The amount of traditional energy sources are finite and the ecological impact of continuing to produce energy using fossil fuels will only exacerbate the carbon footprint. It is for these reasons that photovoltaic modules are becoming a larger and more necessary part the world's electricity production paradigm. Photovoltaic (PV) semiconductor modules are grouped into three categories. 'First generation' monocrystalline and polycrystalline silicon modules that consist of pn junctions created via the addition of impurities known as dopants. Almost 85% of solar cells produced at this time are `first generation' and it is the high production costs of silicon PV modules that motivated the search for new methods and materials to use as PV cells. 'Second generation' PV modules consist of semiconductor thin films. The 'second generation' PV modules in production at this time are copper indium gallium diselenide (CIGS), copper indium gallium (CIG), amorphous silicon (a-Si), and cadmium telluride (CdTe). The 'third generation' PV modules consist of dye-sensitized and organic materials. Thin films use less material, have less stringent production parameters and less waste, making thin films cost effective. In this investigation, solar cells were prepared using un-doped Group II-VI semiconductor thin films that exploit differences in bandoffsets to form effective p-n heterojunctions as a viable low cost alternative to doping. The thin films were deposited by thermal evaporation upon glass substrates coated with indium tin oxide (ITO). A layer of aluminum formed the back contact. Various configurations of the solar cells were produced including: ITO/CdS/CdSe/Al, ITO/ZnTe/CdSe/Al, ITO/CdTe/CdSe/Al, ITO/ZnTe/CdTe/CdS/Al. The solar cells produced have been characterized to determine thin film internal resistances, quantum and 'wall-plug' efficiencies, as well as I-V and spectral response. The open circuit voltage, short circuit current density, fill factor, and efficiency of our best devices were 0.26 V, 4.6 mA, 27.5 and 0.4% respectively. Additional device optimization should be possible and should improve these results. Solar cell design based on band-offset is an effective method for predetermining likely PV structures, while future investigation using Group II-VI semiconductor nanowires and nanorods and employing epitaxial films are likely to enhance the efficiency.

