With the amendment to the German Climate Change Act in 2021, the Federal Government of Germany has set the target to become greenhouse gas neutral by 2045. Reaching this ambitious target requires multisectoral efforts, which in turn calls for interdisciplinary collaboration: the Net-Zero-2050 project of the Helmholtz Climate Initiative serves as an example of successful, interdisciplinary collaboration with the aim of producing valuable recommendations for action to achieve net-zero CO2 emissions in Germany. To this end, we applied an interdisciplinary approach to combining comprehensive research results from ten German national research centers in the context of carbon neutrality in Germany. In this paper, we present our approach and the method behind the interdisciplinary storylines development, which enabled us to create a common framework between different carbon dioxide removal and avoidance methods and the bigger carbon neutrality context. Thus, the research findings are aggregated into narratives: the two complementary storylines focus on technologies for net-zero CO2 emissions and on different framing conditions for implementing net-zero CO2 measures. Moreover, we outline the Net-Zero-2050 results emerging from the two storylines by presenting the resulting narratives in the context of carbon neutrality in Germany. Aiming at creating insights into how complementary and related expertise can be combined in teams across disciplines, we conclude with the project’s lessons learned. This paper sheds light on how to facilitate cooperation between different science disciplines with the purpose of preparing joint research results that can be communicated to a specific audience. Additionally, it provides further evidence that interdisciplinary and diverse research teams are an essential factor for defining solution spaces for complex, interdisciplinary problems.

This study presents a novel energy system modelling approach for the analysis and comparison of global energy transition pathways for the decarbonisation of the electricity sector. The results of the International Energy Agency (IEA), and the Teske/DLR scenarios are each reproduced. Additionally, five new energy transition trajectories, called LUT, are presented. The research examines the feasibility of each scenario across nine major regions in 5-year intervals, from 2015 to 2050, under a uniform modelling environment with identical technical and financial assumptions. The main differences between the energy transition paths are identified across: (1) the average electricity generation costs; (2) energy diversity; (3) system flexibility; (4) energy security; and, (5) transition dynamics. All LUT and Teske/DLR scenarios are transitioned to zero CO2 emissions and a 100% renewable energy system by 2050 at the latest. Results reveal that the LUT scenarios are the least-cost pathways, while the Teske/DLR scenarios are centred around energy diversity with slightly higher LCOE of around 10–20%. The IEA shares similarities with the Teske/DLR scenarios in terms of energy diversity yet depends on the continued use of fossil fuels with carbon capture and storage, and nuclear power. The IEA scenario based on current governmental policies presents a worst-case situation regarding CO2 emissions reduction, climate change and overall system costs.

Background Different strategies have been proposed for transforming the energy system in Germany. To evaluate their sustainability, it is necessary to analyze their macroeconomic and distributional effects. An approach to do this analysis in an integrated consistent framework is presented here. Methods Comparing ten energy transition scenarios with emission reduction targets by 2050 of 80% or 95%, respectively, allows evaluating a broad range of energy system transformation strategies with respect to the future technology and energy carrier mix. For this purpose, an energy system model and a macroeconometric model are combined, thus re-modeling the unified scenarios. An important extension of the model was concerned with the integration of synthetic fuels into the energy-economy model. One focus besides the overall macroeconomic assessment is the regional analysis. For this purpose, own assumptions on the regional distribution of the expansion of renewable energies were developed. Results The effects on gross domestic product (GDP) and employment are similar on average from 2030 to 2050 across the scenarios, with most of the more ambitious scenarios showing slightly higher values for the socioeconomic variables. Employment in the construction sector shows the largest effects in most scenarios, while in the energy sector employment is lower in scenarios with high energy imports. At the regional level, the differences between scenarios are larger than at the national level. There is no clear or stable regional pattern of relative loss and profit from the very ambitious transformation, as not only renewable energy expansion varies, and hydrogen strategies enter the scene approaching 2050. Conclusions From the relatively small differences between the scenarios, it can be concluded that, from a macroeconomic perspective, it is not decisive for the overall economy which (supply side) strategy is chosen for the transformation of the energy system. More effort needs to be put into improving assumptions and modeling approaches related to strategies for achieving the final 20% CO 2 reduction, for example the increasing use of hydrogen.

