171 |
Spherical Silicon for Photovoltaic Application: Material, Modeling, and DevicesGharghi, Majid January 2008 (has links)
Detailed material characterization of spherical silicon is conducted for the first time. Experimental results on crystallinity, impurities, and structural defects are presented to investigate the effect of growth mechanism and processing of the spheres.
Based on the material properties, the spherical bulk is characterized from electronic point of view. A model is developed to interpret photoconductivity decay measurements and extract minority carrier lifetime, the most influential parameter in device performance. The model includes the spherical geometry as well as the radial profile of carrier lifetime and the measurement results are used to characterize the quality of the spheres and the effectiveness of the process steps.
To analyze and predict the performance of spherical cells, a three dimensional opto-electric model is developed. The model separately treats the optical generation and carrier collection and is able to calculate the spectral response and the device characteristics. A simulation tool is created based on this model. The simulation results are of great importance in designing novel structures and optimizing fabrication processes.
The necessary characterization methodologies are developed to measure the spectral response and I-Vcharacteristics of individual cells, as well as an array consisting of several cells.
A new device design with passivated selective emitter is proposed based on simulation results. Plasma processes were developed to selectively etch back the deep emitter of the spherical cells using reactive ion etching, and then passivate the surface using plasma enhanced chemical vapor deposition of silicon nitride. The improvement in characteristics of the fabricated device is characterized using the developed measurement setups.
Industrial up-scaling and manufacturability of the proposed devices and processes are also discussed.
|
172 |
Control and Interfacing of Three Phase Grid Connected Photovoltaic SystemsKhalifa, Ahmed Said January 2010 (has links)
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.
|
173 |
noneHuang, Se-Jing 24 July 2010 (has links)
none
|
174 |
Organic Photovoltaic Cells of Fully Conjugated Poly-(3-hexylthiophene) and Heterocyclic Aromatic PCPDTBTCopolymer Doped with Derivatized FullereneLin, Tzu-chin 20 January 2011 (has links)
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).
|
175 |
A Design and Implementation of a Small Scale Photovoltaic Energy Conversion SystemLee, Cheng-Hsun 13 June 2002 (has links)
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.
|
176 |
Synthesis and characterization of semiconductor thin films for photoelectrochemical energy conversionHahn, Nathan Taylor 13 November 2012 (has links)
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
|
177 |
Utilization of radiant energy from gas turbine and jet enginesDoellner, Oscar Leonard January 1979 (has links)
No description available.
|
178 |
On the dynamics of excitons and charges in organic photovoltaicsRao, Akshay January 2011 (has links)
No description available.
|
179 |
Physical characterisation of polymer:fullerene blends for organic photovoltaic devicesHopkinson, Paul Edward January 2012 (has links)
No description available.
|
180 |
Charge transport in bulk heterojunction organic photovoltaicsLi, Zhe January 2012 (has links)
No description available.
|
Page generated in 0.0552 seconds