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• A PV/T system combined with PCM was proposed and studied. • The overall efficiency of the PV/T-PCM system was investigated in detail. • The thermal regulation strategy was proposed to improve system performance. We present a comprehensive analysis of a solar photovoltaic/thermal system combined with phase change material, i.e., a PV/T-PCM system. A fatty acid was chosen as the PCM with a phase transition temperature of 37 °C. A solar collector filled with PCM, which contained rectangular metal fins to enhance heat transfer, was used to cool the PV. Four-day experimental measurements were carried out under real outdoor climatic conditions in Shanghai, China. During the experiment, we examined two different intermittent thermal regulation strategies using a water circulation loop in the PV/T-PCM system to improve the overall solar energy utilization efficiency, and detailed comparisons were performed. The results indicated that the use of PCM in the solar collector could significantly mitigate the temperature fluctuation of the PV panel and improve the photoelectric efficiency. Due to the low thermal conductivity of fatty acid, the temperature stratification in the solar collector was still significant even with the addition of metal copper fins. The thermal regulation strategy of setting the temperature at 45 °C gave better performance and the overall efficiencies of Case 1 and Case 3 could reach approximately 91%. The overall efficiency of Case 3 and Case 4 was approximately 85% with the thermal regulation strategy of setting the temperature at 50 °C. More heat could be removed from the PCM in the solar collector using the relatively low temperature setting of the thermal regulation strategy. It was concluded that the overall energy utilization ratio of the PV/T-PCM system can be improved through a reasonable thermal regulation strategy; however, further work on the economics analysis of the system is still needed. [ABSTRACT FROM AUTHOR]

Combining a phase change material (PCM) and night ventilation provides a good opportunity to reduce the load of air conditioning in buildings, particularly for a large diurnal temperature fluctuation. This study developed a multiple-relaxation time lattice Boltzmann method to numerically investigate the heat transfer characteristics and energy-saving potential of porous bricks filled with paraffin waxes under a large diurnal temperature fluctuation. A typical day in July for Shanghai, Urumqi, Hohhot, Harbin, and Xining was selected, and its meteorological parameters were deduced using Meteonorm software as the dynamic boundary conditions. The total heat flux from the roof, temperature fluctuation of the interior surface of the roof, and frequency of thermal discomfort (FTD) were calculated. By comparing the results in Shanghai and Urumqi, the impact mechanisms of the diurnal temperature fluctuation on PCM performance were shown in detail for the first time. At the phase transition temperature of 28 °C, the FTD is 7.4% in Urumqi, much lower than 37.2% in Shanghai. The adaptability of the phase transition temperature to climatic parameters is highly significant for the application of PCM in building roofs. The porous brick roofs in Shanghai, Urumqi, Hohhot, Harbin, and Xining exhibited excellent operating characteristics when paraffin waxes with phase transition temperatures of 28 °C, 28 °C, 26 °C, 28 °C, and 24 °C, respectively, were employed. The corresponding FTDs were 37.2%, 7.4%, 0%, 0%, and 0%, and the corresponding total heat fluxes from the roof were 163.3 kJ·m−2, 95.2 kJ·m−2, 23.0 kJ·m−2, 61.6 kJ·m−2, and 0 kJ·m−2. This work can provide guidance for optimizing the combination of PCMs and night ventilation in buildings located in areas with large diurnal temperature fluctuations. [ABSTRACT FROM AUTHOR]

• The PV/T-PCM system with a novel latent heat solar collector was proposed in Shanghai. • The energy and exergy efficiencies were comprehensively compared among five cases. • The thermal regulation strategy played a key role for the energy conversion improvement. • The 45 ℃ intermittent thermal regulation performed best for the PV/T-PCM system. The photoelectric conversion efficiency generally decreases with increasing temperature of a photovoltaic (PV) panel; therefore, temperature control is the key issue in the photovoltaic/thermal (PV/T) system. We experimentally analyzed the energy conversion performance of a PV/T system combined with a latent heat solar collector under the real outdoor climate of Shanghai. The solar collector was filled with the phase change material (PCM) of fatty acid for cooling the PV panel. Five cases under different thermal regulation strategies for the PV/T-PCM system were comprehensively analyzed to optimize the system performance. The results indicated that the temperature stratification of PCM was still significant in the solar collector even when metal fins were employed. The temperature fluctuation of the PV panel can be well alleviated by PCM; however, the PCM was easily overheated under long-term operation of the PV/T-PCM system. Among the five cases, the overall energy efficiency of the PV/T-PCM system with full-time thermal regulation was 5.4% and 22.2% higher than the two systems without thermal regulation, respectively. The relatively low temperature setting of the thermal regulation strategy facilitated the heat transfer from the PCM. In comparison with the full-time thermal regulation strategy, the 45 °C intermittent thermal regulation strategy (Case 4) demonstrated the best performance. The total energy and exergy efficiencies of Case 4 were 86.3% and 15.5%. The exergy efficiency of thermal energy varied slightly in the range of 1.1%–1.4% for the five cases. It was concluded that the energy conversion performance of the PV/T-PCM system could be significantly improved by a suitable intermittent thermal regulation strategy. [ABSTRACT FROM AUTHOR]