Hydrogel-based hydrated salt composite PCMs for TES in agricultural solar energy utilization facility- solar greenhouse

Thermal energy storage (TES) using phase change materials (PCMs) is a critical approach to reduce energy consumption in solar greenhouses. However, commercial PCMs currently face challenges such as high cost, mismatched phase transition temperatures with crop growth requirements, low thermal conductivity, and poor cyclic stability. To address these issues, this study developed a series of composite phase change hydrogels (cPCHs) using Na2SO4·10H2O as the phase change agent, carboxymethyl cellulose (CMC) as the gel monomer, borax as the nucleating agent, Al2(SO4)3 as the crosslinker, and hexagonal boron nitride (BN), graphene (G), and fumed silica (F) as functional additive, with systematic regulation of component ratios. The cPCHs were characterized across multiple scales, including macro-morphology, gel strength, phase transition temperature, latent heat of phase change, water retention, and thermal conductivity. Results showed that H2-2 exhibited a latent heat of 116.6 kJ/kg, stable macro-morphology, and low risk of phase separation. Chemical crosslinking with Al2(SO4)3 further enhanced its mechanical strength. SEM and FTIR indicated that BN, G, and F optimized the hydrogen bond network and thermal conduction pathways, enabling synergistic improvements in water retention and thermal performance. The optimized cPCHs ((BN2 %+F6 %)H) demonstrated superior properties: melting/crystallization temperatures of 31.1 °C and 13.2 °C, a latent heat of 139.1 kJ/kg, and a thermal conductivity of 1.171 W/(m·K). Mini-greenhouse application tests confirmed that it significantly regulated the temperature environment and promoted tomato plant growth. Cycling stability tests, cost analysis, and performance and economic comparisons with commercial PCMs demonstrated the potential of (BN2 %+F6 %)H cPCHs for long-term stable operation and large-scale deployment in greenhouse applications.