New materials for solar thermal storage—solid/liquid transitions in fatty acid esters

Solid/liquid transitions were studied by DSC measurements in the following fatty acid esters: methyl stearate, methyl palmitate, cetyl stearate, cetyl palmitate and their binary mixtures. Four systems, with phase transition temperature close to room temperature and with high enthalpy of transition and low hysteresis, were selected for further studies relevant to passive solar thermal storage. The selected systems were: methyl palmitate and the eutectic mixtures of methyl stearate–methyl palmitate, methyl stearte–cetyl palmitate and methyl stearate–cetyl stearate. The samples, studied in 50 thermal cycles with programmed heating/cooling in the temperature range −10–60°C remained stable. The studies of the samples, having been stored at room temperature, were repeated after an interval of 18 months. The results showed that the relevant thermophysical properties did not change. mmercial building materials (gypsum, bricks) were impregnated homogeneously with the selected molten esters by simple immersion. DSC studies showed that up to ≈30 mass% of esters can be adsorbed in the building materials. The thermal energy available for storage as latent heat of melting amounts to 60 kJ/kg of the composite material.