Energy conversion performance of a PV/T-PCM system under different thermal regulation strategies

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.