Solar power is considered a very promising source for electric power generation. The abundance of sunlight over a large area of the earth surface gives rise to several applications of photovoltaic systems. Electricity can be generated from sunlight either directly by employing the photovoltaic effect, or by using energy from the sun to heat up a working fluid that can be used to power up electricity generators. These two technologies are widely used today to provide power to either stand-alone loads or for connection to the power system grid. Maximum power point tracking (MPPT) is a very important consideration that is taken into account when building a new photovoltaic power system. This is needed in order to extract maximum power output from a PV array under varying atmospheric conditions to maximize the return on initial investments. Several techniques have been used to tackle this problem including perturb and observe (P&O), incremental conductance (IncCond) and fuzzy logic based algorithms. Judging between these techniques is based on their speed of locating the maximum power point (MPP) of a PV array under given atmospheric conditions, besides the cost and complexity of implementing them. The P&O and IncCond algorithms have a low implementation complexity but their tracking speed is slow. Fuzzy logic techniques are faster but suffer from high implementation complexity. One of the goals of this thesis is to present an MPPT algorithm implementation that is based on the fractional open circuit voltage method. This technique is easy to implement and offers a fast tracking speed for the MPP of a PV array. It provides an approximation within 4-5% of the maximum power point, which is a tradeoff between the speed and accuracy of operation around the MPP. It offers a speed advantage in grid connected PV systems. The P&O algorithm, which is very common, is difficult to implement under these conditions due to its poor response time. There is also a need for developing control techniques for three phase grid connected PV systems including a method for DC link voltage control that can stabilize the voltage at the inverter input. This area of research is currently growing with the increase in number of PV installations backed up by government incentives in several countries. In addition to the previously mentioned points, this work is intended to be used in further research to replace the representation of PV arrays as a simple DC source when included in power system studies. That is a basic assumption and does not take into consideration the various dynamics caused by changing solar irradiation and surface temperature of the array.

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Fully conjugated coil-like polymer poly-(3-hexylthiophene) (P3HT) and aromatic heterocyclic copolymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta-[2,1-b;3,4-b¡¬]- dithiophene)-alt-4,7-(2,1,3-benzothiadiazole] (PCPDTBT) were applied separately as donors mixed with derivatized carbon fullerence [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) serving as an acceptor. Single layer photovoltaic cells of ITO/ PEDOT:PSS/polymer:PC61BM/LiF/Al were fabricated to study photovoltaic effect of layer thickness, thermal annealing, composition variance, and processing solvent. At a P3HT:PC61BM weight ratio of 1:1, the thermally annealed photovoltaic cells achieved a conversion efficiency (£bp) of 4.58 % from enhanced contact between cathode and active layer. At a PCPDTBT:PC61BM weight ratio of 1:1.25, the best £bp was 2.62 %. The efficiency difference was due to PCPDTBT:PC61BM was highly phase separated preventing the formation of conductive interpenetrating network to facilitate charge transport. Its device fill factor was limited to be 38 %. Under the same spin coating speed, solutions of different PC61BM concentration would yield different spun film thickness leading to large change in conversion efficiency (£bp). At a constant active layer thickness, £bp tended to be stable indicating that £bp was affected more by the layer thickness than by PC61BM concentration. A layer of mixing P3HT: PCPDTBT: PC61BM would expand the absorption range from visible to near infrared. However, an increased PCPDTBT concentration did not help £bp. This is due to charge transport imbalance between P3HT and PCPDTBT leading to an £bp less than those of individual blends with PC61BM. Device £bp was consistently higher for using a solvent with a boiling point higher than polymer glass transition temperature (Tg).

The design and implementation of a small-scale solar energy conversion system is presented in this thesis. The power circuit of the PV inverter is composed of a push-pull converter and a full-bridge inverter. The inverter converts DC power generated by photovoltaic cells into AC power. This design allows flexible arrangements of various solar cells modules. The systems can supply loads and feed excess power to the grid with unit power factor when operated under grid-connected mode, or supply loads exclusively by operating in the stand-alone mode. In grid-connected mode, it is controlled to follow the variations of solar panel insolation for achieving maximum power point tracking. A 150W prototype of the conversion system is implemented, simulation and experimental results are provided to verify the performance.

The field of solar energy conversion has experienced resurgence in recent years due to mounting concerns related to fossil fuel consumption. The sheer quantity of available solar energy and corresponding opportunity for technological improvement has motivated extensive study of novel light-absorbing semiconductors for solar energy conversion. Often, these studies have focused on new ways of synthesizing and altering thin film semiconductor materials with unique compositions and morphologies in order to optimize them for higher conversion efficiencies. In this dissertation, we discuss the synthesis and electrochemical characterization of a variety of candidate semiconductor materials exhibiting promising characteristics for photoelectrochemical solar energy conversion. Three specific methods of thin film deposition are detailed. The first is a physical vapor deposition technique used to independently tune the morphology and composition of hematite (α-Fe2O3) based materials. Because of hematite’s poor electronic properties, these modifications were able to significantly improve its performance as a photoanode for water oxidation. The second technique is electrodeposition, which was employed to deposit the novel ternary metal oxide, CuBi2O4. The study of these films, along with those prepared by physical vapor deposition, provided insight into the factors limiting the ability of this photo-active material to function as a photocathode for hydrogen evolution from water. The third technique is chemical spray pyrolysis, which was employed to deposit and optimize films of the bismuth chalco-halides BiOI and BiSI. These studies were used to obtain previously unknown properties of these materials relevant to their utilization in photoelectrochemical cells. The manipulation of deposition temperature had significant effects on these properties and dictated the films’ overall photoconversion performance. / text

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