CO2 emissions from global steel production may jeopardize climate goals of 1.5 degrees C unless current steel pro-duction practices will be rapidly decarbonized. At present, primary iron and steel production is still heavily dependent on fossil fuels, primarily coke. This study aims to determine which decarbonization pathways can achieve the strongest emission reductions of the iron and steel industry in Germany by 2050. Moreover, we estimate whether the German iron and steel industry will be able to stay within its sectoral carbon budgets for a 1.5 degrees C or 1.75 degrees C target. We developed three decarbonization scenarios for German steel production: an elec-trification, coal-exit, and a carbon capture and storage (CCS) scenario. They describe a phase-out of coal-fired production plants and an introduction of electricity-based, low-carbon iron production technologies, i.e. hydrogen-based direct reduction and electrowinning of iron ore. The scenarios consider the age and lifetimes of existing coal-based furnaces, the maturity of emerging technologies, and increasing recycling shares. Based on specific energy requirements and reaction-related emissions per technology, we calculated future CO2 emissions of future steel production in Germany. We found that under the decarbonization scenarios, annual CO2 emissions decrease by up to 83% in 2050 relative to 2020. The reductions of cumulative emissions by 2050 range from 24% (360 Mt CO2) under the electrification scenario up to the maximum of 46% (677 Mt CO2) under the CCS scenario compared to a reference scenario. This clearly demonstrates that the technology pathway matters. Nevertheless, the German steel sector will exceed its sectoral CO2 budget for a 1.5 degrees C warming scenario between 2023 and 2037. Thus, drastic measures are required very soon to sufficiently limit future CO2 emissions from German steel production, such as, a rapid decarbonization of the electricity mix, the construction of a hydrogen and CCS infrastructure, or early shutdowns of current coal-based furnaces.

Background Given the multitude of scenarios on the future of our energy systems, multi-criteria assessments are increasingly called for to analyze and assess desired and undesired effects of possible pathways with regard to their environmental, economic and social sustainability. Existing studies apply elaborate lists of sustainability indicators, yet these indicators are defined and selected by experts and the relative importance of each indicator for the overall sustainability assessments is either determined by experts or is computed using mathematical functions. Target group-specific empirical data regarding citizens' preferences for sustainability indicators as well as their reasoning behind their choices are not included in existing assessments. Approach and results We argue that citizens' preferences and values need to be more systematically analyzed. Next to valid and reliable data regarding diverse sets of indicators, reflections and deliberations are needed regarding what different societal actors, including citizens, consider as justified and legitimate interventions in nature and society, and what considerations they include in their own assessments. For this purpose, we present results from a discrete choice experiment. The method originated in marketing and is currently becoming a popular means to systematically analyze individuals' preference structures for energy technology assessments. As we show in our paper, it can be fruitfully applied to study citizens' values and weightings with regard to sustainability issues. Additionally, we present findings from six focus groups that unveil the reasons behind citizens' preferences and choices. Conclusions Our combined empirical methods provide main insights with strong implications for the future development and assessment of energy pathways: while environmental and climate-related effects significantly influenced citizens' preferences for or against certain energy pathways, total systems and production costs were of far less importance to citizens than the public discourse suggests. Many scenario studies seek to optimize pathways according to total systems costs. In contrast, our findings show that the role of fairness and distributional justice in transition processes featured as a dominant theme for citizens. This adds central dimensions for future multi-criteria assessments that, so far, have been neglected by current energy systems models.

A multitude of pathways for decarbonizing energy systems have been formulated. In the development of these scenarios, the focus is often only on system costs at a given CO2 emission reduction. However, when assessing the sustainability of energy systems in a broader sense, many more aspects need to be considered: In addition to greenhouse gas emissions, energy systems induce further environmental and socio-economic impacts and must meet requirements for security of supply and cost efficiency. For assessing the compatibility of a future energy system with sustainability concepts, alternative pathways must be compared holistically using dedicated assessment methods, which is facilitated by multi-attribute decision making methods (MADM). With the target of identifying sustainable transformation pathways, we assess ten transformation scenarios for the example of Germany, using the three MADM methods weighted sum method, PROMETHEE II and TOPSIS. We find that top ranks are not completely stable across methods, but there are scenario clusters which rank high, medium and low for all methods. In the top ranks, there are both less ambitious scenarios that aim at reducing direct CO2 emissions by 80%, and more ambitious scenarios with a reduction by at least 95%. We conclude that scenarios with more ambitious climate protection goals are not necessarily more (or less) sustainable than scenarios that aim for a reduction of 80% only.

