Periodic Table

SOLAR CELL

1A solar cell is an electronic device which directly converts sunlight into electricity. Light shining on the solar cell produces both a current and a voltage to generate electric power.

223Solar Cell OperationExternal Load+-nEmitterpBaseRear ContactFront ContactAnti reflection coatingAbsorption of photon creates an electron hole pair. If they are within a diffusion length of the depletion region the electric field separates them.The electron after passing through the load recombines with the hole completing the circuit.An array of solar cells converts solar energy into a usable amount ofdirect current (DC) electricity.

33Solar Cell I-V Characteristics4VoltageCurrentDarkLightTwice the Light = Twice the CurrentCurrent from Absorption of Photons4PARAMETERS:when the cell is operated atshort circuit,V = 0and the currentIthrough the terminals is defined as theshort-circuit current. It can be shown that for a high-quality solar cell (lowRSandI0, and highRSH) the short-circuit currentISCisIsc= ILwhere IL is the current in Load.

5When the cell is operated at open circuit,I = 0and the voltage across the output terminals is defined as theopen-circuit voltage. Assuming the shunt resistance is high enough to neglect the final term of the characteristic equation, the open-circuit voltageVOCis Voc= nkT ln ( IL + 1)qIowhere : Io= reversesaturation current(ampere)IL= photogenerated current (ampere)n= diode ideality factor (1 for an ideal diode)q=elementary charge (1.6021765 1019 C)k=Boltzmann's constantT=absolute temperature

6The "fill factor", more commonly known by its abbreviation "FF", is a parameter which, in conjunction with Vocand Isc, determines the maximum power from a solar cell. FF = PmVoc x IscWhere Pm = Im x Vm

7Voltage (V)IV Plot8CurrentPowerShort Circuit CurrentOpen Circuit VoltageOperating PointVmpImpPm8Efficiencythe most commonly used parameter to compare the performance of one solar cell to another. Efficiency is defined as the ratio of energy output from the solar cell to input energy from the sun.

The input power for efficiency calculations is 1 kW/m2or 100 mW/cm2. Thus the input power for a 100 100 mm2cell is 10 W and for a 156 156 mm2cell is 24.3 W9

Circuit Diagram

Schematic symbol of solar cell.11I = IL ID - ISH

where:I= output current (ampere)IL= photogenerated current (ampere)ID= diode current (ampere)ISH= shunt current (ampere).

Where:Io= reversesaturation current(ampere)n= diode ideality factor (1 for an ideal diode)q=elementary charge (1.6021765 1019 C)k=Boltzmann's constantT=absolute temperatureVj = V + IRs where:Vj = Voltage across the diode and Shunt resistorV= voltage across the output terminals (volt)I= output current (ampere)RSH= series resistance ().

Parasitic Resistances12Series ResistanceSeries Resistance circuit

Series Resistance I-V Curve

13Shunt ResistanceShunt Resistance Circuit

Shunt Resistance I-V Curve

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