This book provides readers with peer-reviewed research papers presented at the 6th International Conference on Clean Energy and Electrical Systems held in Sendai, Japan, from April 10 to 12, 2025. This proceedings mainly covers theoretical, technical, and practical methods and practices on clean energy and electrical systems. And it includes nuclear energy and "renewable energy." With the continuous growth of energy demand and the increasing awareness of environmental protection in countries around the world, it is urgent and imperative to establish a clean energy innovation research and development, promotion, and application system. The book also covers electricity, fuel, thermal, transportation, and water infrastructures and their development and deployment in different regions around the world. The book includes future development trends with analysis of lifecycle and economical models for successful implementation projects.