Statistical learning methods for photovoltaic energy output prediction
- Authors: Magaya, Aphiwe
- Date: 2024-04
- Subjects: Photovoltaic power generation , Mathematical statistics , Statistics
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64138 , vital:73656
- Description: Predicting solar energy accurately is important for the integration of more renewable energy into the grid, which can help to alleviate the energy demand on traditional coal-powered sources in South Africa. This study aims to assess several statistical learning models to predict the energy output of a 1MW photovoltaic system installed on the Nelson Mandela University South Campus in Gqeberha. Weather data (including temperature, wind speed, wind direction, precipitation, air pressure, and humidity) and solar irradiance data (including global horizontal radiation, diffuse radiation, and direct radiation) are used to predict the energy output of this system using Artificial Neural Networks (ANN), Support Vector Machines (SVM), Multiple Linear Regression (MLR), and Regression Trees (RT). The performance of each of the models was compared and the results indicated that the ANN model performed best. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
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- Date Issued: 2024-04
Validation of Small Punch Testing Methodology to determine the variation in static properties over the build height of Ti-6Al-4V laser metal deposition samples.
- Authors: Viviers, Amy Bronwan
- Date: 2023-04
- Subjects: Photovoltaic power generation , Mechanical properties , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/66344 , vital:74637
- Description: Small Punch Static Testing is a testing methodology which has gained immense popularity in the power generation industry. With the drive to optimise material testing and use of expensive, lightweight materials in specialised engineering, Small Punch Static Testing has been standardised to determine standard mechanical properties of materials. Using the Small Punch Static Testing methodology as outlined in BS EN 10371, additively manufactured Ti-6Al-4V samples were tested in order to determine their theoretical ultimate tensile strength and yield strength and to determine whether there was a significant change in mechanical properties across the build height of an interrupted build direct energy deposition sample. While extremely material specific, this method has been proven to be feasible in determining mechanical properties in samples where material is scarce and no significant relationship between the sample extraction height and mechanical properties is noted. , Thesis (Ma) -- Faculty of Engineering, Built Environment and Technology, 2023
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- Date Issued: 2023-04
On the study of the performance of Photovoltaic power plants
- Authors: Serameng, Tshepo Joba
- Date: 2019
- Subjects: Photovoltaic power generation , Solar energy Power resources Renewable energy sources
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43401 , vital:36873
- Description: Performance monitoring of different module technologies and system configurations of photovoltaic (PV) systems in South Africa is rare, resulting in-few reports being published based on field results of PV systems installed and operated in South Africa. The goal of this work was to analyse and report on the performance of PV systems by evaluating the energy output of various PV system configurations and module technologies in the central part of South African (southern hemisphere) climatic conditions. To achieve this, a 400 kWp PV Solar plant has been installed and monitored since January 2015 at the Eskom Research and Innovation Centre (ERIC) in Rosherville, Gauteng (26°5'5" South, 28°5 8'1" East and 1625 m above mean sea level). The ERIC plant consists of multi-crystalline silicon (mc-Si) and copper indium gallium selenide (CIGS) thin-film technologies. The plant comprises of two 25° fixed-tilt north facing arrays, two east-west single axis tracking arrays and two 10° fixed shed orientation (East and West) for both module technologies and one north-south single axis tracking for mc-Si. The evaluation was achieved by studying the operation of the PV plant under different weather conditions and the impact of different configurations and technologies by analysing mainly in terms of specific yields normalized per m2 (kWh/kWp/m2). The first part of the study investigates the impact on the overall performance of different PV technologies as a function of the module mounting configuration. The second part presents the PVSyst yield validation for the Eskom Research and Innovation Centre (ERIC) solar PV plant. Normalised yield production calculations were performed for a fair comparison of various configurations. Although CIGS technology has a higher specific yield throughout the year, the normalised yield production per m2 shows that mc-Si technology out-performs CIGS in both fixed north facing and east-west tracking configurations. This study provides an insight to identify the optimal configuration and will also give an indication of suitability of PV technology for deployment in the central part of South Africa, once all design parameters are considered. This information is also useful in evaluating the operational benefits of the plant based on the net energy output. The monitored data and operating experience of the reported PV system can be applied for future projects. It is common at the beginning of any project for photovoltaic (PV) simulation tools to be utilized for yield prediction in order to estimate performance that can be expected. The purpose for PVSyst yield validation in this study was to validate the accuracy of the original PVSyst simulation that were performed using the satellite derived data, PVGIS satellite database for the ERIC PV plant. The validation is done using the actual ground measured solar resource datasets on site by importing them into PVSyst. A brief analysis of the results suggests that the PVSyst model seems to overestimate the yield output relative to the measured values. This due to out-door conditions and environmental factors impacting the PV site. These factors include power outages, module degradation and were unknown during the development phases when original simulations were performed. However, based on the statistical criteria and assessment, it can be concluded that the original PVSyst simulation results are accurate enough as per the MBE and RMSE percentages, however it is noted as well that the modified PVSyst results are more correlated to the measured results in comparison.
