Performance analysis on combined heat and power of photovoltaic-thermal module integrated with phase change material-water storage

Use of phase change material (PCM) to generate temperature stratification in water storage tank coupled with unglazed photovoltaic-thermal (PVT) module for combined heat and power generation enhancement was investigated by experimental and numerical analyses. In the experiment, RT42 PCM having melting point of 38–43 °C was filled in a packed-bed of 40 mm diameter spherical capsules contained in a 220 L water storage tank connecting with four units of 200 Wp (watt peak) unglazed PVT module in series. The experiments were performed outdoor with the water mass flow rates of 2.4 and 5.8 LPM. One-dimensional finite difference enthalpy method was used to predict the water and PCM ball temperatures in the tank. The PVT thermal performance was evaluated similarly to that of solar thermal collector, and the electrical performance was calculated from nominal operating cell temperature (NOCT) approach. It could be noticed that the simulated results on the water and the PCM ball temperatures including the module temperature and the maximum generated electrical power of PVT modules agreed well with the experimental data. The model was used to predict the electrical and overall (both thermal and electrical) efficiencies of the PVT modules by considering the positions of the PCM packed-bed, the PCM amount, the circulating water mass flow rate, and the PCM type. It could be found that the position of the packed-bed did not give effect on the PVT module performances but increase of the PCM amount generated higher water temperature stratification in the storage tank which resulted in higher PVT module efficiencies especially in the afternoon. The circulating water also did not give strong effect on the total PVT module performances. For PCM with low melting point, the PVT module performances were higher but the water temperature in the storage tank might be too low for hot water utilization.