*4.1. Limitations*

Known limitations must be considered when reading the results. First, new knowledge given in this study is based on secondary information (reviews). While the progression factors, EC lifecycle, and main use-cases were empirically grounded, the corresponding affordances of UBEM capabilities—and thus the answer to the research question—still needs to be proven through case studies. Second, the development of UBEM tools compared to their original papers are not always comprehensively documented, therefore some information may be outdated and actual UBEM platforms may have more capabilities than described here. In addition, the utility of clustering progression factors by use-case is limited, due to lack of literature on the more unconventional use-cases beyond renewable energy communities. Additionally, limiting the research to western countries introduce a bias for both the progression factors themselves, and their metadata. Further studies, investigating Asian, Latin American and African initiatives could uncover different challenges and enablers, identifying context-specific progression factors for EC development. It must also be noted that the regulatory conditions for the normative alignment of RECs is about to change in the EU, as Member States commitments stated in their National Energy and Climate Plans [103]. This translates to both regulatory/policy factors and economic factors, as there is a recent, clear political statement in support of RECs, which will likely carry over to incentives. However, it is unclear whether and how this translates to other and hybrid use-cases of ECs. While there is a more general CEC and a more restrictive REC definition in EU legislation, if policy goals do not mention for instance community storage, then government subsidies will not be designed for them, their legal entry barriers will still exist, which hinders CES initiation. Therefore, the results (progression factors) must be read per use-case, as not all apply with equal weight. This amplifies the significance of not being able to group progression factors by use-case properly. It is advised for further case studies of novel EC use-cases to document their unique progression factors. Regarding policy, it is recommended that EC definition, and thus related policy instruments are differentiated by use-case. Additionally, the concept of CECs could be appropriated to support experimental, proto-ECs with a legislative pathway to evolve them into more specialized EC categories as their use-cases mature.
