The uses of fossil fuels cause not only the resources exhaustion but also the environmental problems such as global warming. The purposes of this study are to evaluate paths to ward sustainable energy systems and roles of each renewable. In order to realize the purposes, the authors developed the global land use and energy model that figured the global energy supply systems in the future considering the cost minimization. Using the model the authors conducted a simulation in C30R scenario, which is a kind of strict CO2 emission limit scenarios and reduced CO2 emissions by 30% compared with Kyoto protocol forever scenario, and obtained the following results. In C30R scenario bio energy will supply 33% of all the primary energy consumption. How ever, wind and photo voltaic will supply 1.8% and 1.4% of all the primary energy consumption, respectively, because of the limits of power grid stability. The results imply that the strict limits of CO2 emissions are not sufficient to achieve the complete renewable energy systems. In order to use wind and photo voltaic as major energy resources we need not only to reduce the plant costs but also to develop unconventional renewable technologies. .