Summer Training Report-nbst

A Summer Training Report

NanoBright Solar Technologies Pvt. Ltd.

1.0 SOLAR ENERGY

1.1

Introduction Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Only a minuscule fraction of the available solar energy is used. Direct heating or electrical conversion by solar cells are used by solar power equipment to generate electricity or to do other useful work, sometimes employing concentrating solar power. Increasingly, the world over, people are making a transition from conventional energy sources to Solar Power because they find it is more efficient, more economical and much, much more environmentfriendly. Solar Power is as reliable as the Sun: no power cuts, no black outs, no voltage fluctuations. It pays for itself in the long run. After the initial one-time investment on the Solar System, the power is free! In fact, the savings on your electricity bills will ensure that your initial investment on the Solar System is recovered in a few years.

1.2

Energy from the Sun Earth’s land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth ’s surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anticyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived.

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1.3


Solar Insolation Insolation is a measure of solar radiation energy received on a given surface area in a given time. 2 It is commonly expressed as average irradiance in watts per square meter (W/m ) or kilowatt-hours per 2 square meter per day (kW·h/ (m ·day)) (or hours/day). In the case of photovoltaic it is commonly measured as kWh/ (kWp·y) (kilowatt hours per year per kilowatt peak rating). The given surface may be a planet, or a terrestrial object inside the atmosphere of a planet, or any object exposed to solar rays outside of an atmosphere, including spacecraft. Some of the solar radiation will be absorbed while the remainder will be reflected. Most commonly, the absorbed solar radiation causes radiant heating, however, some systems may store or convert some portion of the absorbed radiation, as in the case of photovoltaic or plants. The proportion of radiation reflected or absorbed depends on the object ’s reflectivity or albedo, respectively.

1.4

Solar Constant Sunlight is Earth’s primary source of energy. The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,368 W/m2 (watts per square meter) at a distance of one astronomical unit (AU) from the Sun (that is, on or near Earth). Sunlight on the surface of Earth is attenuated by the Earth ’s atmosphere so that less 2 power arrives at the surface —closer to 1,000 W/m in clear conditions when the Sun is near the zenith.

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1.3


Solar Insolation Insolation is a measure of solar radiation energy received on a given surface area in a given time. 2 It is commonly expressed as average irradiance in watts per square meter (W/m ) or kilowatt-hours per 2 square meter per day (kW·h/ (m ·day)) (or hours/day). In the case of photovoltaic it is commonly measured as kWh/ (kWp·y) (kilowatt hours per year per kilowatt peak rating). The given surface may be a planet, or a terrestrial object inside the atmosphere of a planet, or any object exposed to solar rays outside of an atmosphere, including spacecraft. Some of the solar radiation will be absorbed while the remainder will be reflected. Most commonly, the absorbed solar radiation causes radiant heating, however, some systems may store or convert some portion of the absorbed radiation, as in the case of photovoltaic or plants. The proportion of radiation reflected or absorbed depends on the object ’s reflectivity or albedo, respectively.

1.4

Solar Constant Sunlight is Earth’s primary source of energy. The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,368 W/m2 (watts per square meter) at a distance of one astronomical unit (AU) from the Sun (that is, on or near Earth). Sunlight on the surface of Earth is attenuated by the Earth ’s atmosphere so that less 2 power arrives at the surface —closer to 1,000 W/m in clear conditions when the Sun is near the zenith.

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1.5


Applications of Solar Energy Solar Applications can be broadly characterized as passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Whereas, Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air. Here we will concentrate only on Active techniques. 

Solar Light Energy Photovoltaic are best known as a method for generating electric power by using solar cells to convert energy from the sun into electricity. The photovoltaic effect refers to photons of light knocking electrons into a higher state of energy to create electricity. The term photovoltaic denotes the unbiased operating mode of a photodiode in which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode.

A mono crystalline silicon PV module

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Solar thermal Solar thermal technologies can be used for

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Water heating Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems. The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.

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Water treatment Solar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours. Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions. Solar energy may be used in a water stabilization pond to treat waste water without chemicals or electricity. A further environmental advantage is that algae grow in such ponds and consume carbon dioxide in photosynthesis.

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Cooking Solar cookers use sunlight for cooking, drying and pasteurization. They can be grouped into three broad categories: box cookers, panel cookers and reflector cookers.

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Process heat Evaporation ponds are shallow pools that concentrate dissolved solids through evaporation. The use o of evaporation ponds to obtain salt from sea water is one of the oldest applications of solar energy. o A solar furnace is a structure used to harness the rays of the sun in order to produce high temperatures, usually for industry. This is achieved using a curved mirror (or an array of mirrors) that acts as a parabolic reflector, concentrating light (Insolation) onto a focal point. The temperature at the focal point may reach 3,500 °C (6,330 °F), and this heat can be used to generate electricity, melt steel, make hydrogen fuel or nanomaterials.

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1.5


Advantages and Disadvantages There are many more advantages than di sadvantages of solar energy:  Advantages:

a. Greatly reduced pollution While having much better credentials than fossil fuel for polluting emissions, the environmental costs of manufacturing and constructing solar energy appliances must not be forgotten. Also, consider the wider impacts of burning biomass and of large hydropower schemes. So, advantages of solar energy are still shadowed by some disadvantages. That’s just the nece ssary paradox of life. b. Greatly reduced contribution to global warming One of the greatest advantages of solar energy of course is that there are no carbon dioxide, methane or other emissions that warm the atmosphere. Again, manufacturing and installation of solar appliances are necessarily accompanied by some of those emissions. c.

