The global demand for clean, decentralized energy sources has intensified research into devices that can harvest ambient energy from the environment. Among the various approaches—solar photovoltaics, wind turbines, piezoelectric harvesters— passive radiative cooling stands out because it requires no moving parts and can operate day and night. Radiative‑cooling surfaces radiate heat in the atmospheric “transparent window” (8–13 µm) to the cold sink of outer space (≈3 K), achieving surface temperatures up to under direct sunlight (Raman et al., 2014).
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