Applications, converter topologies, and control schemes are examined for superconductive magnetic energy storage (SMES) systems. Diurnal load leveling for electric utilities and compensation for fluctuations in photovoltaic (PV) power generation are the primary applications discussed. It is demonstrated that a SMES system implemented with standard AC/DC converters offers energy storage capacity large enough, and dynamic response fast enough, to compensate for PV fluctuations due to changes in weather conditions. The method of control is developed so that the charging and discharging of the SMES system are changed in response to PV fluctuations, and the combined SMESIPV power output is smooth and controllable. An innovative control scheme is introduced for SMES that can simultaneously regulate real power and voltage independently without hardware modifications to the standard ACIDC bridge arrangement normally used for coordinated control of real and reactive power. The combination of SMES and PV systems could benefit from DCIDC converters that take advantage of the DC nature of both. It is established that DClDC converters can respond with sufficient speed to handle variations in PV power. A converter topology is devised where two DC/DC converters in cascade effectively maintain a PV array at its maximum power point and simultaneously control a SMES system to compensate for PV fluctuations. An alternative cascade configuration of an AC/DC converter with a DCIDC converter is proposed that could significantly reduce the reactive power requirements and improve the operational characteristics of a large scale SMES system connected to the utility grid. / Master of Science

Triplet-triplet annihilation upconversion (TTA-UC) is a process which converts two low energy photons into one higher-energy excited state. TTA-UC has recently received attention for its potential application to many light driven processes, such as improving efficiency in photovoltaic devices and allowing use of low-energy light sources for in vivo applications, including bioimaging, optogenetics, and photochemotherapy. Each of these applications has a different set of energetic requirements, which has created a need for a diverse library of upconverting materials. Additionally, these applications benefit from improved upconversion efficiency in solid-state, a task that has proven challenging for the traditionally solution-phase process. Macromolecular scaffolds are a promising avenue to tune the electronic communication between chromophores and control intermolecular packing in solid-state. Herein, we report the investigation of dendrimers with annihilator-functionalized termini and linear annihilator polymers as frameworks to control local annihilator concentration and communication. We find that multi-annihilator dendrimers exhibit higher upconversion yields at low concentrations compared to similar concentrations of monomer; however, higher generation dendrimers allow strong interchromophore coupling, which promotes parasitic excimer formation, decreasing relative upconversion yields. Linear annihilator copolymers with alternating anthracene and phenyl or naphthyl bridges had ground state optical properties predictive of interchromophore communication based on bridge connectivity, interchromophore length, and polymer planarity. Non-conjugated, naphthyl polymers were observed to be the most efficient at intramolecular TTA-UC in dilute solutions. In this dissertation, we will discuss current efforts in the field towards control and analysis of intramolecular TTA-UC through design of multi-annihilator macromolecules and novel annihilator scaffolds targeting underutilized regions of the electromagnetic spectrum. In Chapter 1, we list important factors to consider about improving TTA-UC and follow with discussion of reported macromolecular systems and their efforts towards intramolecular TTA-UC. Chapter 2 introduces a series of non-conjugated dendrimers functionalized with anthracene annihilators on the periphery and analyzes their upconversion capabilities as a set of macromolecules with controlled molecular structure. In Chapter 3, we investigate the effect of connectivity between annihilators in alternating co-polymer systems, discussing the impact on ground state photophysical properties and upconversion efficiency. Finally in Chapter 4, we introduce an approach for using computational analysis as a high-throughput tool for identifying potential novel annihilator molecules.

While photovoltaic research conducted to date has been primarily in the areas of utility peak shaving, residential applications, and stand alone applications, this research examines photovoltaic potential as a commercial customer initiated demand side management tool and develops a methodology which can be used to evaluate the value of a PV storage system. The primary focus is on the effect photovoltaic orientation and utility billing practices have on overall system value. Using a year's worth of 10 minute data collected at the Virginia Tech Solar Experimental Station and an academic building load, the effects of array orientation on clear sky photovoltaic production and the match between that production and the building load profile are discussed. The performance of five photovoltaic array configurations for both building energy and demand reduction were simulated. It was shown that arrays facing south-southwest and southwest have lower performance that a south facing array in spite of the presence of an afternoon building load peak. The impact of battery storage as a supplement to a PV system has been examined. The affect of battery efficiency, array orientation, and battery dispatch setpoint on ovarall system value has been investigated. Based on economic assumptions and billing schedules obtained from a medium sized utility, the present value of the various array performances were evaluated. It was found that O&M costs could significantly effect the value being assigned to array configurations with superior performance. Due to the variability of the available insolation, smaller arrays have a greater value than larger arrays. It was shown that the value of a PV storage system is greater than either of the two component systems taken alone. By adding battery storage to the PV system, the optimum system size was increased. / Master of Science

