Yes / Solar energy, amongst all renewable energies, has attracted inexhaustible attention all over the world as a supplier of sustainable energy. The energy requirement of major seawater desalination processes such as multistage flash (MSF), multi-effect distillation (MED) and reverse osmosis (RO) are fulfilled by burning fossil fuels, which impact the environment significantly due to the emission of greenhouse gases. The integration of solar energy systems into seawater desalination processes is an attractive and alternative solution to fossil fuels. This study aims to (i) assess the progress of solar energy systems including concentrated solar power (CSP) and photovoltaic (PV) to power both thermal and membrane seawater desalination processes including MSF, MED, and RO and (ii) evaluate the economic considerations and associated challenges with recommendations for further improvements. Thus, several studies on a different combination of seawater desalination processes of solar energy systems are reviewed and analysed concerning specific energy consumption and freshwater production cost. It is observed that although solar energy systems have the potential of reducing carbon footprint significantly, the cost of water production still favours the use of fossil fuels. Further research and development on solar energy systems are required to make their use in desalination economically viable. Alternatively, the carbon tax on the use of fossil fuels may persuade desalination industries to adopt renewable energy such as solar.

As a clean, abundant, and renewable source of energy with a strategic location in close proximity to global population regions, ocean wave energy shows major promise. Although much wave energy converter development has focused on large-scale power generation, there is also increasing interest in small-scale applications for powering the blue economy. In this thesis, the objective was to optimize the performance of small-sized, portable, oscillating-body wave energy converters (WECs). Two types of oscillating body WECs were studied: bottom hinged and two-body attenuator. For the bottom-hinged device, the goal was to show the feasibility of an oscillating surge WEC and desalination system using numerical modeling to estimate the system performance. For a 5-day test period, the model estimated 517 L of freshwater production with 711 ppm concentration and showed effective brine discharge, agreeing well with preliminary experimental results. The objective for the two-body attenuator was to develop a method of power maximization through resonance tuning and numerical simulation. Three different geometries of body cross sections were used for the study with four different drag coefficients for each geometry. Power generation was maximized by adjusting body dimensions to match the natural frequency with the wave frequency. Based on the time domain simulation results, there was not a significant difference in power between the geometries when variation in drag was not considered, but the elliptical geometry had the highest power when using approximate drag coefficients. Using the two degree-of-freedom (2DOF) model with approximate drag coefficients, the elliptical cross section had a max power of 27.1 W and 7.36% capture width ratio (CWR) for regular waves and a max power of 8.32 W and 2.26% CWR for irregular waves. Using the three degree-of-freedom (3DOF) model with approximate drag coefficients, the elliptical cross section had a max power of 22.5 W and 6.12% CWR for regular waves and 6.18 W and 1.68% CWR for irregular waves. A mooring stiffness study was performed with the 3DOF model, showing that mooring stiffness can be increased to increase relative motion and therefore increase power. / Master of Science / As a clean, abundant, and renewable source of energy with a strategic location in close proximity to global population centers, ocean wave energy shows major promise. Although much wave energy converter development has focused on large-scale power generation, there is also increasing interest in small-scale applications for powering the blue economy. There are many situations where large-scale wave energy converter (WEC) devices are not necessary or practical, but easily-portable, small-sized WECs are suitable, including navigation signs, illumination, sensors, survival kits, electronics charging, and portable desalination. In this thesis, the objective was to optimize the performance of small-sized, oscillating body wave energy converters. Oscillating body WECs function by converting a device's wave-driven oscillating motion into useful power. Two types of oscillating body WECs were studied: bottom hinged and two-body attenuator. For the bottom-hinged device, the goal was to show the feasibility of a WEC and desalination system using numerical modeling to estimate the system performance. Based on the model results, the system will produce desirable amounts of fresh water with suitably low concentration and be effective at discharging brine. The objective for the two-body attenuator was to develop a method of power maximization through resonance tuning and numerical simulation. Based on the two- and three-degree-of-freedom model results with approximate drag coefficients, the elliptical cross section had the largest power absorption out of three different geometries of body cross sections. A mooring stiffness study with the three-degree-of-freedom model showed that mooring stiffness can be increased to increase power absorption.