Infinite energy resource Solar energy is not a finite resource as fossil fuels are. While the sun i s up there it constantly produces all the energy we can use.

d. Reduced maintenance costs While not maintenance-free – what technology really is? – once solar panels, wind- or water power facilities are in place, no fuel or lubricants need to be supplied. e. Falling production costs The financial costs of producing appliances such as solar cells and solar hot water panels are falling as technology develops. Comparatively solar energy is competing with fossil fuels as fossil fuel prices have risen steeply globally in the last few years. Solar energy technology is becoming increasingly efficient. f.

Low running costs With prices of traditional fuels soaring the cost advantages of solar energy are becoming obvious. After installation of the appliance, solar energy is free.

g.

Local application Suitable for remote areas that are not connected to energy grids. In some countries solar panels for domestic use in remote areas are becoming sources for local employment in manufacture and installation. Fossil-fuel poor countries can kick their dependency on this energy and spend their funds on other things through application of solar energy.

h. Health and safety benefits In some poorer countries where people have used kerosene and candles for domestic heating and lighting, respiratory diseases and impaired eyesight have resulted. Many people have been burned through accidents involving kerosene heating. Solar energy, especially with excess energy stored for night-time use, overcomes these problems. i.

Reliability Among the significant advantages of solar energy is that of reliability. Local application and independence from a centrally controlled power grid and energy transport infrastructure is insurance from upheaval through political and economic turmoil.

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Disadvantages:

a. One of the main disadvantages is the initial c ost of the equipment used to harness the suns energy. Sol ar energy technologies still remain a costly alternative to the use of readily available fossil fuel technologies. As the price of solar panels decreases, we are likely to see an increase in the use of solar cells to generate electricity. b. A solar energy installation requires a large area for the system to be efficient in providing a source of electricity. This may be a disadvantage in areas where space is short, or expensive (such as inner cities). c.

Pollution can be a disadvantage to solar panels, as pollution can degrade the efficiency of photovoltaic cells. Clouds also provide the same effect, as they can reduce the energy of the suns rays. This certain disadvantage is more of an issue with older solar components, as newer designs integrate technologies to overcome the worst of these effects.

d. Solar energy is only useful when the sun is shining. D uring the night, your expensive solar equipment will be useless; however the use of solar battery chargers can help to reduce the effects of this disadvantage. e. The location of solar panels can affect performance, due to possible obstructions from the surrounding buildings or landscape.

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2.0 Photovoltaic Cell / Solar Cell

2.1

What is Solar cell / Photovoltaic cell? A photovoltaic/solar Cell is a smallest basic solar-electric device, which generates electricity when exposed to sun light. In other words, it is a device that converts the energy of sunlight directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight such as solar panels and solar cells, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar panels, solar modules, or photovoltaic arrays. Photovoltaic is the field of technology and research related to the application of solar cells in producing electricity for practical use. The energy generated this way is an example of solar energy (also known as solar power ).

2.2

Working Principle of Photovoltaic cell

a.

Simple explanation A photovoltaic (or PV) cell is a specially treated wafer of silicon, sandwiched between two thin contact plates. The top contact is positively charged and the back contact is negatively charged, making it a semiconductor. 

The n-type semiconductor has an abundance of electrons giving it a negative charge, while the p-type semiconductor is positively charged.  Electrons movement at the p-n junction produces an electric field that allows only electrons to flow from the p-type layer to n-type layer.  When the sunlight hits the solar cell, its energy knocks the electrons loose from the atoms in the semiconductor.  When the electrons hit the electrical field, they’re shuttled to the top contact plate and become a useable electric current.

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b.


Detail Explanation

1. Photo generation of charge carriers When a photon hits a piece of silicon, one of three things can happen: 

 

The photon can pass straight through the silicon — this (generally) happens for lower energy photons, The photon can reflect off the surface, The photon can be absorbed by the silicon, if the photon energy is higher than the silicon band gap value. This generates an electron-hole pair and sometimes heat, depending on the band structure.

When a photon is absorbed, its energy is given to an electron in the crystal la ttice. Usually this electron is in the valence band, and is tightly bound in covalent bonds between neighboring atoms, and hence unable to move far. The energy given to it by the photon "excites" it into the conduction band, where it is free to move around within the semiconductor. The covalent bond that the electron was previously a part of now has one fewer electron — this is known as a hole. The presence of a missing covalent bond allows the bonded electrons of neighboring atoms to move into the "hole," leaving another hole behind, and in this way a hole can move through the lattice. Thus, it can be said that photons absorbed in the semiconductor create mobile electron-hole pairs. A photon need only have greater energy than that of the band gap in order to excite an electron from the valence band into the conduction band. However, the solar frequency spectrum approximates a black body spectrum at ~ 6000⁰ K, and as such, much of the solar radiation reaching the Earth is composed of photons with energies greater than the band gap of silicon. These higher energy photons will be absorbed by the solar cell, but the difference in energy between these photons and the silicon band gap is converted into heat rather than into usable electrical energy.

2.

