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Characterisation and modelling of photovoltaic cells and modules under partial shading

Atia, Abdulhamid M Mahmud ORCID: 2023. Characterisation and modelling of photovoltaic cells and modules under partial shading. PhD Thesis, Cardiff University.
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Partial shading in photovoltaic (PV) systems is an inevitable issue that significantly deteriorates their performance. This thesis presents a detailed experimental and theoretical study on the characterisation of solar cells and PV modules under partial shading. The primary focus of this research was to improve accuracy of modelling partially shaded PV modules without the need to include the avalanche breakdown term in the model. The research started by designing an equivalent circuit parameters extraction technique for solar cells and modules, which was used in the investigations of this study. The technique is based on adding a simple iterative process to an analytical method from the literature to optimise the selection of points used to calculate the slopes on current-voltage (I-V) curves. This resulted in an accurate technique with a mean absolute percentage error (MAPE) between calculated and experimental data of less than 2% for all I-V curves presented in this thesis. In addition, the technique showed a good repeatability of the parameters using the experimental set-up of this research. The relative standard deviations (RSDs) of the parameters extracted from four I-V curves measured in sequence were less than ±3%.This technique was then used in investigating the variations of a mono-crystalline (monoSi) solar cell parameters with shading. In addition, the effect of partial shading on the parameters was compared with that of reducing the irradiance uniformly on the cell area, where both effects were found to be nearly identical. The MAPE between I-V curves of partial shading and those of reducing the irradiance did not exceed 1% in two investigated cases. This investigation has confirmed that it is reasonably correct to enter opaque partial shading impact in PV models as a parameter that corresponds to reducing the irradiance uniformly over the whole cell area. Then, the variations of the equivalent circuit parameters with shading were entered in models for a single cell and a PV module to assess whether considering those variations will lead to any improvement in modelling accuracy. The results revealed that the single cell model did not exhibit an appreciable improvement in accuracy. By contrast, the PV module model showed a noticeable improvement at a region on the I-V and power-voltage (P-V) characteristics at which the shaded cell is working in the reverse bias. The parameter responsible for this improvement in accuracy was identified from a systematic study and found to be the shunt resistance (Rsh). Hence, it has been proposed to account for the variations with shading of only the photo-generated current (Iph) and Rsh when modelling partially shaded PV modules. The great advantage of this approach is that it provides an accurate modelling of the reverse bias region without the need to include the avalanche breakdown term in the model. Subsequently, this research focused on the response of a mono-Si PV module when individual solar cells were partially shaded. It was found that there is a correlation between the shape of I-V characteristics under partial shading and broken contact fingers of solar cells. Different experiments, including electroluminescence (EL) imaging, were carried-out to validate this correlation. The correlation reported in this thesis has proved the feasibility of a concept of detecting broken contact fingers in PV modules from measurements of I-V curves with individual cell partial shading under day light.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: 1). Photovoltaic 2). Photovoltaic modules 3). Solar cells 4). Solar cell parameters 5). Partial shading modelling 6). Broken contact fingers 7). Electroluminescence imaging
Date of First Compliant Deposit: 22 June 2023
Last Modified: 22 Jun 2023 09:18

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