Desalination is one of the proposed methods to meet the ever increasing water demands. It can be subdivided into two broad categories, thermal based desalination and electricity based desalination. Multi-effect Distillation (MED), Multi-Stage Flashing (MSF), Membrane Distillation (MD) fall under former and Reverse Osmosis (RO), Electro-Dialysis (ED) fall under later. MD offers an attractive solution for seawater as well as brackish water distillation. It shows highly pure yields, theoretically 100% pure. The overall construction of a MD unit is way simpler than any other desalination systems. MD is a thermally driven diffusion process where desalination takes places in the form of water vapor transport across the membrane. It has low second law efficiency due to parasitic heat losses. The objective of the first part of the investigation is to thoroughly analyze a Direct Contact Membrane Distillation (DCMD) system from the view point of yield and exergy. The insights from exergy analysis are used in a design study, which is used for performance optimization. The first part concludes with a design procedure and design windows for large scale DCMD construction. In the second part of the investigation, focus is moved to waveguide solar energy collector. The idea behind an ideal waveguide is to reduce the complexity of modeling solar energy collection. The mathematical model provided in this analysis can be extended to a family of non-imaging optics in solar energy and serves as a benchmarking analysis tool. A waveguide is suitable for low temperature operations due to limitations on maximum continuous temperature of operation. Thus, it becomes an ideal solution for DCMD applications. A levelized cost analysis is presented for a waveguide powered DCMD plant of a 30,000 capacity. A combination of waveguide and DCMD shows levelized cost of water at $1.80/m³, which is found to be lower than previously reported solar desalination water costs. / Master of Science

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: South Africa has historically been reliant on inexpensive surface and groundwater resources; however, as pressure on these resources continues to grow, seawater desalination has begun to emerge as a potential future supply source. One of the towns earmarked as a candidate for large-scale seawater desalination is Cape Town. In order to maximise the benefits and minimise the costs of such a scheme, the desalination plant needs to be considered as an integral part of the current system. Integrated planning has been lacking at the existing seawater desalination plants in South Africa, most of which were constructed as emergency schemes and are financially cumbersome for the municipalities to operate and manage. Recent research related to inter-basin water transfer schemes has shown that a comprehensive approach is required in assessing water supply from a new scheme in which the system as a whole is modelled stochastically and the estimated water transfer extracted. This comprehensive approach was the foundation of the modelling undertaken in this research. Existing models of the Western Cape system were adapted to include a seawater desalination plant, and short-term and long-term analyses were completed for a variety of possible desalination plant operating scenarios and capacities. The increase in system yield and the annual supply from the desalination plant were determined. First-order capital and operating costs were estimated, and these costs were combined with the annual supply values to calculate and compare unit reference values. The maximum increase in yield was found to occur when the seawater desalination plant is used as a base supply, operational all the time. There was little benefit, in terms of system yield, in using the desalination plant as an emergency supply source only. Unit reference values for the desalination plant decrease as the percentage supply from the desalination plant increases, meaning that the lowest possible cost per cubic metre of water supplied is when the desalination plant is used as a base supply. It was also apparent that the unit reference values decrease with an increase in desalination plant capacity, suggesting that, from an economic perspective, the optimal solution would be to have one large desalination plant operational immediately. The lower the reservoir trigger level at which the desalination plant becomes active, the larger the stochastic variation in the supply from the desalination plant and hence the larger the variation in the costs. Hence, using stochastic modelling to calculate unit reference values is particularly important for integrating a desalination plant into an existing conventional supply system when used as a peak or emergency supply source. / AFRIKAANSE OPSOMMING: Suid-Afrika maak histories staat op goedkoop oppervlak- en grondwaterhulpbronne. Namate druk op hierdie hulpbronne aanhou toeneem, begin seewaterontsouting egter as ’n moontlike toekomstige waterbron na vore tree. Een van die stede wat as ’n kandidaat vir grootskaalse ontsouting