Charge carrier separation There are two main modes for charge carrier separation in a solar cell:  

Drift of carriers, driven by an electrostatic field established across the device. Diffusion of carriers from zones of high carrier concentration to zones of low carrier concentration (following a gradient of electrochemical potential).

In the widely used p-n junction solar cells, the dominant mode of charge carrier separation is by drift.

3. The p-n junction The most commonly known solar cell is configured as a large-area p-n junction made from silicon. As a simplification, one can imagine bringing a layer of n-type silicon into direct contact with a layer of p-type silicon. In practice, p-n junctions of silicon solar cells are not made in this way, but rather by diffusing an n-type dopant into one side of a p-type wafer (or vice versa). If a piece of p-type silicon is placed in intimate contact with a piece of n-type silicon, then a diffusion of electrons occurs from the region of high electron concentration (the n-type side of the junction) into the region of low electron concentration (p-type side of the junction). When the electrons diffuse across the p-n junction, they recombine with holes on the p-type side. The diffusion of carriers does not happen indefinitely, however, because charges build up on either side of the junction and create an electric field. The electric field creates a diode that promotes charge flow, known as drift current that opposes and eventually balances out the diffusion of electron and holes.

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This region where electrons and holes have diffused across the junction is called the depletion region because it no longer contains any mobile charge carriers. It is also known as the space charge region . 4. Connection to an external load

Ohmic metal-semiconductor contacts are made to both the n-type and p-type sides of the solar cell, and the electrodes connected to an external lo ad. Electrons that are created on the n-type side, or have been "collected" by the junction and swept onto the n-type side, may travel through the wire, power the lo ad, and continue through the wire until they reach the p-type semiconductor-metal contact. Here, they recombine with a hole that was either created as an electron-hole pair on the p-type side of the solar cell, or a hole that was swept across the junction from the n-type side after being created there. The voltage measured is equal to the difference in the quasi Fermi levels of the minority carriers, i.e. electrons in the p-type portion and holes in the n-type portion. 5.

Equivalent circuit of a solar cell

The equivalent circuit of a solar cell

The schematic symbol of a solar cell

To understand the electronic behavior of a solar cell, it is useful to create a model which is electrically equivalent, and is based on discrete electrical components whose behavior is well known. An ideal solar cell may be modelled by a current source in parallel with a diode; in practice no solar cell is ideal, so a shunt resistance and a series resistance component are added to the model. The resulting equivalent circuit of a solar cell is shown on the top. Also the schematic representation of a solar cell is shown above.

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2.3

Manufacturing of Solar Cell

a.

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 solar 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.

b.

The Manufacturing Process 

Purifying the silicon

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. The 99 % 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

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.

Sand

Melted Silicon

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Czochralski Process

Mono Crystalline Silicon Ingot

Ingot Slicing

Mono Crystalline Silicon Wafer

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Making silicon wafers

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 wafer0. 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, whic h 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. The wafers are then polished to remove saw marks. (It has recently been found that ro ugher cells absorb light more effectively, therefore some manufacturers have chosen not to polish the wafer.) 

Doping

The doping (adding impurities to) silicon wafers with boron and phosphorous is to introduce a small amount of boron during the Czochralski process. The wafers are then sealed back to back and placed in a furnace to be heated to slightly below the melting point of silicon ( 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

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 v acuum-evaporated. The cells are encapsulated in ethylene vinyl acetate and placed in a metal frame that has a mylar backsheet and glass cover. through a photoresist, silkscreened, or merely deposited on the exposed portion of cells that have been partially covered with wax. All three methods involve a system in which the part of the cell on which a contact is not desired is protected, while the rest of the cell is exposed to the metal. After the contacts are in place, thin strips are placed between cells. The most commonly used strips are tin-coated copper.

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Electrical Contacts

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The anti-reflective coating

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 fo r 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

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 back sheet and a glass or plastic cover.

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2.4


Types of PV cell using silicon

a.

Monocrystalline silicon

They are often made using the Czochralski process. Single-crystal wafer cells tend to be expensive, and because they are cut from cylindrical ingots, do not completely cover a square solar cell module without a substantial waste of refined silicon. Hence most c-Si panels have uncovered gaps at the four corners of the cells. b. Poly- or multicrystalline silicon

They are made from cast square ingots — large blocks of molten silicon carefully cooled and solidified. Poly-Si cells are less expensive to produce than single crystal silicon cells, but are less efficient. US DOE data shows that there were a higher number of multi crystalline sales than mono crystalline silicon sales.

c.

Thin films A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few microns or less in thickness, used to make photovoltaic cells.

The various thin-film technologies currently being developed reduce the amount (or mass) of light absorbing material required in creating a solar cell. This can lead to reduced processing costs from that of bulk materials (in the case of silicon thin films) but also tends to reduce energy conversion efficiency average 7 to 10% efficiency), although many multi-layer thin films have efficiencies above those of bulk silicon wafers. They have become popular compared to wafer silicon due to lower costs and advantages including flexibility, lighter weights, and ease of integration.

