuration and by performing a parametric analysis of the most relevant design parameters of the supply chains, such as biomass availability. This allows drawing general conclusions, independent of any specific geographic features, about the minimum-cost and minimum-emissions system designs and network structures. Moreover, we analyze the Swiss case study to derive specific guidelines concerning the design of hydrogen supply chains deploying carbon capture and storage. We assess the impact of relevant design parameters, such as location of CO 2 storage facilities, techno-economic features of CO 2 capture technologies, and network losses, on the optimal supply chain design and on the competition between the hydrogen and CO 2 networks. Findings highlight the fundamental role of biomass (when available) and of carbon capture and storage for decarbonizing hydrogen supply chains while transitioning to a wider deployment of renewable energy sources. [ABSTRACT FROM AUTHOR]

• Industrial demand-side flexibility holds unique potentials for system stability. • Hereby, it may be an engine for sustainable and inclusive industrial development. • We illustrate guidelines of a corresponding flexibility transition pathway. • We develop a first monitoring approach for a country's flexibility transition. • Our monitoring approach indicates mis-developments and needed countermeasures. In many countries, industry is one of the largest consumers of electricity. Given the special importance of electricity for industry, a reliable electricity supply is a basic prerequisite for further industrial development and associated economic growth. As countries worldwide transition to a low-carbon economy (in particular, by the development of renewable energy sources), the increasing fluctuation in renewable energy production requires new flexibility options within the electricity system in order to guarantee security of supply. It is advanced in this paper that such a flexibility transition with an active participation of industry in general has unique potential: It will not only promote green industrial development, but also become an engine for inclusive industrial development and growth as well as delivering a just transition to a low-carbon economy. Given the high potential of industrial demand-side flexibility, a first monitoring approach for such a flexibility transition is illustrated, which bases on a flexibility index. Our flexibility index allows for an indication of mis-developments and supports an appropriate implementation of countermeasures together with relevant stakeholders. Hence, it holds various insights for both policy-makers and practice with respect to how industrial demand-side flexibility can ensure advances towards an inclusive, just, and sustainable industrial development. [ABSTRACT FROM AUTHOR]

• Community storage systems are conceptualized as complex techno-economic system. • Optimization of the competition between simultaneous residential flexibility options. • Losses due to simultaneous application of flexibility options outweigh the benefits. • Sector coupling constitutes a greater competition factor than demand response. • Community storage systems will become economically profitable in the next few years. Community electricity storage systems for multiple applications promise benefits over household electricity storage systems. More economical flexibility options such as demand response and sector coupling might reduce the market size for storage facilities. This paper assesses the economic performance of community electricity storage systems by taking competitive flexibility options into account. For this purpose, an actor-related, scenario-based optimization framework is applied. The results are in line with the literature and show that community storage systems are economically more efficient than household storage systems. Relative storage capacity reductions of community storage systems over household storage systems are possible, as the demand and generation profiles are balanced out among end users. On average, storage capacity reductions of 9% per household are possible in the base scenario, resulting in lower specific investments. The simultaneous application of demand-side flexibility options such as sector coupling and demand response enable a further capacity reduction of the community storage size by up to 23%. At the same time, the competition between flexibility options leads to smaller benefits regarding the community storage flexibility potential, which reduces the market viability for these applications. In the worst case, the cannibalization effects reach up to 38% between the flexibility measures. The losses of the flexibility benefits outweigh the savings of the capacity reduction whereby sector coupling constitutes a far greater influencing factor than demand response. Overall, in consideration of the stated cost trends, the economies of scale, and the reduction possibilities, a profitable community storage model might be reached between 2025 and 2035. Future work should focus on the analysis of policy frameworks. [ABSTRACT FROM AUTHOR]

