Enhancing the Electrical and Thermal Performance of a Photovoltaic Thermal (PVT) System

A photovoltaic thermal (PVT) system combines a photovoltaic and solar thermal collector to convert sunlight into electrical and thermal energy. However, the cell temperature rise in PVT systems is a significant issue that is widely acknowledged by many studies in the literature. Research studies have found that the cell temperature of the PVT system can be reduced by using different cooling methods such as active or passive cooling. Active cooling methods such as nanofluid are found to be effective in controlling the temperature rise of PVT systems. However, there has been little focus in the current literature about the PVT operational conditions with the nanofluid application for producing optimum performance. 

This thesis presents research undertaken to optimise the performance of PVT systems with Copper Oxide (CuO) nanofluid application. A two-step method was employed to formulate the CuO nanofluid, which included 80 minutes of ultrasonication to ensure particle stability. A numerical equation-based model was developed using the Transient System Simulation Platform (TRNSYS). The application of CuO nanofluid was modelled in TRNSYS by calculating its thermophysical properties through numerical equations and integrating these values into the TRNSYS components. The numerical model was initially verified against the experimental test data of Alous et al. (2019). To validate the numerical model, an experimental test rig was constructed using a 375 Watts PVT system and other components such as a heat exchanger, pump and pipes. CuO nanofluid was used at 0.10% volume concentration and a flow rate of 60 kg/h and 80 kg/h. The data from the experiment served to validate the numerical model. Once the model was validated, further investigation was conducted using the model by varying the nanofluid volume concentration from 0.10%-0.50% and fluid flow at 60 kg/h, 80 kg/h and 120 kg/h. The influence of these inputs was observed on the system’s PV cell temperature, electrical efficiency, thermal efficiency, overall exergy efficiency, net electrical output and pump power consumption. Later, to identify the optimum operating conditions of the TRNSYS model, the data was imported into Design-Expert (DE) software for PVT performance optimisation. 

The numerical model results showed that at 60 kg/h flow, the increment in nanofluid concentration from 0.10%-0.50% caused an increase in electrical efficiency by 1.11% and thermal efficiency by 3.30%, respectively. Similarly, at 0.10% volume concentration, when the mass flow was raised from 60-80 kg/h, the improvement in electrical efficiency was 1.46%. However, for a mass flow rate of 80-120 kg/h, the electrical efficiency of the system dropped ii by 0.08%. This drop could be attributed to higher pump power consumption from the system. Overall, the electrical efficiency improved by 1.36% for 60-120 kg/h mass flow. The thermal efficiency improvements were 4.15%, 1.07% and 5.27%, at the same corresponding flow rate variations. Net electrical output analysis of the system showed that an increase in volume concentration and fluid flow rate changes the density of nanofluid which in turn increases the pump power consumption. 

To balance the pump power consumption and optimise the PVT performance, response surface methodology was applied in the DE software for both single and multi-objective optimisation. The optimum operation point of electrical efficiency was identified as 14.64% at 0.10% volume concentration and 90 kg/h mass flow of fluid. For thermal efficiency, the identified optimum operation point was 34.94% at 0.50% concentration and 120 kg/h mass flow. The overall energy efficiency revealed the optimum output of 49.28% at 0.10% concentration and 88 kg/h mass flow. The overall exergy efficiency showed 16.45% as the optimum value at 0.50% concentration and 60 kg/h mass flow. The multi-objective optimisation study investigated the operation point for producing optimum output collectively from all the output responses. The analysis found that the system can produce optimum output at 0.10% concentration and 91 kg/h mass flow. 

The study has successfully demonstrated that optimisation of nanofluid application is effective in enhancing the performance of the PVT system. The results provide information regarding the individually optimised performance of PVT systems with electrical efficiency, thermal efficiency, overall energy efficiency and overall exergy efficiency of the PVT system. This information can be highly useful for the adoption of PVT systems into applications that require optimum production from a specific output parameter of the system. The study also provides information regarding optimising the performance of PVT outputs collectively to enhance the system’s overall performance. A case study was conducted to assess the impact of the research on the overall PV energy scenario in Australia. Data regarding the installed PV capacity and their contribution to the annual electricity generation in Australia for 2021 was collected from the Australian PV Institute. This data was used to compare against the energy produced by the proposed PVT system in the same PV scenario. The analysis showed that using the proposed PVT design, a significant increment in electrical energy of 16.30% is possible if the current PV systems are replaced with the former.