I. General Goals
II.
1. To become familiar with basic instrumentation methods for electronic measurements (voltmeters and ammeters).
2. To become familiar with the conventional power supplies available in the Lab and understand their capabilities and limitations.
3. To realize basic set-ups for measuring the I-V curve of a solar cell and understand their limitations and advantages as methods of measuring.
4. To become familiar with the use programmable power supplies.
5. To understand and apply the method of four-terminal sensing.
III. Materials and resources employed in the Lab Electronic devices
Solar cells, resistors, potentiometers
Basic measurement instrumentationMultimeters , voltmeters, ammeters
Conventional power suppliesVariable voltage and current sources
Programmable power suppliesFour-quadrant DC power source HP4142B
Ancilliary materialConnecting cables, connectors, sensing probes, …
Programmable power suppliesSolar simulator
IV. Lab Activities
Six set ups will be arranged corresponding to the six experiments taking place in the Lab. For
each experiment there will be a complete description of the components used in the circuital
arrange, as pointed out in the work plan.
1. Activity N°1
1.1. Goals
To determine the Current – Voltage Characteristic (I – V curve) of a Si solar cell employing a
Potentiometer as a load. As the name suggests, this method of measurement is called: The Variable
Resistor Method.
1.2. Set up Description
The set up to be used will be the one indicated in figure 1. The solar simulator will operate as a source of
irradiance which will be assumed constant (fixed operation). The Solar Simulator will was not subjected
to any special analysis consideration either experimentally or theoretically.
Figure 1.1 Variable Resistance Method Arrangement
As shown in figure 1, in order to determine the V – I Characteristic of the cell, Voltmeter 1 and the
Ammeter will measure voltages and currents respectively for different values of the resistance load.
These measurements will be different cell operation points that belong to its I – V curve. The solar
simulator is considered to be approximately three (3) meters apart from the workbench.
1.3. Measured Data
In order to obtain the experimental data, the following steps were practiced:
1) Verification of the DC voltage and current offset points of the digital multimeters to account for the possible systematic uncertainties introduced in the measurements.
2) Based on the offset points registered, it was decided which instruments would serve as a voltmeter and which as an ammeter.
3) Once the multimeters were checked, the measurement process started with the I sc and V oc operating points, followed by the intermediate I – V points.
Table 1.2 shows the experimental results obtained.
Variable Resistor Method Measurements (Set up N°1)
RESISTANCE
Precision: 1 % Range Resolution
Value 6,000 V 0,001 V
(Ω) (mV)
0 6
15 431
18 463
20 478
30 516
40 531
VOLTMETER N°1(Model Fluke 177)
Table 1.2 Measured values using the Variable Resistor Method
1.4. Data Analysis
From the data measured (Table 1.2) and the equipment specifications (Table 1.1), it follows that the experimental data is:
30 516
40 531
70 547
Open Circuit 565
Variable Resistor Method Data
RESISTANCE
Precision: 1 % Range Resolution
Value 6,000 V 0,001 V
(Ω) (mV)
VOLTMETER N°1(Model Fluke 177)
Table 1.3 Experimental data including the uncertainty analysis
V – I curve, it should be measured the short circuit current (Isc) and open circuit voltage (Voc). Taking as
a reference the previous values, a measurement sweep will be done to account for the intermediate
values around the Pmax point.
Pmax=V max∗Imax
Figure 1.2 V – I characteristic of the solar cell
Remarks:- Because the load is a passive element, the measurement is in a single quadrant
- The source is close to the set up so the cables are considered as ideal elements.
- There will be taken as many measurements as potentiometer fixed values.
- The power delivered to the resistor will not be greater than its nominal value.
- Ideally, the circuit behavior does not take into account the voltage drops introduced by the voltmeter and ammeter. For practical purposes, the voltmeter´s internal resistance can be neglected (considered infinite) and only the one corresponding to the ammeter should be considered.
2. Activity N°2
2.1. Experiment´s goal
To determine the current – voltage characteristic (I – V curve) of a solar cell employing a variable resistor
as a load. As the name suggests, the method of measurement is called: The Variable Resistor Method.
2.2. Set up description
As in the previous set up, the source is considered constant.