• Representative pathways can be sought to characterise a larger pathway ensemble. • Clustering performance is sensitive to the distribution of pathways. • K-means is the most robust approach for pathway grouping. • Hierarchical clustering might perform better if pathway distribution is irregular. • Sectoral standardisation can reveal the trade-offs between metrics in each sector. Long-term decarbonisation pathways to achieve ambitious low-carbon targets involve a range of uncertainties. Different energy system modelling approaches can be used to systematically evaluate the influence of the uncertainties, but this often leads to an unmanageable number of pathways. Summarising the large ensemble through a more limited number of representative pathways, to inform stakeholders, can be challenging. This study thus explores how to identify representative decarbonisation pathways using clustering algorithms, which can assist in grouping similar data points in uncategorised datasets, such as pathway ensembles. However, the suitability of clustering algorithms for pathway characterisation has not been investigated to date. Hence, k-means, hierarchical clustering, Gaussian mixture model, spectral clustering, and density-based clustering are adopted for comparisons. An illustrative pathway ensemble for the United Kingdom is applied to evaluate their performance based on cluster validity indices. Three metric transformations, including power, standardisation and sectoral standardisation, are also applied to create three additional sets of pathways for testing. The k-means algorithm is found to outperform others consistently, although hierarchical clustering might also be applicable if the distribution of pathway proximity is uneven. The results also highlight the utility of the approach in revealing distinctive trade-offs between technologies among the identified representative pathways. For instance, the electrification of heating can be replaced by district heating in the residential sector. The described, novel approach can be applied to characterise other sets of pathways, with greater technological details generated by any energy system models, to reveal insights for long-term decarbonisation. [ABSTRACT FROM AUTHOR]

• Energy yield simulation of vertical bifacial PV array in 12 European locations. • Comparison with a conventional PV array (monofacial, equator-oriented, tilted). • Evaluation of market revenues based on historic day-ahead market prices. • Evaluation of LCOE and net present value. • Evaluation of system cost reduction from a macroeconomic perspective for Germany. Thanks to the two diurnal generation peaks, vertical bifacial photovoltaic power plants (VBPV) with a north-south axis represent an option to meet the challenges of a mismatch between electricity demand and the generation profile of conventional photovoltaic systems (C-PV). Despite this promising characteristic, it is hardly possible to assess the technical and economic properties of VBPV on the basis of existing studies. The present work is a contribution to close this gap. Among other things, the conducted analyses included electricity generation, market revenues, levelized costs of electricity (LCOE) and the cost-reducing effect of VBPV in a national electricity system. C-PV was used as a benchmark in all analyses. Electricity generation was simulated at twelve European sites in four countries. It has been found that above a latitude of 50° VBPV generates more electricity than C-PV. Due to the higher investments, VBPV had higher LCOE at all locations investigated. The results also showed that VBPV can generate higher revenues in electricity markets with a high share of C-PV capacity, but that these additional revenues are not yet sufficient to compensate for the higher investments. With an optimising electricity market model, it was also found that VBPV can contribute to reducing system costs in an electricity system with high shares of C-PV capacity. Against the background of the increasing importance of PV for the electricity supply of most European countries, these findings are of particular importance. In summary, it can be said that VBPV has significant potential at both the business and macro-economic level and that decision makers should promote the market entry of this technology. [ABSTRACT FROM AUTHOR]

• Integrated stakeholder preferences towards equality into electricity planning. • Framework for opportunity-focused approach for electricity planning. • Novel combination of economics, utility maximization, and least-cost frameworks. • Co-optimized generation and transmission investments under equality preferences. Access to electricity can lead to enhanced education, business, and healthcare opportunities. Governments in emerging economies are often faced with the challenge of increasing access to electricity and reducing system inequality, while operating under severe budget constraints. This paper develops a methodology for finding the optimal expansion of a power system under the objective of maximizing social benefit, as it relates to distributional equality for electricity access, subject to a budget constraint. This contrasts with traditional models, which minimize the cost of satisfying projected electricity demand. We formulate a generation expansion planning problem as a utility-maximization mixed-integer linear program and apply it to a case study analysis of a low-income country with limited electricity infrastructure. We focus our analysis on understanding how the optimal allocation of generation between centralized and distributed resources is impacted by stakeholder preferences toward equality and different budget levels. We find that a high preference for equality leads to lower overall electricity consumption levels, but improved electrification rates due to greater investment (300–750 km increase) in transmission infrastructure. If stakeholders move from a low to a high equality preference then they could see a 72–87% increase in energy access equality rating depending on the budget. Conversely, indifference to equality leads to higher overall consumption levels in urban areas but reduced electrification rates. This methodology can help decision makers evaluate the social trade-offs between improving energy access, reducing energy inequality and poverty, and increasing total electricity consumption when operating under budget constraints in their countries. [ABSTRACT FROM AUTHOR]