Photovoltaic (PV) systems are a rapidly growing segment in the renewable energy industry.  Though they have humble origins and an uncertain future, the commercial viability of PV has significantly increased, especially in the past decade.  In order to make PV useful, however, significant effort has to go into the power conditioning systems that take the low-voltage dc from the panel and create utility compatible ac output.  Popular architectures for this process include the centralized inverter and the distributed micro-inverter, each with its own advantages and disadvantages.  One attempt to retain the advantages of both architectures is to centralize the inverter function but construct PV panel-level micro-converters which optimize the panel output and condition the power for the inverter.  The main focus of this work is to explore the technical challenges that face the evolution of the dc-dc micro-converter and to use them as a template for a vertically integrated design procedure. The individual chapters focus on different levels of the process:  topology, modulation and control, transient mitigation, and steady-state optimization.  Chapter 2 introduces a new dc-dc topology, the Integrated Boost Resonant (IBR) converter, born out of the natural design requirements for the micro-converter, such as high CEC efficiency, simple structure, and inherent Galvanic isolation.  The circuit is a combination of a traditional PWM boost converter and a discontinuous conduction mode (DCM), series resonant circuit.  The DCM operation of the high-frequency transformer possesses much lower circulating energy when compared to the traditional CCM behavior.  When combined with  zero-current-switching (ZCS) for the output diode, it results in a circuit with a high weighted efficiency of 96.8%.  Chapter 3 improves upon that topology by adding an optimized modulation scheme to the control strategy.  This improves the power stage efficiency at nominal input and enhances the available operating range.  The new, hybrid-frequency method utilizes areas where the modulator operates in constant-on, constant-off, and fixed-frequency conditions depending on duty cycle, the resonant period length, and the desired input range.  The method extends the operating range as wide as 12-48V and improves the CEC efficiency to 97.2% in the 250-W prototype.  Chapter 4 considers the soft-start of the proposed system, which can have a very large capacitive load from the inverter.  A new capacitor-transient limited (CTL) soft-start method senses the ac transient across the resonant capacitor, prematurely ending the lower switch on-time in order to prevent an excessive current spike.  A prototype design is then applied to the IBR system, allowing safe system startup with a range of capacitive loads from 2μF to 500μF and a consistent peak current without the need for current sensing.  Chapter 5 further investigates the impact of voltage ripple on the PV output power.  A new method for analyzing the maximum power point tracking (MPPT) efficiency is proposed based on panel-derived models.  From the panel model, an expression demonstrating the MPPT efficiency is derived, along with a ripple "budget" for the harmonic sources.  These ripple sources are then analyzed and suggestions for controlling their contributions are proposed that enable circuit designers to make informed and cost-effective design decisions.  Chapter 6 illustrates how results from a previous iteration can provide a basis for the next generation's design.  A zero-voltage-switching (ZVS) version of the circuit in Chapter 2 is proposed, requiring only two additional MOSFETs and one inductor on the low-voltage side.  The maximum switching frequency is then increased from 70kHz to 170kHz, allowing for a 46% reduction in converter volume (from 430cm³ to 230cm³) while retaining greater than 97% weighted efficiency. / Ph. D.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for degree of Master of Science in Chemistry / The mandate for renewable energy sources to replace the current reliance on fossil fuels as a primary energy source has recently attracted a lot of research interest. The research has also focussed on bringing the technologies that take into consideration the goal of reducing environmental pollution. Consequently, approaches using photovoltaic (PV) technologies have been a promising arena to tackle the problem facing energy sources. Recently, more focus has been placed on improving the power conversion efficiency (PCE) of PV devices, such as organic and/or organic-inorganic hybrid perovskite solar cells. Therefore, in this work two different materials were applied in two independent PV devices, namely organic and/or organic-inorganic hybrid perovskite solar cells. One study employed nitrogen doped broken hollow carbon spheres (N-bHCSs), with an aim of enhancing the electronic properties of the P3HT:PCBM active layer of an organic photovoltaic (OPV) solar cell. N-bHCSs were successfully synthesized using a horizontal chemical vapour deposition method (H-CVD) employing a template-based method and the carbon was doped using in-situ and ex-situ doping techniques. Pyridine, acetonitrile and toluene were used as both carbon and nitrogen precursors. The dispersity of the SiO2 spheres (i.e. templates) was found to play a role on the breakage of the N-bHCSs. Incorporation of the N-bHCSs into the P3HT:PCBM active layer was found to enhance the charge transfer and this led to less recombination of photogenerated charges in the interface between the donor and acceptor. The current-voltage (I-V) characteristics of the ITO/PEPOT:PSS/P3HT:PCBM:N-bHCSs/Al solar cell devices revealed an increased chargetransport distance due to increased electron density by n-type doping from the N-bHCSs. The second study employed the organic-inorganic hybrid perovskite (CH3NH3PbI3) material as a light harvesting layer in an ITO/PEDOT:PSS/CH3NH3PbI3/PC6BM/Al solar cell device. Initially, the device parameters were optimised to obtain the best performing device. These include parameters such as the degradation of the hybrid film as a function of time and air exposure. A rapid degradation was seen on the device after 24 h of air exposure which was accompanied by the decrease in the PV performance of the device. The degradation was visually seen by the formation of crystal grains (i.e. “islands”) on the perovskite film. / GR2019

The shrinking of the world’s energy sources has prompted an unprecedented interest in renewable and clean energy sources such as photovoltaic (solar) array. Already popular in space and some industrial power system applications, photovoltaic arrays have yet to become a viable source of energy for most terrestrial applications. For several decades now, engineers have been striving to design reliable and affordable solar array based power systems. One popular approach to achieve reliability is the integration of Maximum Power Point Tracking (MPPT) technology in solar power system design. The purpose of this study was to gain more insight into the nature of photovoltaic arrays, in order to help engineers improve solar array systems efficiency and reliability. To this end, a detailed analysis and modeling of the electrical properties and parameters of solar arrays have been presented. Shading effects on solar arrays, as well as the benefits of incorporating MPPT technology in photovoltaic systems have also been studied. Finally an application of MPPT to grid connected systems will be introduced as part of the ongoing efforts of the Power Electronics Lab at the University of Central Florida to participate in the 2005 Future Energy Challenge.

