Urban Expansion of Energiewende in Germany: a Systematic Bibliometric Analysis and Literature Study

Background Despite Germany’s world leadership of Energiewende , there have been mounting challenges, such as the slowdown of German renewable energy growth since 2017, when the Merkel administration dramatically changed the German renewable energy promotion policy from feed-in tariffs to competitive auctions. These challenges pose important research questions about whether and how an emerging urban expansion of Energiewende can serve as a vital solution to counteract the challenges to the energy transition. Answering these research questions provides a unique opportunity to explore the academic and historic foundations of the energy transition and its urban expansion, the emerging events that exemplify urban expansion, and the viable solutions this growing trend of urban expansion might be able to provide to the challenges to the German energy transition. Methods This paper conducted visual and manual bibliometric analyses, examined the results of case studies, and reviewed secondary literature and data on urban expansion of German Energiewende . Results By analyzing the bibliometric and investigative results, this paper identified political, socioeconomic, and technological challenges to Energiewende and a new trend of solar energy expansion in German cities aimed at meeting Germany’s carbon neutrality targets by 2045. The new trend of the urban expansion of the German energy transition manifests itself in the focused research efforts on identifying the vast untapped potential on new building rooftop areas in most populous German cities and/or detached and two-family houses in Germany and the recent booming of building-related solar PV and heating mandates in German cities and states, the expanding solar heating and cooling systems, and the government policy support at various levels in this urban expansion through aggressively strengthening climate and renewable energy targets. Conclusions In search for answers to the recent challenges of Energiewende in Germany, this paper conducted both visual and manual bibliometric analyses and applied desk research and reviews of secondary literature and data. This paper found an emerging trend of the urban expansion of Energiewende , including the awareness of the vast potential and gap of urban solarization and the enhanced urban municipal policies, actors, actions, and accomplishments of exploiting this potential. These findings were based on academic knowledge on the German energy transition and contribute to expanding this academic knowledge. To help more effectively exploit the vast potential in solarizing all German cities, especially the largest ones, this study recommends that further research more closely track the progress of this trend and apply more quantitative tools and approaches in future tracking.