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SOLAR CELL TESTING

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* * BASIC SOLAR CELL TESTING Basic Structure of a Solar Cell Basic Photovoltaic Cell Model This model consists of Built-in voltage Current due to optical generation ... – PowerPoint PPT presentation

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Title: SOLAR CELL TESTING


1
(No Transcript)
2
BASIC SOLAR CELL TESTING
3
Basic Structure of a Solar Cell
4
Basic Photovoltaic Cell Model
  • This model consists of
  • Built-in voltage
  • Current due to optical generation
  • Series resistance
  • Shunt Resistance

5
Key Parameters
  • Open Circuit Voltage, Voc (V)
  • Short Circuit Current Isc (A)
  • Short Circuit Current Density, Jsc (mA/cm2)
  • Max Power Voltage, Vmp
  • Max Power Current, Imp
  • Max photo current
  • Fill Factor, FF
  • Efficiency, ?
  • Diode Ideality Factor
  • Shunt Resistance
  • Series Resistance
  • Reverse Saturation Current or Leakage Current

6
A Solar cell is a diode
A solar cell is a diode and hence an IV curve of
a solar cell under dark conditions will look
similar to that of a diode. When illuminated,
the photons interact with the material to
generate electron hole pairs, which are then
driven in opposite directions by the built-in
potential.
7
Standard Test Conditions
  • AM 1.5G
  • Temperature 25C
  • Important device characteristics can be obtained
    from the I-V measurements.

8
Sunlight Simulator in Clean Room
UV Lamp Housing
Air Mass 1.5 filter installed
Shutter control
Cooling fan must be on
UV Lamp Power Supply Not shown
UV intensity meter and calibration solar cell
9
Procedure for Sunlight Simulator
  • Verify the stage is connected to GND
  • Verify top contact probe R1 is connected to SMU1

10
Procedure for Sunlight Simulator
  • Make sure all fans are working
  • Turn ON the lamp and wait for a few minutes for
    it to stabilize.
  • Open shutter (Remember to wear safety goggles)
  • Using the calibration cell and the sun meter,
    adjust the power supply at about 970W or 1 Sun on
    the sun meter.
  • Replace the calibration cell with the test sample
  • Make top and bottom connections to the Keithley
    4200 SCS.

11
Keithley 4200 SCS tutorial
  • Start KITE.
  • Select vfd in diode section. (1)
  • Set Anode to SMU1 and Cathode to GNDU. (2)
  • Click on Force/Measure button to change sweep
    parameter. (3)
  • Click Run Test/Plan button to start sweep. (4)
  • Click Append button to do another sweep and
    append the data to the previous sweep. (5)

12
Keithley 4200 SCS tutorial
13
Keithley 4200 SCS tutorial
  • To save measured data, select the data tab (6)
    and click save as button on the right (7).
  • To view the graph, select the graph tab (8).
  • To save the graph, right click on the graph and
    select save as.

14
Keithley 4200 SCS tutorial
15
Open Circuit Voltage, Voc (V)
  • In an ideal solar cell, Voc is independent of the
    illumination intensity.
  • The open circuit voltage (Voc) occurs when there
    is no current passing through the cell.
  • V (at I0) Voc
  • To read the open circuit voltage from the graph,
    locate the point on the voltage axis where the
    current is zero.

16
Short ircuit Current Density, Isc
  • The short circuit current Isc corresponds to the
    short circuit condition when the impedance is low
    and is calculated when the voltage equals 0.
  • I (at V0) Isc
  • To read the short circuit current from the graph,
    locate the point on the current axis where the
    voltage is zero.
  • To find the current density Jsc, divide this
    current by the area of the solar cell under test,
    to obtain the current density, Jsc (mA/cm2)

17
Max Power Point
  • Draw a rectangle with the origin, VOC and ISC as
    the 3 corners. The 4th corner will give the
    maximum theoretical power, PT.
  • From the origin, draw a line passing through the
    maximum theoretical power, PT. This is the load
    line

The point where the load line crosses the I-V
curve is the maximum power point, PMAX for the
solar cell, for a given load, with maximum
current and maximum voltage.
18
Max Power Point
  • The voltage at the maximum power point of the
    cell is the maximum voltage, VMP.
  • The current at the maximum power point of the
    cell is the maximum current, IMP
  • From the maximum power point, PMAX , draw a line
    perpendicular to and meet the voltage axis. The
    maximum power voltage, VMP is given by the value
    on the voltage axis. The maximum power current,
    IMP is given by the value on the current axis.