Germany 2050: For the first time Germany reached a balance between its sources of anthropogenic CO2 to the atmosphere and newly created anthropogenic sinks. This backcasting study presents a fictional future in which this goal was achieved by avoiding (∼645 Mt CO2), reducing (∼50 Mt CO2) and removing (∼60 Mt CO2) carbon emissions. This meant substantial transformation of the energy system, increasing energy efficiency, sector coupling, and electrification, energy storage solutions including synthetic energy carriers, sector‐specific solutions for industry, transport, and agriculture, as well as natural‐sink enhancement and technological carbon dioxide options. All of the above was necessary to achieve a net‐zero CO2 system for Germany by 2050.

In the development of climate-friendly energy system transformation strategies it is often ignored that environmental protection encompasses more than climate protection alone. There is therefore a risk of developing transformation strategies whose climate friendliness comes at the expense of higher other environmental impacts. Consequently, an assessment of environmental impacts of energy system transformation strategies is required if undesired environmental side effects of the energy system transformation are to be avoided and transformation strategies are to be developed that are both climate and environmentally friendly. In this paper, ten structurally different transformation strategies for the German energy system were re-modeled (in a harmonized manner). Five of these scenarios describe pathways for a reduction of direct, energy related CO2 emissions by 80%, the other five by 95%. Life cycle-based environmental impacts of the scenarios were assessed by coupling the scenario results with data from a life cycle inventory database focusing on energy and transport technologies. The results show that the transformation to a climate-friendly energy system reduces environmental impacts in many impact categories. However, exceptions occur with respect to the consumption of mineral resources, land use and certain human health indicators, which could increase with decreasing CO2 emissions. The comparison of environmental impacts of moderately ambitious strategies (80% CO2 reduction) with very ambitious strategies (95% CO2 reduction) shows that there is a risk of increasing environmental impacts with increasing climate protection, although very ambitious strategies do not necessarily come along with higher environmental impacts than moderately ambitious strategies. A reduction of environmental impacts could be achieved by a moderate and – as far as possible – direct electrification of heat and transport, a balanced technology mix for electricity generation, by reducing the number and size of passenger cars and by reducing the environmental impacts from the construction of these vehicles.

We present an energy transition pathway constrained by a total CO2 budget of 7 Gt allocated to the German energy system after 2020, the Budget Scenario (BS). We apply a normative backcasting approach for scenario building based on historical data and assumptions from existing scenario studies. The modeling approach combines a comprehensive energy system model (ESM) with REMix-a cost optimization model for power and heat that explicitly incorporates sector coupling. To achieve the necessary CO2 reduction, the scenario focuses on electrifying all end use sectors until 2030, adding 1.5-2 million electric vehicles to the road per year. In buildings, 400,000-500,000 heat pumps would be installed annually by 2030, and the share of district heating would double until 2050. In the scenario, coal needs to be phased out by 2030. Wind and Photovoltaic (PV) capacities would need to more than double to 290 GW by 2030 and reach 500 GW by 2050. The BS results indicate that a significant acceleration of the energy transition is necessary before 2030 and that this higher pace must be maintained thereafter until 2050.

AbstractThis section focuses on technologies that provide heat, and especially process heat, with renewable energy and electrical systems. All the technologies described, except those that use high-temperature geothermal or concentrated solar heat (CSH) for process heat, are used for the OECM 1.5 °C pathways described in Chaps. 5, 6, 7, and 8. The authors have included geothermal and solar technologies to highlight the further technical options available and to underscore that more research is required in the area of renewable process heat.

Sustainable development embraces a broad spectrum of social, economic and ecological aspects. Thus, a sustainable transformation process of energy systems is inevitably multidimensional and needs to go beyond climate impact and cost considerations. An approach for an integrated and interdisciplinary sustainability assessment of energy system transformation pathways is presented here. It first integrates energy system modeling with a multidimensional impact assessment that focuses on life cycle-based environmental and macroeconomic impacts. Then, stakeholders’ preferences with respect to defined sustainability indicators are inquired, which are finally integrated into a comparative scenario evaluation through a multi-criteria decision analysis (MCDA), all in one consistent assessment framework. As an illustrative example, this holistic approach is applied to the sustainability assessment of ten different transformation strategies for Germany. Applying multi-criteria decision analysis reveals that both ambitious (80%) and highly ambitious (95%) carbon reduction scenarios can achieve top sustainability ranks, depending on the underlying energy transformation pathways and respective scores in other sustainability dimensions. Furthermore, this research highlights an increasingly dominant contribution of energy systems’ upstream chains on total environmental impacts, reveals rather small differences in macroeconomic effects between different scenarios and identifies the transition among societal segments and climate impact minimization as the most important stakeholder preferences.

