Positive Energy Districts (PEDs) have the potential of accelerating the decarbonization of urban areas and promoting scalability between cities. The development and real-world implementation of such innovative concepts can be enhanced through urban energy modelling. However, assessing PEDs can be challenging, and information on this topic is scarce and fragmented. The main contribution of this paper is collecting and analyzing challenges and limitations of energy modelling software for assessing PEDs through five case studies in Italy, Spain, The Netherlands, Denmark and Canada. Case studies are assessed first from a modelling approach, then the main identified challenges and limitations of modelling tools for PEDs are discussed, and finally, various ongoing trends and research needs in this field are suggested.