Shortwave emitters enable radiative cooling of above-ambient vertical surfaces

Radiative cooling offers an energy-efficient pathway for dissipating heat from devices such as data centers, power systems, and industrial equipment. Yet, its application is constrained by the prevalence of vertical surfaces and the limited effectiveness of existing materials for objects operating above ambient temperature. Here, we report a thermal radiator featuring broadband mid-infrared emission and elevated shortwave emissivity (2.5-8 µm, 91.4%), designed to enhance radiative coupling with both the atmosphere and surrounding structures. This radiator significantly outperforms conventional selective emitters regarded as optimal for vertical ambient cooling. Under direct sunlight and a 600 W m^-2 heat load on a vertical surface, the radiative cooler reduces device temperatures by approximately 18.6 °C and 27.0 °C compared to a selective emitter and an uncoated surface, respectively. The material further exhibits exceptional mechanical robustness, thermal stability, and environmental durability, highlighting its potential for real-world thermal management in vertically oriented, high-temperature systems.