The transition to a low-carbon energy system will involve a major redesign of the energy system, primarily around renewable sources. Existing energy system planning models are insufficient for guiding this transition, primarily because they do not capture enough of the technological, geographic, and societal details that are important when designing an energy system around new renewable sources of energy. Expanding such models to capture these details would make them even less comprehensible and transparent than they are now. Instead, we propose a new modelling framework, the Sustainable Energy Transitions Laboratory (SENTINEL). Extensive collaboration with stakeholders will inform the development and refinement of the SENTINEL framework, both through an initial evaluation of user needs, and then through a set of participatory case studies. The SENTINEL framework will be completely modular in structure. Many separate models will each go into a great deal of detail about specific aspects of the transition to a low-carbon energy system. The models will be able to be easily linked together to answer a wide range of different questions. Since any given user is likely to need to use only a subset of the models, the task of understanding how those models operate will be manageable. All of the models and data will be accessible via an online platform. The platform will contain a user interface, as well as making source code and data open source, supplemented by supporting documentation and guidance. This will enable other models to be added to the SENTINEL framework and online platform over time. We will disseminate the results and promote the platform to the appropriate target audiences: policy-analysts; model developers; and research scientists. We will organize an annual conference, to build a community of model users and developers to carry this work forward. We plan to continue the platform and conferences long after the project is completed.