It is still possible to comply with the Paris Climate Agreement to maintain a global temperature ‘well below +2.0 °C’ above pre-industrial levels. We present two global non-overshoot pathways (+2.0 °C and +1.5 °C) with regional decarbonization targets for the four primary energy sectors—power, heating, transportation, and industry—in 5-year steps to 2050. We use normative scenarios to illustrate the effects of efficiency measures and renewable energy use, describe the roles of increased electrification of the final energy demand and synthetic fuels, and quantify the resulting electricity load increases for 72 sub-regions. Non-energy scenarios include a phase-out of net emissions from agriculture, forestry, and other land uses, reductions in non-carbon greenhouse gases, and land restoration to scale up atmospheric CO2 removal, estimated at −377 Gt CO2 to 2100. An estimate of the COVID-19 effects on the global energy demand is included and a sensitivity analysis describes the impacts if implementation is delayed by 5, 7, or 10 years, which would significantly reduce the likelihood of achieving the 1.5 °C goal. The analysis applies a model network consisting of energy system, power system, transport, land-use, and climate models.

Background : Given the multitude of scenarios on the future of our energy systems, multi-criteria assessments are increasingly called for to analyze and anticipate long-term effects of possible pathways with regards to their environmental, economic and social sustainability. While economic and ecologic indicators are covered through energy systems modelling and life cycle sustainability assessments, approaches to the social sustainability of future energy systems remain methodologically under-developed. Previous studies have either focused only on the social acceptance of single energy technologies or used expert-based environmental and economic indicators with social implications. Approach and results : We argue that in order to gather empirical insights on the social sustainability of future energy systems and to integrate it in multi-criteria assessments, citizens’ preferences and values need to be more systematically analyzed while informing their decisions more transparently with full life cycle data. Given the lack of theoretical underpinnings of sustainability and of empirical insights into citizens’ perceptions of sustainability with respect to future energy systems, we further argue that an explorative research design is needed. Therefore, next to six focus groups, we conducted a discrete choice experiment. The method is currently becoming more popular to analyze individuals’ preference structures for energy technologies or investments. As we show in our paper, it can be fruitfully applied to study the values and trade-offs of citizens with regards to sustainability issues. Our combined empirical methods provide two main insights with strong implications for the future development and assessment of energy pathways: While environmental and climate-related effects significantly influenced citizens’ preferences for or against certain energy pathways, total systems and production costs were of far less importance to citizens than the public discourse suggests. Conclusions : Our findings are contrary to the focus of many scenario studies that seek to optimize pathways according to total systems costs. The role of fairness and distributional justice in transition processes featured as a dominant theme in all focus groups. This adds central dimensions for future multi-criteria assessments that, so far, have been neglected by current energy systems models.

The energy system transformation in Germany is a challenge for society, economy and politics and has several impacts on multiple scales. This paper investigates the effects of the trajectories towards net zero emissions by 2050 through focusing on the spatial dimension of impacts, benefits, and losses for different stakeholders and technologies. Spatial heterogeneity in the energy transition means that regions enjoying benefits from decarbonization might diverge from regions experiencing losses, and that there are different geographical potentials and challenges. The question arising is one of the need for redistribution between benefits and losses, whilst ensuring that all stakeholders remain willing to act as frontrunners in the transformation of the energy system. Inclusion and participation in the process, together with a carefully targeted mixed set of regional energy policy, combining tax solutions and incentives for acceptance of required measures could facilitate a successful, efficient policy-supported energy transition.

The accelerated urbanization and industrialization in China is leading to major challenges due to rising energy demand and emissions. Cities in particular play an important role in the decision-making and implementation processes for the energy transition. However, they often have only limited local energy potential and are heavily dependent on supply regions. We therefore assess how a predominantly renewable power supply can be implemented based on the availability of local or imported renewable resources. We present a case study in which an advanced energy system model is parametrized and applied to address questions which are relevant to the transformation of the energy system in China. The model is capable of simultaneously optimizing investment decisions and hourly power balances of a scenario year, taking into account different storage technologies, regional power exchange and policy constraints such as carbon cap, carbon price and renewable portfolio standards. The study takes the Beijing-Tianjin-Hebei metropolitan region with Inner Mongolia as a supply region—considered as exemplary regions characterized by heterogeneous infrastructures, resources and consumption—as its model. Starting from a context-related normative energy scenario, we analyze a possible future electricity system under various assumptions using the Renewable Energy Mix (REMix) energy system model developed at the DLR (German Aerospace Center). Depending on the estimated potentials of renewable energies, technology costs and the projected electricity demand, the metropolitan region is mainly supplied with imported wind and solar power. A sensitivity analysis considers installed capacities, annual generation, CO2 emissions and costs. The results indicate that the assumption of storage costs is of great importance for the future total costs of an electricity system. Variations in other parameters led to different generation portfolios with similar system costs. Our results provide insights into future regional infrastructure needs, and underline the importance of regional coordination and governance for the energy transition in China.

