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Energy Source Fact Files. Solar cells sources

Energy Source Fact Files. Solar cells sources

    Solar Cell

    Photovoltaic solar cells are thin silicon disks that convert sunlight into electricity. These disks act as energy sources for a wide variety of uses, including: calculators and other small devices; telecommunications; rooftop panels on individual houses; and for lighting, pumping, and medical refrigeration for villages in developing countries. Solar cells in the form of large arrays are used to power satellites and, in rare cases, to provide electricity for power plants.

    When research into electricity began and simple batteries were being made and studied, research into solar electricity followed amazingly quickly. As early as 1839, Antoine-Cesar Becquerel exposed a chemical battery to the sun to see it produce voltage. This first conversion of sunlight to electricity was one percent efficient. That is, one percent of the incoming sunlight was converted into electricity. Willoughby Smith in 1873 discovered that selenium was sensitive to light; in 1877 Adams and Day noted that selenium, when exposed to light, produced an electrical current. Charles Fritts, in the 1880s, also used gold-coated selenium to make the first solar cell, again only one percent efficient. Nevertheless, Fritts considered his cells to be revolutionary. He envisioned free solar energy to be a means of decentralization, predicting that solar cells would replace power plants with individually powered residences.

    With Albert Einstein’s explanation in 1905 of the photoelectric effect—metal absorbs energy from light and will retain that energy until too much light hits it—hope soared anew that solar electricity at higher efficiencies would become feasible. Little progress was made, however, until research into diodes and transistors yielded the knowledge necessary for Bell scientists Gordon Pearson, Darryl Chapin, and Cal Fuller to produce a silicon solar cell of four percent efficiency in 1954.

    Further work brought the cell’s efficiency up to 15 percent. Solar cells were first used in the rural and isolated city of Americus, Georgia as a power source for a telephone relay system, where it was used successfully for many years.

    A type of solar cell to fully meet domestic energy needs has not as yet been developed, but solar cells have become successful in providing energy for artificial satellites. Fuel systems and regular batteries were too heavy in a program where every ounce mattered. Solar cells provide more energy per ounce of weight than all other conventional energy sources, and they are cost-effective.

    Only a few large scale photovoltaic power systems have been set up. Most efforts lean toward providing solar cell technology to remote places that have no other means of sophisticated power. About 50 megawatts are installed each year, yet solar cells provide only about. 1 percent of all electricity now being produced. Supporters of solar energy claim that the amount of solar radiation reaching the Earth’s surface each year could easily provide all our energy needs several times over, yet solar cells have a long way to go before they fulfill Charles Fritts’s dream of free, fully accessible solar electricity.

    Raw Materials

    The basic component of a solar cell is pure silicon, which is not pure in its natural state.

    To make solar cells, the raw materials—silicon dioxide of either quartzite gravel or crushed quartz—are first placed into an electric arc furnace, where a carbon arc is applied to release the oxygen. The products are carbon dioxide and molten silicon. At this point, the silicon is still not pure enough to be used for solor cells and requires further purification.

    Pure silicon is derived from such silicon dioxides as quartzite gravel (the purest silica) or crushed quartz. The resulting pure silicon is then doped (treated with) with phosphorous and boron to produce an excess of electrons and a deficiency of electrons respectively to make a semiconductor capable of conducting electricity. The silicon disks are shiny and require an anti-reflective coating, usually titanium dioxide.

    The solar module consists of the silicon semiconductor surrounded by protective material in a metal frame. The protective material consists of an encapsulant of transparent silicon rubber or butyryl plastic (commonly used in automobile windshields) bonded around the cells, which are then embedded in ethylene vinyl acetate. A polyester film (such as mylar or tedlar) makes up the backing. A glass cover is found on terrestrial arrays, a lightweight plastic cover on satellite arrays. The electronic parts are standard and consist mostly of copper. The frame is either steel or aluminum. Silicon is used as the cement to put it all together.

