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Title: Experimental and numerical modelling of mid-concentration photovoltaic concentrator systems
Author: Adkins, Deborah Anne
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2012
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For photovoltaics to achieve wide-scale implementation it is essential that their cost is reduced while maintaining or exceeding the present level of solar to electrical conversion performance. Concentrating solar energy onto a photovoltaic cell allows a reduction in the output electricity cost, if the cost of the concentrator is less than that of the displaced photovoltaic materials. Photovoltaic cell efficiency is shown to decrease with increasing temperature, causing the photovoltaic cells to exhibit both short-term (efficiency loss) and long term (irreversible damage) degradation due to excessive temperatures. Hence the analysis of thermal management is an important issue in photovoltaic power generating systems for both one-sun (lx) and concentrated applications. This thesis presents an experimental and numerical study of solar cell temperature in a midconcentration silicon photovoltaic concentrator (CPV), with a geometric concentration ratio of 42X. Experimental and computational fluid dynamic (CFO) modelling of heat transfer in six designs of CPV device is carried out. A detailed experimental study was designed and carried out in order to investigate the temperature and initial boundary conditions of the two initial CPV prototypes, with a without passive cooling arrangements, operating under standard test conditions (STC) in conjunction with the effect of environmental variables, namely the irradiance incident on the plane-of-array of the CPV module, the local wind speed and the ambient temperature on the operating temperatures of the CPV prototypes. The operating temperature is shown to depend strongly on the irradiance, less so on the wind speed and is found to be insensitive to short term fluctuations in ambient temperature. Temperature profiles of the CPV prototypes were measured experimentally with thermocouples placed both internally and externally along the enclosure and walls aJong the length of each CPV module. To investigate the performance of the CPV devices under a fixed set of repeatable environmental conditions, a solar simulator was designed and built to facilitate indoor testing at a range of illumination levels (0 to 1000W 1m2) and environmental conditions. Reviewing the results it was found that the spectrum and uniformity of irradiance source incident the plane of a single module (1 x 0.lm) is of great importance. The solar simulator was also found to artificially increase the module operating temperature, with greater temperatures recorded during indoor testing. Wind speed and direction measurements were taken in order to establish the module convective heat transfer coefficient (CHTC) which was determined to relatively insensitive to wind direction and to be a power law function of the mean wind speed. In the second phase of the work, three dimensional numerical studies of the photovoltaic concentrator prototypes were developed using ANSYS Fluent Computational Fluid Dynamic (CFD) software to solve the mass, momentum and energy transfer governing equations. The simulations provided thermal and dynamic maps of the fluid flow and the heat transfer between the cell and the passive cooling systems. The results show that a maximum of seven radial fins (CPV design 3) of 27mm height, 3.3mm thickness with a 4 degree taper can be effectively used to reduce the solar cell temperature, from 97.8"C with no cooling fins to 67.7"C with seven fins, measured at nominal operating cell temperature (NOCT) conditions. In addition. to validate the model. experimental measurements of temperature and flow characteristics are compared with experimental data. Numerical results of the CPV operating temperature are shown to have a strong correlation with experimental data with a maximum 0.3% deviation from experimental data for prototype one and a maximum 1.5% deviation from experimental data for prototype two. Simulation models are shown to be important design tools for predicting a photovoltaic concentrator's experimental and real world performance. Informed design decision making and optimisation is a significant goal of this work.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available