This paper presents the results of a case study of applying a systematic and proven process of technology portfolio planning with the use of scenario analysis to renewable energy developments in Taiwan. The planning process starts with decision values of technology development based on a survey of society leaders. It then generates, based on expert opinions and literature search, a set of major technology alternatives, which in this study include: wind energy, photovoltaic, bio-energy, solar thermal power, ocean energy, and geothermal energy. Through a committee of technical experts with diversified professional backgrounds, the process in this study next constructs three scenarios (“Season in the Sun”, “More Desire than Energy”, and “Castle in the Air”) to encompass future uncertainties in the relationships between the technology alternatives and the decision values. Finally, through a second committee of professionals, the process assesses the importance and risks of these alternative technologies and develops a general strategic plan for the renewable energy technology portfolio that is responsive and robust for the future scenarios. The most important contributions of this paper are the clear description of the systematic process of technology portfolio planning and scenario analysis, the detailed demonstration of their application through a case study on the renewable energy development in Taiwan, and the valuable results and insights gained from the application.