In this paper, a single-inductor triple-source quad-mode energy harvesting interface with automatic source selection is developed for multi-source energy harvesting. The interface employs buck-boost topology to convert the energy from photovoltaic (PV) cells and thermoelectric generator (TEG) to a regulated 1.2-V output. The proposed converter has four operating modes: harvesting mode (HM), recycling mode (RM), storage mode (SM), and backup mode (BM). The operating mode is selected automatically according to the input and load conditions to appropriately transfer the energy. The proposed reversely polarized energy recycling (RPER) technique extends the available output power range by 10x with 25.3% efficiency improvement at low input voltage. The measurement results demonstrates the proposed interface achieves the peak efficiency of 82.1%.