Systems Perspectives on Circular Energy Supply Chains: Diversification, Supply-Risk Reduction, and Self-Limiting Recovery Paths in Istanbul’s Waste-to-Energy Transition (2020–2024)

Municipal waste management is conceptualized as a circular energy supply chain in which waste flows through parallel recovery pathways. This study examines Istanbul’s waste-to-energy transition between 2020 and 2024 using portfolio decomposition, concentration indices (Herfindahl–Hirschman index, effective source count, Theil index), and a qualitative stock–flow interpretation of İSTAÇ facility-level data. Electricity generation rose from 457 GWh in 2020 to 1332 GWh in 2024; the Herfindahl–Hirschman index fell from 1.00 to 0.47, and the effective source count rose from 1.0 to 2.1. Energy-from-waste and biomethanization accounted for 73% of the increase, while landfill-gas recovery plateaued at 690–698 GWh, contributing the remaining 27%. The study introduces the concept of a self-limiting recovery path: a technology whose resource base is depleted jointly by physical decay and a policy-mediated reduction in its replenishment. Plant-level evidence at the largely closed Odayeri site is consistent with this mechanism, though it cannot rule out ordinary gas decay kinetics or a capacity ceiling as alternatives; the reading is offered as plausible rather than demonstrated. Unlike conventional lock-in pathways, a self-limiting pathway generates self-eroding feedback, suggesting landfill gas is best treated as a transitional bridge technology. The study contributes to path-dependency theory and circular energy supply-chain research.