geïdentifiseer is, is Kaapstad. Vir die meeste moontlike voordele teen die laagste moontlike koste, moet so ’n ontsoutingsaanleg as ’n integrale deel van die huidige stelsel beskou word. Geïntegreerde beplanning het tot dusver tekortgeskiet by bestaande ontsoutingsaanlegte in Suid-Afrika, wat merendeels as noodskemas opgerig is en waarvan die bedryf en bestuur ’n finansiële las op munisipaliteite plaas. Onlangse navorsing oor skemas vir tussenbekkenwateroordrag toon dat ’n omvattende benadering vereis word om watervoorsiening uit ’n nuwe skema te beoordeel. Volgens so ’n benadering word die stelsel in die geheel stogasties gemodelleer en die geraamde wateroordrag onttrek. Dié omvattende benadering was dan ook die grondslag vir die modellering wat in hierdie navorsing onderneem is. Bestaande modelle van die Wes-Kaapse stelsel is aangepas om ’n ontsoutingsaanleg in te sluit, en kort- en langtermynontledings is vir verskeie moontlike ontsoutingsaanlegvermoëns en -bedryfscenario’s voltooi. Die toename in stelselopbrengs en die jaarlikse watervoorsiening uit die ontsoutingsaanleg is bepaal. Kapitaal- en bedryfskoste van die eerste orde is geraam, welke koste toe met die jaarlikse voorsieningswaardes gekombineer is om eenheidsverwysingswaardes te bereken en te vergelyk. Die maksimum toename in opbrengs blyk te wees wanneer die ontsoutingsaanleg as ’n basisbron dien wat te alle tye in werking is. Wat stelselopbrengs betref, was daar weinig voordeel in die gebruik van die aanleg as ’n noodwaterbron. Eenheidsverwysingswaardes vir die ontsoutingsaanleg neem af namate die persentasie voorsiening uit die aanleg toeneem, wat beteken dat die laagste moontlike koste per kubieke meter water verkry word wanneer die ontsoutingsaanleg as ’n deurlopende basisbron dien. Dit was ook duidelik dat die eenheidsverwysingswaardes afneem met ’n toename in aanlegvermoë, wat te kenne gee dat die optimale oplossing uit ’n ekonomiese oogpunt sou wees om onmiddellik een groot ontsoutingsaanleg in bedryf te stel. Hoe laer die opgaardamvlak waarop die ontsoutingsaanleg in werking tree, hoe groter die stogastiese variasie in watervoorsiening uit die aanleg, en hoe groter die variasie in koste. Daarom is die gebruik van stogastiese modellering om eenheidsverwysingswaardes te bereken veral belangrik vir ’n ontsoutingsaanleg wat as ’n spits- of noodwaterbron dien.

Water shortage issues have been growing concerns in many cities around the world in recent years, especially in Eastern cities of Australia, which is the driest continent on the earth. The aim of this PhD thesis is a development of a model to study the use of waste incineration energy supplemented by alternative energy to power seawater desalination. It is to aid the freshwater supply of a drought stricken city in Eastern Australia. My work contributes to a development of efficient model in a simpler understandable way to reduce efforts required for modelling complex multi domain problems. This research is motivated by the successive severe drought conditions that affected many Australian cities in the past few years, compounded with an additional strain from a fast growing population. While we dump our waste into the Australian landscape, in more densely populated cities in Europe and Asia, the waste is incinerated to obtain thermal energy for various purposes. The waste is used as an energy source while at the same time reducing the amount of space needed for landfill. Seawater desalination has been uccessfully practiced for quite some time particularly in the Middle Eastern countries. To deal with increasing water shortage crisis, many cities around the world have opted or are considering seawater desalination to supplement their freshwater supply. The combination of both - waste incineration and seawater desalination - has rarely been studied. This is a twofold problem that requires modelling the problem of water demand and supply together with waste incineration to find a sustainable solution. This is a complex task. The effort needed for this can be reduced by using a modelling approach that is more efficient than the traditionally used statistical approaches. In this thesis, I present a comprehensive model developed using a dynamic system approach combined with artificial neural networks. It simulates water demand and supply as well as the possible amount of the desalinated water that can be produced using the energy from clean city waste incineration. This is done while taking in various influential factors including population growth and irregular weather patterns. This research comprises a literature review on seawater desalination and waste incineration, the establishment of water demand and supply dynamics of Gold Coast City as my case study and identifying any modelling difficulties that need to be overcome. This is followed by the development of a comprehensive model and its components, model calibration and simulation experiments. It was found that with the energy of waste incineration, up to 60% of the freshwater demand could be fulfilled by seawater desalination in a sustainable way.

