session2 report

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)


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.




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°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°2(Model HP E2378A)

AMMETER (Model Fluke 87)

3. Set up N°3:


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.


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


- In this case the source voltmeter is close to the set up.




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.



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.




4.3. Measurement

In order to obtain the V – I curve, it must be measured the short circuit current (Isc) and open circuit



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:


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



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.



5.3. Measurement

In order to obtain the V – I curve, it must be measured the short circuit current (Isc) and open circuit



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:


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.



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.



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

session2 report

Documents

iv curve

experimental data

intermediate i v points

method of measurement

current offset points

measured values

current voltage characteristic

si solar cell