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A Thin film Module

Advantages of Crystalline Silicon and Amorphous Silicon Thin Film

Crystalline Silicon

a - Si Thin-Film

Highest power per area

Output less affected by temperature

Requires less racking & support material

Less manufacturing materials used

Fewer modules means lower number shipping costs

Lower cost per watt

Large number of module choices

Good aesthetics for building – integrated applications

Greatest inverter flexibility

Less embodied energy (faster energy payback) Non glass substrates possible More shade tolerant

Disadvantages of Crystalline Silicon and Amorphous Silicon Thin Film

Crystalline Silicon

a - Si Thin-Film

Higher cost per watt

Lower power per area

Higher temperatures affect output more

Takes months to stabilize output

Low shade tolerant

Twice as much rack material required

Individual cell visibility

More modules mean higher shipping costs Lower series – string capacity Less suitable for battery charging Requires more combiner boxes Limited inverter flexibility Fewer module manufacturer choices.

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2.5


Parameters and Technical Specification of a typical Manufactured Solar Cell 

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Solar cells are available in the sizes of 100mmX100mm, 125mmX125mm, 156mmX156mm, 208mmX208mm. The power generated will vary according to the sizes as (assume efficiency of 15%) 1.5W, 2.25W, 3.5W, 6W. In a solar array, cells are connected in series/parallel to get high voltage/current. Such combination of cells generally includes 36, 48, 54, 72 cells. The dimensions of a solar cell will range from 2mX0.7m to 1mX0.5m. To check the performance of a solar module the following parameters are to be considered. They are 1) Pmax—Maximum power 2) Vmpp—Voltage at maximum power point 3) Impp—Current at maximum power point 4) Voc—Open circuit voltage 5) Isc—Short circuited current 6) Rs—Series resistance 7) Rsh—Shunt resistance 8) η –Efficiency = Pmax/Area 9) Fill Factor— (Vmpp X Impp)/( Voc X Isc) To find the above parameters SUN SIMULATOR is used. It is also called MODULE TESTER. For example: Solar Cell Features and characteristics: o o o o o o o o

Type: Q6L-1480 Mode: C-Si, Multi Crystalline Format: 156*156mm Thickness: average-220u Isc: 7.69A Voc: 610mv Pmax: 3.601 Efficiency: 14.8%

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2.6 Parts of PV module

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Teflon film or Polytetrafluoroethylene film Teflon brings a very high level of light transmittance in the operating wavelength range of the solar cells. It is lighter and less fragile than glass and shows very little degradation over a long period of time. It also offers excellent mechanical strength, reliability, and flexibility to conform to non-standard shapes - while maintaining its structural integrity. Ethylene vinyl acetate (EVA) resin It is used in the photovoltaics industry as an encapsulation material for silicon cells in the manufacture of photovoltaic. The material has good clarity and gloss, barrier properties, low-temperature toughness, stress-crack resistance, hot-melt adhesive water proof properties, and resistance to UV radiation. It is used as sheets that surround and protect silicon wafers and module circuitry. Photovoltaic Cell (Discussed earlier in Part 2.1) Tedlar Film or Polyvinyl fluoride (PVF) film Tedlar films are used as the backing sheet for photovoltaic modules for their excellent strength, weather resistance, UV resistance, and moisture barrier properties. Polyethylene terephthalate (PET) thermoplastic Junction Box At the back of the PV module is a junction/ terminal box, made of PET thermoplastic resin. It is an enclosure on the module where PV strings are electrically connected and where protection devices can be located, if necessary. Aluminum Support Structure It supports all delicate parts of a PV module and provides rigidity to work with it in transportation as well as in fixing it on rigid structures for making a PV array.

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A Multi Crystalline PV Module

2.7

Electrical Characteristics of a PV Module 

Solar Modules Power Characteristics: The current and power outputs of photovoltaic modules are approximately proportional to sunlight intensity. At a given intensity, a module's output current and operating voltage are determined by the characteristics of the load. If that load is a battery, the battery's internal resistance will dictate the module's operating voltage. An V-I curve is simply all of a module's possible operating points, at a given cell temperature and light intensity. Increases in cell temperature increase current slightly, but drastically decrease voltage. Maximum power is derived at the knee of the curve.

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Tilt angle: To capture the maximum amount of solar radiation over a year, the solar array should be tilted at an angle approximately equal to a site's latitude, and facing within 15° of due south. To optimize winter performance, the solar array can be tilted 15° more than the latitude angle, and to optimize summer performance, 15° less than the latitude angle. At any given instant, the array will output maximum available power when pointed directly at the sun.

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Module tracking: A tracker mount follows the path of the sun from east to west, keeping the solar modules facing directly toward the sun from dawn to dusk. This can result in a 25% increase in your daily energy production during the summer as compared to the same solar array on a fixed mount. The north-south tilt axis can be adjusted seasonally for peak performance throughout the year. As the sun moves across the sky from east to west, the Track Rack follows it at approximately 15° per hour continually.

Single axis tracking



Dual Axis Tracking

Standard test conditions: o o o

2

Insolation-1000W/m Cell operating Temperature- 25⁰c/cell Air mass-1.5

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2.8 Applications and implementations Solar cells are often electrically connected and encapsulated as a module. Photovoltaic modules often have a sheet of glass on the front (sun up) side, allowing light to pass while protecting the semiconductor wafers from the elements (rain, hail, etc.). Solar cells are also usually connected in series in modules, creating an additive voltage. Connecting cells in parallel will yield a higher current. Modules are then interconnected, in series or parallel, or both, to create an array with the desired peak DC voltage and current. The power output of a solar array is measured in watts or kilowatt. In order to calculate the typical energy needs of the application, a measurement in watt-hours, kilowatt-hours or kilowatt-hours per day is often used. A common rule of thumb is that average power is equal to 20% of peak power, so that each peak kilowatt of solar array output power corresponds to energy production of 4.8 kWh per day (24 hours x 1 kW x 20% = 4.8 kWh) To make practical use of the solar-generated energy, the electricity is most often fed into the electricity grid using inverters (grid-connected photovoltaic systems); in stand-alone systems, batteries are used to store the energy that is not needed immediately. Solar cells can also be applied to other electronics devices to make it self-power sustainable in the sun. There are solar cell phone chargers, solar bike light and solar camping lanterns that people can adopt for daily use.

