The transition to sustainable manufacturing has become a central priority for modern industry, driven by rising energy costs, environmental regulations, and the global push for decarbonization. Industry 4.0 technologies offer a unique opportunity to enhance energy efficiency through the use of intelligent systems, smart sensors, real-time data analytics, and interconnected infrastructures. Despite increasing attention to sustainability, research often lacks a system-level perspective on how these technologies jointly contribute to energy optimization in practice. This paper addresses this gap by proposing a conceptual synthesis of energy-efficient solutions within smart manufacturing systems. It outlines core principles of energy efficiency management and introduces system-level approaches enabled by Industry 4.0 technologies. Particular emphasis is placed on sustainability functions such as digital supply chain integration, predictive energy analytics, and lean-based energy monitoring. Furthermore, the article identifies open research directions including the need for political-technological alignment and tailored frameworks for SMEs. The originality of this work lies in its interdisciplinary perspective that connects energy efficiency with intelligent manufacturing strategies through the lens of Industry 4.0. By integrating technological developments with sustainability imperatives, the study contributes to current discourse and offers practical insights for researchers, policymakers, and industry stakeholders aiming to build more resilient and resource-conscious production systems.