Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Technology: Electrical Engineering (Energy) in the Department of Electrical, Electronic and Computer Engineering at the Cape Peninsula University of Technology, South Africa. / In photovoltaic power systems, the DC/AC conversion efficiency depends on weather conditions causing PV inverters to operate under fluctuating input power from PV modules. The peak efficiency stated by the inverter manufacturers are often used by project designers to estimate how much power PV plants can produce. However, the varying nature of the DC input power to the inverters, occasioned by varying irradiation and temperature, leads to deviations of the actual efficiency from the peak efficiency. Literature surveys prove that inverter efficiencies must be evaluated against local irradiation profiles to get more precise annual energy yield estimations, since meteorological conditions and solar irradiation profiles vary from one site to another around the planet.

Honors Project--Smith College, Northampton, Mass., 2009. / Includes bibliographical references (p. 49-50).

Thesis (M.S.)--Humboldt State University, 2009. / Includes bibliographical references (leaves 163-167). Also available via Humboldt Digital Scholar.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis investigates methods to extract the maximum amount of electrical energy from a py panel. The thesis is divided into four parts, focussing on different aspects relating to this topic. The first part will investigate the role that py energy is likely to play in South Africa's future energy scenario, by looking at topics like the greenhouse effect and the economics of energy production. Secondly the thesis will look at how to position py panels optimally for maximum energy generation through the year. A software model of a py panel is developed which can calculate available py energy and energy generation costs for a given location, based on parameters like the positioning of the py panel and historic weather data. Thirdly the optimal design of a maximum power point tracker is investigated. The optimal design, based on a k-sweep voltage ratio maximum power point tracking algorithm, is implemented using a DSP controlled boost converter circuit. Finally, the best methods to store energy generated using py panels are explored. Energy storage technologies are compared for rural, off-grid applications in South Africa, and the design and implementation of a pulse-charging lead-acid battery charging strategy is explained. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek maniere waarop die maksimum hoeveelheid elektriese energie vanuit 'n py paneelonttrek kan word. Die tesis word in vier dele verdeel, wat elkeen fokus op 'n ander aspek van die onderwerp. Die eerste kyk na die rol wat PV energie potensieël kan speel in die toekomstige energie produksie binne Suid Afrika, deur te kyk na onderwerpe soos die kweekhuis effek, en die ekonomiese sy van energie produksie. Tweedens kyk die tesis na metodes om 'n py paneeloptimaal te posisioneer vir maksimum energie deur die jaar. 'n Sagteware model van 'n PV paneel word ontwikkel wat die hoeveelheid beskikbare energie, en die kostes daarvan, kan bereken vir 'n spesifieke plek, gebaseer op PV paneel data en vorige jare se atmosferiese data. Derdens word agtergrond oor maksimum drywingspunt volgers gegee, en die ontwerp en bou van 'n k-variërende, spannings verhouding maksimum kragpunt volger verduidelik, geimplimenteer deur van 'n DSP en 'n opkapper baan gebruik te maak. Laastens word die beste maniere om PV energie te stoor, vir landelike toepassings weg vanaf die Eskom netwerk, ondersoek. Alle beskikbare tegnologieë word eers vergelyk met mekaar, waarna die ontwerp en bou van 'n puls-laai loodsuur batterylaaier verduidelik word.

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.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Chemistry / Master / Master of Philosophy