Figure 2.1 Remarks:- Because the load is a passive element, the measurement is in a single quadrant
- The source is far to the set up so the cables are considered non ideal elements.
- There will be taken as many measurements as potentiometer fixed values.
- The power delivered to the resistor will not be greater than its nominal value.
- Ideally, the circuit behavior does not take into account the voltage drops introduced by the voltmeter and ammeter. For practical purposes, the voltmeter´s internal resistance can be neglected (considered infinite) and only the one corresponding to the ammeter should be considered.
1.5. Measured Data
RESOLUTION
Set up N°2: Variable Resistor Method
RESISTANCE
Precision: 1 % Range Resolution Range Resolution Range
Value 6,000 V 0,001 V 3,000 V 0,001 V 400 mA
(Ω) (mV) (mV) (mA)
0 6 7 29.515 431 440 25.3
VOLTMETER N°1(Model Fluke 177)
VOLTMETER N°2(Model HP E2378A)
AMMETER (Model Fluke 87)
2.3. Data Analysis
15 431 440 25.318 463 471 23.120 478 486 21.730 516 522 16.140 531 535 12.670 547 550 7.6
565 565 0
Set up N°2: Variable Resistor Method
RESISTANCE
∞
VOLTMETER N°1(Model Fluke 177)
VOLTMETER N°2(Model HP E2378A)
AMMETER (Model Fluke 87)
3. Set up N°3:
3.1. Experiment´s goal
To determine the current – voltage characteristic (I – V curve) of a solar cell employing a variable resistor
as a load. As the name suggests, the method of measurement is called: The Variable Resistor Method.
3.2. Set up description
As in the previous set up, the solar source is considered constant.
Figure 3.1Remarks:- Because the load is a passive element, the measurement is in a single quadrant
- The source is far to the set up so the cables are considered non ideal elements.
- In this case the source voltmeter is close to the set up.
- There will be taken as many measurements as potentiometer fixed values.
- The power delivered to the resistor will not be greater than its nominal value.
- Ideally, the circuit behavior does not take into account the voltage drops introduced by the voltmeter and ammeter. For practical purposes, the voltmeter´s internal resistance can be neglected (considered infinite) and only the one corresponding to the ammeter should be considered.
3.3. Measurements
In order to obtain the V – I curve, it should be measured the short circuit current (Isc) and open circuit
voltage (Voc). Taking as a reference the previous values, a measurement sweep will be done to account
for the intermediate values around the Pmax point.
Pmax=V max∗Imax
4. Set up N°4:
4.1. Experiment´s goalTo determine the current – voltage characteristic (I – V curve) of a solar cell employing a variable voltage
source. As the name suggests, the method of measurement is called: The Variable Voltage Source Four
Wire Method.
4.2. Set up description
As in the previous set up, the solar source is considered constant.
Figure 4.1
Remarks:- Because the load is an active element, the measurement is in a single or multiple quadrant depending
on the value set for the variable voltage source.
- The source is far to the set up so the cables are considered non ideal elements.
- In this case the source voltmeter is close to the set up.
- Ideally, the circuit behavior does not take into account the voltage drops introduced by the voltmeter and ammeter. For practical purposes, the voltmeter´s internal resistance can be neglected (considered infinite) and only the one corresponding to the ammeter should be considered.
4.3. Measurement
In order to obtain the V – I curve, it must be measured the short circuit current (Isc) and open circuit
voltage (Voc). Taking as a reference the previous values, a measurement sweep will be done to account
for the intermediate values around the Pmax point.
Pmax=V max∗Imax
Figure 4.2
Figure 4.3
Optimum resolution range from 0 to Vmax (I ~ ISC, variable V)
Poorer resolution from Vmax to VOC ( V ~ VOC, variable I)
5. Set up N°5:
5.1. Experiment´s goal
To determine the current – voltage characteristic (I – V curve) of a solar cell employing a variable current
source. As the name suggests, the method of measurement is called: The Variable Current Source Four
Wire Method.
Ideally:
I=I AV v=V src
V=R A∗I A+V src
5.2. Set up description
As in the previous set up, the solar source is considered constant.
Figure 5.1
Remarks:- Because the load is an active element, the measurement is in a single or multiple quadrant depending
on the value set for the variable current source.
