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An experimental and computational investigation of a hybrid photovoltaic and solar thermal cell

Appropriate solar spectrum usage : the novel design of a photovoltaic thermal system

  • Authors: Elshik, Ebrahim , Bester, Rudolf , Nel, Andre
  • Date: 2017
  • Subjects: Sustainable buildings , Photovoltaic power systems , Renewable energy sources
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/217739 , uj:21677 , Citation: Elshik, E., Bester, R. & Nel, A. 2017. Appropriate solar spectrum usage : the novel design of a photovoltaic thermal system.
  • Description: Abstract: The path towards zero energy buildings is fraught with many challenges, the onsite renewable energy production to drive consumer appliances that are not low or zero energy is an important challenge. Therefore, developing the energy production such that the production mode is matched to the usage mode is the simplest manner to improve efficiency. As such, energy consumption for lighting could be significantly reduced by optimizing the building`s design to maximize direct daylight usage, similarly cooking using solar stoves, or water heating using solar geysers eliminates the need for PV cells to generate electricity. The most important energy consumption in most buildings is HVAC (accounting for approximately 40% of a building`s energy consumption) which can be addressed with the use of a solar power absorption chiller. This article introduces the design of a novel solar concentrated photovoltaic thermal (CPVT) system that produces electricity and thermal energy simultaneously from the same surface area. The goal of the proposed system is to provide sufficient heat for an absorption cooling system, water heating as well as to produce electricity in a cost effective way. The CPVT system is designed to operate over a wide spectrum (400nm upward contains around 90% of the incident solar radiation spectrum). In the proposed system, solar irradiation is highly concentrated (to the equivalent intensity of approximately 100 suns) onto a single point, using a dual axis sun tracking concentrator with a Fresnel lens. A filter then separates the infrared (IR) from the visible light (VL) components using an imaging lens (viz. a hot mirror which has approximately a 98% filter efficiency). The IR is then utilized for heating while the VL components power the PV cell. The efficiency of the electricity generation in the PV cell improves when the IR component is removed from the incident solar irradiance. High-temperature high pressure water, at approximately 95-120oC (203–248oF), is generated by the IR and serves as a heat source for the absorption cooling system (lithium bromide water / ammonia-water). The proposed system is expected to deliver electricity at the rate of 0.08 W/cm2 (0.2032 W/in2) of PV cell area, and around 0.04W/cm2 (0.1.016 W/in2) collector area. Given that the ratio of collector area to PV cell area is ±9:1 this allows us to design the relative size to suit the building requirements.
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Comparative study of different photovoltaic MPPT techniques under various weather conditions

  • Authors: Farayola, Adedayo Mojeed
  • Date: 2017
  • Subjects: Photovoltaic power systems , Photovoltaic power generation
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/262879 , uj:27785
  • Description: M.Ing. (Electrical Engineering) , Abstract: Photovoltaic (PV) energy has become the most growing renewable energy source that serves as an alternative to fossil energy as it is considered cheap, less polluted, etc. Photovoltaic system works under both uniform irradiance and partial shaded weather conditions and exhibits both local peak power and global peak power during partial shaded conditions. Maximum power point tracking (MPPT) techniques are being used in PV systems to track the local power peak. However, MPPT systems may fail to track the global peak power. Online MPPT techniques such as Perturb&Observe (P&O) and incremental conductance (IC) are considered economical and easy to implement. However, these online methods underachieve due to some flaws such as oscillating power near maximum power point (MPP) and poor response owing to the sudden change in irradiance with P&O and IC. MPPT techniques are algorithms used in photovoltaic (PV) system to extract maximum power from the PV panel. Offline techniques such as the curve fitting polynomial (CFP) technique use prediction and fitting method in order to track the MPP. However, lower order CFP does not extract maximum power from the panel due to inaccurate fitting of the real P-V curve. The use of supervised machine learning techniques which include artificial neural network (ANN) and artificial neuro-fuzzy inference system (ANFIS) have improved the maximum power point tracking (MPPT) process which increased the PV systems efficiency. This first contribution of this dissertation presents a reconfiguration approach that uses series-connected distributive MPPT (DMPPT). DMPPT is used to track the global peak in order to extract maximum power from the PV array system under uniform irradiance and partial shaded weather conditions. The second contribution is the implementation of improved models of online Perturb&Observe and modified incremental conductance MPPT techniques that work well under sudden change in irradiance, temperature, and with minimal oscillating power near MPP. The third contribution is the state of the art of the sixth-order curve fitting polynomial MPPT technique that can extract maximum power from a PV panel under varied weather conditions. The fourth contribution is to introduce the use of SVM classifier for optimization and MPPT purpose in a PV system...
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Computer aided design of systems for solar powered water pumping by photovoltaics