A Thesis submitted for the faculty of Science at the University of Witwatersrand Johannesburg, in the fulfilment for the degree of Doctor of Philosophy in Chemistry. Johannesburg, November 2016. / The synthesis of carbon spheres (solid and hollow) for application in organic photovoltaics and chemical sensors is a means of using inexpensive and readily processable carbons to eliminate global warming and to monitor harmful gases. The synthesis conditions used to make solid carbon spheres can also be used to tailor their structural, paramagnetic and thermal properties. More so, the ability to tailor the morphology, surface, structural and electronic properties of the hollow carbon spheres by a templating method is an added advantage to their applicability in electronic devices. Solid carbon spheres were synthesized by a vertically oriented chemical vapor deposition (CVD) reactor using acetylene as a carbon source and argon or hydrogen as the carrier gas. The flow rates of the acetylene or carrier gases determined the particle sizes of the carbon spheres. Annealing of carbon spheres in hydrogen resulted in an increase in thermal stability, fewer defects and narrower paramagnetic signals relative to the carbon spheres annealed in argon gas. In contrast, carbon spheres annealed in argon exhibited an increase in the number of defects, a decrease in thermal stability and broader paramagnetic signals. Doped carbon spheres portrayed an increase in ID/IG ratios, a decrease in thermal stability and stronger paramagnetic signals due to the presence of defects induced by nitrogen. The N doped carbon spheres synthesized in H2 comprised of 48% pyridinic-N, 22% pyrrolic-N and 24% quaternary -N while the N doped spheres obtained in the presence of Ar had 17% pyridinic- N, 20% pyrrolic-N and 49% quaternary-N. The presence of a higher percentage of pyridinic- N confirms the presence of more edge defects in carbon spheres synthesized under H2 gas corroborating with the stronger paramagnetic signal observed from the ESR spectra. Consequently, a higher N/C ratio was exhibited in the N doped CSs obtained in the presence of H2 (4.96) than in the presence of Ar (3.68). This could be attributed to the presence of edge defects in carbon spheres synthesized in the presence of H2 gas. The induction of edge defects in carbon spheres in the presence of H2 gas without the aid of a metal catalyst opens a platform for regulating surface and catalytic reactions using H2 gas. Pristine and mesoporous SiO2 spheres were synthesized using a modified Stober method. Carbonization of the pristine SiO2, pristine SiO2@PVP, mesoporous SiO2 and mesoporous SiO2@PVP spheres was carried out using a bubbling method with toluene as the carbon source and argon as the carrier gas in a CVD reactor for 1 h. Upon SiO2 removal, hollow carbon nanostructures of varying morphologies were obtained. The polyvinylpyrrolidone (PVP) adsorption time, PVP concentration, SiO2 mesoporosity, SiO2 particle size dispersion, and carbonization time played a role in the formation of unique hollow carbon nanostructures; complete HCSs, broken HCSs, deformed HCSs, edge connected, open ended, wormlike and bubble-like HCSs. The mesoporous broken HCSs and open ended HCSs portrayed a hierarchical structure with a bimodal pore size distribution. The surface area properties of these materials and the ease of control of the carbon morphology gives an insight into the application of these materials as dye adsorbents. The effect of the size dispersion of Au@SiO2 sphere templates for the synthesis of hollow carbon structures was evaluated using a CVD nanocasting method. The diameter of the template, the presence of the gold nanoparticles and the amount of PVP determined the size, thickness and shape of the synthesized carbon nanostructures. Carbonization (and SiO2 removal) of Au@polydispersed silica spheres for 1 h gave a graphene-like HCS layer while longer times (2-4 h) gave nanotube like (or worm like) HCSs. These results highlight the potential use of Au@carbon core shell structures for the generation of few layered graphene-like unusual nanostructures. As a proof of concept, the wormlike carbon structures were incorporated in organic solar cells and found to give a measurable photovoltaic response. The incorporation of Au nanospheres and nanorods in a hole transport layer (PEDOT:PSS) of a solar cell device increased the current density and the photo-conversion efficiency of the device due to the local surface plasmon resonance and enhanced light scattering effects of gold. However, high series resistance and leakage currents were obtained due to barrier centres created by uneven dispersion of Au nanaorods within the polymer matrix. The performance of bulk heterojunction organic photovoltaic cells based on poly(3-hexylthiophene- 2,5-diyl) (P3HT) and 6,6-phenyl-C61-butyric acid methyl ester (PCBM) processed from chlorobenzene solution can be enhanced by solution heat treatment of the blend. The morphology of films spin coated from the heat treated blend solution reveals a more favourable diffusion of PCBM into the P3HT matrix than heating of the individual solutions separately. The films obtained from heat treated P3HT and PCBM solutions had a more homogeneous dispersion and enhanced light absorption than