This article assesses the impact of extensive deployment of indigenous and external renewable energy sources on a local electricity system (Sardinia Island), and it discusses the main challenges faced by the European power grids in integrating high shares of renewable-based generation technologies. The article presents scenarios for the Sardinian power system in 2030 and the results of steady-state analyses in extreme (renewable) generation and consumption conditions. These results are combined with the assessment of key technology development trends to explain how this can affect the development of a European supergrid.