  • Authors: Lujara, Nelson Kakuru
  • Date: 2012-08-23
  • Subjects: Photovoltaic power systems , Photovoltaic power generation , Solar energy , Computer-aided design
  • Type: Thesis
  • Identifier: uj:3116 , http://hdl.handle.net/10210/6537
  • Description: D.Ing. , Low system efficiency is a critical problem in photovoltaic (PV) applications due to low efficiency of solar cells. Despite this shortcoming, stand-alone PV systems, have proven to be economical and reliable choices in some applications such as telecommunications, vaccine refrigeration and water pumping in remote locations. In this study, CAD algorithms for the design of PV water pumping systems have been developed with the objective of maximizing the conversion efficiency from the solar irradiation to the potential energy of water by taking into account the variations in the pumping head. The study starts by developing loss models of various sub-systems in the photovoltaic dc and ac motor drive water pumping systems. Using MathCad, these models are then used in the simulation of the system. The simulation results are verified experimentally using their equivalent circuit configurations. The efficiency of the array, the pump and the motor are found to be the most critical parameters for the performance of the systems. The efficiencies of other components, such as the inverter, have also been shown to have a significant effect. The study has shown that for operation at the maximum power point, the inclusion of a maximum power tracker is necessary in a dc motor drive system but may be eliminated in PWM inverter-fed induction motor drive systems through proper matching of the system components. The study has further shown that matching of the drive system and the load with the insolation is essential, since maximum system efficiency occurs at a specific head, which varies as the insolation changes. Prior investigation of site insolation variations is therefore a critical requirement.
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Design framework for the development of an efficient heat recovery system in Photovoltaic Modules for the suitability of low-medium temperature applications

  • Authors: Maditsi, Koketso
  • Date: 2019
  • Subjects: Photovoltaic power systems , Heat recovery
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/444961 , uj:38910
  • Description: Abstract: Energy regeneration through heat recovery is practically possible for maximizing energy obtained from the sun, by recovering and reusing the heat that is typically lost within energy dependent electrical equipment. Solar thermal systems utilize flat plates or evacuated tube collectors which absorb the heat from the sun. Similarly, Photovoltaic (PV) systems absorb solar irradiation to generate electricity. A combination of both technologies results in Solar Photovoltaic/Thermal (PV/T) systems wherein thermal plates or liquid contained tubes cool PV collectors resulting in increased efficiency. Solar Photovoltaic/Thermal Optimised (PV/TO) is simply a PV/T module with an improved thermal output designed and investigated in this research study. The PV cooling mechanism is important because excessive heat in PV panels generates high resistance, which impedes the performance of the solar cell and in the process, results in lower efficiency. PV/T systems are also known to produce low thermal output which makes them unsuitable for applications already serviced by market-ready solar thermal systems. The study is aimed at developing an efficient and cost effective heat recovery system which has been designed specifically to improve the thermal output without compromising the electrical output of the PV/T module. To achieve this, a survey was conducted to understand the PV/T technology market share compared to other solar technologies. Furthermore, a prototype was developed to investigate the effect of Peltier cooling method on PV cells. Two models (PV/T and PV/TO) were developed using Autodesk Inventor Professional and simulated using Autodesk CFD Simulation. The results from the simulations were then used with support from the mathematical models developed to determine the economic performance study of the two models. The survey results showed that only 11% of the respondents are actively participating in PV/T related matters. The experimental results showed that Peltier cooling improves performance by 1.1% higher than conventional cooling methods. The results from economic performance study showed that PV/TO model can archive over 100% solar fraction for the DHW demand of 800 litres/day using only 4 panels whereas PV/T model for the same demand and panel size archives just under 80% of the solar fraction using 9 panels. The overall results showed that PV/TO model optimise thermal output by over 150% and can compete with market-matured solar thermal technologies. , M.Tech. (Mechanical Engineering)
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Designing photovoltaic based energy systems using data acquisition and cloud computing

