This paper presents a long-term open source energy planning model for Denmark, Estonia, Finland, Latvia, Lithuania, Poland, and Sweden, as part of the preparation of a Pan-European model within the Horizon 2020 REEEM project. The model is built using the Open Source Energy Modelling System (OSeMOSYS) and is conceived as a stakeholder engagement model, comprehensive but accessible. It aims to lower the threshold to join and contribute to a model-based discussion about the optimal decarbonisation pathways for the energy supply of the region. The lowest net present value for the modelled system and period (2015-2050) is calculated by using linear optimization. Existing and planned trans-border transmission capacity between the included countries is considered in the model. New projects are also allowed as far as economically optimal. The electricity exchangeto countries not covered by the model are not modelled as of yet. Ten fuels are used by the technologies defined in the model, namely biomass, coal, geothermal, heavy fuel oil, hydro, natural gas, nuclear, wind and waste. In addition to technology parameters like investment cost, fuel cost, and fixed and variable operation and maintenance cost, an increasing emission penalty for carbon dioxide is defined, which represents the cost related to the emission of greenhouse gases (similar to the European emission trading system). The model provides insights on how the cross-border electricity exchange might develop in the modelled period while decarbonizing the energy sector and considering the unequal distribution of (renewable) resources. But most importantly, the model builds the base for the first fully open source energy model for Europe, including the used data. It shall be conceived as a comprehensive modular tool for engagement in the field of European energy planning, especially for learning in academia, but also by the integration into an open engagement game for decision makers and stakeholders.