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3.0 PHOTOVOLATIC SYSTEMS

3.1

Introduction Renewable energy resources will be an increasingly important part of power generation in the new millennium. Besides assisting in the reduction of the emission of greenhouse gases, they add the muchneeded flexibility to the energy resource mix by decreasing the dependence on fossil fuels. In other hand, deregulation of the electric utility industry is providing an opportunity for higher penetration and use of distributed resources (DR). Distributed resources are generation sources that can be located at or near loads. Distributed resources can provide benefits that bulk power generation cannot. PV systems are ideally suited for distributed resource applications. Photovoltaic (PV) systems produce DC electricity when sunlight shines on the PV array, without any emissions. The DC power is converted to AC power with an inverter and can be used to power local loads or fed back to the utility. The PV application can be grouped depending the scheme of interaction with utility grid: grid connected, stand alone, and hybrid. PV systems consist of a PV generator (cell, module and array), energy storage devices (such as batteries), AC and DC consumers and elements for power conditioning. Definition: A photovoltaic system is a system which uses solar cells to convert sunlight into electricity. It consists of multiple components, including cells, mechanical and electrical connections and mountings and means of regulating and/or modifying the electrical output.

A typical block diagram showing the process of generating Usable Energy from Sunlight.

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3.2


Components of a typical Solar PV System        

Photovoltaic Cell- Thin squares, discs, or films of semiconductor material that generate voltage and current when exposed to sunlight. Module- A configuration of PV cells laminated between a clear glazing and an *Panel- One or more modules. Array- One or more panels wired together at a specific voltage. Charge Controller- Equipment that regulates battery voltage. Battery Bank- A medium that stores direct current electrical energy. Inverter- An electrical device that changes direct current to alternating current. DC Loads- Appliances, motors, and equipment powered by dir ect current. AC Loads- Appliances, motors, and equipment powered by alternating current.

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3.2.1


Solar batteries Solar batteries store power generated from the sun and discharge the power as needed (through an inverter).There are two types of batteries that are most popularly used in solar electric systems.  FLOODED LEAD-ACID battery

They are batteries with plates made of pure lead, lead-antimony, or lead-calcium immersed in an acid electrolyte. Flooded lead acid batteries have the longest track record in solar electric use and are still used in the majority of stand-alone solar systems. They have the longest life and the least cost per amphour of any of the choices. They also require regular maintenance in the form of watering, equalizing charges and keeping the top and terminals clean. Lead acid batteries are 100% recyclable.

Flooded Lead Acid Batteries Manufactured By Su- Kam  VRLA battery

A VRLA battery (valve-regulated lead-acid battery) is the designation for low-maintenance lead-acid rechargeable batteries. These batteries are often colloquially called sealed lead-acid batteries, but they always include a safety pressure relief valve. As opposed to flooded batteries, a VRLA cannot spill its electrolyte if it is inverted. VRLA batteries use much less electrolyte (battery acid) than traditional leadacid batteries.

VRLA Batteries Manufactured By Amara Raja Inc., India VRLA batteries are commonly further classified as:  Absorbed glass mat battery  Gel battery

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




Absorbent glass mat (AGM) Absorbent glass mat is a class of VRLA battery in which the electrolyte is absorbed into a mat of fine glass fibers. The plates in an AGM battery may be flat like a wet cell lead-acid battery in a rectangular case. In cylindrical AGMs, the plates are thin and wound, like most consumer disposable and rechargeable cells, into spirals so they are also sometimes referred to as spiral wound. The spiral construction allows purer lead in the plates, since the plate no longer needs to support its own weight as in traditional cells. Their specific power is very good and they can be charged and discharged quite rapidly, however their specific energy tends to be lower than traditional flooded batteries. They are often used in high performance electric vehicles due to their high power density. Gel battery A gel battery (also known as a "gel cell") is a VRLA battery with a jellified electrolyte; the sulfuric acid is mixed with silica fume, which makes the resulting mass gel-like and immobile. Unlike a flooded wet-cell lead-acid battery, these batteries do not need to be kept upright. Gel batteries reduce the electrolyte evaporation, spillage (and subsequent corrosion issues) common to the wet-cell battery, and boast greater resistance to extreme temperatures, shock, and vibration. Chemically they are the same as wet (non-sealed) batteries except that the antimony in the lead plates is replaced by calcium. Comparison of VRLA batteries with flooded lead-acid cells Compared with flooded lead-acid cells, VRLA batteries offer several advantages. The battery can be mounted in any position, since the valves only operate on over pressure faults. Since the battery system is designed to be recombinant and eliminate the emission of gases on overcharge, room ventilation requirements are reduced and no acid fume is emitted during normal operation. The volume of free electrolyte that could be released on damage to the case or venting is very small. There is no need (nor possibility) to check the level of electrolyte or to top up water lost due to electrolysis, reducing inspection and maintenance. Compared to flooded batteries, VRLA batteries are more sensitive to high temperature environments and more vulnerable to thermal run-away during abusive charging conditions.

