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Given the growing concern over climate change, air pollution, rising energy prices, and the uncertain reliability of conventional fuel sources, solar power has become more popular in a variety of applications. Solar power is free, safe, abundant, renewable, and has few negative impacts on the environment. The photovoltaic array is substantially influenced with unpredictable environmental conditions (sun illumination and array temperature), which in turn, results in nonlinear Voltage-Current (or Power-Voltage, Power-Current) characteristics. These characteristics make it difficult to estimate the maximum power operating point. To extract the maximum power available from photovoltaic (PV) arrays on a continuous basis, a device called the Maximum Power Point Tracker (MPPT) is needed to continuously deliver the highest possible power to the load given unpredictable variations in environmental conditions. The PV system used in our experiment has a maximum 300W capability. Two sets of PV arrays are used in parallel to demonstrate the scalability of the system; each branch consists of three series-connected PV modules that are individually rated at 50W. Two DC-DC buck-type converters are implemented. A 24V battery bank is used as a power storage unit and is also connected to the load. An MC-based 56F8013 and its demonstration board from Freescale are employed to implement different MPPT control schemes, with multiple-PWM channels. The design can therefore adequately handle two main independent switches for each power converter. Several MPPT control algorithms are validated and comparatively analyzed in both indoor and outdoor experiments in real time. A new control strategy (called Adaptive Hill-Climbing) is proposed as a modified version of the conventional Hill-Climbing method using an optimally adaptive power window. Other methods including dp/dv method and IncCond method are also implemented in the PV system. The experimental investigation is conducted using these control topologies to seek continuously varying Maximum Power Point (MPP) from solar arrays. The experimental results show that the new proposed control method strongly outperforms the other methods. This thesis shows that the proposed MPPT can increase the power generated by PV arrays by up to at least 30% more than a PV system without an MPPT. The proposed MPPT system is adaptive to environmental disturbances; it is flexible and can be expanded to an N-parallel PV system. / Thesis / Master of Applied Science (MASc)

The advancement of quantum dot sensitized solar cell (QDSSC) technology depends on optimizing directional charge transfer between light absorbing quantum dots, TiO2, and a redox mediator. Kinetically, reduction of oxidized quantum dots by the redox mediator should be rapid and faster than the back electron transfer between TiO2 and oxidized quantum dots to maintain photocurrent. Thermodynamically, the reduction potential of the redox mediator should be sufficiently positive to provide high photovoltages. To satisfy both criteria and enhance power conversion efficiencies, we introduced charge transfer spin-crossover MnII/III complexes as promising redox mediator alternatives in QDSSCs. High photovoltages ~ 1 V were achieved by a series of Mn poly(pyrazolyl)borates, with reduction potentials ~0.51 V vs Ag/AgCl. Back electron transfer rates were slower than Co(bpy)3, where bpy = 2,2'-bipyridine. This is indicative of a large barrier to recombination imposed by spin-crossover in these complexes. By capitalizing on these characteristics, efficient MnII/III-based QDSSCs can be achieved with more soluble Mn-complexes. In hybrid bulk heterojunction solar cells (HBHJs), light-absorbing conjugated polymers are interfaced with films of nanostructured TiO2. Photovoltaic action requires photoelectrons in the polymer to transfer into the TiO2, and therefore, polymers are designed with lowest unoccupied molecular orbital levels higher in energy than the conduction band of TiO2 for thermodynamically favorable electron transfer. Currently, the energy level values used to guide solar cell design are referenced from the separated materials, neglecting the fact that upon heterojunction formation material energetics are altered. With spectroelectrochemistry, we discovered that spontaneous charge transfer occurs upon heterojunction formation between poly(3-hexylthiophene) (P3HT) and TiO2. It was determined that deep trap states in TiO2 accept electrons from P3HT and form hole polarons in the polymer. This equilibrium charge separation alters energetics through the formation of interfacial dipoles and results in band bending that inhibits desired photoelectron injection into TiO2, limiting HBHJ solar cell performance. New guidelines for improved photocurrent are proposed by tuning the energetics of the heterojunction to reverse the direction of the interfacial dipole, enhancing photoelectron injection. / Master of Science

This project is a proposal on the versatile use of glass, its properties and technologies as well as its aesthetic qualities. A photovoltaic charging station for electric scooters is proposed for the Virginia Tech campus, combined with a bus shelter to allow mobility and integration of transportation. / Master of Science

