Novel application of lignin biopolymer for radiative cooling

•Wood derived biopolymer lignin for radiative cooling application is investigated.•Lignin-upgraded biopolymer shows a temperature 3.7 °C below ambient temperature.•A radiative cooling power ~ 77 W/m2 is reported.•Solar cell's operating temperature has been reduced by 3 °C using this radiative cooler. Conventional plastics and composites that we mostly use are derived from petroleum which is a non-renewable resource. Plenty of these plastics are designed for a single purpose and end up in landfills, causing significant environmental impact since the degradation rate is extremely slow and can take centuries. On the other hand, biopolymers are sustainable, yearly renewable, and environment-friendly solution to the current problem associated with conventional plastics. In this paper, lignin, a biodegradable polymer derived from wood, has been utilized for radiative cooling applications. In this radiative cooling process, an optimized structure exchanges heat with the surrounding environment and can effectively cool down to a temperature below ambient temperature. Here we are reporting a lignin-upgraded polymer film that shows a cooling power of 77 W/m2 under direct sunlight irradiance and achieves a surface temperature that is 3.7 °C below the ambient temperature. Integrating this structure with solar cell has reduced the operating temperature of the cell by 3 °C while showing an absolute efficiency increase of 0.45% compared to the reference cell under the AM1.5G solar spectrum. This approach can easily be applied to a large area at a low cost and is a significant step forward for the large-scale implementation of radiative cooling technology.