Evaluation of photovoltaic thermal system performance with different nanoparticle sizes via energy, exergy, and irreversibility analysis

The PVT system efficiency generally depends on diverse factors, such as design parameters, solar radiation intensity, and the concentration and type of nanofluid, among other major factors. The present work focuses on the effect of nanoparticle size on a nanofluid-based PVT collector system with a spiral-flow absorber. Besides nanoparticle size, the system is experimentally investigated at various flow rates, nanoparticle concentrations, and different working conditions. Moreover, PV efficiency is also calculated and compared with thermal efficiency by employing both energy and exergy analyses. The rate of exergy loss in PVT is calculated in order to provide a appropriate understanding of the key factors that affect the overall performance of such systems. The most important factor significantly affecting the PVT net efficiencies is the absorber outlet temperature, which illustrates the trade-off between the temperature increase and the increase of the potential concentration factor. The nanoparticles are milled several times to produce four groups based on particle size, such as A (2–5 nm), B (22–29 nm), C (34–50 nm), and D (75–92 nm). The nanofluid thermal conductivity of groups A, B, C, and D compared to water increased by approximately 50.0 %, 45.7 %, 34.7 %, and 21.4 %, respectively. The viscosity of these aggregates increased compared to water by approximately 12.9 %, 6.4 %, 4.3 %, and 3.2 %, respectively. There were no observed changes in density with changing groups. The stability of the prepared aggregates was close to the superiority of group A with the smallest nanoparticles. Group A, due to its higher thermal conductivity compared to the rest of the fluids tested, provided the best electrical and thermal energy, but it consumed more pumping energy due to its high viscosity. Therefore, the results show that the electrical and thermal exergy of group A, as well as the entropy generation and irreversibility, were higher than the rest groups, which indicates higher losses. The data calculated hereby should be useful in determining the optimal operating condition of the nanofluid PVT based on nanoparticle size. • The effect of varying nanoparticle sizes in nanofluid-based PVT systems is studied. • Group (2-5 nm) nanofluids demonstrated a 50% increase in thermal conductivity compared to water. • Both energy and exergy analyses were performed to compare PV efficiency with thermal efficiency. • Smaller nanoparticles with higher viscosity enhance thermal conductivity but require greater pumping energy. • The focus was on the effect of nanoparticle size that provides the optimal operating conditions for nanofluid-PVT systems.