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.

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.

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.

With an expected accelerated urbanization process until 2050, China is facing big challenges of mitigating CO₂ emissions, especially in the eastern coastal metropolitan regions. Since cities are the hubs for innovation regarding new technologies and infrastructures, investments and governance, they are playing an important role in decision-making and implementation processes on the way to a decarbonized economy and society. The national and provincial administrations in China have already started to address the issue of energy system transition toward a low-carbon pathway, but long-term integrated transition plans are not yet available on a regional level. In our paper, we therefore consider the main challenges of the energy system transition, such as efficiency improvement, coal reduction, decarbonization of transport, and multisector electrification with regional integration, focusing on two eastern coastal metropolitan regions of China. A systematic review of current near-term policies reveals how far these challenges have already been addressed on different administrative levels and which gaps may exist from an external perspective. Based on the current decision- and policy-making processes among national, regional, provincial and municipal levels, policy implications are identified with regard to an effective energy system transition in eastern China.