A novel volumetric absorber integrated with low-cost D-Mannitol and acetylene-black nanoparticles for solar-thermal-electricity generation

Low-medium temperature phase change materials (PCMs) act as a predominant role in one-sun solar thermal energy conversion and storage, attracting increasing attention in recent years. However, highly thermal conductive PCMs relying on the doping of a high dose of thermally conductive particles would limit the light absorption just at its top surface and decrease its bulk thermal storage density. In this work, we designed a volumetric solar absorber integrated with a D-Mannitol (DM) based PCM loaded with a low concentration (0.05 wt%) of acetylene black nanoparticles other than a high concentration of over 5 wt%. Such a method maintains a high phase change enthalpy of DM (295.2 kJ/kg) while achieving an enhanced heat transfer and hence a uniform temperature distribution. Compared to conventional surface absorbers with PCM, the volumetric absorber significantly reduces the temperature difference inside the bulk materials, from 103.1 °C of the surface absorber to 62.7 °C of the volumetric absorber with a thickness of 10 mm. Their photo to thermal charge and discharge performance was investigated for the first time in their based solar thermoelectric generator (STEG) system, which show that the volumetric absorber could reach 198.2 °C on bottom of the PCM and the corresponding open circuit voltage is 0.65 V. Such performance data are significantly better than the corresponding results from the surface absorber of 135.1 °C and 0.45 V, respectively, demonstrating successfully the significant performance enhancement by our volumetric absorber. This paper definitely deepens our understanding of volumetric absorbers and their based device design and applications in solar-thermal-electricity systems.