Reviewing Municipal Energy System Planning in a Bibliometric Analysis: Evolution of the Research Field between 1991 and 2019

In the context of the energy transition, energy system planning is becoming increasingly relevant for decentralized systems. Motivated by the strong increase of publications on municipal energy system planning (MESP), these studies are subjected to a bibliometric analysis in this paper. The 1235 articles, which are based on the Web of Science database, are examined using the R-tool bibliometrix. The study shows that China is the most important contributor with 225 articles, followed by the USA (205) and Germany (120). Most cross-country collaborations were conducted between China and Canada, focusing mainly on uncertainties in MESP. Among the institutions, the North China Electric Power University is responsible for most articles (42). The core journals on MESP are Energy, Applied Energy, Energy Policy, Energies and Renewable Energy, which published 37% of the 1235 articles. Publications on MESP focus on renewable energies, optimization and hybrid energy systems. Furthermore, district heating seems to be a core topic in MESP and is addressed in three of the top five most cited articles. The demonstration of global research trends in MESP can support researchers in identifying the relevant issues regarding this expanding and transforming research area

Energy system analysis of energy autonomous municipalities

Attention on decentralised autonomous energy systems has increased exponentially in the past three decades, as demonstrated by the absolute number of real-world projects and the share of publications in the corpus of scientific literature. This is due to the energy transition and the related environmental awareness as well as the desire of citizens to play an active role in energy supply and to be less dependent on central markets and structures. However, local decision-makers, who often lack the necessary expertise, need decision support in energy system planning. To this end, this thesis follows the objective to develop novel methods for the technical, economic and environmental assessment of a large number of completely energy autonomous municipalities and their impacts on the overall energy system. Completely energy autonomous municipalities are disconnected from the gas and electricity grid and supply themselves with energy from plants owned and operated by the municipality. Novel methods of energy system analysis were developed in this thesis as part of seven original research articles. Germany is used as a case study, but the general approach, methods and results are transferable to other contexts. First of all, the 11,131 German municipalities were clustered with regard to their suitability for decentralised energy systems. Based on this municipality typology, representative municipalities were selected to be investigated in an already existing holistic municipal energy system optimisation model (RE³ASON). This model was extended by novel and transferable approaches to design deep geothermal plants and district heating networks. These base-load capable technologies were selected to reduce the storage costs in energy autonomous municipalities. The technical feasibility and economic expenditures of energy autonomy could finally be determined in all 11,131 German municipalities by combining the extended energy system optimisation model with a stepwise linear regression. The energy system optimisations showed that in the case of complete energy autonomy, deep geothermal plants in combination with district heating networks could reduce the total costs by up to 50%. On average, the energy system costs until 2030 in German municipalities increase by about 0.41 €/kWh in the energy autonomous case compared to the optimised reference case with grid connection. While a technical potential to achieve energy autonomy is present in 56% of the German municipalities, there seem to be no economic advantages through energy autonomy compared to the optimised reference energy system. The novel methodological approach of this thesis enabled to obtain optimisation results for a high number of energy systems (6,314 municipalities) with practicable computational expenses. In addition to the original data and planning tools published alongside the articles, the findings of this thesis can also support local decision makers in determining suitable municipal energy systems. In order to increase the realizability of the case study results, some methodological extensions should be investigated in future studies such as other perspectives than that of a central planner, higher temporal model resolutions or social aspects like consumer acceptance of specific technologies or a security of supply below 100%

Reviewing energy system modelling of decentralized energy autonomy

Research attention on decentralized autonomous energy systems has increased exponentially in the past three decades, as demonstrated by the absolute number of publications and the share of these studies in the corpus of energy system modelling literature. This paper shows the status quo and future modelling needs for research on local autonomous energy systems. A total of 359 studies are roughly investigated, of which a subset of 123 in detail. The studies are assessed with respect to the characteristics of their methodology and applications, in order to derive common trends and insights. Most case studies apply to middle-income countries and only focus on the supply of electricity in the residential sector. Furthermore, many of the studies are comparable regarding objectives and applied methods. Local energy autonomy is associated with high costs, leading to levelized costs of electricity of 0.41 $/kWh on average. By analysing the studies, many improvements for future studies could be identified: the studies lack an analysis of the impact of autonomous energy systems on surrounding energy systems. In addition, the robust design of autonomous energy systems requires higher time resolutions and extreme conditions. Future research should also develop methodologies to consider local stakeholders and their preferences for energy systems

The feasibility of energy autonomy for municipalities: local energy system optimisation and upscaling with cluster and regression analyses

The sheer number of alternative technologies and measures make the optimal planning of energy system transformations highly complex, requiring decision support from mathematical optimisation models. Due to the high computational expenses of these models, only individual case studies are usually examined. In this article, the approach from the author’s PhD thesis to transfer the optimisation results from individual case studies to many other energy systems is summarised. In the first step, a typology of the energy systems to be investigated was created. Based on this typology, representative energy systems were selected and analysed in an energy system optimisation model. In the third step, the results of the representative case studies were transferred to all other energy systems. This approach was applied to a case study for determining the minimum costs of energy system transformation for all 11,131 German municipalities from 2015 to 2035 in the completely energy autonomous case. While a technical potential to achieve energy autonomy is present in 56% of the German municipalities, energy autonomy shows only low economic potential under current energy-political conditions. However, energy system costs in the autonomous case can be greatly reduced by the installation and operation of base-load technologies like deep-geothermal plants combined with district heating networks. The developed approach can be applied to any type of energy system and should help decision makers, policy makers and researchers to estimate optimal results for a variety of energy systems using practical computational expenses

