| dc.description.abstract | Concentrated photovoltaic systems (CPV) have demonstrated the potential to achieve a high conversion power compared to conventional photovoltaic panels (PV) especially for areas with high solar irradiance. Under higher concentration ratios, solar cells can work at higher efficiencies by reducing the area of the solar cell and replacing it with optical components to collect the incident light more effectively. This is considered an efficient way to decrease the system cost without sacrificing the solar energy absorbed. However, the development of this emerging technology faces a number of challenges, one of them being the high temperature resulting from the increase in the concentration ratios. The solar cells may be subjected to damage if the temperature exceeds the limit recommended by the manufacturer.
This thesis investigates a number of innovative solutions for the development of high concentrator photovoltaics (HCPV) receivers. The work outlines the characteristics of the concentrator photovoltaic systems from different perspectives, the solar cell types, and optics classifications. The existing thermal management techniques, the advantages of nanotechnology in solar thermal applications, and the literature on the optical filters are also reviewed.
The thermal, electrical, and optical characterisations of the properties of the materials used in this research are introduced. The impact of the coolant type such as nanofluids, and heat sink design on the Multijunction (MJ) solar cell performance is investigated experimentally and theoretically. Water in comparison with the ethylene glycol and water mixture and syltherm oil using finned minichannel heat sink offers the best cell temperature uniformity. However, the highest outlet temperature is achieved using syltherm oil 800 especially for a concentration ratio above 1000 suns which is suitable for heat recovery applications that require a high temperature. Significant enhancement in the thermal conductivity of aluminium oxide/water and silicon dioxide/water nanofluids at different concentrations are measured in comparison with the distilled water. The thermal conductivity values were entered into COMSOL-Multiphysics software and the heat transfer effectiveness of the nanofluids was enhanced in comparison with water reaching 1.15 in the case of Al2O3/water at 5%, while in the case of using SiO2/water it reached 1.11 using a finned channel heat sink. Higher solar cell temperature uniformity is observed by using nanofluids in comparison with using water only as the maximum MJ solar cell temperature decreased by 3.6 °C at a concentration of 2000 suns in the case of using SiO2/water.
The serpentine configuration has been investigated along with the straight channel heat sink for use in the HCPV applications. The centre inlet serpentine showed high electrical and thermal efficiencies until the concentration ratio of 2000 suns providing high-temperature uniformity and keeping the solar cell temperature below the recommended limit. The feasibility of using an infrared (IR) optical filter as a temperature regulator for the HCPV is explored. The IR filter successfully protects the single-junction solar cell from cracking and enhanced the cell efficiency by 180% at a solar irradiance of 400 W/m2.
Detailed performance analysis of the focal spot area of the Fresnel Lens is presented to build a solid base of knowledge for higher concentration ratios. Uniform electrical and thermal distribution has been detected within the focal spot showing the highest measured power at the centre of the MJ cell of 2.5 W. The numerical results using the finite element method (FEM) are validated with the indoor experimental results of the test section replicating the experimental conditions in the laboratory. The effect of different working conditions is reported throughout the research. Although the MJ solar cell temperature was below the recommended limit, the temperature can be decreased even further if a high thermal conductivity thermal paste is utilised emphasizing its importance in reducing the temperature. | en_GB |
