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We present a radiative cooling material capable of enhancing albedo while reducing ground surface temperatures beneath fielded bifacial solar panels. Electrospinning a layer of polyacrylonitrile nanofibers, or nanoPAN, onto a polymer-coated silver mirror yields a total solar reflectance of 99 %, an albedo of 0.96, and a thermal emittance of 0.80. The combination of high albedo and high emittance is enabled by wavelength-selective scattering induced by the hierarchical morphology of nanoPAN, which includes both thin fibers and bead-like structures. During outdoor testing, the material outperforms the radiative cooling power of a state-of-the-art control by ∼20 W/m²and boosts the photocurrent produced by a commercial silicon cell by up to 6.4 mA/cm²compared to sand. These experiments validate essential characteristics of a high-albedo radiative-cooling reflector with promising potential applications in thermal and light management of fielded bifacial panels. 

From pasta to biological tissues to contact lenses, gel and gel-like materials inherently soften as they swell with water. In dry, low-relative-humidity environments, these materials stiffen as they de-swell with water. Here, we use semi-dilute polymer theory to develop a simple power-law relationship between hydrogel elastic modulus and swelling. From this relationship, we predict hydrogel stiffness or swelling at arbitrary relative humidities. Our close predictions of properties of hydrogels across three different polymer mesh families at varying crosslinking densities and relative humidities demonstrate the validity and generality of our understanding. This predictive capability enables more rapid material discovery and selection for hydrogel applications in varying humidity environments.