Photovoltaic thermal systems (PVT) are solar energy conversion systems that produce both electricity and heat simultaneously. PVT systems seeking to minimize temperature of solar cells become more significant with the increased thermal and electrical efficiency of the working fluids (water and nanofluids) employed in the solar thermal system. The major objective of this research is to investigate the thermal, electrical and overall performance of the photovoltaic thermal (PVT) system with different weight fractions of MWCNT/water nanofluids (φ = 0.3%, 0.6% and 1%) and water. A sheet and tube PVT system model geometry, which has been simplified to rectangular PV cell, absorber plate, cylindrical pipe, and fluid domain geometries to investigate outlet and PV cell temperature of photovoltaic thermal (PVT) system between different weight fractions of MWCNT/water nanofluids (φ = 0.3%, 0.6% and 1%) and water with varying fluid inlet velocities from 0.02 m/s to 0.08 m/s using ANSYS FLUENT. The results show that increasing the inlet fluid velocity and weight fraction of the working fluid improves thermal and electrical efficiency. The highest improvement in thermal and electrical efficiency at 0.08m/s inlet fluid velocity for the weight fractions, φ = 1% of MWCNT/water nanofluids is 7.8% and 0.03% compared to water. In addition, the weight fractions, φ = 0.3% of MWCNT/water nanofluids is 4.46% and 0.01% and the weight fractions, φ = 0.6% of MWCNT/water nanofluid is 6.72% and 0.02%. Additionally, the maximum increase of overall efficiency at 0.08m/s inlet fluid velocity for the weight fractions, φ = 1% of MWCNT/water nanofluids is 7.83% compared to water while the weight fractions, φ = 0.3% of MWCNT/water nanofluids is 4.43% and the weight fractions, φ = 0.6% of MWCNT/water nanofluid is 6.74% at inlet fluid velocity of 0.08 m/s. As a result of the research, it was discovered that using MWCNT/water nanofluids improves the performance of PVT systems.

Although, the effect of mass flow rate and solar irradiance variation is present in literature, it is still of significant interest to investigate the extent of the effect especially when utilizing a custom absorber design. In this paper, the effect of changing the mass flow rate and solar irradiance on the performance and temperature uniformity of a PVT using a custom spiral absorber design is simulated using ANSYS CFD software. By increasing the mass flow rate, the temperature uniformity and the performance parameters such as the average PV temperature, water outlet temperature, thermal and electrical efficiency all increase. By increasing the irradiance level, performance and temperature uniformity drop albeit at a smaller degree compared to change observed in mass flow rate variation. Amongst the tested range, the optimum mass flow rate and solar irradiance levels for best performance are 40 kg/h and 800 – 1000 , respectively.

The integration of Phase Change Material (PCM) with the Solar Photovoltaic Thermal (PVT) serves as heat storage to enhance the system's performance. Temperature rises have an undesirable effect on efficiency results in a diminishment in the amount of energy produced by the solar panel. Parametric analysis and temperature investigation are involved in improving the performance of the system. The variation of performance will assist in developing an optimized PVT-PCM system. The model is validated by comparison from published journals on the studies related to phase change material implemented in solar PVT. For the variation of mass flow rate, the overall efficiencies achieved by 10 kg/h, 30 kg/h, 50 kg/h and 70 kg/h are 90.82%, 90.54%, 90.48% and 90.46%, respectively. In addition, solar irradiance of 200 W/m2, 450 W/m2 and 800 W/m2 produced 91.17%, 90.82% and 90.33% of overall efficiencies. Increased in flow rate requires stronger pumps which increase the total cost of the system. Therefore, identifying the optimal flow rate might help to achieve an appropriate thermal efficiency while sustaining in low costs. Finally, this paper presented a numerical investigation of PCM acts as promising elements incorporated in the PVT system that has the capability to reduce the temperature of the PVT-PCM system.

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