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3.2.2


Charge Controller It is a component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.

A Simple Charge controller and a MPPT Charge Controller manufactured by Phocos If a non-self-regulating solar array is connected to lead acid batteries with no overcharge protection, battery life will be compromised. More sophisticated controllers utilize pulse width modulation (PWM) or maximum power point tracking (MPPT) to assure the battery is being fully charged. The first 70% to 80% of battery capacity is easily replaced, but the last 20% to 30% requires more attention and therefore more complexity. The circuitry in a controller reads the voltage of the batteries to determine the state of charge. Designs and circuits vary, but most controllers read voltage to control the amount of current flowing into the battery as the battery nears full charge. The final function of modern solar charge controllers is preventing reverse-current flow. At night, when solar panels aren’t generating electricity, electricity can actually flow backwards from the batteries through the solar panels, draining the batteries. The charge controller disconnects the solar panels from the batteries when no energy is coming and so stopping reverse current flow.

Features of a charge controller: Reverse current leakage protection - by disconnecting the array or using a blocking diode to prevent current loss into the solar modules at night. Low-voltage load disconnect (LVD) - to reduce damage to batteries by avoiding deep discharge. System monitoring - analog or digital meters, indicator lights and/or warning alarms. Overcurrent protection - with fuses and/or circuit breakers. Mounting options - flush mounting, wall mounting, indoor or outdoor enclosures. System control - control of other components in the system; standby generator or auxiliary charging system, diverting array power once batteries are charged, transfer to secondary batteries. Load control - automatic control of secondary loads, or control of lights, water pumps or other loads with timers or switches. Temperature compensation - utilized whenever batteries are placed in a non-climate controlled space. The charging voltage is adjusted to the temperature. Pulse Width Modulation (PWM) - an efficient charging method that maintains a battery at its maximum state of charge and minimizes sulfating build-up by pulsing the battery voltage at a high frequency. 

    







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

3.2.3


Maximum Power Point Tracking (MPPT) - a new charging method designed to extract the most power possible out of a solar module by altering its operating voltage to maximize the power output.

Inverters (KW/KVA) The inverter is a basic component of PV systems and it converts DC power from the batteries or in the case of grid-tie, directly from the PV array into high voltage AC power as needed. Inverters of the past were inefficient and unreliable while today's generation of inverters are very efficient (85 to 97%) and reliable.

A 250W inverter manufactured by Su-Kam Solar inverters may be classified into three broad types:  Stand-alone inverters It is used in isolated systems where the inverter draws its DC energy from batteries charged by photovoltaic arrays and/or other sources, such as wind turbines, hydro turbines, or engine generators. Many stand-alone inverters also incorporate integral battery chargers to replenish the battery from an AC source, when available. Normally these do not interface in any way with the utility grid, and as such, are not required to have anti-islanding protection.  Grid tie inverters These match phase with a utility-supplied sine wave. Grid-tie inverters are designed to shut down automatically upon loss of utility supply, for safety reasons. They do not provide backup power during utility outages.  Battery backup inverters . These are special inverters which are designed to draw energy from a battery, manage the battery charge via an onboard charger, and export excess energy to the utility grid. These inverters are capable of supplying AC energy to selected loads during a utility outage, and are required to have anti-islanding protection. Inverters are compared by three factors: Continuous wattage rating Hour after hour, what amount of power in watts can the inverter deliver. Surge Power how much power and for how long can an inverter deliver the power needed to start motors and other loads. Efficiency How efficient is the inverter at low, medium and high power draws. 





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3.2.4


Solar PCU (power conditioning unit)

Solar Power Conditioning unit (PCU) is an integrated system consisting of a solar charge controller, inverter and a Grid charger. It provides the facility to charger the battery bank either through Solar array or Grid. The PCU continuously monitors the state of Battery Voltage, Solar Power output and the loads. Due to sustained usage of power, when the Battery voltage falls below a preset level, the PCU will automatically transfer the load to the Grid and also charge. Once the Batteries are charged to a preset level, the PCU cuts off the Grid from the system and will restore to feeding the loads from the battery bank & also restore to charging the battery from the Available Solar power. The PCU always gives preference to the Solar Power and will use Grid/DG power only when the Solar Power/ Battery charger is insufficient to meet the load requirement.

Solar PCU comes with following salient features: Instantaneous sine wave control Grid interactive, bi-directional inverter MPPT based solar charge controller High conversion efficiency Advanced communication interface Sophisticated LCD display External remote provision       

3.2.5

Loads The appliances and devices (TV's, computers, lights, water pumps etc.) that consume electrical power are called loads. It is very important to examine your power consumption and equalize it with your solar panel power consumption.