- The solar source is far to the set up so the cables are considered non ideal elements.
- In this case the source voltmeter is close to the set up.
- Ideally, the circuit behavior does not take into account the voltage drops introduced by the voltmeter and ammeter. For practical purposes, the voltmeter´s internal resistance can be neglected (considered infinite) and only the one corresponding to the ammeter should be considered.
5.3. Measurement
In order to obtain the V – I curve, it must be measured the short circuit current (Isc) and open circuit
voltage (Voc). Taking as a reference the previous values, a measurement sweep will be done to account
for the intermediate values around the Pmax point.
Pmax=V max∗Imax
Figure 5.2
Figure 5.3
Optimum resolution range from Vmax to VOC (V ~ VOC, variable I)
Poorer resolution from 0 to Vmax ( I ~ ISC, variable V)
6. Set up N°6:
6.1. Experiment´s goal
To determine the current – voltage characteristic (I – V curve) of a solar cell employing a programmable
power supply. As the name suggests, the method of measurement is called: The Programmable Power
Supply Four Wire Method.
6.2. Set up description
As in the previous set up, the solar source is considered constant.
Ideally:
I=I AV v=V LOAD
V=R A∗I A+V LOAD
Figure 6.1
Remarks:- Because the load is an active element, the measurement is in a multiple quadrant.
- The solar source is far to the set up so the cables are considered non ideal elements.
- In this case the source voltmeter is close to the set up.
- Ideally, the circuit behavior does not take into account the voltage drops introduced by the voltmeter and ammeter. For practical purposes, the voltmeter´s internal resistance can be neglected (considered infinite) and only the one corresponding to the ammeter should be considered.
6.3. Measurement
It is an electronic instrument that may act as o Positive or negative voltage source being able to
supply/drain any current o Positive or negative current source being able to provide any voltage. In
addition, it provides
One or several voltmeters
One or several ammeters
It is typically computer controlled and uses specific software
Figure 6.3 HP4142B: Programmable power supply used at IES
Figure 6.5
Figure 6.4
MATERIAL DESCRIPTION MEASUREMENTS
NOTES
∞0
R (Ω) V ± ΔV (V)
Table 6.2 Table 6.1 Measurements in the V max−V OC region
V. Lab session report outline
1. Materials and methods: describe the instruments used for the measurements and their accuracy.
2. PART I: For each circuit include a section with:
Tables and graphs with the measurements taken.
A comment about the conditions of the measurement (simplicity for measuring Pmax, Isc, Voc, speed, stability, …)
A general comment about the set-up in comparison with the previously tested.
PART II: Answer the questions proposed in the next page
What would be the ideal characteristics of a voltage source for measuring I-V curves of solar cells?
In set-ups 1 to 6 the voltmeters have changed location in the circuit, while the ammeter has remained unmoved. Why?
Is there any special consideration about the location of the ammeter in the circuit?
True or false (please comment): “For measuring very small solar cells, it might not be necessary to apply the four-wire method”.
What is a SMU? Please include a brief explanation (~1/2 page)
What is LabView? Please include a brief explanation (~1/2 page)
What is GPIB? Please include a brief explanation (~1/2 page)
Sketch a flow diagram for an optimized program to measure the I-V curve of a solar cell using a 4-quadrant power supply.
PART III: Each member of the team write a brief paragraph commenting personal difficulties (both practical and conceptual) found in this lab session.
Part IV: references used
Apendice 1Materials and Instruments Description
A1.1 Instruments Specifications
Table A.1 Digital Multimeters Fluke 175, 177 and 179 Specifications
Table A.2 Digital Multimeter Fluke 87 Specifications
A1.2 Instruments and Materials Pictures
Figure A1.1 Digital Multimeters Fluke 87, 177 and 179.
Figure A1.2 Digital Multimeter Power Supply Model AGILENT 34401A
Figure A1.3 Potentiometer set
Figure A1.3 Programmable power supply used at IES
Apendice 2Uncertainty Analysis
A2.1 Definitions
A2.2 Calculations
(measured value of x )=xbest+δ xδ x=Accuracy ±([% of Reading ]+[Counts ]), where:
xbest:True value
δ x: Uncertainty