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.

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.

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.

The reputation of nanofluids as a convenient heat transfer media has grown in recent years. The synthesis of nanofluids is often challenging, particularly carbon-based nanofluids, due to the rapid agglomeration of the nanoparticles and the instability of the nanofluids. In this regard, surface modification and surfactant addition are potential approaches to improve the physical and thermal properties of carbon-based nanofluids that have been studied and the structural, morphological, and thermal characteristics of surface-oxidised carbon nanofibre (CNF)-based nanofluids has been characterised. Commercial CNF was first subjected to three different acid treatments to introduce surface oxygen functional groups on the CNF surface. Following the physical and thermal characterisation of the three surface-oxidised CNFs (CNF-MA, CNF-MB, and CNF-MC), including Raman spectroscopy, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM), the CNF-MB was selected as the best method to synthesise the surface-oxidised CNF-based nanofluid. A total of 40 mL of ultrapure water was used as a pure base fluid and mixed with the surface-oxidised CNF at a concentration range of 0.1–1.0 wt.%, with a fixed of 10 wt.% amount of polyvinylpyrrolidone (PVP). The thermal conductivity of CNF-based nanofluid was then characterised at different temperatures (6, 25, and 40 °C). Based on the results, surface oxidation via Method B significantly affected the extent of surface defects and effectively enhanced the group functionality on the CNF surface. Aside from the partially defective and rough surface of CNF-MB surfaces from the FESEM analysis, the presence of surface oxygen functional groups on the CNF wall was confirmed via the Raman analysis, TGA curve, and FTIR analysis. The visual sedimentation observation also showed that the surface-oxidised CNF particles remained dispersed in the nanofluid due to the weakened van der Waals interaction. The dispersion of CNF particles was improved by the presence of PVP, which further stabilised the CNF-based nanofluids. Ultimately, the thermal conductivity of the surface-oxidised CNF-based nanofluid with PVP was significantly improved with the highest enhancement percentage of 18.50, 16.84, and 19.83% at 6, 25, and 40 °C, respectively, at an optimum CNF concentration of 0.7 wt.%.

Graphene nanoplatelets (GNP) have garnered significant interest owing to their remarkable mechanical properties, making them ideal materials for enhancing the heat transfer properties of nanofluids. However, the agglomeration of GNP in water-based nanofluids remains a significant challenge, limiting their practical applications. In this study, a comprehensive investigation into the formulation of water-based nanofluids using GNP is presented, with a focus on the incorporation of polyvinylpyrrolidone (PVP) as a surfactant to enhance their stability and dispersion. The nanofluid formulations were systematically prepared with varying concentrations of GNP and PVP to optimize their thermal properties. Additionally, the thermal conductivity and viscosity of the nanofluids were examined over a range of temperatures and concentrations. The results show that the formulation of GNP with 0.6 wt.% shows great potential as a nanofluid with 0.6611 W/mK and 1.22 mPa.s for thermal conductivity and viscosity, respectively. The findings also demonstrate that the incorporation of PVP significantly improves the stability and dispersion of GNP in water, leading to enhanced thermal conductivity and manageable viscosity. These findings contribute to the application of this nanofluid in various industries, specifically solar energy.

This study investigated the performance and efficiency of a photovoltaic thermal (PV/T) system utilizing a metal-based nanofluid, specifically MgO nanofluid. This research proposes MgO as nanoparticle to mix with base fluid because it demonstrated to have superior features with the highest thermal conductivity and lowest viscosity among the metal oxide. The nanofluid offered improved thermophysical properties that enhanced the PV/T system performance. The study focused on formulating a stable nanofluid, determining its thermophysical properties, and analysing the overall system performance. 0.2wt% MgO nanofluid were successfully developed and demonstrated excellent stability over a 14-day period by using a two-step method which 20 minutes of homogenization at 1000rpm and 30 minutes of ultrasonication. Tests were conducted to determine the thermal conductivity and viscosity of the nanofluid at various concentrations and temperatures. Results showed that increasing the concentration and temperature enhanced thermal conductivity, while viscosity increased with concentration but decreased with temperature. The thermal and electrical efficiencies of the PV/T system at various irradiances (200W/m2, 500W/m2 and 800W/m2), and flow rates (10L/h, 20L/h, 30L/h) were examined, calculated and compared between water and the MgO nanofluid as working fluids. At 10L/h, it was observed that nanofluid had the highest 74% of thermal efficiency increment compared to the water at 500W/m2 followed by 71% at 200w/m2 and 55% at 800W/m2. Also, Nanofluid demonstrated a 5% increase in electrical efficiency at 200W/m2, 2.1% increase at 500W/m2, and 1.9% increase at 800W/m2 compared to water. The nanofluid exhibited superior thermal and electrical efficiency compared to water, indicating its potential for improving system performance hence, surpassing the performance of a standalone PV system.