Les petites unités de dessalement au point d’usage sont une alternative pour l’accès à l'eau potable des communautés isolées de zones côtières ou insulaires. Dans cette thèse, la distillation membranaire (MD) est le procédé de choix pour l’application visée. De plus, les lieux d’implantation ciblés souffrent souvent d’un manque d’accès à l’énergie, mais la plupart d’entre eux sont exposés à des niveaux élevés de radiation solaire. Afin de réduire les pertes de chaleur du système et d'intensifier le procédé, un module intégrant des membranes planes de MD sous vide (VMD) et un collecteur solaire à plaque plane (FPC) apparaît comme une technologie possible. Cette étude a pour objectifs d’étudier la faisabilité de ce concept et de déterminer les paramètres de l’équipement et les conditions opératoires les plus favorables pour l’application visée en cherchant à réduire la consommation d’électricité (par des panneaux photovoltaïques PV) et améliorer simultanément l’efficacité énergétique et la production d’eau dans l’ensemble du module VMD-FPC. Les analyses de sensibilité et les optimisations multi-objectifs sont effectuées à partir de séries de simulations. La productivité quotidienne peut atteindre 96 L pour une surface de module de 3 m2. Un coût énergétique quasi-constant d’une puissance PV de 4,2 à 5,0 W L-1 est observé, permettant d’ajuster la capacité du système. Pour une puissance PV limitée à 130 W (installation mobile), plus de 30 L de distillat peuvent être obtenus avec une surface de 0,83 m2 par une belle journée d'été à Toulouse, en tenant compte des paramètres de fonctionnement optimisés et des matériaux réels. / Small-scale desalination at the point of use offers a potential access to drinking water to communities living in remote coastal areas or isolated islands. In this dissertation, Membrane Distillation (MD) is the applied technology for the aforementioned application scenario. Moreover, the target places are also often in the lack of stable and centralized heat and power supply, while most of them benefit from high solar radiations. In order to further reduce the system heat loss and to intensify the process, the integration in the same module of flat-sheet distillation membranes for Vacuum MD (VMD) and direct solar heating by flat-plate collector (FPC) appears as a possible option. This study aims to explore the feasibility of this concept and to determine the more favorable design and operating conditions for the target application. The main task in this regard is to reduce electricity consumption (provided by photovoltaic PV panels) and simultaneously improve the energy efficiency and water production throughout the VMD-FPC module. The sensitivity analyses and multi-objective optimizations are conducted based on series of simulations. Results show that the potential daily productivity of the system can reach up to 96 L for a module surface area of 3 m2. A quasi-constant power cost of PV of 4.2 - 5.0 W L-1 is observed, permitting a flexible adjustment of the system capacity. Under a limitation of an average PV power of 130 W, more than 30 L of distillate can be obtained with a surface area of 0.83 m2 on a sunny summer-day in Toulouse, taking the optimized operating parameters and real-world material properties into account.

Der Gegenstand dieser Arbeit ist eine neue Optimierungsmethode zur Minimierung der Produktkosten von Kraftwerksprozessen ohne und mit nachgeschalteten Anwendungen. Diese Methode, die Planern und Projektanten als Werkzeug zur Auslegung von Kraftwerken dienen soll, wird erläutert und exemplarisch zur Optimierung eines ausgewählten Gas- und Dampfturbinenkraftwerkes verwendet. Im Rahmen der Untersuchungen werden dabei zwei Varianten betrachtet: Der Kraftwerksentwurf/-betrieb ohne und mit Auskopplung von Energie- und Stoffströmen. Beim Kraftwerksentwurf/-betrieb mit Auskopplung von Energie- und Stoffströmen wird das Gas- und Dampfturbinenkraftwerk mit einer nachgeschalteten hybriden Meerwasserentsalzungsanlage verknüpft. Zur Identifizierung der jeweils zu optimierenden Komponenten/Parameter werden bei der neuen Methode Elemente der thermo- bzw. exergoökonomischen Analyse und der Sensitivitäts- und Trendlinienanalysen verwendet. Die Optimierung selbst folgt dem Koordinatenverfahren nach Gauß und Seidel. Anhand der Optimierungsergebnisse und der Kriterien ’Auswahl/Beitrag der Komponenten/Parameter’ sowie ’Rechenumfang’ wird die neue Optimierungsmethode mit bekannten thermo- bzw. exergoökonomischen Optimierungsmethoden (Quadranten-/Matrix-Methode, thermo-/exergoökonomische Kennzahlen-Methode) verglichen und bewertet. Zur Ergebnisdiskussion werden Parameterstudien erstellt. Abschließend werden Empfehlungen zur Gestaltung des untersuchten Gas- und Dampfturbinenkraftwerkes gegeben und Ansätze für weiterführende Forschungsarbeiten in der Kraftwerkstechnik abgeleitet.