Net-Zero-2050 aims for a national roadmap for net-zero CO2 emissions by 2050, including integrated scenario analyses and negative emission technology assessment. The aim of this project briefing is to clarify the overall carbon budget available for Germany to comply with the global long-term temperature limit of well below 2°C of the Paris Agreement.

In order to analyse long-term transformation pathways, energy system models generally focus on economical and technical characteristics. However, these models usually do not consider sustainability aspects such as environmental impacts. In contrast, life cycle assessment enables an extensive estimate of those impacts. Due to these complementary characteristics, the combination of energy system models and life cycle assessment thus allows comprehensive environmental sustainability assessments of technically and economically feasible energy system transformation pathways. We introduce FRITS, a FRamework for the assessment of environmental Impacts of Transformation Scenarios. FRITS links bottom-up energy system models with life cycle impact assessment indicators and quantifies the environmental impacts of transformation strategies of the entire energy system (power, heat, transport) over the transition period. We apply the framework to conduct an environmental assessment of multi-sectoral energy scenarios for Germany. Here, a 'Target' scenario reaching 80% reduction of energy-related direct CO2 emissions is compared with a 'Reference' scenario describing a less ambitious transformation pathway. The results show that compared to 2015 and the 'Reference' scenario, the 'Target' scenario performs better for most life cycle impact assessment indicators. However, the impacts of resource consumption and land use increase for the 'Target' scenario. These impacts are mainly caused by road passenger transport and biomass conversion.

Today, transportation contributes significantly to greenhouse gas emissions and air pollution. However, new technologies are emerging and existing technologies are being further improved. This article presents the results of a comprehensive study on the development of drive-trains, resulting electricity and fuel consumption as well as emissions of CO2 and selected air pollutants in land transport in Germany. This includes a quantitative assessment of technological potentials and of resulting energy consumption and emissions. The scenario building followed an explorative approach. Only the scenario depicting a consistent transition towards electrified mobility and regulated emissions from the energy system leads to a significant reduction in transport related CO2 emissions. Yet, the analysis shows that it is unlikely that the German emission reduction target in 2030 for the transport sector will be met. Nevertheless, the integrated scenario analysis demonstrates that only a joint de-carbonization of both transport and electricity systems lead to a significant reduction of emissions.

Der vorliegende zweite Teil - Sektorenkopplung und Wasserstoff: Zwei Seiten der gleichen Medaille knupft an diesem Punkt an. Er befasst sich detailliert mit moglichen Nutzungspfaden von Wasserstoff in den Sektoren Verkehr, Industrie und Warme sowie mit dem systemisch wichtigen Aspekt der Ruckverstromung. Am Beispiel aktueller Forschungsarbeiten im DLR wird dargestellt, welche Potenziale sich durch die Kopplung der verschiedenen Energieverbrauchssektoren bei der Erzeugung und Nutzung von Wasserstoff ergeben. Diese Synergien ebnen den Weg zu einer effizienteren und flexibleren Nutzung von erneuerbarer Energie. Neben den technologischen Einsatzmoglichkeiten spielen daruber hinaus die Infrastruktur sowie dazugehorige Sicherheitsaspekte bei der Nutzung von Wasserstoff eine gewichtige Rolle. Weiterhin wird im DLR auf dem Gebiet der Energiesystemanalyse an der Einschatzung der Auswirkungen grosskaliger Wasserstoffinfrastrukturen auf das bestehende und zukunftige Energiesystem geforscht. Dies beinhaltet auch die Fragestellungen, ob ein klimaneutrales Energiesystem aus heutiger Sicht uberhaupt ohne Wasserstoff denkbar ist, bzw. wie gros der Wasserstoffbedarf und das -angebot in solchen Zielszenarien ausfallt. Zudem werden Umwelteinwirkungen untersucht und Lebenszyklusanalysen erstellt.