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3.3


Types of a typical Photovoltaic System Photovoltaic power systems are generally classified according to their functional and operational requirements, their component configurations, and how the equipment is connected to other power sources and/or electrical loads (appliances).  PV direct  Stand-alone PV systems  Grid-tie (battery-free) PV systems  Grid-tie with battery backup PV systems

PV DIRECT PV Direct systems are usually very simple systems where the photovoltaic panel is connected directly to a motor or pump which matches the voltage and amperage output of the panel. When the sun shines and the PV panel produces electricity, the device runs--when the sun is not available, the device stops. This system is often used for livestock where a well-pump lifts water out of the ground to a watering trough in remote locations. Other applications include solar powered attic fans, irrigation systems and small day-time garden waterfalls or fountains.

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STAND-ALONE PV systems The Off-Grid or Stand-Alone PV System incorporates large amounts of battery storage to provide power for a certain number of days (and nights) in a row when sun is not available. The array of solar panels must be large enough to power all energy needs at the site and recharge the batteries at the same time. Most Stand-Alone systems benefit from the installation of more than one renewable energy generator and may include Wind and/or Hydro power. A gas generator is often employed for emergency backup power.

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GRID-TIE (BATTERY FREE) The simplest and most cost effective PV design for many sites is the "Grid-Tie" (sometimes referred to as intertied or utility-interactive) system. This system cannot provide backup power during periods when the electric grid is down (even if the sun is shining) but for sites with fairly reliable grid power, this is usually the best system choice.

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GRID-TIE WITH BATTERY BACKUP The Grid-Tie with Battery Backup system can also push excess electricity produced to the electric utility grid but has the added feature of batteries in order to power some selected backup loads when the grid is down. With this benefit come increased complexity, cost and maintenance requirements.

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4.0 PHOTOVOLTAIC SYSTEM DESIGN

Introduction A series of steps are involved in designing a Photovoltaic system which starts from Load calculation, Battery and array sizing, Inverter and charge controller sizing, etc. which leads to a complete design and pricing information about the system. The steps involved in designing any PV system ranging from a small few watt system to megawatts system. Step 1:

Application of the system: For powering up home appliances, industries, offices, banks mainly for rural electrification, power stations, stand-alone applications, solar power satellites, solar road ways, utility interactive systems, water pumping systems etc.,

Step 2:

Location of the site: The choice of a proper location is the first and the very essential step in solar system design procedure. Even t he most carefully planned solar system doesn’t work satisfactory, if the

location wasn’t properly chosen. It is critical that the modules are exposed to sunlight without shadowing at least from 9 am to 3 pm; therefore, the properties and values of solar insolation should be studied. The modules have to be fixed with proper tilt angle allowing the system efficient operation .

A Tool for the site analysis [Solar Pathfinder] - The Solar Pathfinder has been the standard in the solar industry for solar site analysis for decades. Its panoramic reflection of the site instantly provides a full year of accurate solar/shade data, making it the instrument of choice.

Step 3:

Load Calculation: APPLIANCES

Nominal Voltage

AC Watts DC Watts

Total AC Watts

Total DC Watts

QTY

Hours of operation

Energy

Total Energy

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Step 4:

Battery Sizing: Battery Bank Voltage = System voltage (DC) Number of Days of Autonomy

= 3 Days (for non-critical Loads) = 5 Days (for critical Loads) =

Battery Depth of Discharge

Days (Customer specified)

= 80% (For Stationary Lead Acid Batteries)

Size of Batteries (Load Ampere hours): =

   ⁄       

Step 5:

Array Sizing: Fixed Tilted: same tilt angle throughout the year. Overall System Losses = Mismatch Losses (3%) + Dirt Losses (5%) + Wiring Losses (2% to 3%) = 10% 0

Temperature Factor: Power reduces 0.5% for every 1 C rise in temperature.

Max. Power of Array =

        

Number of modules = Total watts of the panel / Total watt-peak rating. Number of modules in series = Max. Voltage of the panel / Open circuit voltage of the system (V oc ) Number of modules in parallel = Total no. of modules / No. of modules in series Note: 1). ALR (Array to Load Ratio Factor)

= 1.1 for critical loads = 1 for non-critical loads 2). Temperature Factor shall be calculated considering the average maximum temperature.

Step 6:

Charge Controller Sizing: Charge controller current = (no. of modules × I sc ) × energy lost in the system Voltage = System Voltage Status display: Minimum display for “ON Charge”, “Load disconnected”. Instrumentation: As offered by the manufacturer.

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Step 7:

Inverter Sizing: Inverter rating (VA) = Total AC Watts / power factor Surge wattage = Sum of wattage of surge loads * 3 Input DC Voltage = system voltage.

Step 8:

Wire sizing: PV system wiring is substantially different from conventional AC wiring as they generally use lower voltage and often have larger wire sizes compared to AC systems.

Wire size selection is based on two important criterions - Ampacity and Voltage drop. Ampacity refers to the current carrying ability of a wire. The larger a wire is, the greater its capacity to carry current. Using a wire with an Ampacity less than the current flow will cause the wire to overheat leading to losses and even fire. Voltage drop is the loss of voltage due to a wire's resistance and length. It is important to take into consideration the voltage drop and minimize the energy loss in the wiring in designing the wiring for your PV system. Using a larger wire size, decreasing the current flow or decreasing the length of the wire is the solution to reduce voltage drop. A good design practice is to keep the wiring voltage loss at 2%. Array to Charge Controller limit the voltage drop to 3%, all other cables between 3% - 4% voltage drop. Step 9:

Switch Gear Equipment: All electrical equipment must be listed for the voltage and current ratings necessary for the application. Circuit breakers, cables, inverters, fuses, array combiner box, lightning arrester, disconnector switches. Step 10:

Grounding: The structures and modules should be grounded with a ground conductor. Separate earth point should be provided.

