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Development novel solar concentrator-thermal absorber for a hybrid PV-TE system

Alnajideen, Mohammad 2021. Development novel solar concentrator-thermal absorber for a hybrid PV-TE system. PhD Thesis, Cardiff University.
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Photovoltaics (PV) cell performance presents a strong dependence on the solar irradiance spectral distribution and this dependence becomes significant after using optical elements for concentrating PVs, aiming to increase the power output and reduce the materials cost. In addition, the concentrated solar irradiance contributes to the heat generation within the PV cell, hence, the heat dissipated by the PV cell can be collected by a thermal receiver and delivered as useful energy. This conventional method, which known as “PV-thermal hybrid system” enables full-spectrum solar energy utilisation, but it presents significant challenges that affect the performance and durability of PV cells. In this research, we introduce an innovative design for a Photovoltaic- Thermoelectric Generator (PV-TEG) hybrid system based on a spectrum splitting approach to address the spectral mismatch between incident solar irradiance and PV cells and the challenges facing conventional PV hybrid configurations. This work describes systematic experimental investigations into the design, construction and characterisation of the novel PV-TEG system, reflecting the state-of-art of simultaneous spectrum splitting and light concentration to a PV cell while transmitting the IR radiation to a thermal absorber to drive a TEG. A new indoor testing condition for nearly full-spectrum solar energy applications was established to spectrally match the sunlight. An evaluation study was conducted to investigate the performance of commercial optical light filters and their spectral dependence on the angle of the light incidence. A characterisation study of PV cells and optical filters was implemented to establish a solid knowledge on the relationship between the spectral response of the PV cells and the characteristics of the incident spectrum and to quantify the heat absorbed by a thermal absorber material. The outcome of these optimisation studies was beneficial to identify the suitable combinations of filters and PV cells and the optimum filters angle required for the hybrid system. Moreover, a number of solar concentration technologies were explored to assist in selection a suitable concentrator design to facilitate the development of the hybrid system and the V-trough Solar Concentrator (VSC) was chosen since commercial filters are only available as flat architectures. A set of high-performance VSCs were designed and fabricated using 3D printing technology and highly reflective thin-film mirrors. The VSCs were tested as a benchmark to validate the methods and procedure employed for fabrication and characterisation of concentrators. It has been evidenced that the fabricated VSCs exhibit concentration ratios ranging from 1.7x to 5.6x and corresponding optical efficiency of 88%-94%, representing the best values published to date. Furthermore, a novel Onagraceae VSC (OVSC) design was developed as a result of systematic investigation to improve the concentration ratio of the conventional design of VSC and the optical efficiency of crossed VSC. The results showed that the OVSC exhibits significantly higher concentration ratio (by 40% - 60%) than the conventional VSC of the same trough angles. The increase in the concentration ratio is obtained without affecting the angular response, which is usually a challenging trade-off in the design of solar viii concentrators. The advantage of the OVSC can be seen from a different angle – in order to obtain the same concentration ratio, an OVSC uses less reflector materials and has a better angular response than its corresponding conventional VSC, making it a better alternative for low cost CPVapplications for the future. The novel hybrid PV-TEG system was designed and constructed incorporating optical filters, which facilitate sunlight spectral management to increase the functionality and efficiency of solar energy conversion. The experimental results demonstrate that the total efficiency of the hybrid system is 6.3% higher than that of a similar system with an identical design, except for using an aluminium concentrator without a TEG module. The additional TEG power is due to harvesting the energy in the IR spectrum that has no use in the PV cell. The systematic investigations on the relationship between the power output and geometry of TEG modules indicate that the size of the TEG module plays an important role in minimising the heat loss from the thermal absorber and consequently improving the efficiency of thermal energy harvesting by the TEG module. The results from the hybrid system under the increased light concentration provide direct experimental evidence that significant improvement can be achieved by increasing the concentration ratio. Additional benefit of increasing the light concentration is to reduce the cost of the system, which was indicated by the economic analysis. The results also confirm that the feasibility of satisfactory spectral separation using commercial filters despite the optical loss that exist with these filters. Further investigations and recommendations for improving the efficiency of spectrum splitting solar energy systems were also provided at the end of this work.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Solar Energy, Photovoltaic, Thermoelectric, Spectrum Splitting, Solar Concentrator, Hybrid PV-TE System
Date of First Compliant Deposit: 25 October 2021
Last Modified: 25 Oct 2021 11:47

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