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- Date Issued: 2019
On the design, evaluation and performance of an energy efficient solar house with integrated photovoltaics
- Authors: Ziuku, Sosten
- Date: 2011-06
- Subjects: Solar energy , Solar energy -- Environmental aspects , Photovoltaic power generation
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10353/27473 , vital:67331
- Description: The design, construction and performance monitoring of an energy efficient house with integrated photovoltaics is considered. Unlike conventional housing, the house design combines energy efficiency measures and renewable energy technologies into one building structure. The objective of the study was to investigate the feasibility of using energy efficient solar designs to regulate indoor thermal environment, and determine thecost effectiveness and environmental benefits of such housing designs. The use of ordinary photovoltaic panels as a building element for South Africa’s latitude and meteorological conditions was also investigated. The house model was designed using Autodesk Revit architecture and Ecotect building simulation software. Electrical performance was analyzed using RETScreen and PVDesignPRO software. In addition to passive solar design features and clerestory windows, the design has solar water heaters for hot water supply. The designed energy efficient building integrated photovoltaic (EEBIPV) house was built at the University of Fort Hare. A 3.8 kW BIPV generator was mounted on the north facing roof in such a way that the solar panels replace conventional roofing material. A data acquisition system that monitors thermal and electrical performance was installed. The grid independent house has been occupied since February 2009 and its winter indoor thermal efficiency improved from 70 to more than 78% after ceiling installation. Models for indoor thermal performance and BIPV energy and exergy contributions were developed. The avoided energy consumption from the grid has potential to reduce carbon emissions by 12.41 tons per annum. The total building cost per m2 of floor area compares favourably with the cost of commercial middle-to-upper income domestic housing units without energy efficiency measures and building integrated photovoltaics. The research output provides a good framework for the integration of passive solar designs, natural ventilation and lighting, solar water heaters and building integrated photovoltaics into new and existing housing units. , Thesis (MSci) -- Faculty of Science and Agriculture, 2011
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- Date Issued: 2011-06
Spatially resolved opto-electric measurements of photovoltaic materials and devices
- Authors: Thantsha, Nicolas Matome
- Date: 2010
- Subjects: Photovoltaic cells , Photovoltaic power systems , Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10520 , http://hdl.handle.net/10948/1123 , Photovoltaic cells , Photovoltaic power systems , Photovoltaic power generation
- Description: The objective of this study is to characterize and analyse defects in solar cell devices. Materials used to fabricate solar cells are not defects free and therefore, there is a need to investigate defects in cells. To investigate this, a topographical technique was developed and employed which uses a non-destructive methodology to analyse solar cells. A system was built which uses a technique based on a laser beam induced current (LBIC). LBIC technique involves focusing light on to a surface of a solar cell device in order to create a photo-generated current that can be measured in the external circuit for analyses. The advantage of this technique is that it allows parameter extraction. Parameters that can be extracted include short-circuit current, carrier lifetime and also the external and internal quantum efficiency of a solar cell. In this thesis, LBIC measurements in the form of picture maps are used to indicate the distribution of the localized beam induced current within solar cells. Areas with low minority carrier lifetime in solar cells are made visible by LBIC mapping. Surface reflection intensity measurements of cells can also be mapped using the LBIC system developed in this study. The system is also capable of mapping photo-generated current of a cell below and above room temperature. This thesis also presents an assessment procedure capable of assessing the device and performance parameters with reference to I-V measurements. The dark and illuminated I-V characteristics of solar cells were investigated. The illuminated I-V characteristics of solar cells were obtained using a defocused laser beam. Dark I-V measurements were performed by applying voltage across the cell in the dark and measuring a current through it. The device parameters which describe the behaviour of I-V characteristic were extracted from the I-V data using Particle Swarm Optimization (PSO) method based on a one-and two-diode solar cell models. Solar cells of different technologies were analysed, namely, single-crystalline (c-Si) and multicrystalline (mc-Si) silicon, Edge-defined Film-fed Growth Si (EFG-Si) and Cu(In,Ga)(Se,S)2 (CIGSS) thin film based cells. The LBIC results illustrated the effect of surface reflection features and material defects in the solar cell investigated. IQE at a wavelength of 660 nm were measured on these cells and the results in general emphasised the importance of correcting optical losses, i.e. reflection loss, when characterizing different types of defects. The agreement between the IQE measurements and I-V characteristics of a cell showed that the differences in crystal grains influence the performance of a mc-Si cell. The temperature-dependence of I-V characteristics of a CIGSS solar cell was investigated. The results showed that, for this material, the photo response is reduced at elevated temperatures. In addition to LBIC using a laser beam, solar spectral radiation was employed to obtained device performance parameters. The results emphasised the effect of grain boundaries as a recombination centres for photo-generated hole-pairs. Lastly, mesa diode characterizations of solar cells were investigated. Mesa diodes are achieved by etching down a solar cell so that the plateau regions are formed. Mesa diodes expose the p-n junction, and therefore mesa diode analysis provides a better way of determining and revealing the fundamental current conduction mechanism at the junction. Mesa diodes avoid possible edge effects. This study showed that mesa diodes can be used to characterize spatial non-uniformities in solar cells. The results obtained in this study indicate that LBIC is a useful tool for defect characterization in solar cells. Also LBIC complements other characterization techniques such as I-V characterization.
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- Date Issued: 2010
Investigation of device and performance parameters of photovoltaic devices
- Authors: Macabebe, Erees Queen Barrido
- Date: 2009
- Subjects: Photovoltaic cells , Solar cells , Photovoltaic power systems , Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10538 , http://hdl.handle.net/10948/1003 , http://hdl.handle.net/10948/d1012890 , Photovoltaic cells , Solar cells , Photovoltaic power systems , Photovoltaic power generation
- Description: In order to investigate the influence of parasitic resistances, saturation current and diode ideality factor on the performance of photovoltaic devices, parameter extraction routines employing the standard iteration (SI) method and the particle swarm optimization (PSO) method were developed to extract the series resistance, shunt resistance, saturation current and ideality factor from the I-V characteristics of solar cells and PV modules. The well-known one- and two-diode models were used to describe the behavior of the I-V curve and the parameters of the models were determined by approximation and iteration techniques. The SI and the PSO extraction programmes were used to assess the suitability of the one- and the two-diode solar cell models in describing the I-V characteristics of mono- and multicrystalline silicon solar cells, CISS- and CIGSS-based solar cells. This exercise revealed that the two-diode model provides more information regarding the different processes involved in solar cell operation. Between the two methods developed, the PSO method is faster, yielded fitted curves with lower standard deviation of residuals and, therefore, was the preferred extraction method. The PSO method was then used to extract the device parameters of CISS-based solar cells with the CISS layer selenized under different selenization process conditions and CIGSS-based solar cells with varying i-ZnO layer thickness. For the CISS-based solar cells, the detrimental effect of parasitic resistances on device performance increased when the temperature and duration of the selenization process was increased. For the CIGSS-based devices, photogeneration improved with increasing i-ZnO layer thickness. At high forward bias, bulk recombination and/or tunneling-assisted recombination were the dominant processes affecting the I-V characteristics of the devices. v Lastly, device and performance parameters of mono-, multicrystalline silicon and CIS modules derived from I-V characteristics obtained under dark and illuminated conditions were analyzed considering the effects of temperature on the performance of the devices. Results showed that the effects of parasitic resistances are greater under illumination and, under outdoor conditions, the values further declined due to increasing temperature. The saturation current and ideality factor also increased under outdoor conditions which suggest increased recombination and, coupled with the adverse effects of parasitic resistances, these factors result in lower FF and lower maximum power point. Analysis performed on crystalline silicon and thin film devices utilized in this study revealed that parameter extraction from I-V characteristics of photovoltaic devices and, in particular, the implementation of PSO in solar cell device parameter extraction developed in this work is a useful characterization technique.
