Photonic thermal management of overhead cables via high-thermal-conductivity radiative cooling.

As the thermal backbone of urban energy infrastructure, transmission cables directly affect the stability and resilience of modern cities. However, high operating temperatures, driven by Joule heating and solar radiation, critically limit the ampacity of overhead transmission lines, particularly under extreme climate conditions. Such high temperatures constrain electricity delivery and pose systemic risks to essential services and long-term urban sustainability. To overcome this challenge, we adopt a high thermal conductivity radiative cooling (HTCRC) coating comprising hexagonal boron nitride (h-BN) nanoparticles embedded in a polydimethylsiloxane matrix to reduce cable temperature. Enabled by photonic thermal management, this composite structure simultaneously achieves high solar reflectance (0.92) through efficient light scattering, strong mid-infrared emissivity via polymer vibrational modes (0.95), and enhanced thermal conductivity (1.28 W m⁻¹ K⁻¹). Outdoor experiments demonstrate notable daytime cooling of simulated HTCRC-coated power cables, maintaining safe operating temperatures even under intense solar exposure. In addition, thermal modeling based on the CIGRE 601 standard reveals a 6-10% increase in ampacity across representative hot-climate cities globally. These findings highlight high thermal conductivity radiative cooling as an effective and scalable strategy to enhance urban power grid performance, improve energy delivery security, and support the development of climate-resilient cities under rapidly growing electricity demand driven by electrification and the expanding energy footprint of artificial intelligence.