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|Title:||Exploration of module topologies for energy yield optimization when non-uniform conditions are dominant|
|Keywords:||Renewable Energy Sources|
|Abstract:||Photovoltaic systems, which convert solar energy to electrical energy, are an attractive solution for future clean energy provision on site. However, the performance of commercial PV installations degrades non-linearly with the presence of non-uniform operating conditions. The reliability and future operation of the PV modules can be compromised by potential creation of hot spots, especially in locations where non-uniform conditions and partial shading are frequent. The performance of the PV array degrades non-linearly when operating under non-uniform conditions. Partial shading can occur in different levels of the PV array, between PV modules or within the module itself. The focus of this thesis is for partial shading which occurs on the module level. Conventional modules do not allow all cells to operate on their Maximum Power Point (MPP) when partial shading conditions are present. The design of custom topologies, based on the specific run-time operating conditions of the module, thus allowing the majority of the cells to operate at their MPP, showed promising results in terms of recovered power. This led to the investigation of module topologies which would enable multiple run-time configurations depending on the current operating conditions of the PV module (partial shading, irradiation, ambient temperature, wind velocity). The granularity level of the module was explored by taking into consideration the increased manufacturing cost due to additional elements and the increased resistivity in the active path of the current. A cell-string architecture is proposed where the cell-string string is defined as the minimum power producing element and cannot be divided at run-time. Dynamic elements (switches), local converters and a supporting network are added to allow extraction of more power during conditions of partial shading. A methodology is proposed to select how cell-strings are formed in the PV module and the characteristics of the required supporting electrical network to enable reconfiguration. Two main templates are examined; a row/column template and a snake-like template. In order to evaluate the performance of different module configurations, a detailed and accurate simulation environment is required. A highly accurate physics-based bottom-up model is used, where all additional elements are included. This allows the comparison of different module templates in terms of energy-yield. Simulations have been performed under relevant and realistic operating conditions. Both static and dynamic shading scenarios have been considered and the performance of different module topologies has been evaluated and benchmarked to current industrial solutions. Such a benchmark allows to determine the energy-yield gain that can be expected by the different proposed templates. This together with other cost aspects, e.g. initial fabrication cost and complexity of control scheme, allows to determine the most promising configurations. Also, long-term financial analysis is performed for the two most promising reconfigurable templates. Finally a method to speed-up the simulation process is introduced|
|Appears in Collections:||Διδακτορικές Διατριβές - Ph.D. Theses|
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