Experimental investigation and numerical modelling of a concentrating photovoltaic/thermal system (CPVT) based on point focus Fresnel lenses (PFFL)

Hmouda, Rida Ali (2023) Experimental investigation and numerical modelling of a concentrating photovoltaic/thermal system (CPVT) based on point focus Fresnel lenses (PFFL). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Climate change is one of the biggest environmental, political, economic, technological, and social challenges of the 21st century. The increasing cost of fossil fuels further exacerbates this. To mitigate greenhouse gas emissions to a tolerable level, the world energy system needs to transition to renewable energy sources. Solar energy is one of the most suitable alternatives in this regard. Solar photovoltaic (PV) and solar thermal technologies are the two most widely available solar technologies. However, one of the main drawbacks of PV technology is its relatively low energy conversion efficiency and land use requirements. Multi-junction photovoltaic (MJPV) solar cells have been developed to overcome these limitations. These cells are a new generation of PV technology that offers higher efficiency, better response to high solar concentration, and lower temperature coefficients. However, they tend to be more expensive. Concentrator photovoltaic (CPV) systems can address these challenges and replace expensive MJPV materials with cost-effective concentrator optics elements. However, high solar radiation concentrations can lead to an increase in cell temperature, necessitating cooling. Concentrated photovoltaic thermal (CPVT) systems have emerged as a solution, enabling the simultaneous production of electrical and thermal energy. This dissertation focuses on the theoretical and experimental evaluation of a CPVT system's electrical and thermal performance. An indoor prototype CPVT model was designed, built, and tested at the Thermofluid Laboratory. The model incorporates a sun simulator, pointfocus Fresnel lenses (PFFL), MJPV cells, copper heat sinks, and a copper pipe flow loop. The design aims to reduce MJPV module temperature and enhance heat transfer to the heat transfer fluid (HTF) in the flow channel, enabling high electrical and thermal energy production. A numerical model was developed to simulate the performance of the CPVT design and validated using experimental data from indoor test campaigns. The CPVT model was tested and simulated under various design parameters. The experimental results indicated that the prototype CPVT model achieved electrical and thermal efficiencies of 34.73% and 54.7%, respectively. The corresponding electrical and thermal energy outputs were measured at 42.75 W and 67.89 W, respectively. The results obtained from Computational Fluid Dynamics (CFD) simulations showed that the highest electrical efficiency of 36.47% was recorded at a mass flow rate of 0.025 kg/s and a concentration ratio (CR) of 100X. Conversely, the lowest electrical efficiency of 25.56% was observed at a mass flow rate of 0.0029 kg/s and a CR of 500X. The CFD analysis also highlighted that the highest thermal efficiency of 73.0% was achieved at a mass flow rate of 0.0029 kg/s and a CR of 500X, while the lowest thermal efficiency of 61.5% was observed at a mass flow rate of 0.025 kg/s and a CR of 100X. Regarding power output, the highest recorded electrical energy output was 389.3 W, obtained with a mass flow rate of 0.5 kg/s and a CR of 1000X. Similarly, the highest thermal energy output was 1028.5 W, attained with a mass flow rate of 0.1 kg/s and a CR of 1000X. The CFD results also revealed that the outlet temperatures varied between 18.1 to 72.5 °C, depending on the mass flow rate and CRs. This temperature range makes the CPVT system suitable for various applications such as swimming pool water heating, domestic hot water, and space heating. The numerical model used in this study was validated with indoor experimental data, and demonstrated good agreement in the average cell temperature with a maximum deviation of 4.58% at a flow rate of 0.0029 kg/s and a minimum deviation of 1.14% at a flow rate of 0.025 kg/s. These validation results indicate that the model is accurate and reliable and can be used for further optimization and analysis of the CPVT system.

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