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Photo Voltaic CELLS AND COMP0NENTS:SOLAR FACTSOne day sunshine could supply all the worlds energy for 4 to five years.All solar lights are wireless. They are not hooked up to external sources of power.The suns full intensity and brightness is 1000w/m^2.Solar lighting is sometimes preferred for applications where the need is temporary (fairs, mining sites, Olympics, introduction of real estate developments, etc.).Solar intensity can be dimensioned according to micro climate and site specific conditionSolar-powered outdoor lighting is virtually maintenance-free, since the batteries require no water or other regular service.

Relative Solar Radiation on Earth:

While the solar radiation incident on the Earth's atmosphere is relatively constant, the radiation at the Earth's surface varies widely due to:atmospheric effects, including absorption and scattering;local variations in the atmosphere, such as water vapour, clouds, and pollution;latitude of the location; andthe season of the year and the time of day.These changes include variations in the overall power received, the spectral content of the light and the angle from which light is incident on a surface.The variability is due to both local effects such as clouds and seasonal variations, as well as other effects such as the length of the day at a particular latitude.Desert regions tend to have lower variations due to local atmospheric phenomena such as clouds. Equatorial regions have low variability between seasons.

Relative solar radiation on earth

World Solar Energy Map

Sun Altitude Angle - Latitude and Seasons

When the Sun is directly overhead, its light (and energy) is concentrated upon the smallest possible surface area of the ground that it can strike (and be absorbed by). However, when the Sun is lower in the sky, its light/energy strikes the ground obliquely, and is thus spread out over a larger areaRegions of our planet at high latitudes (near the North and South Poles) receive far less concentrated solar energy than do regions at low latitudes (in the tropics near the equator).Our seasons also influence how much solar radiation strikes a square meter of ground in a given place on the planet's surface at a given time of year.The Sun is "higher in the sky" in the summer and "lower in the sky" in winter.The hottest objects in the universe radiate mostly gamma rays and x-rays. Cooler objects emit mostly longer-wavelength radiation, including visible light, thermal infrared, radio, and microwaves.

the average intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meterIf for just one hour, you could capture and re-use all the solar energy arriving over a single square meter at the top of the atmosphere directly facing the Sunan area no wider than an adults outstretched arm spanyou would have enough to run a refrigerator all day.the total solar irradiance is the maximum power the Sun can deliver to a surface that is perpendicular to the path of incoming light. Because the Earth is a sphere, only areas near the equator at midday come close to being perpendicular to the path of incoming light. Everywhere else, the light comes in at an angle. The progressive decrease in the angle of solar illumination with increasing latitude reduces the average solar irradiance by an additional one-half.

Origin of Photo Voltaic Cells:

The termphoto voltaic comes from the Greek:phos means light and voltaic from the Italian Physicist Volta,after whom the unit volts named. In 1839, at age 19, experimenting in his father's laboratory, he built the world's first photovoltaic cell. Willoughby Smith first described the "Effect of Light on Selenium during the passage of an Electric Current" in an article that was published in the 20 February 1873 issue of Nature.It was not until 1883 that the first solid state photovoltaic cell was built, by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions. The device was only around 1% efficient.In 1888 Russian physicist Aleksandr Stoletov built the first cell based on the outer photoelectric effect discovered by Heinrich Hertz earlier in 1887.Albert Einstein explained the underlying mechanism of light instigated carrier excitationthe photoelectric effectin 1905, for which he received the Nobel prize in Physics in 1921.

Anatomy of Solar Cell:

Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect.Solar Cell is a device that converts the light energy into electrical energy based on the principal of photovoltaic effect.Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material.A solar cell is composed of semiconductor material. A typical silicon PV cell is composed of a thin wafer consisting of an ultra-thin layer of phosphorus doped (N-type) silicon on top of a thicker layer of boron doped (P-type) silicon.P- type: A P-type material is one in which the holes are majority charge carriers i.e. they are positively charged materials (++++).

N-type: A N-type material is one in which electrons are majority charge carriers i.e. they are negatively charged materials (----)It is the energy from within the band gap from where greater no of charge carriers (holes in p-type and electrons in n-type) get excited to become charge carrier.

Working of photo voltaic cell:

Photovoltaics is the direct conversion of light into electricity at the atomic level.The operation of a photovoltaic (PV) cell requires 3 basic attributes:The absorption of light, generating either electron-hole pairs or excitons.The separation of charge carriers of opposite types.The separate extraction of those carriers to an external circuit.A solar cell is essential a PN junction with a large surface area. The N-type material is kept thin to allow light to pass through to the PN junction.

Working of PV cell

Light travels in packets of energy called photons. The depletion region with the diode is the area around the PN junction where the electrons from the N-type silicon, have diffused into the holes of the P-type material.When a photon of light is absorbed by one of these atoms in the N-Type silicon it will dislodge an electron, creating a free electron and a hole. The free electron and hole has sufficient energy to jump out of the depletion zone.. If a wire is connected from the cathode (N-type silicon) to the anode (P-type silicon) electrons will flow through the wire. The electron is attracted to the positive charge of the P-type material and travels through the external load (meter) creating a flow of electric current. The hole created by the dislodged electron is attracted to the negative charge of N-type material and migrates to the back electrical contact. .MAXIMIZING EFFICIENCYOne way to get around this limitation is to use two (or more) different cells, with more than one band gap and more than one junction, to generate a voltage. These are referred to as "multijunction" cells (also called "cascade" or "tandem" cells). Multijunction devices can achieve a higher total conversion efficiency because they can convert more of the energy spectrum of light to electricity.Much of today's research in multijunction cells focuses on gallium arsenide as one (or all) of the component cells. Such cells have reached efficiencies of around 35% under concentrated sunlight. Other materials studied for multijunction devices have been amorphous silicon and copper indium diselenide.

As an example, the multijunction device below uses a top cell of gallium indium phosphide, "a tunnel junction," to aid the flow of electrons between the cells, and a bottom cell of gallium arsenide.Multijunction cells consist of several layers, each tuned to a particular wavelength of light. As shown below, each layer has a peak efficiency at a certain wavelength, making the combination of layers in the multijunction cell efficient over a wider range of wavelengths.

Types of PV CellsMonocrystalline Photovoltaic Solar Panel: Made from a large crystal of silicon. Monocrystalline solar panels are the most efficient and most expensive panels currently available. Because of their high efficiency, they are often used in applications where installation square footage is limited, giving the end user the maximum electrical output for the installation area available.

Polycrystalline Photovoltaic Solar Panel

Characterized by its shattered glass look because of the manufacturing process of using multiple silicon crystals, polycrystalline solar panels are the most commonly seen solar panels. A little less efficient than monocrystalline panels, but also less expensive.

Amorphous Silicon "Thin Film" Photovoltaic Solar Panel

These panels can be thin and flexible which is why they are commonly referred to as "Thin Film" solar panels. Amorphous silicin solar panels are common for building integrated photovoltaics (BIPV) applications because of their many application options and aesthetics. They are cheaper and are not effected by shading. Drawbacks are low efficiency, loss of wattage per sq. ft. installed and heat retention. They can be manufactured using silicon, copper indium diselenide (CIS) or cadmium telluride (CdTe)