TY - JOUR A1 - Kachirayil, Febin A1 - Weinand, Jann Michael A1 - Scheller, Fabian A1 - McKenna, Russell T1 - Reviewing local and integrated energy system models: insights into flexibility and robustness challenges JF - Applied Energy N2 - The electrification of heating, cooling, and transportation to reach decarbonization targets calls for a rapid expansion of renewable technologies. Due to their decentral and intermittent nature, these technologies require robust planning that considers non-technical constraints and flexibility options to be integrated effectively. Energy system models (ESMs) are frequently used to support decision-makers in this planning process. In this study, 116 case studies of local, integrated ESMs are systematically reviewed to identify best-practice approaches to model flexibility and address non-technical constraints. Within the sample, storage systems and sector coupling are the most common types of flexibility. Sector coupling with the transportation sector is rarely considered, specifically with electric vehicles even though they could be used for smart charging or vehicle-to-grid operation. Social aspects are generally either completely neglected or modeled exogenously. Lacking actor heterogeneity, which can lead to unstable results in optimization models, can be addressed through building-level information. A strong emphasis on cost is found and while emissions are also frequently reported, additional metrics such as imports or the share of renewable generation are nearly entirely absent. To guide future modeling, the paper concludes with a roadmap highlighting flexibility and robustness options that either represent low-hanging fruit or have a large impact on results. Y1 - 2022 U6 - https://doi.org/10.1016/j.apenergy.2022.119666 SN - 1872-9118 VL - 324 SP - 119666 EP - 119666 ER - TY - JOUR A1 - Hermann, Julian A1 - Kachirayil, Febin A1 - Lohrmann, Alena A1 - Scheller, Fabian A1 - Roskosch, Dennis A1 - McKenna, Russell T1 - A critical reflection on modelling approaches for heat pumps and building envelope retrofits in local energy system optimisations JF - Applied Energy N2 - Integrating heat pumps and adopting building envelope retrofit (BER) measures is vital for decarbonising the built environment. This paper systematically reviews modelling approaches for these technologies within 84 local energy system optimisation studies. Our findings show that most studies simplify heat pump operation using a constant coefficient of performance (COP), perfect modulation, or a fixed heating capacity. While existing methods account for temperature-dependent COPs, only a few studies include more advanced approaches considering additional impacts. Two main approaches for modelling BER measures are identified: pre-defined retrofit sets with exogenous heat demand or an integrated retrofit selection with endogenous heat demand. While the pre-defined approach offers lower computational effort, it limits the BER solution space. The integrated approach achieves the opposite: a wider solution space but higher complexity. Moreover, only two studies consider the impact of BER measures on the heat supply temperature, an essential link between retrofit measures and heat pump efficiency. Based on our qualitative review, we derive recommendations for energy system modellers. For modelling heat pumps, we recommend using a temperature-dependent COP and heating capacity, as well as a lower modulation limit. Regarding BER measures, the integrated approach should be used for smaller scales (single buildings) while the pre-defined sets are suitable for larger scales. Finally, we propose a research agenda to address limitations and gaps in the current modelling approaches, such as addressing the performance gap between existing COP estimations and heat pump field performance and including a more detailed method for the heat supply temperature. Y1 - 2025 U6 - https://doi.org/https://doi.org/10.1016/j.apenergy.2025.126525 SN - 0306-2619 VL - 400 PB - Elsevier BV ER -