Spatial high-resolution socio-energetic data for municipal energy system analyses

Acknowledgements The authors gratefully acknowledge the financial support of the PhD College “Energy and Resource Efficiency” (ENRES), from the Federal State of Baden-Wuerttemberg, for funding the first author’s PhD studentship. The second author gratefully acknowledges the support of the Smart City Accelerator project (https://smartcitiesaccelerator.eu/about-smart-cities-accelerator/), which supported his contribution to this article. Furthermore, we acknowledge support by the KIT-Publication Fund of the Karlsruhe Institute of Technology. The usual disclaimer applies.Peer reviewedPublisher PD

Reviewing local and integrated energy system models : insights into flexibility and robustness challenges

Funding Information: The contribution by Jann M. Weinand was supported by the Helmholtz Association under the program “Energy System Design”. Acknowledgements The contribution by Jann M. Weinand was supported by the Helmholtz Association under the program “Energy System Design”.Peer reviewedPublisher PD

An efficient solver for multi-objective onshore wind farm siting and network integration

Existing planning approaches for onshore wind farm siting and network integration often do not meet minimum cost solutions or social and environmental considerations. In this paper, we develop an approach for the multi-objective optimization of turbine locations and their network connection using a Quota Steiner tree problem. Applying a novel transformation on a known directed cut formulation, reduction techniques, and heuristics, we design an exact solver that makes large problem instances solvable and outperforms generic MIP solvers. Although our case studies in selected regions of Germany show large trade-offs between the objective criteria of cost and landscape impact, small burdens on one criterion can significantly improve the other criteria. In addition, we demonstrate that contrary to many approaches for exclusive turbine siting, network integration must be simultaneously optimized in order to avoid excessive costs or landscape impacts in the course of a wind farm project. Our novel problem formulation and the developed solver can assist planners in decision making and help optimize wind farms in large regions in the future

Assessing the potential contribution of excess heat from biogas plants towards decarbonising German residential heating

This paper analyses the current technical potential for utilising excess heat from German biogas plants, in order to supply local settlements through district heating. Based on a survey of around 600 biogas plant operators, the fractions of excess heat in these plants are analysed. A heuristic is developed to match biogas plants (heat sources) with local settlements (sinks) in order to determine a least-cost district heating supply for residential buildings. Two criteria are employed, namely the CO2 abatement costs and the payback period, which represent the macro- and microeconomic perspectives respectively. Based on the survey, a mean fraction of 40% excess heat is determined, which is in agreement with other empirical studies. Extrapolating this fraction to the German biogas plant stock leads to technically feasible CO2 savings of around 2.5 MtCO2/a. Employing the criteria of CO2 abatement costs and payback period yields about 2 MtCO2/a below CO2 abatement costs of 200 €/tCO2 and below a payback period of 9 years respectively. This represents about 0.25% of the total German CO2 emissions in 2016 or around 2.5% of all CO2 in residential buildings. If threshold values of 80 €/tCO2 and 5 years are employed, to reflect the German government’s suggested external cost of carbon and an expected payback period from an investor’s point of view respectively, the carbon reduction potential is about 0.5 MtCO2 and 0.75 MtCO2 respectively. These potentials are concentrated in around 3,500 of 11,400 municipalities, where district heating from biogas plants could reduce CO2 emissions per capita by an average of 250 kgCO_2/a and cover 12% of the total heating demand

Competent, trustworthy, and likeable? Exploring which peers influence photovoltaic adoption in Germany

Little is known about the role of active peer effects (interpersonal contact) compared to passive peer effects (noticing or seeing) regarding residential photovoltaic (PV) diffusion. Recent literature suggests that peer effects are determined by the perceived credibility of one’s active peer connections regarding PV and passive peer effects. Utilising data from a survey of German house owners who either own a PV or indicate purchase intention (N = 1,165), this paper explores the underlying mechanisms of active peer effects during different stages of PV adoption decision-making. Our findings suggest that the perceived credibility of peers on PV related issues is positively associated with the reported number of adopters in the decision-maker’s peer group (passive peer effect) and also with the progress in the PV adoption decision process. Furthermore, we find a relationship between the perceived credibility of peers regarding PV and the reported influence strength of peer interactions throughout the decision-making processes of German householders, suggesting that subjective evaluations of peers play a role in active peer effects. Finally, we observe an association between the rate of self-initiated peer interactions about PV for respondents with a higher reported number of peers that have adopted PV, suggesting that passive effects (knowing peer PV adopters) play a role in initiating active peer interactions. These results are significant for all sub-groups, regardless of the decision progress. From a policy-making perspective, “bottom-up” efforts such as peer consultation and community-led outreach should be promoted in Germany to empower potential adopters