19
Fill Factor
  • Fill Factor is the measure of the quality of the
    solar cell. It is the ratio of the maximum power,
    Pmax to the theoretical power, PT.
  • FF PMAX/PT
  • FF IMP . VMP/
    Isc . Voc
  • Fill Factor is a number between 0.0 and 1.0. The
    higher the number, the better the solar cell

20
Efficiency
  • Efficiency is the ratio of the electrical power
    output POUT, compared to the solar power input,
    PIN, into the PV cell
  • ? POUT/PIN
  • POUT PMAX (W/m2)
    (Imp)(Vmp)/area (Jmp)(Vmp)
  • Where Jmp Imp/area
  • For Standard Test
    Conditions
  • PIN 1000 (W/m2) 100(mW/cm2)

21
Reverse Saturation Current
  • The saturation current I0, is the current that
    flows in the reverse direction when the diode is
    reverse biased. It is also called as the leakage
    current.

Specified voltage point for leakage current
measurement
22
Shunt Resistance
  • Shunt resistance is the change in the voltage for
    change in the unit current and is ideally equal
    to infinity.

23
Series Resistance
  • Series resistance is due to
  • Resistance of the metal contacts
  • Ohmic losses in the front surface of the cell
  • Impurity concentrations
  • Junction depth
  • Series resistance reduces both short circuit
    current and maximum power output of the cell

24
Series Resistance
  • For the measurement of internal series
    resistance, 2 I-V curves of different irradiance
    but of the same spectrum and at the same
    temperature are necessary.
  • The series resistance is calculated as
  • RS (V2-V1)/(ISC1 ISC2)

25
Diode Ideality Factor
  • The diode ideality factor n, is an indicator of
    the behavioral proximity of the device under
    test, to an ideal diode.
  • n is between 1 and 2, ideally equal to 1.

26
Alternate view of I/V Plot
Current plot with 1 sun illuminating the solar
cell
Dark current plot (no sunlight)
Zero voltage, zero current point
27
Max photocurrent
Max photocurrent about 160mA
28
Voc and Isc
Isc where V 0 About 150mA
Voc where I 0 About 0.5v
Jsc (Isc)/area of cell in cm2
29
For Pmax point
1) Draw a horizontal line from Isc
2) Draw a vertical line from Voc
3) Draw a line from origin to where they intersect
30
For Pmax point
Pmax - Max Power point
Imax 75mA
Vmax .35v
Jmp Imp/ area of cell
31
Fill Factor
  • Fill Factor is a number between 0.0 and 1.0, the
    higher the number, the better the solar cell
  • Fill Factor is the ratio of the maximum power,
    Pmax to the theoretical power, PT.
  • FF PMAX/PT
  • FF IMP . VMP/
    Isc . Voc
  • For the previous sample
  • FF (.075A)(.35V)/(.150A)(.50V)
  • FF .02625 VI/.0750 VI
  • FF .35 (unit less)

32
Efficiency
  • Assume for previous example, area of cell 6 cm2
  • ? POUT/PIN
  • POUT PMAX (W/m2)
    (Imp)(Vmp)/area
  • PMAX (.075mA)(.35V) .026W 26mW for 6cm2
  • PMAX 4.3 mW/cm2
  • For Standard Test
    Conditions
  • PIN 1000 (W/m2) 100(mW/cm2)
  • n 4.3 mW/cm2/100mW/cm2
  • n 4.3

33
Assignment on I/V plots due next class
  • There will be a test on solar cell I/V plot
    analysis
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