Photovoltaic Design And Installation For Dummies 645l5a

SOLAR ENERGY 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 environment-friendly. 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. 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 anti-cyclones. 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.

Solar Insolation Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter (W/m2) or kilowatt-hours per square meter per day (kW·h/ (m2·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.

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 power arrives at the surface—closer to 1,000 W/m2 in clear conditions when the Sun is near the zenith.

Applications of Solar Energy Solar Applications can be broadly characterized as ive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic s and solar thermal collectors to harness the energy. Whereas, ive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and deg 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

Solar thermal Solar thermal technologies can be used for 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. 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. Cooking Solar cookers use sunlight for cooking, drying and pasteurization. They can be grouped into three broad categories: box cookers, cookers and reflector cookers. Process heat o Evaporation ponds are shallow pools that concentrate dissolved solids through evaporation. The use 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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Advantages and Disadvantages There are many more advantages than disadvantages 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 necessary 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 is 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 s, windor 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 s 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 s 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.

Disadvantages: a. One of the main disadvantages is the initial cost of the equipment used to harness the suns energy. Solar energy technologies still remain a costly alternative to the use of readily available fossil fuel technologies. As the price of solar s 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 s, 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. During 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 s can affect performance, due to possible obstructions from the surrounding buildings or landscape.

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Photovoltaic Cell / Solar Cell 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 s and solar cells, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar s, 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). Working Principle of Photovoltaic cell a.

Simple explanation A photovoltaic (or PV) cell is a specially treated wafer of silicon, sandwiched between two thin plates. The top is positively charged and the back 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 plate and become a useable electric current.

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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 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 lattice. 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 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 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. P a g e |8

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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 s are made to both the n-type and p-type sides of the solar cell, and the electrodes connected to an external load. 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 load, and continue through the wire until they reach the p-type semiconductor-metal . 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.

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.

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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 ed through a heated zone several times in the same direction. This procedure "drags" the impurities toward one end with each . 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