• Probabilistic simulation of security of electricity supply in central Europe. • Quasi-absolute levels of security of supply are unlikely to be maintained in future scenarios. • Sensitivity of security of supply towards meteorological influences is increasing. • Dependency on contributions from neighboring countries is growing. • Relevance to coordinate capacity planning on an international level is demonstrated. Against the backdrop of expansions of intermittent renewable energy capacity, planned nuclear phase-outs, and current debates on the additional mothballing of coal-fired power plants in central Europe, there is a substantial increase in uncertainty regarding security of electricity supply. In this context, we present a probabilistic and scenario-based analysis of impacts on security of supply for Germany as a case-study in the medium-term perspective (years 2020, 2022, and 2023). For our analysis, we introduce the energy security assessment module of the JERICHO energy system model from RWTH Aachen University. Our model allows for an hourly probabilistic simulation of security of supply and accounts for stochastic characteristics of (non-)availability of conventional generators, renewable feed-in, electricity demand, and import potentials from central-European countries. To increase the robustness of results, we use a comprehensive dataset of temperature, wind speeds, solar radiation and water levels from weather years 1986 to 2015 as input for our simulations. Our results indicate that Germany is unlikely to maintain its quasi-absolute levels of security of supply in the near future with a mean Loss of Load Expectation (LoLE) of up to 2.6 h in scenario year 2023. However, this does not necessarily imply that future levels of security of supply are insufficient. There is need for further assessments on identifying threshold levels for security of supply, which are economically efficient and acceptable for society. Our results also indicate that the sensitivity of security of supply for meteorological changes increases with reductions of conventional power plants. Finally, we demonstrate that the dependency of security of supply on imports from neighboring countries increases substantially calling for increased international coordination of national energy policies. [ABSTRACT FROM AUTHOR]

• Mapped evolution of China's policy mix for sustainable energy transition 1981–2020. • Over time China forms complex policy mix by layering and packaging instruments. • China has increased the diversity and number of policy instruments used. • Rise in charges on emissions and decrease in subsidies for renewables is observed. • Policy experimentation dominates policy instruments used to reduce carbon emissions. Global warming and the acute domestic air pollution in China have necessitated transition to a sustainable energy system away from coal-dominated energy production. Through a systematic review of the national policy documents, this study investigates the policy mix adopted by the Chinese government to facilitate its energy transition and how that policy mix has evolved between 1981 and 2020. The chronological analysis emphasizes two dimensions of temporal changes in the policy mix: (1) changes in the policy intensity and density, and (2) the shift in policy instrument combinations. The policy mix has evolved from a few authority-based instruments to the current response that has a large density of instruments with a good diversity of instrument types. The Chinese government imposes an increasing policy intensity on air pollution abatement and a decreasing policy intensity on renewable energy support, and experiments with innovative policy instruments to reduce carbon dioxide emissions. The evolutionary trajectory features layering new policy instruments, calibrating existing ones and some degree of policy replacement and sequencing. Overall, the study shows that the Chinese government has adopted a complex mix of policy instruments to abate emissions (e.g. carbon dioxide and sulphur dioxide) in the coal-based energy system and to support renewable energy technologies. The study provides an in-depth understanding of Chinese policy design in the environment and energy fields and contributes to the public policy literature by filling a research gap – the comparative lack of empirical analyses on the temporal changes in the policy mixes. [ABSTRACT FROM AUTHOR]