Protection: MOV Lightening (Metal Oxide Varistor) should be provided in the array combiner box. Lightning arrester must be providing for large solar PV systems.

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Step 11:

Bill of Materials: Material to be procured is described in the following layout. S.

Material Description

Qty

Specifications

Manufacturer

Supplier / Vendor

No. 1 2 3

Step 12: System Performance: Once installed, System is monitored for a year to know the performance and efficiency of the system. Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Solar radiation on horizontal surface Tilt Angle Tilt Factor Solar radiation On tilted surface Array Ampere hours Gross Array Ampere hours NET Load Ampere hours Ampere hours Deficit / Excess Minimum Battery State of charge Optimum Tilt Angle

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A typical view of a utility interactive PV Power system

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5.0 TYPICAL PV SYSTEM DESIGN OF 1KW

Introduction: This is an example of a solar PV system design of 1kW, which is done in NanoBright Solar Technologies Pvt. Ltd. Corporate building. The loads have been powered by solar energy which is going to run on AC power. It is a 48V system in which DC power produced by the solar panel is converted into AC power by using inverter which is utilized by AC loads in the laboratory. This is a utility interactive solar PV system.

Application of this system: To power up the NBST laboratory.

Location of site:

Hyderabad 0 Latitude: 17.27 N 0 Longitude: 78.28 E 0 Optimum Tilt angle =17

Load data:Appliances

Power(watts)

Quantity

Watts*Quantity 480

No. of hours of Operation 2

Total Wh. [energy] 960

Soldering stations

80

6

Regulated power supply

220

4

880

2

1760

Tube lights

40

5

200

2

800

Fan

55

2

110

2

220

C.F.L

8

4

32

2

64

1702W

Total

3404Wh

Battery sizing: Total battery bank capacity=

      =

 = 295.486 Ah 

Total battery voltage needed = 12V Since 120Ah, 12V Battery is available Number of batteries in series =

   = 48/12 = 4 in series.   

Number of batteries in parallel =

   = 265/120 =2 in parallel.   

Total number Batteries = Series × Parallel = 8 Batteries. The required battery bank capacity: 12V, 240Ah. Since we have taken the batteries of C 10 rating they can withstand the total battery capacity.

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Array sizing: Peak sun hours in Hyderabad

= 5.17 hrs

Over all losses

= 0.9

Temperature factor

= 0.87

PCU efficiency

= 0.9

Battery efficiency

= 0.9

As we don’t have any critical loads, thus, ALR = 1 Array size in W =

         =

 

Number of modules =

=1038Wp

        = 1040/130 = 8 modules.

Number of modules in series =

           =88/21 = 4 modules in series.

[Since the system is a MPPT based system the max. voltage =88V, V oc =21V]

Number of modules in parallel =

       = 8/4= 2 modules in parallel.

Power Conditioning Unit (PCU): The power conditioning unit consists of both inverter and charge controller. This is a single phase output, bidirectional inverter system. PCU operates in parallel to the grid utility. Batteries are charged from the solar array through the charge controller. Additional energy will be exported to the grid via same bidirectional PCU system. Whenever grid voltage and frequency goes beyond the operating range, the PCU will be disconnected from the grid. The PCU will supply the continuous power to the load without any interruption.

PCU:

2kw

Type:

Bidirectional inverter.

Charger type:

MPPT Based.

Input from PV array :

40-88V.

Output:

240V.

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Bill of material: Component 1.

Solar Modules

2.

Battery

Rating 130Wp, 12V 12V,120Ah

3.

PCU

2KW

5.

Module Support Structures Array Combiner Box

6.

Battery Rack

4.

7. 8.

1

AC Power Distribution Panel DC Power 8 Way Distribution Panel

8

Multi crystalline

8

SMF-Power Safe MPPT charger/MOSFET based PWM Technology Inverter Bidirectional, Pure sinusoidal,50Hz,240V AC,1-Phase

1

Galvanized Iron

1

IP65 Protection -PVC

IP65 Protection 1

IP65 Protection-Double Door,100A,SPN

From Array combiner box to PCU, For battery wiring. Multi strand single core copper wire with PVC insulated

2

Cables 6mm

10. Circuit Breakers

Grid input to PCU, Load Wiring. Multi strand single core copper wire with PVC insulated

2

63A

2

Battery, Array

16A

1

Grid

10A

1

Load

Hard ware-Bolts, Nuts, Lugs, Crimp 11. Terminals, splices, Cable Glands Miscellaneous (S-6 Fischer, PVC box 12. type 0.25'/1'/1.25', PVC spring type, Vaseline) 13. Energy Meters EarthingCopper earthing Set 15. Civil Works 14.

Description

Acid Proof colour coating

16mm 9.

Qty.

Stainless Steel-SS304/M.S Galvanized with complete plain and lock washers

10-40A, 240V

2

AC side & DC Side-Digital

2

System/equipment-NEC Standard

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Wiring Diagram of the PV System

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Photographs of the 1KW PV System Installed

1 KW Photovoltaic system placed on terrace of the company

Battery Bank, PCU, Distribution Panel & Monitoring system

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Summer Training Report-nbst

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