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SOLAR
PHOTOVOLTAICSYSTEMS
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Advantages of Solar PVSystemIt converts solar energy directly into electricalenergy without going through thermal-mechanical link. It has no moving parts.Solar PV systems are reliable , modular , durableand generally maintenance free.
These Systems are quiet , compatible withalmost all environments, expected life span of 20years or more.It can be located at the place of use and henceno distribution network is required.
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Disadvantages of Solar PVSystem
At present the costs of solar cells are high,making them economically uncompetitive withother conventional power sources.
The efficiency of solar cells are low.Large no. of solar cell modules are required togenerate power.As solar energy is intermittent, some kind of electrical energy storage is required, whichmakes the whole system more expensive.
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Solar Cell characterisitics
The above figure shows the I-V characteristics.I= Isc-Io {Exp( V/Vt)-1}Where Io is the reverse saturation current , Vt is thevoltage equivalent of temperature and at roomtemperature its value is 26 mV.We have Vt=KT/qWhere K is the boltzmanns constant, T is thetemperature in K and q is the charge of an electron.
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Equivalent Circuit The I-V characteristics is derived for ideal condition,considering the internal series resistance of the cell is zeroand the shunt resistance is infinite.
In actual practice both have infinite values, so thecharacteristics are modified.An additional shunt current flows in the shunt branch.
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Effect of variation of Isolation andTemperature :- As the isolation variesthroughout the day the PV characteristicschanges. The short circuit voltage and opencircuit current increases with the increase inintensity.
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Energy Losses and Efficiency:- The Conversionefficiencies of commercially produced single crystalcells are in the range of 12-15%. Various loss
mechanisms lead to limit the conversion efficiency.Maximizing the performances:- Maximum values of open circuit voltage and short-circuit current, low seriesresistance and high shunt resistance will lead to highfill factor.
Cell Sizes:- Size of the cell affects the performance of the cell. So as per current industry standards cells areof various types:- round single crystalline, square singlecrystalline, square multicrystalline.
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SOLAR CELLCLASSIFICATION
On Basis of thickness
of active material
On Basis of typeof junction
structure
On basis of type
of activematerial usedin its fabrication
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On basis of thickness of Activematerial
1)bulk material where the base material is itself an
active material.2)thin film cell where a deposition of active material
substrate is there.
On basis of type of junctionstructure
pn homojunction cell, pn heterojunction cell, pnmultijuntion cell, metal semiconductor schottky
junction, p-i-n semiconductor junction.
On basis of type of active material
used in its fabrication Single crystal, multicrystalline silicon, amorphoussilicon(a-Si) cell, gallium arsenide(GaAS) cell, CopperIndium diselenide cell(CIS), cadmium telluridecell(CdTe) and Organic PV cell.
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SOLAR CELL :- It is basically a bulk silicon cellwhere the bulk material is the p-type silicon. Athin layer of n-type silicon is formed at the topsurface. There is anti-reflective coating,textured rear surface.SOLAR PV MODULE :-It is the basic buildingblock of a PV system. It is the interconnection of a number of cells and all these cells should havethe same characteristics. Partial shadowing maydamage the module.SOLAR PV PANEL :-Several solar modules areconnected in series/parallel to increase thevoltage/current ratings. Solar panel is a group of several modules connected in series parallelcombination in a frame that can be mounted ona structure. The combination of such panels arecalled as an SOLAR ARRAY .
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A typical panel: Series-Parallel Connection of modules.
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MAXIMIZING THE SOLAR PVOUTPUT AND LOAD MATCHING
The best use of Solar PVsystem is made bymaximizing the output.First by mechanically
orienting the Panel for suntracking to receivemaximum solar radiation.Secondly by electrically
tracking the operatingpoint by manipulating theload.
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MAXIMUM POWER POINTTRACKER(MPPT)
To receive the maximum power, the load must adjustitself accordingly to track the maximum power point.Generally MPPT is an adaptation of dc-dc switchingvoltage regulator.A buck-boost Converter is normally used.
Three possible strategies for operation of MPPT are:-
1)By monitoring dynamic and static impedances.2)By monitoring the power Output.3)By fixing the output voltage.
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MPPT using a Buck-Boost Converter
LAR PV Y TEM
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LAR PV Y TEMCLASSIFICATION
Central Power Station System :- Theseare conceptually similar to any otherconventional power station. They feed power tothe grid to meet day time peak loads. Thecapital costs are high.
Distributed System :- This system is muchmore successful and unique. It can be furtherclassified into 3 types:
1)Stand-alone System2)Grid-Interactive System3)Hybrid Solar PV System (Consumer
applications)
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Stand-alone Solar PV system :-Located atthe load center and dedicated to meet all theelectrical loads of a village/community or aspecific set of loads basically in remote or ruralareas which have no access to grid supply.
Grid-Interactive System:- It is connectedto utility grid with two-way metering system. It ismeant for the whole village of community. It isrelatively a bigger system.
Hybrid Solar PV system:- These systemsare meant for low energy consumer devices.Basically designed for indoor applications.
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A general stand-alone solar PV system
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A general Grid-Interactive solar PV system
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SOLAR PV APPLICATIONSGrid-Interactive PV Power generation Water pumping for the purpose of drinking or forirrigation during the sunshine hours.Besides water pumping, Lighting is the second mostimportant application of stand-alone system.Used for Medical Refrigeration of life saving drugs.Village Power :- Solar PV power can meet low energydemands of many remote, small, isolated villages.Solar PV panel are ideally suited for Telecommunicationand Signaling Applications such as local telephoneexchange, radio and TV broadcasting.
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A 200 KW Grid-Interactive plant at punjab
Solar Ligh ting
Water Pumping
Solar Lantern
