Concern about global warming calls for an advanced approach for designing an energy system to reduce carbon emissions as well as to secure energy security for each country. Conventional energy systems tend to introduce different technologies with high conversion efficiency, leading to a higher average efficiency. Advanced energy systems can be achieved not by an aggregate form of conversion technologies but by an innovative system design itself. The concept of LCS (low carbon society) is a unique approach having multi-dimensional considerations such as social, economic and environmental dimensions. The LCS aims at an extensive restructuring of worldwide energy supply/demand network system by not only replacing the conventional parts with the new ones, but also integrating all the necessary components and designing absolutely different energy networks. As a core tool for the LCS design, energy-economic models are applied to show feasible solutions in future with alternatives such as renewable resources, combined heat and power, and smart grid operations. Models can introduce changes in energy markets, technology learning in capacity, and penetration of innovative technologies, leading to an optimum system configuration under priority settings. The paper describes recent trials of energy models application related to waste-to-energy, clean coal, transportation and rural development. Although the modelling approach is still under investigation, the output clearly shows possible options having variety of technologies and linkages between supply and demand sides. Design of the LCS means an energy systems design with the modelling approach, which gives solution for complex systems, choices among technologies, technology feasibility, R&D targets, and what we need to start.