A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, a physical and chemical phenomenon. It is a form of photoelectric cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance, vary when exposed to light. Individual solar cell devices can be combined to form modules, otherwise known as solar panels. In basic terms a single junction silicon solar cell can produce a maximum open-circuit voltage of 0.5 to 0.6 volts. Solar cells are described as being photovoltaic, irrespective of whether the source is sunlight or an artificial light, they are used as a photodetector, detecting light or other electromagnetic radiation near the visible range, or measuring light intensity. The operation of a photovoltaic cell requires three basic attributes: The absorption of light, generating either electron-hole pairs or excitons; the separation of charge carriers of opposite types.
The separate extraction of those carriers to an external circuit. In contrast, a solar thermal collector supplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation from heat. A "photoelectrolytic cell", on the other hand, refers either to a type of photovoltaic cell, or to a device that splits water directly into hydrogen and oxygen using only solar illumination. Assemblies of solar cells are used to make solar modules that generate electrical power from sunlight, as distinguished from a "solar thermal module" or "solar hot water panel". A solar array generates solar power using solar energy. Multiple solar cells in an integrated group, all oriented in one plane, constitute a solar photovoltaic panel or module. Photovoltaic modules have a sheet of glass on the sun-facing side, allowing light to pass while protecting the semiconductor wafers. Solar cells are connected in series and parallel circuits or series in modules, creating an additive voltage.
Connecting cells in parallel yields a higher current. Strings of series cells are handled independently and not connected in parallel, though as of 2014, individual power boxes are supplied for each module, are connected in parallel. Although modules can be interconnected to create an array with the desired peak DC voltage and loading current capacity, using independent MPPTs is preferable. Otherwise, shunt diodes can reduce shadowing power loss in arrays with series/parallel connected cells; the photovoltaic effect was experimentally demonstrated first by French physicist Edmond Becquerel. In 1839, at age 19, he built the world's first photovoltaic cell in his father's laboratory. Willoughby Smith first described the "Effect of Light on Selenium during the passage of an Electric Current" in a 20 February 1873 issue of Nature. In 1883 Charles Fritts built the first solid state photovoltaic cell by coating the semiconductor selenium with a thin layer of gold to form the junctions. Other milestones include: 1888 – Russian physicist Aleksandr Stoletov built the first cell based on the outer photoelectric effect discovered by Heinrich Hertz in 1887.
1905 – Albert Einstein proposed a new quantum theory of light and explained the photoelectric effect in a landmark paper, for which he received the Nobel Prize in Physics in 1921. 1941 – Vadim Lashkaryov discovered p-n-junctions in Cu2O and Ag2S protocells. 1946 – Russell Ohl patented the modern junction semiconductor solar cell, while working on the series of advances that would lead to the transistor. 1954 – the first practical photovoltaic cell was publicly demonstrated at Bell Laboratories. The inventors were Daryl Chapin and Gerald Pearson. 1958 – solar cells gained prominence with their incorporation onto the Vanguard I satellite. Solar cells were first used in a prominent application when they were proposed and flown on the Vanguard satellite in 1958, as an alternative power source to the primary battery power source. By adding cells to the outside of the body, the mission time could be extended with no major changes to the spacecraft or its power systems. In 1959 the United States launched Explorer 6, featuring large wing-shaped solar arrays, which became a common feature in satellites.
These arrays consisted of 9600 Hoffman solar cells. By the 1960s, solar cells were the main power source for most Earth orbiting satellites and a number of probes into the solar system, since they offered the best power-to-weight ratio. However, this success was possible because in the space application, power system costs could be high, because space users had few other power options, were willing to pay for the best possible cells; the space power market drove the development of higher efficiencies in solar cells up until the National Science Foundation "Research Applied to National Needs" program began to push development of solar cells for terrestrial applications. In the early 1990s the technology used for space solar cells diverged from the silicon technology used for terrestrial panels, with the spacecraft application shifting to gallium arsenide-based III-V semiconductor materials, which evolved into the modern III-V multijunction photovoltaic cell used on spacecraft. Improvements were gradual over the 1960s.
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Industrial Tomography Systems
Industrial Tomography Systems plc abbreviated to ITOMS or ITS, is a manufacturer of process visualization systems based upon the principles of tomography. Headquartered in Manchester, UK, the company provides instrumentation to a variety of organisations across a range of sectors. Industrial Tomography Systems began as an incubator company in 1997, responsible for commercializing technologies developed by University of Manchester Institute of Science and Technology. Founders included a number of academics who had helped to develop tomography technology, such as Professors Brian Hoyle and Mi Wang and Professor Richard Williams. Industrial Tomography Systems has over a dozen staff based in the company's headquarters, has systems installed in a number of global companies, including Johnson Matthey, GlaxoSmithKline and Nestlé. In addition, the company has collaborated with major engineering firms, such as Philadelphia Mixers, to host international tomography workshops that showcase its technologies.