In recent years there has been a growing interest in moving away from large centralized power generation toward distributed energy resources. Solar energy generation presents several benefits for use as a distributed energy resource, especially as a peaking power source. One drawback of solar energy sources is the need for energy storage for the system to be utilized for a significant percentage of the day. One way of avoiding adding energy storage to a solar generation system while still maintaining high system utilization is to design the power conversion subsystem to also provide harmonic and reactive compensation. When the sun is unavailable for generation, the system hardware can still be utilized to correct for harmonic and reactive currents on the distribution system. This system's dual-purpose operation solves both the power generation need, and helps to improve the growing problem of harmonic and reactive pollution of the distribution system. A control method is proposed for a system that provides approximately 1 kW of solar generation as well as up to 10 kVA of harmonic and reactive compensation simultaneously. The current control for the active was implemented with the synchronous reference frame method. The system and controller was designed and simulated. The harmonic and reactive compensation part of the system was built and tested experimentally. Due to the delay inherent in the control system from the sensors, calculation time, and power stage dynamics, the system was unable to correct for higher order harmonics. To allow the system to correct for all of the harmonics of concern, a hybrid passive - active approach was investigated by placing a set of inductors in series with the AC side of the load. A procedure was developed for properly sizing the inductors based on the harmonic residuals with the compensator in operation. / Master of Science

This research project deals with the development of a methodology to analyse and design photovoltaic-based power systems. A microcomputer-based interactive photovoltaic (PV) performance analysis package has been developed. This package can be used for screening analysis of various sites, module characteristics and system configurations. Basic elements of this package include: ( i) resource assessment; ( ii) site analysis; (iii) technology assessment; (iv) optimization and choice of system configurations; and (v) life-cycle cost analysis. The resource assessment part of the package is used to estimate the hourly, daily and monthly global horizontal, fixed tilt and one-axis tracking insolation for any site under cloudless sky condition. Site elevation, latitude, longititude and Julian date information are used for this purpose. This insolation level determines the upper limit of possible irradiance at the site under consideration. This value can be adjusted on the basis of climatic conditions (e.g., occurrences of cloudy days and rainfall) prevailing in the area. The site analysis deals with the site's economic and environmental evaluation. The parameters involved in these evaluations are the total land area, the effective area of the site, the area of forest destroyed, the loss of use of the site, the total number of people who are affected by the project, the number of people who benefit from the project, and the purchase price of the site. The technology assessment part of the package deals with the process of creating electricity from solar energy. The D.C. power output of the array is determined by using the global irradiation, the manufacturer-supplied efficiency and dimensions of the module, and the total area of the array. The A.C. power can also be evaluated depending on the power conditioning unit (PCU) efficiency. The optimization and the choice of the system configuration part of the package is used for determining the most optimum use of the candidate site in terms of land availability, land cost and the best possible mix of various PV modules for optimizing the cost of the PV energy within the existing constraints. Finally a life-cycle cost analysis is performed which includes cost of operation, cleaning, maintenance, spare parts, tilting, module, module support, inverter, charge controller, backup system and energy storage. It also takes into consideration the lifetime of the inverter, charge controller, the module, the backup system and the energy storage system. This package has been applied to analyse the performance of various PV modules in two locations. One of the biggest advantages of this package is that it is based on TURBO PASCAL language and runs on the IBM-PC and compatible microcomputers. Thus it is very portable from one operating environment to another, and users can be trained in its application quite easily. / M.S.

A major issue encountered in the large scale use of Photovoltaic (PV) energy sources for the production of electricity is the variability of the resource itself. Extensive fluctuations of the PV generation may cause dynamic operational problems for an electric utility. In order to remedy this situation it is proposed that fuel cell power plants be operated in parallel with PV arrays. This hybrid operation will help to smooth out the fluctuating PV output. Because of its high ramping capability the fuel cell will be able to absorb such fluctuations. An overall methodology is presented to evaluate the PV system in a large utility. This methodology has two parts-planning and operation. The aim of the planning study is to determine the capacity credit of a PV system based on the loss of load probability (LOLP). Long term SOLMET data is used to determine the nature of available insolation at a particular site. The expected value of hourly insolation is used in the planning study. The aim of the operation study is to validate the results of planning study in the shorter operational time frame, and determine the fuel cell requirements and associated operating cost savings for each penetration level of PV. A technique to find the maximum penetration level of PV, without causing any economic penalty, is presented. It is found that the penetration level can be increased up to 15.62% of peak load by adding fuel cells to the system under consideration. The annual peak load for this system is taken as 6400 MW. It must be mentioned here that, similar evaluations for other systems may yield somewhat different results. This technique is general enough such that it can be used for other intermittent sources of generation as well. / Ph. D.

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