• An escalating $25 tax on electricity reduces carbon emissions and increase jobs. • Fuel switching has a greater impact than demand reduction in decreasing carbon. • Household carbon tax dividends would exceed household utility bill increases. • Job impacts vary across regions, influenced by path dependencies and resources. • This paper introduces meta-modeling to the climate policy modeling community. While the environmental benefits of carbon taxes are well documented, their employment impacts are not. We simulate an escalating $25/tCO 2 tax on the U.S. electricity system and estimate the resulting employment effects using a computable general equilibrium model. Meta-modeling of the results reveals how carbon taxes influence costs, prices, fuel shares and jobs. Overall, we estimate that the carbon tax would increase U.S. employment – e.g., by 511,000 jobs in 2030. Regional heterogeneities are explained, in part, by the path dependency of electricity portfolios and by regional resource variations. The carbon tax would motivate significant CO 2 emission reductions, as well as utility bill increases that could on average be offset by carbon tax dividends. The possibility of inter-regional wealth transfers is highlighted, underscoring the importance of revenue recycling and other policy features that promote inclusive benefits. [ABSTRACT FROM AUTHOR]

• The contributors to the change in global renewable energy use are analyzed. • A new variant of a structural decomposition analysis introduces energy transition. • Energy transition contributed little to the change in global renewable energy use. • Also the global effects of changes in trade structure are very small. • Affluence, population growth and technology changes are the main contributors. This study investigates the growth in global renewable energy use between 2000 and 2014. To identify its main contributors and their geographical distribution, a structural decomposition analysis is applied to global multi-regional input-output tables. A new variant of this type of analysis is developed that introduces energy transition (i.e. the substitution of non-renewable energy by renewable energy) as one of the contributors. Global renewable energy use rose by 22.1 Exa Joules (EJ), from 57.8 EJ in 2000 to 79.9 in 2014. The contribution of energy transition at the global level to this 22.1 EJ increase was small and positive (+1.3 EJ). As for the geographical distribution of the effects, positive effects are found for the European Union and the United States, negative effects for China, India, and the Rest of the World (which includes many developing and emerging countries). Trade structure changes also had a small effect on global renewable energy use (+1.1 EJ). The main contributions were the worldwide changes in: technology and overall energy efficiency (−23.6 EJ); consumption per capita (+32.2EJ); and population (+11.0 EJ). [ABSTRACT FROM AUTHOR]

• 100% RE can supply an energy intensive economy under harsh climate conditions. • Substantial storage capacities are needed to compensate seasonality of heat demand. • Electrical heating becomes the main source of heat. • 100% RE can provide energy at a cost of 45 €/MWh for heat and 56 €/MWh for power. Transition towards 100% renewable energy supply is a challenging aim for many regions in the world. Even in regions with excellent availability of wind and solar resources, such factors as limited availability of flexible renewable energy resources, low flexibility of demand, and high seasonality of energy supply and demand can impede the transition. All these factors can be found for the case of Kazakhstan, a mostly steppe country with harsh continental climate conditions and an energy intensive economy dominated by fossil fuels. Results of the simulation using the LUT Energy System Transition modelling tool show that even under these conditions, the power and heat supply system of Kazakhstan can transition towards 100% renewable energy by 2050. A renewable-based electricity only system will be lower in cost than the existing fossil-based system, with levelised cost of electricity of 54 €/MWh in 2050. The heat system transition requires installation of substantial storage capacities to compensate for seasonal heat demand variations. Electrical heating will become the main source of heat for both district and individual heating sectors with heat cost of about 45 €/MWh and electricity cost of around 56 €/MWh for integrated sectors in 2050. According to these results, transition towards a 100% renewable power and heat supply system is technically feasible and economically viable even in countries with harsh climatic conditions. [ABSTRACT FROM AUTHOR]