This work aims to investigate the application and replicability of parametric solar design to both existing and future development urban areas in two extreme climate conditions: Øvre Rotvoll in Norway (subarctic climate) and Ravine Blanche in Reunion Island (tropical humid climate). The interplay between urban morphology and its potential for passive and active solar energy strategies has been investigated. The methodology combines the parametric modelling software Rhinoceros-Grasshopper, with two Radiance-based solar simulation tools to optimise the solar potential of a district. The application of a new workflow is studied over the computation of various design scenarios in an existing urban environment at both the district and the building scale. The results show differences and similarities between climate-specific interventions that can be used as supportive instruments for the ongoing local planning processes. The study demonstrates how parametric optimisation allows maximising the solar potential of urban areas at different latitudes despite climatic and urban densification constraints.