In 2011, Industrial Tomography Systems was recognised as a "global leader in its field" after it was short-listed in the Institution of Engineering and Technology Innovation Awards. In an interview with the Manchester Evening News, Primrose attributed the success of the company to being able to offer tailored solutions that are designed to meet the needs of individual applications, as well as having a coordinated network of international distributors and agents. Industrial Tomography Systems' scanning technology works on a similar principle to CAT scanners that are used in hospitals to see inside the human body: by passing an electric current rapidly between pairs of electrodes that are in contact with the process media, real-time images of the industrial process can be extrapolated from measuring the resulting difference in voltages. Since 2001, the company has developed a range of instruments based upon different types of tomography, which are outlined below. Industrial Tomography Systems' instrumentation that utilizes the principles of electrical impedance tomography & electrical resistance tomography include: z8000, p2+, v5r.
These systems have been used to visualize processes involving mixing, bubble columns, packed beds and separations. Electrical capacitance tomography instruments released by the company include: m3000c, m3000dual, m3c; these instruments are used when the phases in a process are non-conducting, with readings instead based upon electrical permittivity rather than electrical conductivity. As such, ECT instruments can be used in similar processes to those where ERT is deployed, including flows, fluidized beds, pneumatic conveying; until mid-2013, Industrial Tomography Systems supported one instrument based upon ultrasound spectroscopy technology: the u2s. In 2015, Industrial Tomography Systems launched their industry changing Densitometer, a system which uses no nuclear power sources. Based on electrical resistance tomography, this new measurement system can take data independent of flow regime and concentration of measure materials which are neutrally buoyant; the instrument is supplied as a pipe based a standard IP67 instrument enclosure.
The device has gone on to make a huge impact in the dredging sector, due to its environmentally friendly technology. Years of listening to industry professionals complain about their batch mixers has prompted ITS to develop the Mix-itometer, which utilises tomography solutions to resolve mixing problems; the Mix-itometer probe when placed inside batch mixers, replacing an existing baffle, measures average concentration and a mixing index by surveying more than 200 locations inside the process vessel. Mix-itometer software provides users with a visual representation of mixing upon a PC-based interface. Findings published in AAPS's PharmSciTech in 2005 indicate that Industrial Tomography Systems' technology is able to monitor the on-line measurement of solids distributed in a stirred tank, the performance of industrial pressure filters, flow profiles and velocity measurements. Additionally Primrose claims that, due to the non-invasive nature of tomography technology, it can be used to create images of industrial processes in hard-to-reach places, such as in pipelines that contain radioactive/toxic materials.
Fluid dynamics Mettler Toledo Multiphase flow Industrial Tomography Systems plc website
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word refers to visible light, the visible spectrum, visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared and the ultraviolet. This wavelength means a frequency range of 430–750 terahertz; the main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to create sugars in the form of starches, which release energy into the living things that digest them; this process of photosynthesis provides all the energy used by living things. Another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has replaced firelight; some species of animals generate their own light, a process called bioluminescence.
For example, fireflies use light to locate mates, vampire squids use it to hide themselves from prey. The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays and radio waves are light. Like all types of EM radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed; the absorbed energy of the EM waves is called a photon, represents the quanta of light. When a wave of light is transformed and absorbed as a photon, the energy of the wave collapses to a single location, this location is where the photon "arrives."
This is. This dual wave-like and particle-like nature of light is known as the wave–particle duality; the study of light, known as optics, is an important research area in modern physics. EM radiation, or EMR, is classified by wavelength into radio waves, infrared, the visible spectrum that we perceive as light, ultraviolet, X-rays, gamma rays; the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, lower frequencies have longer wavelengths; when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. EMR in the visible light region consists of quanta that are at the lower end of the energies that are capable of causing electronic excitation within molecules, which leads to changes in the bonding or chemistry of the molecule. At the lower end of the visible light spectrum, EMR becomes invisible to humans because its photons no longer have enough individual energy to cause a lasting molecular change in the visual molecule retinal in the human retina, which change triggers the sensation of vision.