  • Authors: Mabunda, N.E.
  • Date: 2017
  • Subjects: Cloud computing , Automatic data collection systems , Photovoltaic power systems
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/285938 , uj:30931
  • Description: D.Phil. (Electrical and Electronic Engineering) , Abstract: Population growth and technology advancements are amongst many factors that have led to the increasing electrical energy capacity demands. Several economic, security and environmental factors form obstacles to the expansion of electrical energy supply. Adding to damage caused to the earth’s ozone layer, the majority of electrical energy infrastructures require long transmission lines for the transmission of power to their respective destinations. There is a recent security concern of copper cable theft. Well-designed standalone PV system can contribute to solving the above-mentioned challenges. The design of PV systems is complex due to variations of its main source, i.e. the sun’s solar irradiance. Various organizations made efforts to assist designers with meteorological data, however they failed to cover every corner of this planet and some of the data is sold at expensive rates. This research’s main objective is to simplify the design of PV systems by using Data Acquisition System (DAS) and cloud computing. Two DAS based tools were designed to aid with collection of solar site analysis and load analysis data. The first of the two DAS based tools collects solar energy power samples by employing four small 1 W, 5 V panels, each elevated by 20 degrees. These solar panels are oriented to point to the four primary compass directions, i.e. North, East, West and South. Four panels enable the capturing of solar energy from all directions whilst identifying the directions, which are producing the highest energy during specific time intervals. The DAS acquired solar energy is saved during every 1 % (10 W/m2) change and this occurs once in every three minutes. This DAS acquired data is later transferred to the cloud for storage and sharing. The second DAS based tool is used to collect load analysis data. This device has a built-in current transformer that detects the current that is drawn by the connected load and step down transformer to detect corresponding voltage changes. Power factor is ignored because this research interest lies within the domestic environment. Energy is calculated every one second and saved as a cumulative sum of 25 Wh increments. The algorithms within the two data collection tools, only add new entries to the records whenever there is a significant change of values, as a result, the number of saved data records is optimized, and ultimately this minimizes cloud storage requirements. Both DAS tools employ the National Instruments (NI) myRIO data acquisition (DAQ) cards to collect and process incoming voltage signals. The DAQ card's...
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Investigating the integration of power line communications and low-voltage solar photovoltaic systems

  • Authors: Ndjiongue, Alain Richard
  • Date: 2013-12-09
  • Subjects: Building-integrated photovoltaic systems , Photovoltaic power systems , Direct energy conversion
  • Type: Thesis
  • Identifier: uj:7866 , http://hdl.handle.net/10210/8759
  • Description: M.Ing. (Electrical Engineering Science) , One of the challenges of modern technology is remote control in real-time. Wireless technologies are used to control solar systems connected or not connected to the grid. Nevertheless wireless communications present some defects when they are facing basements of buildings and thick walls. To overcome that weakness, wire technologies seem to be the solution. The use of power line communications (PLC) technology presents a financial advantage, given the fact that PLC uses power wire to transmit data. PLC did an interesting leap forward in the last few years, and this drives researchers to carry out research in that field of Electrical Engineering. The advantages offered by PLC cannot be over-emphasized, but neither should the inherent problems affecting its commercial take-off be underestimated. This work creates a background study for experimental measurement and eventual implementations on PLC. A 2FSK modulation was implemented at CENELEC B standards, and the carrier signal was sent through a low wattage solar microinverter. The inverter was built in compliance with the IEEE 1547 standard. Two different coupling circuits were also built as well as the transceiver. The entire system was fed by a 250 W- 18 V monocrystalline solar panel. This investigation presents many options to integrate a communication system in a solar system. The case study has shown that a message sent through an H-bridge inverter is related to many parameters such as the modulation scheme, the coding techniques, the type of control and the DC link voltage. The result presents a very weak probability, which implies that the other options should be investigated.
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Light filtered concentrated photovoltaic thermal system

  • Authors: Elshik, Ebrahim A. M. , Bester, Christiaan Rudolf , Nel, André Leon
  • Date: 2017
  • Subjects: Photovoltaic power systems , Solar heating , Light filtration
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/217746 , uj:21678 , Citation: Elshik, E.A.M., Elshik, E.R. & Nel, A.L. 2017. Light filtered concentrated photovoltaic thermal system.
  • Description: Abstract: PV cells generate electricity, but the electrical output is only one component of the total energy produced by a photovoltaic array. A typical PV module has an ideal conversion efficiency of around ±15%, with the remaining energy generated as heat. This heat can raise the temperature by as much as 50°C above ambient temperature, resulting in two concerns: possible structural damage; and PV cell efficiency decreases as temperature increases. Crystalline cells are affected by temperature and their performance drops as cell temperature rises. In the case of combined photovoltaic thermal cells it has been shown that for each 1°C increase in temperature, the power output drops by approximately 0.5% which results in limiting the harvested energy This article aims to introduce the concept of a concentrated Photovoltaic thermal system using an optical filtering technique. To this end concentrated sunlight is filtered into its major components and then utilised in a more appropriate way. The visible light is directed onto a standard PV surface while infrared is filtered before striking the PV surface and directed to a water column for heating purposes.
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Photovoltaic system maximum power point tracking under partial shaded weather conditions using machine learning algorithms

