The article discusses the development of a supercooled phase change material (PCM) using erythritol, a sustainable mid-temperature PCM with high latent heat, and carrageenan (CG), a bio-derived food thickener. The addition of CG improves the solid-liquid interfacial energy, enhancing the supercooling behavior of erythritol, allowing it to maintain a stable supercooled state below −30 °C. This ultrastable supercooling is crucial for long-term seasonal thermal energy storage in severe cold regions. The study also demonstrates that ultrasonication can be used to trigger the release of latent heat stored in the CG-thickened erythritol, making it a promising eco-friendly PCM for high-performance seasonal solar energy storage. The research highlights the potential of this approach to address the challenge of decarbonizing space and water heating systems, which account for a significant portion of energy consumption in buildings.The article discusses the development of a supercooled phase change material (PCM) using erythritol, a sustainable mid-temperature PCM with high latent heat, and carrageenan (CG), a bio-derived food thickener. The addition of CG improves the solid-liquid interfacial energy, enhancing the supercooling behavior of erythritol, allowing it to maintain a stable supercooled state below −30 °C. This ultrastable supercooling is crucial for long-term seasonal thermal energy storage in severe cold regions. The study also demonstrates that ultrasonication can be used to trigger the release of latent heat stored in the CG-thickened erythritol, making it a promising eco-friendly PCM for high-performance seasonal solar energy storage. The research highlights the potential of this approach to address the challenge of decarbonizing space and water heating systems, which account for a significant portion of energy consumption in buildings.