    The Manufacturing Process

    Purifying the silicon

    • 1 The silicon dioxide of either quartzite gravel or crushed quartz is placed into an electric arc furnace. A carbon arc is then applied to release the oxygen. The products are carbon dioxide and molten silicon. This simple process yields silicon with one percent impurity, useful in many industries but not the solar cell industry.
    • 2 The 99 percent pure silicon is purified even further using the floating zone technique. A rod of impure silicon is passed through a heated zone several times in the same direction. This procedure drags the impurities toward one end with each pass. At a specific point, the silicon is deemed pure, and the impure end is removed.

    Making single crystal silicon

    • 3 Solar cells are made from silicon boules, polycrystalline structures that have the atomic structure of a single crystal. The most commonly used process for creating the boule is called the Czochralski method. In this process, a seed crystal of silicon is dipped into melted polycrystalline silicon. As the seed crystal is withdrawn and rotated, a cylindrical ingot or boule of silicon is formed. The ingot withdrawn is unusually pure, because impurities tend to remain in the liquid.

    Making silicon wafers

    • 4 From the boule, silicon wafers are sliced one at a time using a circular saw whose inner diameter cuts into the rod, or many at once with a multiwire saw. (A diamond saw produces cuts that are as wide as the wafer- 5 millimeter thick.) Only about one-half of the silicon is lost from the boule to the finished circular wafer—more if the wafer is then cut to be rectangular or hexagonal. Rectangular or hexagonal wafers are sometimes used in solar cells because they can be fitted together perfectly, thereby utilizing all available space on the front surface of the solar cell.

    After the initial purification, the silicon is further refined in a floating zone process. In this process, a silicon rod is passed through a heated zone several times, which serves to ‘drag the impurities toward one end of the rod. The impure end can then be removed. Next, a silicon seed crystal is put into a Czochralski growth apparatus, where it is dipped into melted polycrystalline silicon. The seed crystal rotates as it is withdrawn, forming a cylindrical ingot of very pure silicon. Wafers are then sliced out of the ingot.

    Doping

    • 6 The traditional way of doping (adding impurities to) silicon wafers with boron and phosphorous is to introduce a small amount of boron during the Czochralski process in step #3 above. The wafers are then sealed back to back and placed in a furnace to be heated to slightly below the melting point of silicon (2,570 degrees Fahrenheit or 1,410 degrees Celsius) in the presence of phosphorous gas. The phosphorous atoms burrow into the silicon, which is more porous because it is close to becoming a liquid. The temperature and time given to the process is carefully controlled to ensure a uniform junction of proper depth. A more recent way of doping silicon with phosphorous is to use a small particle accelerator to shoot phosphorous ions into the ingot. By controlling the speed of the ions, it is possible to control their penetrating depth. This new process, however, has generally not been accepted by commercial manufacturers.

    Placing electrical contacts

    • 7 Electrical contacts connect each solar cell to another and to the receiver of produced current. The contacts must be very thin (at least in the front) so as not to block sunlight to the cell. Metals such as palladium/silver, nickel, or copper are vacuum-evaporated

    This illustration shows the makeup of a typical solar cell. The cells are encapsulated in ethylene vinyl acetate and placed in a metal frame that has a mylar backsheet and glass cover.

    The anti-reflective coating

    • 9 Because pure silicon is shiny, it can reflect up to 35 percent of the sunlight. To reduce the amount of sunlight lost, an anti-reflective coating is put on the silicon wafer. The most commonly used coatings are titanium dioxide and silicon oxide, though others are used. The material used for coating is either heated until its molecules boil off and travel to the silicon and condense, or the material undergoes sputtering. In this process, a high voltage knocks molecules off the material and deposits them onto the silicon at the opposite electrode. Yet another method is to allow the silicon itself to react with oxygen- or nitrogen-containing gases to form silicon dioxide or silicon nitride. Commercial solar cell manufacturers use silicon nitride.

    Encapsulating the cell

    • 10 The finished solar cells are then encapsulated; that is, sealed into silicon rubber or ethylene vinyl acetate. The encapsulated solar cells are then placed into an aluminum frame that has a mylar or tedlar backsheet and a glass or plastic cover.