A methodology is developed to study the interrelations between photovoltaics (PV) and storage systems in the context of demand side management. This study concentrates on the most prominent types of storage systems and photovoltaic technologies, which are lead acid batteries and single crystalline silicon cells and amorphous silicon cells, respectively. The methodology concentrates on the daily operating cost of the system. Only from a detailed comparison of alternatives can we develop a system that maximizes the benefits of photovoltaics and storage systems, while remaining cost competitive. This methodology consists of several steps that include; simulation runs to determine yearly energy production and consumption, life cycle costing, and analysis of daily cost graphs. During the analysis several items including photovoltaic and storage system technologies, different demand limits and demand charges, and different amounts of load control and purchased electricity as well as different PV and electricity costs are discussed, and the following conclusions are reached. The type of photovoltaics used plays an important role in the system design. The amorphous cells seem to have a lower performance degradation in cloudy or hazy conditions, but single crystalline cells have a lower operating cost especially when there is high sunlight. The cost of photovoltaics also has a great effect on the daily operating cost. By keeping the cost of photovoltaics low (around $2.00/watt), the overall daily operating cost decreases while increasing the photovoltaic array size. This shows that photovoltaics can have a positive economic benefit. The effect of battery cost and on the daily operating cost is minimal. This is because its cost per day is a small part of the total daily operating cost. On the other hand, the demand limit and demand charge greatly effect the magnitude of the daily operating cost. The main component of the daily operating cost is purchased electricity. The daily operating cost increases as the cost of purchased electricity increases. / Master of Science

No description available.

In order for photovoltaic systems to gain acceptance as viable energy sources, they must have a sufficient life span and must be optimized to provide maximum power. In order to achieve these goals, several maximum power point tracking (MPPT) algorithms have been developed to ensure the photovoltaic (PV) system operates at maximum efficiency despite changes in temperature, shading, and age of the solar cells. However, the connection of multiple PV systems in parallel cannot be achieved using a single MPPT control due to the characteristic differences in each solar array's orientation, illumination, temperature, composition, and age. The mismatch of the individual PV systems can limit the power output and reliability of the systems, as well as reduce the expected lifetime. Multi-channel PV systems require MPPT controls for each channel, as well as communication between channels so that power extraction is shared among channels. Therefore, an algorithm is presented which includes MPPT and promotes equal power sharing between the sources and the load in order to make multichannel PV systems more robust, reliable, and efficient. The algorithm is implemented using a digital signal processor (DSP), and the validity of the algorithm will be proven using modeling techniques and through the construction of a prototype two-channel PV system. Once the viability of the two channel system has been proven, the expansion of the system to an n-channel system will be discussed.

This dissertation introduces a new operational tool for integrating a photovoltaic (PV) system into the utility's generation mix. It is recognized at the outset, that much of the existing research concentrated on the central PV system and its operations have concluded that technical problems in PV operation will override any value or credit that can be earned by a PV system, and that penetration of a PV plant in the utility will be severely limited. These are real problems and their solutions are sought in this dissertation. Judging from the drawbacks of the static approach, it is felt that a new approach or methodology needs to be developed which would give a central station PV plant its due share of credit. This dissertation deals mainly with the development and implementation of this new approach -- a dynamic rule-based dispatch algorithm which takes into account the problems faced by the dispatch operator during a dispatch interval and channels those into a knowledge base. The new dynamic dispatch requires forecasts of photovoltaic generations at the beginning of each dispatch interval. A Box-Jenkins time-series method is used to model the sub-hourly solar irradiance. The irradiance data at any specific site is stripped of its periodicities using a pre-whitening process which involves parameterization of certain known atmospheric phenomena. The pre-whitened data series is considered stationary, although some non-stationarity might be introduced by the discontinuities in the data collection during night hours. This model is extended to yield forecast equations which are then used to predict the photovoltaic output expected to occur at certain lead times coinciding with the economic dispatch intervals. A rule-based (RB) dispatch algorithm is developed in this dissertation. The RB is introduced to operate as a substitute for the dispatch operator. Some of the dispatcher's functions are routine jobs, while some require specialized knowledge or experience. The RB is given these two qualities through a number of rules. This algorithm works in tandem with a conventional economic dispatch algorithm. The functions of the two are coordinated by another algorithm which oversees the now of information and records them. The RB gives one of 16 possible solutions as and when required. These solutions are written as rules which manipulate the non-committable generation to achieve an optimal solution. The RB system during its operation supervises the fact that the PV generation are kept at the maximum level possible under all constraints. The case study revealed that the thermal generating units which are scheduled by the unit commitment are able to absorb most of the small to medium variations present in the PV generations. In cases of large variations during a single interval, the thermal generators reach their response limits before they can reach their maximum or minimum generation, thus causing mismatches in the load and generation. The mismatches are then picked up by the non-committable sources of generation, comprised of pumped storage units, hydro generation plant, or by interconnection tie-lines. If none of these are sufficient, changes are made in the PV generation schedule. It is concluded that results depend on the time of the year and the specific utility. The time of the year information is reflected in the load demand profile. Most utilities in the U.S. have single peaks in summer and double peaks in winter. Also, the time of the peak load occurrence varies with season. The utility generating capacity mix influences the results greatly. / Ph. D.

Thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Renewable and Sustainable Energy at the Stellenbosch University. / Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: This project investigated the feasibility of incorporating photovoltaic cells into plastic roof tiles using injection moulding. Such tiles have the potential to provide robust and distributed electricity contained within the building envelope. Current-voltage curves of amorphous silicon modules were measured under illumination using the PVPM 2540C power measuring instrument, both before and after moulding. The efficiency after moulding was reduced by 53% to 88%, with modules that were heated for longer being degraded more. Thus the duration of exposure to high temperatures affected the extent of performance reduction during moulding. This suggested that faster moulding at a lower temperature or faster cooling could solve the problem. Economic feasibility was examined by calculating the levellised cost of electricity provided by the tiles. A large-scale development in the Western Cape was simulated using a typical meteorological year of weather data and using the anisotropic diffuse irradiance model of Perez et al. (1988). Avoided costs due to replaced roofing, avoided costs due to electricity distribution infrastructure, and Clean Development Mechanism credits were accounted for. The cost of energy calculated was R11/kWh in 2010 rands, which did not compete with the price of conventional grid-based electricity at R1.8/kWh. The importance of the cost of balance-of-system components, such as the inverter, and not only of the photovoltaic modules, was highlighted for future cost reductions. Several clear guidelines for manufacturing photovoltaic roof tiles were discovered. The most important of these was that many bypass diodes make the system more robust. / AFRIKAANSE OPSOMMING: Hierdie projek het die haalbaarheid van die integrasie van fotovoltaïse selle in plastiek dakteëls deur spuitvorming ondersoek. Sulke dakteëls het die vermoë om robuuste en verspreide elektrisiteit te lewer, sonder om die gebou se vorm te verander. Stroom-spanning kurwes van struktuurlose silikon eenhede is onder verligting gemeet met die PVPM 2540C kragmeet instrument, voor en na spuitvorming. Die doeltreffendheid na spuitvorming is met 53% tot 88% verminder, met groter vermindering in die eenhede wat langer warm was. Dus het die duur van blootstelling aan hoë temperature die mate van vermindering van doeltreffendheid beïnvloed. Dit het suggereer dat óf vinniger spuitvorming by laer temperature óf vinniger verkoeling die probleem kan oplos. Ekonomiese haalbaarheid is ondersoek deur die koste van die elektrisiteit wat deur die dakteëls gelewer is te bereken. ’n Groot behuisingsontwikkeling in die Wes-Kaap is gesimuleer deur ’n tipiese weerkundige jaar van weerdata en die anisotroop model vir verspreide ligstraling van Perez et al. (1988) te gebruik. Vermyde kostes van vervangde dakteëls, vermyde kostes van elektrisiteit distribusie infrastruktuur en krediete van die Meganisme vir Skoonontwikkeling is in ag geneem. Die elektrisiteitskoste was R11/kWh in 2010 se randwaarde, wat nie mededingend met die R1.8/kWh koste van gewone netwerk elektrisiteit was nie. Die belang van die kostes van die res van die installasieonderdele, soos die wisselrigter, en nie net die fotovoltaïse eenhede nie, is beklemtoon vir kostevermindering in die toekoms. Verskeie duidelike riglyne vir die vervaardiging van fotovoltaïse dakteëls is voorgestel. Die belangrikste van hierdie was dat meer omloopdiodes die installasie meer robuust maak. / Centre for Renewable and Sustainable Energy Studies

Project report presented in partial fulfilment of the requirements for the degree of Master of Engineering at the University of Stellenbosch. / Thesis (MScEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2008. / Three SunSlates™ were investigated to predict the performance of a fully installed system. The three slates were mounted on a fixed tilt of 30°, but with different orientations. The tilt is close to latitude of the Stellenbosch site, which is 33.92°. The one faces due east, another due west and last due north. This is to determine the effect that orientation has on the energy from the SunSlates™. Another slate, also facing north, was mounted on an adjustable framework. The framework was used to adjust the tilt angle of the slate, the orientation of the slate was constantly north. This slate was used to determine the effect of tilt on the total daily energy produced by the slate. To determine the performance of the slates daily measurements of temperature, solar insolation and wind was taken. These were used to investigate the effects on the SunSlates™. During the test period, which scheduled from September to November, the results show a difference, smaller than commonly believed, in the daily and annual energy delivered from the differently orientated slates. The slates facing east and west, however, have similar energy outputs, even though the power profiles differ. The north facing slate has the highest annual energy output, as expected. It was found that during the months of summer, November to January, the optimal tilted slate (Slate tilted to have a incidence angle of 0° from solar rays at noon) had a slightly lower energy output, but higher maximum power output per day than the 30 degree tilted slate. This is in contrast to the energy output predictions for the winter months where in the winter the energy can be as much as double that of the 30 degree tilted slate. The thorough testing and expert installation of the SunSlates™ are essential. From the case study it can be seen that some problems during installation, possibly a single faulty slate or shadowing, can cause a complete system to lose 30% of its efficiency. / Centre for Renewable and Sustainable Energy Studies

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy