The paper describes two limiting scenarios that lead to a sustainable energy system in Western Europe toward the end of the next century. The scenarios consider exclusively solar energy futures - one based on centralized solar technologies (Hard scenario) and the other on decentralized user-oriented technologies (Soft scenario). While both scenarios eliminate Western Europe's dependence on domestic and foreign fossil energy sources, the Hard Solar scenario requires substantial imports of solar produced hydrogen. Fundamental but different changes of the whole energy system, economic structure and lifestyles are necessary in order to achieve sustainable solar energy futures in the scenarios.