    Quality Control

    Quality control is important in solar cell manufacture because discrepancy in the many processes and factors can adversely affect the overall efficiency of the cells. The primary research goal is to find ways to improve the efficiency of each solar cell over a longer lifetime. The Low Cost Solar Array Project (initiated by the United States Department of Energy in the late 1970s) sponsored private research that aimed to lower the cost of solar cells. The silicon itself is tested for purity, crystal orientation, and resistivity. Manufacturers also test for the presence of oxygen (which affects its strength and resistance to warp) and carbon (which causes defects). Finished silicon disks are inspected for any damage, flaking, or bending that might have occurred during sawing, polishing, and etching.

    During the entire silicon disk manufacturing process, the temperature, pressure, speed, and quantities of dopants are continuously monitored. Steps are also taken to ensure that impurities in the air and on working surfaces are kept to a minimum.

    The completed semiconductors must then undergo electrical tests to see that the current, voltage, and resistance for each meet appropriate standards. An earlier problem with solar cells was a tendency to stop working when partially shaded. This problem has been alleviated by providing shunt diodes that reduce dangerously high voltages to the cell. Shunt resistance must then be tested using partially shaded junctions.

    An important test of solar modules involves providing test cells with conditions and intensity of light that they will encounter under normal conditions and then checking to see that they perform well. The cells are also exposed to heat and cold and tested against vibration, twisting, and hail.

    The final test for solar modules is field site testing, in which finished modules are placed where they will actually be used. This provides the researcher with the best data for determining the efficiency of a solar cell under ambient conditions and the solar cell’s effective lifetime, the most important factors of all.

    The Future

    Considering the present state of relatively expensive, inefficient solar cells, the future can only improve. Some experts predict it will be a billion-dollar industry by the year 2000. This prediction is supported by evidence of more rooftop photovoltaic systems being developed in such countries as Japan, Germany, and Italy. Plans to begin the manufacture of solar cells have been established in Mexico and China. Likewise, Egypt, Botswana, and the Philippines (all three assisted by American companies) are building plants that will manufacture solar cells.

    Most current research aims for reducing solar cell cost or increasing efficiency. Innovations in solar cell technology include developing and manufacturing cheaper alternatives to the expensive crystalline silicon cells. These alternatives include solar Windows that mimic photosynthesis, and smaller cells made from tiny, amorphous silicon balls. Already, amorphous silicon and polycrystalline silicon are gaining popularity at the expense of single crystal silicon. Additional innovations including minimizing shade and focusing sunlight through prismatic lenses. This involves layers of different materials (notably, gallium arsenide and silicon) that absorb light at different frequencies, thereby increasing the amount of sunlight effectively used for electricity production.

    A few experts foresee the adaptation of hybrid houses; that is, houses that utilize solar water heaters, passive solar heating, and solar cells for reduced energy needs. Another view concerns the space shuttle placing more and more solar arrays into orbit, a solar power satellite that beams power to Earth solar array farms, and even a space colony that will manufacture solar arrays to be used on Earth.

    Where To Learn

    Books

    Bullock, Charles E. and Peter H. Grambs. Solar Electricity: Making the Sun Work for You. Monegon, Ltd., 1981.

    Komp, Richard J. Practical Photovoltaics. Aatec Publications, 1984.

    Making and Using Electricity from the Sun. Tab Books, 1979.

    Periodicals

    Crawford, Mark. DOE’s Born-Again Solar Energy Plan, Science. March 23, 1990, pp. 1403-1404.

    Waiting for the Sunrise, Economist. May 19, 1990, pp. 95.

    Edelson, Edward. Solar Cell Update, Popular Science. June, 1992, p. 95.

    energy, source, fact, files, solar

    Murray, Charles J. Solar Power’s Bright Hope, Design News. March 11, 1991, p. 30.

    Energy Source Fact Files!

    To help you get thinking about energy, we’ve got some great pages all about it!

    Solar Power: Energy Source Fact File!

    What is solar power? What’s a Photovoltaic cell, and how does it convert light into power?

    Here’s the need-to-know stuff about the energy source, solar power!

    Description

    The Sun is a star and without it there would be no life on Earth. This is why the Sun is called the ultimate source of energy.

    The Sun’s energy is produced by a process called nuclear fusion. Every second, the Sun emits vast amounts of energy, much of which is light. This solar radiation can be converted into electricity!

    Where can you find solar power?

    Solar panels can be found all over the world but they are most cost-effective in places where there is a lot of sunshine.

    to click.

    Researchers at Sheffield University are investigating now much energy solar can produce. Their project is called called PV_Live – it lets you can see how much energy solar power is producing right now in the UK!

    How is it made into electricity?

    Solar cells, also known as Photovoltaic (PV cells), convert sunlight directly into electricity. When sunlight hits the surface of the cell this causes electrons to move. This creates a current in each cell, which is combined to produce useful amounts of electricity.

    PV cells are combined in solar panels and mounted on the roofs of buildings. They can also be used to power devices such as calculators and watches!

    What are the advantages of using solar power?

    • Solar energy is plentiful, free, and renewable.
    • Solar panels do not produce any carbon dioxide emissions when converting solar power into electricity.
    • Solar power can be used to create electricity in remote places where it might be very hard to get electricity through the National Grid.

    What are the disadvantages of using solar power?

    • It can be costly to fit enough solar panels to power a home or building.
    • PV cells are less efficient in cloudy countries such as the UK.

    We’ve got a whole series about energy, electricity, and power generation! It’s called Curious Kate, and you can listen to it below!

    Energy Source Fact Files!

    Learn about different types of energy and how they help generate electricity!

    Energy Source Fact Files!

    Learn about different types of energy and how they help generate electricity!

    energy, source, fact, files, solar

    How Are Solar Panels Made? What Solar Panels Are Made of How They Are Manufactured

    Solar energy’s popularity has rapidly increased in the last several years, making a significant impact on the energy market. According to the Solar Energy Industries Association, the U.S. has installed enough solar to power 13.1 million homes and total U.S. solar capacity is projected to more than double by 2024.

    As solar energy use becomes more prevalent, so does information about how it’s harnessed and used. Photovoltaic, or solar, panels can often be found in both commercial and residential areas. How are these panels made, and what materials are used to manufacture them?

    The table below outlines the raw materials and parts comprising a solar panel.

    Silicon is the basic material for conductive electrical components. Before it can be used, it must undergo a treatment process that removes impurities and converts it to pure silicon, or polysilicon. The industry shouldn’t face material shortages any time soon; silicon is abundant, making up one-quarter of the earth’s crust by weight.

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    Once the silicon is rid of impurities, it is turned into ingots, which are pure silicon cylinders. The ingots are made from a crystal of silicon that is dipped into polycrystalline silicon. The impurities remain in the melted liquid, so the ingot forms as a completely pure cylinder. From there, the ingot is sliced into.5-millimeter-thick wafers, which are shaped into rectangular or hexagonal shapes so they can fit tightly together.

    Boron and phosphorus are added to the wafers through a doping process. The wafers are heated in order to allow atoms from these elements, or dopants, to enter the silicon. When these elements are added to the polysilicon, the first result is an excess of electrons, which is then followed by a deficiency of them. This allows the polysilicon to act as a semiconductor.

    To conduct a large amount of electricity, many cells must be connected together by electrical contacts. The group is then connected to the receiver. An anti-reflective coating is applied to the panel to prevent loss of sunlight and wasted energy. The cells are then sealed into a rubber or vinyl acetate, framed in aluminum and covered in glass or plastic.

    Silicon: Raw Material in Solar Cells

    Silicon is the second most common element in the earth’s crust. According to the Minerals Education Coalition, it isn’t found pure in nature; rather, it’s found combined with oxygen in rocks such as obsidian, granite, and sandstone, in a form known as silica. Silicon can be mined from quartzite, mica, and talc, but sand is its most abundant ore source. The silicon in solar panels is manufactured through a reduction process in which the silica is heated with a carbon material and the oxygen is removed, leaving behind purer, metallurgical-grade silicon.

