This book offers an interdisciplinary examination of sustainable energy engineering, integrating mechanical systems, industrial biotechnology, artificial intelligence, and circular economy principles. It explores renewable energy conversion, hydrogen production, biomass valorization, energy storage, and system integration. The role of biotechnology in biorefineries, waste valorization, and carbon utilization is emphasized. AI, digital twins, and predictive analytics are highlighted for optimizing energy systems. Technologies are evaluated through sustainability frameworks combining technical, economic, environmental, and circularity metrics. Bridging multiple disciplines, the volume provides a scientific foundation for developing resilient, low-carbon energy infrastructures supporting global net-zero goals and sustainable industrial development.