Abstract
While the transition from traditional energy sources to renewable energy is necessary to reduce greenhouse gas (GHG) emissions, it introduces new challenges related to material use, both in quantity and type, potentially leading to resource scarcity, biodiversity loss, and waste accumulation. Therefore, incorporating circular economy (CE) principles into the design and planning of energy systems becomes essential. Despite the growing recognition of circularity, current assessments in energy systems focus on economic performance and GHG emissions. In this work, we propose a metric for quantifying circularity of energy systems based on the CE assessment framework MICRON, addressing the gap between CE metrics and energy systems planning. The framework is adapted to energy systems by accounting for the specific characteristics of energy technologies and by incorporating metrics associated with critical material use, scarcity, and durability. Its applicability is demonstrated through a case study of energy system planning at the University of Wisconsin-Madison, considering a grid-connected system with solar, wind, and lithium-ion battery technologies. Results show that wind-only portfolios achieve higher overall circularity scores than solar-only and hybrid systems, reflecting the higher efficiency and availability of wind energy. Hybrid systems exhibit higher durability and more efficient material use by avoiding system oversizing. Regarding decarbonization strategies, reducing grid reliance and associated emissions does not necessarily improve circularity, as energy storage is required to ensure reliability. Storage systems increase material demand, the share of critical materials, and replacement frequency. Finally, a sensitivity analysis was performed, highlighting that end-of-life recovery is a key factor influencing circularity.