    From there, the grade must be further purified into polysilicon, the solar-grade purity of which is 99.999 percent. To yield polysilicons of different grades, several processes may be applied to the element. For electronic-grade polysilicon, which has a higher purity percentage, the metallurgical-grade silicone must pass through hydrogen chloride at extremely high temperatures and undergo distillation. But to yield a solar-grade end product, the silicone goes through a chemical refinement process. In this process, gases are passed through melted silicon to remove impurities such as boron and phosphorus. In its pure form, solar-grade silicon is then turned into cylinders called ingots, which are then sliced into the small conductive pieces that absorb the sunlight in solar panels.

    Ingots Wafers: The Backbone of Solar Cells

    Several types of wafers are cut from the ingots: monocrystalline, polycrystalline and silicon ribbons. They differ in terms of their efficiency in conducting sunlight and the amounts of waste they produce.

    Monocrystalline wafers are thinly cut from a cylindrical ingot that has a single-crystal structure, meaning that it is comprised of a pure, uniform crystal of silicon. A diamond saw is used to cut the wafers off the cylinder, resulting in a circular shape. However, since circles don’t fit tightly together, the circular wafers are further cut into rectangle or hexagonal shapes, resulting in wasted silicon from the pieces that are removed. According to GreenRhinoEnergy.com, this wasted silicon can be recycled into polysilicon and recut. Researchers are trying to find ways to create monocrystalline cells without so much cutting and waste.

    Polycrystalline, sometimes called multicrystalline, ingots are made of multiple crystal structures. They may produce less waste, but they are not as efficient as monocrystalline. The ingots are cube-shaped because they are made from melted silicon poured into a shaped cast. This means the wafers can be cut directly into the desired shape, creating less waste.

    Silicon ribbons are thin sheets of multicrystalline silicon. They are so thin that they don’t have to be sliced into wafers. While the thin sheets, or thin films, are flexible, can be used in interesting ways and are less expensive to manufacture, they’re not as durable as wafers and they require more support than other solar panel structures.

    Solar Cells: Adding Dopants to Activate the Wafer

    While the silicon wafers are complete at this point, they won’t conduct any energy until they go through the doping process. This process involves the ionization of the wafers and the creation of a positive-negative (p-n) junction. The wafers are heated in cylinders at a very high temperature and put into water. Then the top layer of the cylinder is exposed to phosphorus (a negative electrical orientation) while the bottom layer is exposed to boron (a positive electrical orientation). The positive-negative junction of the cell allows it to function properly in the solar panel.

    After this step, only a few more things need to happen in order to create a functioning cell. Because silicon naturally reflects sunlight, there is a considerable risk of losing much of the potential energy from the sun that the cells are supposed to absorb. To minimize this reflection, manufacturers coat the cells with antireflective silicon nitride, which gives the cells the final blue color we see in installed panels.

    From there, manufacturers implement a system for collecting and distributing the solar energy. This is done through a silk-screen or screen-printing process in which metals are printed on both sides of the cell. These metals make a roadmap for the energy to travel through on its way to the receiver.

    Solar Panels: Assembling Cells Into Useful Devices

    Solar panel manufacturers employ different proprietary processes to produce their final solar panel products. But, in general, this is an automated process in which robots do the work. First, the cells must be put together to form a big sheet. According to Solar World, a leading manufacturer of solar panels, its process involves soldering six strings of ten cells each, making a rectangle of 60 cells. Each rectangular matrix is laminated onto glass and quickly becomes a larger panel. From there, the panel needs to be framed so that it is sturdy and protected from any weather it will endure.

    In addition, the framing must house the electrical equipment that links the panels together and receives the energy.

    Where Does Polysilicon Come From?

    Polysilicon has one origin: silica. Silica is mined from the earth and is found in sand, rock, and quartz. Because silica has a dioxide component, it must be taken to a plant, where it is converted to silicon through a heating process. According to the United States Geological Society, there are six domestic companies that produce silicon materials at eight plants. These are all located east of the Mississippi River. Imported silicon comes from all around the world, including China, Russia, Japan, Brazil, South Africa, Canada, Australia, and others.

