Boyu Li,Wenpeng Hong,Haoran Li,Jingrui Lan,Junliang Zi
Configuring a nanofluid spectrum splitter (NSS) with the thermally decoupled photovoltaic/thermal (PV/T) system is a feasible approach to achieve net-zero emissions. In this work, the gold nanofluid was used in the PV/T system as an optical filter because of the abilities to manage energy balance and enhance thermal collection. The energy distribution management was optimized via the NSS thickness ( L ) and nanoparticle concentration ( C ) based on exergy efficiency analysis. The results indicated that a higher nanoparticle concentration and NSS thickness enhanced output thermal energy and solar utilization efficiency. The solar utilization efficiency and merit function reached 88.50% and 2.48 at C = 75 ppm and L = 20 mm if the worth factor ω = 3. Furthermore, the optimized concentration was only 20 ppm, which achieved the highest exergy efficiency of 13.71%.The NSS-assisted PV/T device reached the highest equilibrium temperature of 49.9 °C at L = 18 mm. Moreover, the exergy efficiency reached 12.77%, which was higher than that at L = 22 mm, due to the heat loss. These findings suggest that energy distribution can be flexibly controlled according to the demand of service users, and an optimized NSS thickness can improve thermal energy storage .
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.
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