Der Gegenstand dieser Arbeit ist eine neue Optimierungsmethode zur Minimierung der Produktkosten von Kraftwerksprozessen ohne und mit nachgeschalteten Anwendungen. Diese Methode, die Planern und Projektanten als Werkzeug zur Auslegung von Kraftwerken dienen soll, wird erläutert und exemplarisch zur Optimierung eines ausgewählten Gas- und Dampfturbinenkraftwerkes verwendet. Im Rahmen der Untersuchungen werden dabei zwei Varianten betrachtet: Der Kraftwerksentwurf/-betrieb ohne und mit Auskopplung von Energie- und Stoffströmen. Beim Kraftwerksentwurf/-betrieb mit Auskopplung von Energie- und Stoffströmen wird das Gas- und Dampfturbinenkraftwerk mit einer nachgeschalteten hybriden Meerwasserentsalzungsanlage verknüpft. Zur Identifizierung der jeweils zu optimierenden Komponenten/Parameter werden bei der neuen Methode Elemente der thermo- bzw. exergoökonomischen Analyse und der Sensitivitäts- und Trendlinienanalysen verwendet. Die Optimierung selbst folgt dem Koordinatenverfahren nach Gauß und Seidel. Anhand der Optimierungsergebnisse und der Kriterien ’Auswahl/Beitrag der Komponenten/Parameter’ sowie ’Rechenumfang’ wird die neue Optimierungsmethode mit bekannten thermo- bzw. exergoökonomischen Optimierungsmethoden (Quadranten-/Matrix-Methode, thermo-/exergoökonomische Kennzahlen-Methode) verglichen und bewertet. Zur Ergebnisdiskussion werden Parameterstudien erstellt. Abschließend werden Empfehlungen zur Gestaltung des untersuchten Gas- und Dampfturbinenkraftwerkes gegeben und Ansätze für weiterführende Forschungsarbeiten in der Kraftwerkstechnik abgeleitet.

This thesis project investigates, analyzes, designs, simulates, constructs and tests a dual-axis solar tracker system to track the sun and concentrates the heat of the sunlight, using a Fresnel lens, into a small area, which is above of an evaporator, to increase the temperature of the seawater to convert it into freshwater. The dual-axis solar tracker was designed with the main objectives that the structure was portable, dismountable, lightweight, low cost, corrosion resistant, wires inside pipes, accurate, small size, follow the sun automatically, off-grid (electrical), use green energy (solar powered), and has an empty area right below of the lens. First, a 500 mm diameter flat Fresnel lens was selected and simulated based on an algorithmic method achieved by a previous PhD student at UNT using MATLAB®, to give the optimization lens dimensions. The lens profile was drawn with AutoCAD®, then output profile lens was simulated in COMSOL Multiphysics®. The objective was to provide the high efficiency, optimum and high precision of the focal rays and heat to the receiver of the evaporator. A novel dual-axis solar tracker system was then designed that is portable, dismountable, lightweight and corrosion resistant. The solar tracker tracks the sun in two axis of rotation automatically during the day time, maximizing the angles of inclination on each axis. After testing computer simulations, the dual-axis solar tracker system was constructed and tested. Last, a detailed cost analysis was performed of the entire project. The outcome of this work can be applied for desalination seawater purposes or other any Fresnel lens application that require a focal high temperature directed by dual-axis solar tracker system.