    Solar Cells

    Solar cells are in fact large area semiconductor diodes. Due to photovoltaic effect energy of light (energy of photons) converts into electrical current. At p-n junction, an electric field is built up which leads to the separation of the charge carriers (electrons and holes). At incidence of photon stream onto semiconductor material the electrons are released, if the energy of photons is sufficient. Contact to a solar cell is realised due to metal contacts. If the circuit is closed, meaning an electrical load is connected, then direct current flows. The energy of photons comes in packages which are called quants. The energy of each quantum depends on the wavelength of the visible light or electromagnetic waves. The electrons are released, however, the electric current flows only if the energy of each quantum is greater than WL. WV (boundaries of valence and conductive bands). The relation between frequency and incident photon energy is as follows:

    h. Planck constant (6,626·10.34 Js), μ. frequency (Hz)

    Crystalline solar cells

    Among all kinds of solar cells we describe silicon solar cells only, for they are the most widely used. Their efficiency is limited due to several factors. The energy of photons decreases at higher wavelengths. The highest wavelength when the energy of photon is still big enough to produce free electrons is 1.15 μm (valid for silicon only). Radiation with higher wavelength causes only heating up of solar cell and does not produce any electrical current. Each photon can cause only production of one electron-hole pair. So even at lower wavelengths many photons do not produce any electron-hole pairs, yet they effect on increasing solar cell temperature. The highest efficiency of silicon solar cell is around 23 %, by some other semi-conductor materials up to 30 %, which is dependent on wavelength and semiconductor material. Self loses are caused by metal contacts on the upper side of a solar cell, solar cell resistance and due to solar radiation reflectance on the upper side (glass) of a solar cell. Crystalline solar cells are usually wafers, about 0.3 mm thick, sawn from Si ingot with diameter of 10 to 15 cm. They generate approximately 35 mA of current per cm 2 area (together up to 2 A/cell) at voltage of 550 mV at full illumination. Lab solar cells have the efficiency of up to 30 %, and classically produced solar cells up to 20 %.

    Wafers and crystalline solar cells (courtesy: SolarWorld)

    Amorphous solar cells

    The efficiency of amorphous solar cells is typically between 6 and 8 %. The Lifetime of amorphous cells is shorter than the lifetime of crystalline cells. Amorphous cells have current density of up to 15 mA/cm 2. and the voltage of the cell without connected load of 0.8 V, which is more compared to crystalline cells. Their spectral response reaches maximum at the wavelengths of blue light therefore, the ideal light source for amorphous solar cells is fluorescent lamp.

    Surface of different solar cells as seen through microscope (courtesy: Helmholtz-Zentrum Berlin)

    Solar Cell Models

    The simplest solar cell model consists of diode and current source connected parallelly. Current source current is directly proportional to the solar radiation. Diode represents PN junction of a solar cell. Equation of ideal solar cell, which represents the ideal solar cell model, is:

    IL. light-generated current [1] (A), Is. reverse saturation current [2] (A) (aproximate range 10.8 A/m 2 ) V. diode voltage (V), VT. thermal voltage (see equation below), VT = 25.7 mV at 25°C n. diode ideality factor = 1. 2 (n = 1 for ideal diode)

    Thermal voltage VT (V) can be calculated with the following equation:

    k. Boltzmann constant = 1.38·10.23 J/K, T. temperature (K) q. charge of electron = 1.6·10.19 As

    FIGURE 1: Ideal solar cell model

    FIGURE 2: Real Solar cell model with serial and parallel resistance [3] Rs and Rp, internal resistance results in voltage drop and parasitic currents

    The working point of the solar cell depends on load and solar irradiation. In the picture, I-V characteristics at short circuit and open circuit conditions can be seen. Very important point in I-U characteristics is Maximum Power Point, MPP. In practice we can seldom reach this point, because at higher solar irradition even the cell temperature increases, and consequently decreasing the output power. Series and paralell parasitic resistances have influence on I-V curve slope. As a measure for solar cell quality fill-factor, FF is used. It can be calculated with the following equation:

