PV cells

The next choice is the type of solar cells to use. Cells come in a wide variety of shapes and sizes. The most frequently encountered shapes are square, pseudo square (square with angled corners) and round. I chose a pseudo square shaped single crystal cell that was rated at 4 amps at. 55 volt per cell. These cells were purchased as cosmetically blemished and off spec (sub standard) thus, they were available at a reduced price. Each cell is 5 in length and width. 

As stated earlier, there are three basic types of cells the single crystal cell, the polycrystaUine 

When shopping for cells, you can purchase new cells with no flaws or new cells with flaws, either cosmetic or those that are off specification. Off spec cells are cells that did not have the expected output when tested at the factory. They are still good cells, but may not provide the current and voltage that would make them suitable for a commercial panel. When considering off spec cells, keep in mind that the lowest output cell on a panel is what the panel s final output will be. So, be sure that the lowest output cell is within your acceptable limits. 

Cosmetic flaws can be anything from chips off the sides or corners, discoloration, or lack of reflective coating. Cells can be just cosmetically flawed and putting out full output or they can be cosmetically flawed and off spec. For instance, a lack of reflective coating on parts of a cell (cosmetic blemish) can reduce their output as they will reflect more and not absorb as much light. 

Higher current cells are larger and cost more per cell. However, larger cells mean fewer tab and bus connections to make, and they reduce the number of cells needed to produce a given amount of current. 

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Since the first photovoltaic (PV) cells were fabricated for the U.S. space program in 1958, PV technology has evolved from once being a very high cost but essential and effective space power source to later becoming a small but diversified and enduring worldwide industry (1 6). Led by firms based in the United States, Japan, and Germany, this industry serves multiple markets (see Photovoltaic cells). 

Taken as a group, PV cells comprise soHd-state devices in which photons of light coUide with atoms and transfer thek energy to electrons. These electrons flow into wkes that ate connected to the cells, thereby providing current to electrical loads. 

StiU another method used to produce PV cells is provided by thin-fiLm technologies. Thin films ate made by depositing semiconductor materials on a sohd substrate such as glass or metal sheet. Among the wide variety of thin-fiLm materials under development ate amorphous siUcon, polycrystaUine sUicon, copper indium diselenide, and cadmium teUuride. Additionally, development of multijunction thin-film PV cells is being explored. These cells use multiple layers of thin-film sUicon alloys or other semiconductors tailored to respond to specific portions of the light spectmm. 

In addition, other utiUties are installing estabUshed solar cells in a growing number of tests that may lead to a mass market. The studies may indicate the extent to which solar cells can be used to avoid installation costs for new distribution lines between conventional power plants and remote customers buildings. Also, among other objectives, PV cells may provide an economical means of helping to supply demand during peak summer periods in northern climates. 

Photovoltaic devices typically consist of a series of thin semiconductor layers that are designed to convert sunlight to dkect-current electricity (see Semiconductors). As long as the device is exposed to sunlight, a photovoltaic (PV) cell produces an electric current proportional to the amount of light it receives. The photovoltaic effect, first observed in 1839, did not see commercial appHcation until the 1950s when photovoltaic modules were used to power early space sateHites. Many good descriptions of the photovoltaic phenomenon are available (7). 

The photoelectric effect (the creation of an electrical current when light shines on a photosensitive material connected m an electrical circuit) was first obseiwed in 1839 by the French scientist Edward Becqiierel. More than one hundred years went by before researchers in the United States Bell Laboratories developed the first modern PV cell in 1954. Four years later, PV was used to power a satellite in space and has provided reliable electric power for space exploration ever since. 

The fact that solar energy is an intermittent energy resource means that energy storage systems (e.g., batteries, ultracapacitors, flywheels, and even hydrogen) will be required if solar energy is to be utilized widely. In addition, a variety of toxic chemicals are used in the manufacture of PV cells however, studies of the risks associated with their manufacture and disposal indicate little threat to surroundings and the environment. 

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

Water is involved in most of the photodecomposition reactions. Hence, nonaqueous electrolytes such as methanol, ethanol, N,N-d i methyl forma mide, acetonitrile, propylene carbonate, ethylene glycol, tetrahydrofuran, nitromethane, benzonitrile, and molten salts such as A1C13-butyl pyridium chloride are chosen. The efficiency of early cells prepared with nonaqueous solvents such as methanol and acetonitrile were low because of the high resistivity of the electrolyte, limited solubility of the redox species, and poor bulk and surface properties of the semiconductor. Recently, reasonably efficient and fairly stable cells have been prepared with nonaqueous electrolytes with a proper design of the electrolyte redox couple and by careful control of the material and surface properties [7], Results with single-crystal semiconductor electrodes can be obtained from table 2 in Ref. 15. Unfortunately, the efficiencies and stabilities achieved cannot justify the use of singlecrystal materials. Table 2 in Ref. 15 summarizes the results of liquid junction solar cells prepared with polycrystalline and thin-film semiconductors [15]. As can be seen the efficiencies are fair. Thin films provide several advantages over bulk materials. Despite these possibilities, the actual efficiencies of solid-state polycrystalline thin-film PV solar cells exceed those obtained with electrochemical PV cells [22,23]. 

PEC Setups with Multijunction and Multiple PV Cells 7.6.1 PEC Setup with Tandem Cells... 

The PV efficiency of the CIGS2 cell prepared on glass with transparent conducting back contact, as measured at the NREL, was 5.95%. Calculated PEC efficiency of two such PV cells... 

Somani, P. R. Dionigi, C. Murgia, M. Palles, D. Nozar, P. Ruani, G. 2005. Solid-state dye PV cells using inverse opal Ti02 films. Solar Energy Mater. Solar Cells 87 513-519. 

Organic PV cells, 23 44 Organic pyrophosphates, 79 42 Organic reactions, microwave-accelerated solvent- free, 76 555—584 Organic reactions, sulfur in, 23 568 Organic reactions, use of thallium in, 24 635-636... 

Photovoltaic (PV) cells, 23 32-53. See also Photovoltaic materials commercial history of, 23 49—51 conducting polymer applications, 7 541 polymethine dyes in, 20 516—517 selenium, 22 100, 103 spectrum and band gap of, 23 37-39 structure of, 22 220-221 third generation, 23 44 workings of, 23 32-37 Photovoltaic detectors, 19 133, 138 Photovoltaic detectors/arrays/focal planes, 19 163-164... 

Quantum computers, 77 61 Quantum dot materials, 22 142 Quantum dot PV cells, 23 44 Quantum dots... 

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