those obtained from solutions heat treated separately. There was a significant improvement in the performance for devices made from a solution heat treated blends relative to the non-treated blend; a maximum power conversion efficiency of 3.5% and a fill factor up to 43% was achieved under Air Mass 1.5 at 100 mW/cm2 illumination. This study also reports on the sensing characteristics of ammonia in humid environment by hollow carbon spheres, hollow carbon spheres-polyvinylpyrrolidone composite and annealed hollow carbon spheres, at 20°C and 40°C. For device fabrication, a surfactant assisted method was used to homogeneously disperse the hollow carbon spheres, allowing their deposition onto an interdigitated electrode by casting. An enhanced response and recovery time of the devices was observed at the higher working temperature. Annealing of the hollow carbon spheres resulted in a tremendous decrease in the humidity dependent ammonia sensing due to a decrease in the number of the oxygenated groups and defects in their structure. The presence of hydroxyl groups on the pristine hollow carbon sphere surface resulted in an enhanced proton conductivity. However, the ammonia sensitivity at high relative humidity in the pristine hollow carbon spheres is negligible due to the inhibition of ammonia adsorption sites by the high concentration of water molecules. The sensor response was investigated by varying both ammonia concentration and relative humidity, determining the topology of the response as a function of these two variables, and applying a tristimulus analysis in an attempt to determine the ammonia concentration independently of the relative humidity. This study demonstrates the critical role played by humidity and surface chemistry in the ammonia sensing properties of hollow carbon spheres. The studies reveal the day to day application of ammonia sensors, with temperature and humidity playing a critical role in the carbon based sensor response and recovery of the materials. These carbon based sensors that simultaneously measure ammonia and relative humidity could be applied in agricultural industries to monitor ammonia concentration in soils, fishponds and in food industries to monitor meat spoilage. / LG2017

As the rapid development of the applications of unconventional semiconductors in the 21th century, the new electronic and bioengineering revolutions based on solid state devices have become possible, that is facilitated through the understanding of electron or energy transfer process at the functionalized interfaces of organic semiconductors and two-dimensional (2D) materials. Especially in applications of photovoltaics and biosensors, the attributes of the interfaces play an important role in performance advancement. In this thesis, I have focused on the utilization of organic small molecule semiconductors as energy cascade materials to modify the interfaces between donor and acceptor of P3HT/PC₆₁BM binary organic solar cell, so as to improve the device performance. The charge transfer process at the interface of P3HT and functionalized graphene has also been investigated through P3HT/functionalized graphene blending photovoltaic devices. Moreover, I have concentrated on the interface of single layer MoS₂ and fluorescently-labeled DNA, where the electrons were transferred from fluorescent groups of DNA to MoS₂, resulting in fluorescence quenching. This quenching characteristic can be useful in other related biosensors. / In Chapter 1, an introduction to organic semiconductors and two-dimensional materials for applications in photovoltaics and biosensors has been presented. In Chapter 2, the experimental details used in this thesis have been discussed. / In Chapter 3, a novel small organic semiconductor molecule (CPA) with ambipolar attribute as an energy cascade material has been employed, to fabricate bulk heterojucntion solar cells. The organic photovoltaic devices with ternary structures, demonstrates a step of energy cascade to assist charge transfer between the electron-donating P3HT and electron-accepting PC₆₁BM. The ternary structure offers a distinct platform and an easily applicable approach to overcome shortcomings in P3HT-PC₆₁BM system by increasing the attainable product of short circuit current (JSC) and open circuit voltage (VOC). This ternary structure also retains the simplicity of a single processing step for photoactive layer. / In Chapter 4, to explore the potential of the p-type small organic semiconductor DTDCTB as energy cascade material in ternary blend bulk heterojunction (BHJ) solar cells, I have studied a BHJ system based on poly (3-hexylthiophene) (P3HT), [6,6]-phenyl C₆₁ butyric acid methyl ester (PC₆₁BM) and DTDCTB. This ternary structure demonstrates the improvement of power conversion efficiency (PCE) as compared to that of the binary devices composed of P3HT/PC₆₁BM alone. A systematic spectroscopic study was carried out to elucidate the underlying mechanism. Wavelength-dependent external quantum efficiency measurement confirmed the DTDCTB contribution to the increased photocurrent. Photoinduced spectroscopy and transient photovoltage measurements unambiguously revealed that the charges generated in DTDCTB were efficiently transferred to and transported in P3HT and PC₆₁BM. The results also suggested that despite the realization of cascade charge transfer, the bimolecular charge recombination process in the ternary system is still dominated by the P3HT/PC₆₁BM interface. / In Chapter 5, a simple method by using aryl diazonium salt reaction has been devised to achieve covalent bond formation by altering the hybridization of carbon atom in configuration of sp² to sp³. Afterwards the group of benzoic acid has been grafted onto pristine graphene, to open a band gap of this two-dimensional material. It was well functionalized, dissolved in organic solvents to provide the various of fabrication processes for electron devices. The LUMO of functionalized graphene below the LUMO of P3HT and close to that of PC₆₁BM indicates its suitability as an electron-acceptor for OPV applications. Then the bulk heterojunction solar cells composed of P3HT/functionalized graphene composite as active layer have been further prepared, achieving a PCE efficiency of 1.1%. / In Chapter 6, a novel MoS₂-based fluorescent biosensor for DNA detections via hybridization chain reactions (HCRs) has been demonstrated. MoS₂, as an emerging nanomaterial, has excellent fluorescence quenching ability and distinct adsorption properties for single- and double-stranded DNA. In the sensing method, MoS₂ nanosheets were used to suppress the background signal and control the “on” and “off” states of fluorescence emission of the detection system with and without the presence of the target DNA. In addition, the signal generation was amplified through the target-triggered HCRs between two hairpin probes. The utilization of MoS₂ and HCRs guaranteed the high sensitivity of the detection strategy with the detection limit of 15pM. The biosensor also exhibited very good selectivity over mismatched DNA sequences. The detection took place in solutions and requires only one “mix-and-detect” step. The high sensitivity, selectivity, and operational simplicity demonstrate that MoS₂ can be a promising nanomaterial for versatile biosensing. / In Chapter 7, I provide the conclusions and a brief prospect of the further development in ternary system of perovskite solar cells and in based-two dimensional materials micro-fluidic biological monitoring FET. / 對於二十一世紀，隨著人們對非传统半导体材料应用的發展有著迫切的需求，新的基於固態器件的電子工程和生物工程的革命正在悄然進行，這是基於對有機半導體材料和二維層狀材料的功能化的界面上發生的電子或者能量轉移的理解，特別是在太陽能電池器件和生物傳感器方面上的應用。本論文主要是關注與利用有機半導體小分子作為能級梯級材料去调节P3HT/PC₆₁BM二元有機光伏器件中給體與受體見的界面，從而得到更好性能的器件。同時也關注了P3HT和功能化的石墨烯界面上的電荷轉移，并通過P3HT/功能化石墨烯混合有機光伏器件來研究界面上的電荷轉移。另外，還關注了單層硫化鉬和螢光標記的DNA間的界面，在這個界面上DNA螢光基團的能量會轉移到二硫化鉬上從而導致螢光淬滅，並且應用這一淬滅特性在生物傳感上。 / 在第一章中，本論文對有機半導體和二維材料在光伏器件和生物傳感器件中的應用給出了一個簡單的介紹。第二章展示了論文涉及到的檢測方法。 / 在第三章中，本論文利用一種新型的具有雙極性的有機半導體小分子(CPA)作為能級梯級材料去製作異質結太陽能器件。這些具有三元體系結構的太陽能器件展示了能級梯級變化的過程，這個過程是為了改善電子給體P3HT和電子受體PC₆₁BM間的電荷轉移。這種三元體系結構提供了一種顯著而且簡單的方法來克服P3HT-PC₆₁BM二元體系的不足，并通過提高其短路電流和開路電壓的乘積來實現，同時保持簡單的一步光敏層的製作方式。 / 在第四章中，為了探索P型有機半導體小分子DTDCTB能否作為級聯材料在有機異質結太陽能器件中使用，本論文研究了三元體系包含P3HT，PC₆₁BM和DTDCTB的有機異質結太陽能器件。這種三元結構器件展現出更佳的性能對比與P3HT/PC₆₁BM二元體系器件。另外，三元體系中電荷轉移的內在機制通過一系列系統的光譜來闡明。光誘導光譜和瞬態光電壓測試明確的揭示了DTDCTB中產生的電荷會被有效的通過P3HT和PC₆₁BM傳輸走。這些結果還表明，儘管存在級聯電荷傳輸，但是雙分子間的電荷複合過程主要發生在P3HT/PC₆₁BM界面。 / 第五章提出一個簡單的通過使用芳香基重氮鹽反應的方法，實現了碳碳共價鍵合成的反應，這種反應是通過改變碳原子sp²雜化成sp³雜化的方式進行的，而且可以移植苯甲酸官能團到原味的石墨烯上來打開石墨烯的帶隙。石墨烯這種二維層狀材料通過明確的的功能化后，可以溶在有機溶劑中從而提供了其作為電子器件的製作工藝的多元化。功能化后的石墨烯的LUMO能級比P3HT的LUMO能級要低，並且接近于PC₆₁BM的LUMO能級，這一特性意味著功能化后的石墨烯作為電子受體在有機光伏器件中的應用是可行的。因此，本論文進一步展示了以P3HT和功能化后的石墨烯複合材料作為光敏層的異質結太陽能器件，並且其具有1.1%的光電轉化效率。 / 在第六章中，本論文提出了一種新型基於二硫化鉬的螢光生物傳感器，這一傳感器通過雜交連鎖反應(HCRs)應用於DNA檢測。二硫化鉬作為新興的納米材料，有著對單鏈或者雙鏈DNA的良好螢光淬滅和顯著的吸附特性。在此檢測方法中，二硫化鉬納米片被用來抑制背景信號，並且通過存在或者不存在目標DNA來控制檢測體系中螢光發射的開啟和閉合。另外，檢測信號通過兩個髮夾型DNA探針間的目標觸發的HCR方法放大。通過使用二硫化鉬和HCR實現了高靈敏度的檢測，其檢測極限是15pM。這個傳感器對於DNA的錯配具有良好的選擇性。這個檢測在溶解中進行，並且僅僅需要簡單的一步混合來實現。高的靈敏度、選著性和工藝簡單等特性表明了二硫化鉬這種納米材料可以在多種生物檢測中使用。 / 第七章三元體系鈣鈦礦結構光伏器件和基於二維材料微流生物檢測器件的應用。 / Ye, Lei. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Title from PDF title page (viewed on 04, October, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Paolo Rava. / Ph.D.