Within the European programme Socio Economic Research on Fusion (SERF), technical-economic system studies are carried out to evaluate the potential role of nuclear fusion as a new energy supply technology in the global energy system of the future (2050 and beyond). The research activity of the Institute for Theoretical and Computational Physics contributes via the Austrian OEAW-EURATOM Association to this particular SERF objective. In collaboration with the Max-Planck Institute for Plasma Physics in Garching and the IER in Stuttgart, a first basic global energy model was developed. It is a technical-economic model of the global energy system with a detailed description of energy technologies, where in a first step the world is described as one aggregated region. The time horizon of the energy model reaches from the year 1990 up to 2100. The state-of-the-art modelling tools, including the TIMES model generator, provided by the Energy Technology System Analysis Programme of the International energy Agency, were utilised. A first assessment of the role of fusion power in the long-term has been carried out. In a next step this model is extended to a partial equilibrium energy model (price elasticity of final energy demands). To obtain a more consistent description of the future development of both, the energy system and single energy technologies, the advanced feature of Endogenous Technological Learning is included.