    IMPP. MPP current (A), VMPP. MPP voltage (V) Isc. short circuit current (A), Voc. open circuit voltage (V)

    In the case of ideal solar cell fill-factor is a function of open circuit parameters and can be calculated as follows:

    Where voc is normalised Voc voltage (V) calculated with equation below:

    k. Boltzmann constant = 1,38·10.23 J/K, T. temperature (K) q. charge of electron = 1,6·10.19 As, n. diode ideality factor (-) Voc. open circuit voltage (V)

    For detailed numerical simulations more accurate models, like two diode model, should be used. For additional explanations and further solar cell models description please see literature below.

    Solar Cell Characteristics

    Samples of solar cell I-V and power characteristics are presented on pictures below. Typical point on solar cell characteristics are open circuit (when no load is connected), short circuit and maximum power point. Presented characteristics were calculated for solar cell with following data: Voc = 0,595 mV, Isc = 4,6 A, IMPP = 4,25 A, VMPP = 0,51 V, and PMPP temperature coefficient γ =.0,005 %/K. Calculation algorithm presented in the book Photovoltaik Engineering (Wagner, see sources) was used.

    FIGURE 3: Solar cell I-V characteristics for different irradiation values

    FIGURE 4: Solar cell power characteristics for different irradiation values

    FIGURE 5: Solar cell I-V characteristics temperature dependency

    FIGURE 6: Solar cell power characteristics temperature dependency

    [1] Sometimes term photocurrent IPh is also used.
    [2] Sometimes term dark current Io is also used.
    [3] For paralell resistanse term shunt resistor Rsh is also used.

    Simulation Tools

    Open Photovoltaics Analysis Platform. Open Photovoltaics Analysis Platform (OPVAP) is a group of software used in the field of solar cells, which include analyzing experimental data, calculating optimum architecture based on your materials, and even some research assistant tools such as PicureProcess.

    Organic Photovoltaic Device Model. Organic Photovoltaic Device Model (OPVDM) is a free 1D drift diffusion model specifically designed to simulate bulk-heterojuncton organic solar cells, such as those based on the P3HT:PCBM material system. The model contains both an electrical and an optical solver, enabling both current/voltage characteristics to be simulated as well as the optical modal profile within the device. The model and it’s easy to use graphical interface is available for both Linux and Windows.

    Other Technologies. Links

    NanoFlex Power. flexible organic solar cells.

    sphelar power. spherical solar cells technology.

    Solar Cell

    The Solar Cell block represents a solar cell current source.

    The solar cell model includes the following components:

    Solar-Induced Current

    The block represents a single solar cell as a resistance Rs that is connected in series with a parallel combination of the following elements:

    energy, source, fact, files, solar

    The following illustration shows the equivalent circuit diagram:

    I = I p h − I s ( e ( V I R s ) / ( N V t ) − 1 ) − I s 2 ( e ( V I R s ) / ( N 2 V t ) − 1 ) − ( V I R s ) / R p

    • Ir is the irradiance (light intensity), in W/m 2. falling on the cell.
    • Iph0 is the measured solar-generated current for the irradiance Ir0.
    • k is the Boltzmann constant.
    • T is the Device simulation temperature parameter value.
    • q is the elementary charge on an electron.

    The quality factor varies for amorphous cells, and is typically 2 for polycrystalline cells.

    The block lets you choose between two models:

    • An 8-parameter model where the preceding equation describes the output current
    • A 5-parameter model that applies the following simplifying assumptions to the preceding equation:
    • The saturation current of the second diode is zero.
    • The impedance of the parallel resistor is infinite.

    If you choose the 5-parameter model, you can parameterize this block in terms of the preceding equivalent circuit model parameters or in terms of the short-circuit current and open-circuit voltage the block uses to derive these parameters.

    All models adjust the block resistance and current parameters as a function of temperature.

