Storage of solar energy with wax
PCMs store energy on the phase transition from solid to liquid and release this energy in the reversed transition from liquid to solid. Once the transition temperature is reached, the material continues to absorb large amounts of heat at an almost constant temperature. This is known as latent heat of the transition. In the EU-funded project ENTAS (Enhancing thermal properties of PCM using nano materials), scientists investigated novel PCM composites with improved thermo-physical properties. A number of composite materials were thoroughly explored, including paraffin wax and lauric acid mixed with two types of expanded graphite. Due to the phase change, paraffin wax is suited for capturing thermal energy and supplying hot water and space heating. Efforts were mainly devoted to conducting microstructural and morphological analyses of the PCM paraffin wax with varying concentration of carbon additives. Results helped scientists establish a correlation between the structure and thermo-physical properties of the PCM composites. Using a thermoanalytical technique, the team measured the latent heat of the PCM composites. Through infrared spectroscopy analysis, ENTAS also investigated how the distribution and concentration affect thermal properties such as thermal conductivity. Scientists observed for the first time intermolecular interaction between paraffin wax and the one type of expanded graphite, which they believe accounts for the much narrower temperature range around their phase-change temperature. Operation over very narrow temperature intervals favours latent heat storage as storage density increases. PCM composites absorbing a large amount of energy and with high storage capacity make it possible to design compact systems that store energy in the form of latent heat. Energy storage can contribute to a better use of renewable energy in the electricity system since it can balance electricity supply and demand; the produced energy is stored when the conditions favour renewable energy, but demand may be low.
Keywords
Solar energy, wax, phase-change materials, latent heat, ENTAS