  • Authors: Nkambule, Mpho Sam
  • Date: 2019
  • Subjects: Photovoltaic cells , Photovoltaic power systems , Artificial intelligence , Machine learning
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/418317 , uj:35462
  • Description: Abstract: The rapid growth of demand of electrical energy and depletion of fossil opened door for renewable energy. The expeditious broadening of Photovoltaic (PV) energy has attracted the private and government precinct world-wide, due to the reduction of costs and being cleaner source of energy. However, most of the maximum power point tracking (MPPT) controllers are inefficient under rapidly changing environmental conditions. In addition, under partial shading conditions (PSC) MPPT controllers fail to track global maximum power point (GMPP). Therefore, it is essential to propose an MPPT controller that will be able to locate GMPP using historical weather data. The work is undertaken to investigate the feasibility of using machine learning (ML) based MPPT techniques to harness maximum power on a PV system under PSC. If successful, the ML based MPPT algorithms could lead to a reduction in power losses in a PV system. In this dissertation, certain contributions to the field of PV systems and ML based were made by introducing two online and eleven artificial intelligence (AI) MPPT techniques, by presenting four experiments under different weather conditions. The first contribution is concerned with an MPPT system that harvests maximum power under PSC, using Johannesburg real-time weather data. The system consists of an MPPT controller cascaded with a PID controller, to reduce errors of the MPPT algorithms, to improve the system’s performance. First, the system evaluates and compares the online [Perturb & Observe (P&O) and Incremental Conductance (INC)], to determine the most powerful MPPT algorithm. Secondly, the system validates the performance of the eleven AI MPPT methods [Fuzzy Logic Control (FLC) and Recurrent Neural Network (RNN), Support Vector Machines (SVM), the Weighted K-nearest neighbour (WK-NN), a Gaussian process regression (GPR), Decision Tree (DT), Multivariate linear regression (MLR), Linear discriminant analysis (LDA), Naïve Bayes classifier (NBC), Bagged Tree (BT) and Boosted Tree (BoT)] under PSC. The ML based techniques are evaluated using four types of error [root mean squared error (RMSE), mean absolute error (MAE), Mean squared error (MSE) and R-squared (𝑅2)]. For the first experiment, online methods are empirically compared in the form of four case studies conducted under various weather conditions. The results showed that INC performed significantly better than P&O under PSC. INC overperformed P&O in all case studies in terms of power extraction. Nevertheless, P&O has less settling time around maximum power point... , M.Phil. (Electrical and Electronic Engineering)
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The impact of inverter side PV plant on HVDC commutation failures

  • Authors: Simelane, Nondumiso Patricia
  • Date: 2020
  • Subjects: Photovoltaic power systems , Electric power distribution , Electric current converters , Building-integrated photovoltaic systems
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/413211 , uj:34803
  • Description: M.Phil. (Electrical Engineering in Power and Energy Systems) , Abstract: The high-voltage direct current (HVDC) system is a crucial technology in transmission; however, this system suffers from commutation failure. Commutation failure is defined as an adverse dynamic event that occurs when a converter valve that is supposed to turn off continues to conduct without transferring its current to the next valve in the firing sequence. Commutation failure disturbs the power transfer, yields a large overcurrent in the converter, and causes a voltage drop in an alternating current (AC) network. Although commutation failure in HVDC systems has been studied using many other compensating devices, academic researchers have not given enough attention to evaluating the impact of distributed generation (DG) on the power system. Within this gap and based on the publications researched, no published material could be found regarding the impact of a photovoltaic (PV) plant on HVDC commutation failures. This research project seeks to focus on the impact of an inverter side PV plant on HVDC commutation failures. In this dissertation, the objective is to evaluate the impact of the inverter side PV plant on HVDC commutation failures. The case studies are done by considering the commutation failure severity, the magnitudes of the remaining voltages after different types of faults occurring, and the recovery time required to clear a fault. Case studies are performed in a network with a PV plant and also without a PV plant. The network was set up in Power System Computer-Aided Design (PSCAD) software to find the critical voltages. Further simulations were done in this study using Power System Simulator for Engineering (PSS/E) software. A network by Conférence Internationale des grandes réseaux...
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