There exist animals that are sensitive to various types of infrared, but not by means of quantum-absorption. Infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, how these animals detect it. Above the range of visible light, ultraviolet light becomes invisible to humans because it is absorbed by the cornea below 360 nm and the internal lens below 400 nm. Furthermore, the rods and cones located in the retina of the human eye cannot detect the short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, in much the same chemical way that humans detect visible light. Various sources define visible light as narrowly as 420–680 nm to as broadly as 380–800 nm. Under ideal laboratory conditions, people can see infrared up to at least 1050 nm.
Plant growth is affected by the color spectrum of light, a process known as photomorphogenesis. The speed of light in a vacuum is defined to be 299,792,458 m/s; the fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at this same speed in vacuum. Different physicists have attempted to measure the speed of light throughout history. Galileo attempted to measure the speed of light in the seventeenth century. An early experiment to measure the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Using a telescope, Rømer observed one of its moons, Io. Noting discrepancies in the apparent period of Io's orbit, he calculated that light takes about 22 minutes to traverse the diameter of Earth's orbit. However, its size was not known at that time. If Rømer had known the diameter of the Earth's orbit, he would have calculated a speed of 227,000,000 m/s. Another, more accurate, measurement of the speed of light was performed in Europe by Hippolyte Fizeau in 1849.
An electronic circuit is composed of individual electronic components, such as resistors, capacitors and diodes, connected by conductive wires or traces through which electric current can flow. To be referred to as electronic, rather than electrical at least one active component must be present; the combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, data can be moved from one place to another. Circuits can be constructed of discrete components connected by individual pieces of wire, but today it is much more common to create interconnections by photolithographic techniques on a laminated substrate and solder the components to these interconnections to create a finished circuit. In an integrated circuit or IC, the components and interconnections are formed on the same substrate a semiconductor such as silicon or gallium arsenide. An electronic circuit can be categorized as an analog circuit, a digital circuit, or a mixed-signal circuit.
Breadboards and stripboards are common for testing new designs. They allow the designer to make quick changes to the circuit during development. Analog electronic circuits are those in which current or voltage may vary continuously with time to correspond to the information being represented. Analog circuitry is constructed from two fundamental building blocks: parallel circuits. In a series circuit, the same current passes through a series of components. A string of Christmas lights is a good example of a series circuit: if one goes out, they all do. In a parallel circuit, all the components are connected to the same voltage, the current divides between the various components according to their resistance; the basic components of analog circuits are wires, capacitors, inductors and transistors. Analog circuits are commonly represented in schematic diagrams, in which wires are shown as lines, each component has a unique symbol. Analog circuit analysis employs Kirchhoff's circuit laws: all the currents at a node, the voltage around a closed loop of wires is 0.
Wires are treated as ideal zero-voltage interconnections. Active components such as transistors are treated as controlled current or voltage sources: for example, a field-effect transistor can be modeled as a current source from the source to the drain, with the current controlled by the gate-source voltage. An alternative model is to take independent power sources and induction as basic electronic units; when the circuit size is comparable to a wavelength of the relevant signal frequency, a more sophisticated approach must be used, the distributed element model. Wires are treated as transmission lines, with nominally constant characteristic impedance, the impedances at the start and end determine transmitted and reflected waves on the line. Circuits designed according to this approach are distributed element circuits; such considerations become important for circuit boards at frequencies above a GHz. In digital electronic circuits, electric signals take on discrete values, to represent logical and numeric values.
These values represent the information, being processed. In the vast majority of cases, binary encoding is used: one voltage represents a binary'1' and another voltage represents a binary'0'. Digital circuits make extensive use of transistors, interconnected to create logic gates that provide the functions of Boolean logic: AND, NAND, OR, NOR, XOR and all possible combinations thereof. Transistors interconnected so as to provide positive feedback are used as latches and flip flops, circuits that have two or more metastable states, remain in one of these states until changed by an external input. Digital circuits therefore can provide both logic and memory, enabling them to perform arbitrary computational functions; the design process for digital circuits is fundamentally different from the process for analog circuits. Each logic gate regenerates the binary signal, so the designer need not account for distortion, gain control, offset voltages, other concerns faced in an analog design; as a consequence complex digital circuits, with billions of logic elements integrated on a single silicon chip, can be fabricated at low cost.
Such digital integrated circuits are ubiquitous in modern electronic devices, such as calculators, mobile phone handsets, computers. As digital circuits become more complex, issues of time delay, logic races, power dissipation, non-ideal switching, on-chip and inter-chip loading, leakage currents, become limitations to the density and performance. Digital circuitry is used to create general purpose computing chips, such as microprocessors, custom-designed logic circuits, known as application-specific integrated circuit. Field-programmable gate arrays, chips with logic circuitry