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- Date Issued: 2009
On the evaluation of spectral effects on photovoltaic modules performance parameters and hotspots in solar cells
- Authors: Simon, Michael
- Date: 2009
- Subjects: Photovoltaic cells , Energy dissipation , Electric power production , Photovoltaic power generation , Solar energy , Spectral energy distribution
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11593 , http://hdl.handle.net/10353/257 , Photovoltaic cells , Energy dissipation , Electric power production , Photovoltaic power generation , Solar energy , Spectral energy distribution
- Description: The performance of photovoltaic (PV) modules in terms of their ability to convert incident photon to electrical energy (efficiency) depends mostly on the spectral distribution of incident radiation from the sun. The incident spectrum finally perceived by the module depends strongly on the composition of the medium in which it has traveled. The composition of the earth’s atmosphere, which includes, amongst others, water vapour, gases such as carbon dioxide and oxygen, absorbs or scatters some of the sunlight. The incident solar spectrum is also modified by the diffuse aspect of radiation from the sky which strongly depends on aerosol concentration, cloudiness and local reflection of the earth’s surface. Although it is well known that the changes in outdoor spectrum affect device performance, little work has been conducted to support this theory. This is probably due to lack of spectral data or in certain instances where data is available, little knowledge of interpreting that data. The outdoor spectral data that one obtains in the field does not come clearly for just simple interpretation. Different analytical interpretation procedures have been proposed, all trying to explain and quantify the spectral influence on PV devices. In this study an assessment methodology for evaluating the effects of outdoor spectra on device performance parameters during the course of the day, seasons and or cloudy cover has been developed. The methodology consists of developing a device dependant concept, Weighted Useful Fraction (WUF) using the outdoor measured spectral data. For measuring PV module’s performance parameters, a current-voltage (I-V) tester was developed in order to monitor the performance of six different module technologies. The Gaussian distribution was used to interpret the data. For hot-spot analysis, different techniques were used, which include Infrared thermographic technique for identifying the hot-spots in the solar cells, SEM and EDX techniques. The AES technique was also used in order to identify other elements at hot-spots sites that could not be detected by the EDX technique. iii Results obtained indicate that multicrystalline modules performance is affected by the changes in the outdoor spectrum during summer or winter seasons. The modules prefer a spectrum characterized by WUF = 0.809 during summer season. This spectrum corresponds to AM 2.19 which is different from AM 1.5 used for device ratings. In winter, the mc-Si module’s WUF (0.7125) peaks at 13h00 at a value corresponding to AM 1.83. Although these devices have a wider wavelength range, they respond differently in real outdoor environment. Results for mono – Si module showed that the device performs best at WUF = 0.6457 which corresponds to AM 1.83 during summer season, while it operates optimally under a winter spectrum indicated by WUF of 0.5691 (AM2.58). The seasonal changes resulted in the shift in WUF during day time corresponding to the “preferred” spectrum. This shift indicates that these devices should be rated using AM values that correspond to the WUF values under which the device operates optimally. For poly-Si, it was also observed the WUF values are lower than the other two crystalline-Si counterparts. The pc-Si was observed to prefer a lower AM value indicated by WUF = 0.5813 during winter season while for summer it prefers a spectrum characterized by WUF = 0.5541 at AM 3.36. The performance of the single junction a-Si module degraded by 67 percent after an initial outdoor exposure of 16 kWh/m² while the HIT module did not exhibit the initial degradation regardless of their similarities in material composition. It was established that the WUF before degradation peaks at 15h00 at a value of 0.7130 corresponding to AM 4.50 while the WUF after degradation “prefers” the spectrum (WUF = 0.6578) experienced at 15h30 corresponding to AM value of 5.57. Comparing the before and after degradation scenarios of a-Si:H, it was observed that the device spends less time under the red spectrum which implies that the device “prefers” a full spectrum to operate optimally. The degradation of a-Si:H device revealed that the device spectral response was also shifted by a 7.7 percent after degradation. A higher percentage difference (61.8 percent) for spectral range for the HIT module is observed, but with no effects on device parameters. Seasonal changes (summer/winter) resulted in the outdoor spectrum of CuInSe2 to vary by WUF = 1.5 percent, which resulted in the decrease in Isc. This was ascertained by iv analyzing the percentage change in WUF and evaluating the corresponding change in Isc. The analysis showed that there was a large percentage difference of the module’s Isc as the outdoor spectrum changed during the course of the day. This confirmed that the 17 percent decrease in Isc was due to a WUF of 1.5 percent. In mc-Si solar cells used in this study, it was found that elemental composition across the entire solar cell was not homogenously distributed resulting in high concentration of transition metals which were detected at hot spot areas. The presence of transition metals causes hot-spot formation in crystalline solar cells. Although several transition elements exist at hot-spot regions, the presence of oxygen, carbon, iron and platinum was detected in high concentrations. From this study, it is highly recommended that transition elements and oxygen must be minimized so as to increase the life expectancy of these devices and improve overall systems reliability
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- Date Issued: 2009