The pristine evolution of polymer-like celluloid was discovered in the nineteenth century, during a period of resource scarcity, and thus, polymer became a critical innovation for modern green energy technologies. This chapter describes the assisted polymers to enhance sustainable power systems. To date, polymers have been applied in various manufacturing sectors, such as wind turbine blades with lightweight polymer materials, solar panels with encorage parts of polymers, increased battery potential through electrolytes, and preparing membranes in fuel cells to facilitate proton exchange. Despite the polymers having abundant advantages from the aforementation, however, the sustainability is still addressed. Mostly producing polymers are produced from fossil fuels and have a notorious impact on he filed of recycling. For this reason, the principles of design for circularity have been focused on bio-based feedstocks, recyclable thermoplastics (e.g., vitrimers), and depolymerization strategies, to raise performance and response to the environment. Case studies highlight interdisciplinary breakthroughs, either recyclable thermoplastic wind blades or organic photovoltaics. This chapter concludes by outlining grand challenges: closing the recycling loop, overcoming performance-sustainability trade-offs, and ensuring long-term stability in harsh environments. A paradigm shift toward “sustainable polymers” is urged, where materials innovation aligns with circular economy principles to support a truly green energy transition.