RESUMEN
Seasonal storage of solar thermal energy through supercooled phase change materials (PCM) offers a promising solution for decarbonizing space and water heating in winter. Despite the high energy density and adaptability, natural PCMs often lack the necessary supercooling for stable, long-term storage. Leveraging erythritol, a sustainable mid-temperature PCM with high latent heat, we introduce a straightforward method to stabilize its supercooling by incorporating carrageenan (CG), a bio-derived food thickener. By improving the solid-liquid interfacial energy with the addition of CG the latent heat of erythritol can be effectively locked at a very low temperature. We show that the composite PCM can sustain an ultrastable supercooled state below -30 °C, which guarantees no accidental loss of the latent heat in severe cold regions on Earth. We further demonstrate that the common ultrasonication method can be used as the key to unlocking the latent heat stored in the CG-thickened erythritol, showing its great potential to serve as a high-performance, eco-friendly PCM for long-term seasonal solar energy storage.