To achieve net-zero greenhouse gas emissions by mid-century, various sustainable energy technologies are being rapidly developed worldwide. This book presents recent advancements in sustainable energy technologies, including renewable energy sources such as solar, wind, bioenergy, and hydropower, as well as hydrogen technologies and energy storage solutions. It addresses key aspects of energy conversion systems associated with renewable energy technologies and their applications. The book features chapters based on selected high-quality papers from the 2025 9th International Conference on New Energy and Applications, which explore cutting-edge solutions and best practices in green and clean energy technologies. Its primary objective is to educate readers about the development and implementation of sustainable energy technologies that can achieve zero-carbon or zero-greenhouse-gas energy systems.