The current pressure on water bodies is a structural problem that may compromise the satisfaction of future water demand and the good status of the natural environment. Activities such as wastewater reuse or desalination provide an additional source of water resources to meet demand without the need to increase natural water abstractions. In addition, reuse also contributes to improving water quality by limiting abstractions and reducing discharges. However, reuse has not been widespread as a source of supply in resource-rich contexts. In resource-abundant areas, the high cost of reusing water is a strong disincentive to its use, which puts the focus on reducing pollution through discharge without assessing the potential of reuse as an additional source of resources. The use of reclaimed water has a great margin for development that should be exploited in the coming years to obtain a guarantee of supply and an improvement in the environmental quality of water in the current context of increasing scarcity. However, the financial and environmental situation of reuse requires the involvement of the public sector. In this work, two instruments with the potential to facilitate the development of reuse have been studied. The first of these is photovoltaic self-consumption, in order to reduce the cost of energy consumption of wastewater treatment plants, given that this is their main financial operating cost. This possibility, however, has shown little capacity to reduce these costs since, except in the case of the floating photovoltaic installation, the cost of electricity from self-consumption is higher or similar to the market price. If we consider the reduction of greenhouse gas emissions derived from self-consumption, this alternative is much more competitive. The situation is, once again, of an activity that presents financial losses and environmental benefits derived from the current excess of emissions. The responsibility lies with the public sector in the same way as in the case of reuse. Water tariffs, as one of the main revenues from water treatment, is an instrument that can be evaluated with a view to increasing revenues through an increase in the price of water. The results obtained show large differences in the impact of such an increase depending on the region but make it clear that the potential for additional revenue from this possibility is small. This analysis has also shown that there is a problem in the current tariffs that reduces their effectiveness by not valuing the type of household. The problem lies not in the structure of the tariff or the number of household members, but in the characteristics of the household. By not taking these into account and calculating the bill without these details, the tariffs are not fully effective. In conclusion, both reuse and photovoltaic self-consumption are beneficial activities for society, but the financial costs involved in their implementation require the involvement of a public sector with a reduced capacity to increase current revenues.

We analyze a toy model for p-n junction photovoltaic devices by simulating photoexcited state dynamics in silicon nanowires. One nanowire is approximately circular in cross section with a diameter of d = 1.17 nm. The other has an approximately rhombic cross-section with d1 = 1.16 nm and d2 = 1.71 nm. Both nanowires have been doped with aluminum and phosphorus atoms and capped with gold leads. We use Boltzmann transport equation (BE) that includes phonon emission, carrier multiplication (CM), and exciton transfer. BE rates are computed using non-equilibrium finite-temperature many-body perturbation theory (MBPT) based on Density Functional Theory (DFT) simulations, including excitonic effects from Bethe-Salpeter Equation. We compute total charge transfer amount generated from the initial photoexcitation and find an enhancement when CM is included. In particular, we see between 78% and 79% enhancement in the smaller wire, while we see 116% enhancement in the larger nanowire

No description available.

<P> In this thesis, several methods of material integration into organic photovoltaic devices are investigated by fabricating solution processed and vacuum coated devices. Each of these methods is aimed at examining and improving one or more of the four critical factors that determine solar cell efficiency: (1) photovoltage, (2) light absorption, (3) exciton separation, and ( 4) charge collection. To investigate and improve photovoltage, the photovoltaic properties of different M-Phthalocyanine/Fullerene (M-Pc/C60 ) blends are measured and demonstrate an improved open circuit voltage (Voc) using trivalent-metal phthalocyanine. Rubrene is also added to the tl-Pc/C60 cells and shown to systematically increase the Voc. To improve light absorption, two new device structures are developed: the parallel tandem cell and the heteromorphic cell. The parallel tandem cell is demonstrated using both all-vacuum coated materials as well as a combination of vacuum and solution processed materials. Results show definitive and significant current contribution from the near-infrared (NIR) wavelengths, and concomitant increase in photocurrent and power conversion efficiency (PCE). The heteromorphic cell demonstrates the integration of two polymorphs of the same M-Pc, yielding a broader external quantum efficiency (EQE) spectrum in the IR region and an increase in the overall PCE. To investigate exciton separation and charge collection, time of flight photoconductivity studies are performed on varying compositions of solution processed polymer/fullerene films as well as pristine and blended M-Pc:C60 films. Results verify the necessity for balanced carrier transport in blended systems, and t he importance of carrier mobility for achieving high fill factors. Finally, the stability of a relatively new polythiophene (PQT-12) in an organic solar cell is investigated , and shown to significantly increase the device lifetime as compared to the standard P3HT polymer. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.