    You can model any number of solar cells connected in series using a single Solar Cell block by setting the parameter Number of series-connected cells per string to a value larger than 1. Internally the block still simulates only the equations for a single solar cell, but scales up the output voltage according to the number of cells. This results in a more efficient simulation than if equations for each cell were simulated individually.

    Temperature Dependence

    Several solar cell parameters depend on temperature. The solar cell temperature is specified by the Device simulation temperature parameter value.

    The block provides the following relationship between the solar-induced current Iph and the solar cell temperature T:

    I p h ( T ) = I p h ( 1 T I P H 1 ( T − T m e a s ) )

    • TIPH1 is the First order temperature coefficient for Iph, TIPH1 parameter value.
    • Tmeas is the Measurement temperature parameter value.

    The block provides the following relationship between the saturation current of the first diode Is and the solar cell temperature T:

    I s ( T ) = I s ( T T m e a s ) ( T X I S 1 N ) e ( E G ( T T m e a s − 1 ) / ( N V t ) )

    where TXIS1 is the Temperature exponent for Is, TXIS1 parameter value.

    The block provides the following relationship between the saturation current of the second diode Is2 and the solar cell temperature T:

    I s 2 ( T ) = I s 2 ( T T m e a s ) ( T X I S 2 N 2 ) e ( E G ( T T m e a s − 1 ) / ( N 2 V t ) )

    where TXIS2 is the Temperature exponent for Is2, TXIS2 parameter value.

    The block provides the following relationship between the series resistance Rs and the solar cell temperature T:

    R s ( T ) = R s ( T T m e a s ) T R S 1

    where TRS1 is the Temperature exponent for Rs, TRS1 parameter value.

    The block provides the following relationship between the parallel resistance Rp and the solar cell temperature T:

    R p ( T ) = R p ( T T m e a s ) T R P 1

    where TRP1 is the Temperature exponent for Rp, TRP1 parameter value.

    Predefined Parameterization

    There are multiple available built-in parameterizations for the Solar Cell block.

    This pre-parameterization data allows you to set up the block to represent components by specific suppliers. The parameterizations of these solar cell modules match the manufacturer data sheets. To load a predefined parameterization, double-click the Solar Cell block, click the hyperlink of the Selected part parameter and, in the Block Parameterization Manager window, select the part you want to use from the list of available components.

    The predefined parameterizations of Simscape™ components use available datsources for the parameter values. Engineering judgement and simplifying assumptions are used to fill in for missing data. As a result, expect deviations between simulated and actual physical behavior. To ensure accuracy, validate the simulated behavior against experimental data and refine component models as necessary.

    For more information about pre-parameterization and for a list of the available components, see List of Pre-Parameterized Components.

    Thermal Port

    You can expose the thermal port to model the effects of generated heat and device temperature. To expose the thermal port, set the Modeling option parameter to either:

    • No thermal port — The block does not contain a thermal port and does not simulate heat generation in the device.
    • Show thermal port — The block contains a thermal port that allows you to model the heat that conduction losses generate. For numerical efficiency, the thermal state does not affect the electrical behavior of the block.

    For more information on using thermal ports and on the Thermal Port parameters, see Simulating Thermal Effects in Semiconductors.

    The thermal port model, shown in the following illustration, represents just the thermal mass of the device. The thermal mass is directly connected to the component thermal port H. An internal Ideal Heat Flow Source block supplies a heat flow to the port and thermal mass. This heat flow represents the internally generated heat.

    The internally generated heat in the solar cell is calculated according to the equivalent circuit diagram, shown at the beginning of the reference page, in the Solar-Induced Current section. It is the sum of the i 2 R losses for each of the resistors plus the losses in each of the diodes.

    The internally generated heat due to electrical losses is a separate heating effect to that of the solar irradiation. To model thermal heating due to solar irradiation, you must account for it separately in your model and add the heat flow to the physical node connected to the solar cell thermal port.

    Examples

    Solar Cell Power Curve

    Generate the power-voltage curve for a solar array. Understanding the power-voltage curve is important for inverter design. Ideally the solar array would always be operating at peak power given the irradiance level and panel temperature.

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