The escalating global demand for clean and sustainable energy has underscored the urgent need to transition from fossil-based systems to renewable alternatives. However, the efficiency, scalability, and environmental impact of current renewable technologies present significant challenges. This chapter explores the transformative role of micro- to nano-scale bio-based materials in addressing these limitations and advancing the development of next-generation renewable energy systems. It begins with an overview of key renewable energy sources such as solar, wind, hydro, geothermal, and bioenergy and highlights their importance in mitigating climate change and ensuring long-term energy security. The chapter introduces a range of bio-based materials, including nanocellulose, biochar, carbon-based nanomaterials, polymer nanocomposites, and metal-organic frameworks (MOFs), emphasizing their renewable origins, tunable properties, and functional versatility. Applications of these materials are discussed in the context of energy storage (batteries and supercapacitors), photovoltaic systems, biofuel production, hydrogen storage, and energy harvesting from wind and wave technologies. By enhancing performance, reducing environmental impact, and enabling circular resource use, these materials offer promising solutions for sustainable and scalable energy innovations. The chapter concludes by synthesizing key findings and outlining future directions for the integration of bio-based nanomaterials in renewable energy technologies.