Voltage and current in a series and parallel connection of solar cells
ENT
2.2
Keywords
Solar energy, photovoltaics, solar cell, series connection, and parallel connection
Principle
A single solar cell supplies only 0.5 V. This is not sufficient for operating light-emitting diodes or a small light bulb. In order to generate more voltage, several solar cells are connected in series.
The aim of this experiment is to demonstrate the characteristics of series or parallel connections of solar cells by measuring the open-circuit voltage and short-circuit current and by comparing these values to the values of a single solar cell.
Equipment
*2 Connector, angled, module DB
*2 Connector, T-shaped, module DB
*2 Junction, module DB
*2 Solar cell, module DB
*1 Clamp on a holder for the demonstration board
Additional equipment
09401-02
09401-03
09401-10
09470-00
02164-00
1 Demo physics board with a stand
1 Support rod "PASS", l = 630 mm
1 Lamp socket E27 with a reflector and holder
02150-00
02027-55
06751-01
1 Filament lamp 230 V/120 W with a reflector 06759-93
**1 Cobra4 Wireless-Manager
**1 Cobra4 Wireless-Link
**1 Cobra4 Sensor-Unit Energy
**1 Holder for hand-held meters
**1 measure software for Cobra4
1 Connecting cable, 500 mm, red
1 Connecting cable, 500 mm, blue
1 Connecting cable, 500 mm, yellow
1 PC, USB port, XP, Vista, Win7
* Included in the ENT 1 set
** Included in the Cobra4 extension set
12600-00
12601-00
12656-00
02161-00
14550-61
07361-01
07361-04
07361-02
09492-88
12608-88
Fig. 1: Experiment set-up for series connection
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ENT
2.2
Voltage and current in a series and parallel connection of solar cells
Note
The concepts of open-circuit voltage and short-circuit current should be explained to the students. It should also be explained how to measure the short-circuit current, since in a circuit, an ammeter is always connected in series with a resistor. In this case, however, the resistor is simply a wire. This is why the ammeter must be connected directly to the solar cell.
It is also important to use a high-resistance voltmeter and a low-resistance ammeter. This is why the
Ampere measuring range is used on the Cobra4 Sensor-Unit Energy. There, the internal resistance is only 33 m Ω .
Under great heat, the power of the solar cell decreases. This is why the lamp must be switched off immediately after every measurement.
Set-up
-
-
-
Set the circuit up as shown in Fig. 3.
Fasten the clamp on the holder tightly to the upper edge of the board above the solar cell and clamp in the PASS support rod.
Fasten the lamp to the support rod (Fig. 2).
The distance between the middle of the solar cell and the lamp front should be approximately 35 cm.
Fig. 2: Lamp set-up
2
Fig. 3: Experiment set-up for voltage measurement
PHYWE Systeme GmbH & Co. KG © All rights reserved P9502260

Voltage and current in a series and parallel connection of solar cells
ENT
2.2
Procedure
-
-
Start the PC and Windows.
Connect the Cobra4 Wireless Manager to the USB port of the PC.
-
-
-
Start the "measure" software package on the PC.
Connect the Cobra4 Wireless-Link to the Cobra4 Sensor-Unit. After it has been switched on, the
Sensor-Unit will be automatically detected and an ID number will be assigned to the Cobra4 Wireless-Link. This number will be displayed. The communication between the Cobra4 Wireless Manager and the Cobra4 Wireless-Link is indicated by way of the data LED.
Switch the Cobra4 Wireless-Link with the connected Cobra4 Sensor-Unit on. The Sensor-Unit and the electrical quantities U , I , P , and W are displayed as the measuring channels.
Fig. 4: Voltage measurement
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ENT
2.2
Voltage and current in a series and parallel connection of solar cells
1. Voltage measurement
1.1 Single solar cell
-
-
-
Load the experiment "ENT 2.2 - Voltage" (Experiment > Open experiment > …).
Aim the lamp at the solar cell and switch it on.
Start the measurement data recording process in "measure" .
-
-
-
-
Perform a single measurement .
Switch the lamp off.
1.2 Series connection
-
-
Set up a series connection of two solar cells as shown in Fig. 1.
Switch the lamp on and align it.
Perform a single measurement .
Switch the lamp off.
-
-
-
-
1.3 Parallel connection
-
Set a parallel connection up as shown in Fig. 5.
-
Switch the lamp on and align it.
Perform a single measurement .
Stop the measurement data recording process in "measure" .
Switch the lamp off.
Transfer the measurement values to the "measure" main program.
4
Fig. 5: Experiment set-up for a parallel connection
PHYWE Systeme GmbH & Co. KG © All rights reserved P9502260

Voltage and current in a series and parallel connection of solar cells
ENT
2.2
-
2 Current measurement
-
Set the circuit up as shown in Fig. 6.
-
-
-
-
-
Call up a new measurement with Cobra4 .
Load the experiment "ENT 2.2 - Current"
(Experiment > Open experiment > …).
Ensure that the red plug is connected to the
A socket of the Cobra4 Sensor-Unit Energy.
Perform several individual measurements in the same way as for the voltage measurement of only one solar cell, and also of two solar cells connected in series and in parallel.
Transfer the measurement values to the
"measure" main program.
Switch the lamp off.
Observation
Fig. 6: Experiment set-up for measuring the current
The parallel connection supplies approximately the same voltage as a single solar cell. The series connection, however, supplies approximately twice the voltage.
In a series connection, approximately the same current is reached as in the case of a single solar cell, whereas in a parallel connection, the values for the current are approximately twice as high.
Fig. 7: Current measurement evaluation
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ENT
2.2
Voltage and current in a series and parallel connection of solar cells
Evaluation
If the function "Survey" is used in "measure", it becomes very clear that the voltage in a series connection is twice as high as the voltage of a single solar cell. In a parallel connection of two cells, the current is approximately twice as high as the current of a single cell. The current is subject to higher measurement errors, since it depends on the light intensity and the illumination of the solar cells in the light cone is not always identical.
Voltage
Single solar cell
0.52 V
Series connection
1.02 V
Parallel connection
0.51 V
Current 149 mA 146 mA 302 mA
This follows the laws for electric series and parallel connections. In a series connection, the current is identical at any location, whereas the voltage is added up based on the individual voltage sources. In a parallel connection, on the other hand, this is exactly the other way round. The voltage is identical at any location and the current is added up.
Application
Solar modules consist of several solar cells that are connected in series. For larger installations, these modules are connected in series as well as in parallel. The advantage of this is that in the event of a failure of individual cells, the power loss is minimised. These types of solar installations can be used directly. Often, however, higher voltages are generated with the aid of transformers and inverters in order to feed the electrical energy into the existing power network.
Notes
Corresponding student experiments TESS EN
2.3 Voltage and current in a series connection
of solar cells (P9511300)
2.4 Voltage and current in a parallel connection
of solar cells (P9511400)
For the execution of the experiment without a PC, the items on the list (page 1) that are marked with (**) must be replaced with the following items:
Experiment P9502263
1 Cobra4 Mobile-Link
1 Cobra4 Sensor-Unit Energy
1 Cobra4 Display-Connect, transmitter and receiver set
1 Holder for hand-held meters
1 Large-scale display
Experiment P9502200
1 Analog demonstration multimeter ADM 2
12620-00
12656-00
12623-88
02161-00
07157-93
13820-00
6 PHYWE Systeme GmbH & Co. KG © All rights reserved P9502260