Improving energy efficiency of photovoltaic/thermal systems by cooling with PCM nano-emulsions: An indoor experimental study

This study was to evaluate the application of phase change material nano-emulsions as novel coolants for improving the overall efficiency of liquid-cooled photovoltaic/thermal systems. A self-designed lab-scale photovoltaic/thermal module was constructed with serpentine cooling tube of two different geometries. Two phase change material nano-emulsions with a melting point 29 °C or 38 °C were evaluated at various flow rates and solar irradiance periods on the energy and exergy efficiencies. The total thermal-equivalent energy efficiency was 84.41% on average and 89.23% maximum for the module by employing the nano-emulsion, in comparison to 79.95% and 83.23% in the water-cooled system, while the total exergy efficiency was 10.69% with the nano-emulsion, even lower than that of 11.66% with water. The results also suggested that latent heat release in a narrow temperature range was essential for a better energy performance using the nano-emulsion as a coolant. A relatively low flow rate of the nano-emulsion was usually favorable to the overall energy efficiency in consideration of pump power. Moreover, particle size and thermal properties of the nano-emulsion before and after the operation in the systems showed only marginal differences, indicating the high stability for long-term usage in liquid-cooled photovoltaic/thermal systems with performance enhancement.