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Test Methods - PV-Modules and Strings

  • Updated

This article discusses a brief overview of the common methods for testing PV-Modules and Strings.


There are several methods to test a PV-Module (or string) to check for certain faults. 

While most of these tests are commonly used in the Solar field, some cannot be performed with a Tigo MLPE inline (or attached) to the PV-Modules.

Test Method

PV-Module or String
(w/o Tigo)

TS4 Wireless
(M, S, O)

 TS4 Fire Safety
(PLC)
Open Circuit Test mceclip0.png mceclip0.png mceclip1.png
Short Circuit Test mceclip0.png mceclip1.png mceclip1.png
I-V Curve Tracer mceclip0.png mceclip1.png mceclip1.png

Insulation Test

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Earth Resistance Test

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Special Notes:

The TS4 Flex MLPE comes in 2 models:

  • Wireless Data Communication (TS4-M, S and O)
  • Powerline Communication (TS4-F and 2F)

TS4-M, S and O series communicate their Rapid Shutdown (RSD) response via wireless signal. Any test that requires the MLPE units to not be in RSD, must have the CCA/TAP Signal present. 

Tigo TS4-F and 2F (Fire Safety) MLPEs use PLC signaling and require a completed circuit, in order to not be in RSD. Any test that requires an open circuit or a break in signaling, would not be possible. 

Both TS4 families (wireless and PLC) offer various protective functions that (if placed under Isc conditions), could invalidate the results.

 

Open Circuit Test

An open circuit test measures the open circuit voltage of the module, or string. Compare that value to the expected open circuit of the module(s) spec sheet.

  1. Requires a DC voltage meter.
  2. Can help detect intermittent connection issues or open sub-circuits inside the panel, such as diodes or solder traces.
  3. Please keep in mind that you can shake or hit the PV module during this test and the results may vary due to an intermittent or loose connection in the module.

This test can only identify completely broken panel issues, but is the easiest testing method. 

Please see this video on YouTube as an example:
https://www.youtube.com/watch?v=Hey1QZkYFSQ

 

Note: While you cannot measure for traditional Voc on the TS4-F family, you can still use this method to check for the RSD Safety Voltage, which is 0.6 V per MLPE in the string.

 

Short Circuit Test

A short circuit test measures the short circuit current of the module, or string. Compare that current value to the expected short circuit current of the module spec sheet, given sunlight conditions

  1. Requires a DC current meter.
  2. Can help detect an intermittent connection or weak panel that can not sustain current unload.
  3. Please keep in mind that you can shake or hit the PV module during this test and the results may vary due to an intermittent or loose connection in the module

This test can identify more complicated panel issues, more accurately than an Open Circuit Test.

Please see this video on YouTube as an example
https://www.youtube.com/watch?v=Hey1QZkYFSQ

 

I-V Curve Tracer

An I-V curve tracer will test a panel from open circuit to short circuit and all points in between under load. IMPORTANT, this will provide the most accurate indication into the health and performance of the PV module.

  1. Requires an I-V curve tracer

Although, this can be the most accurate method of PV-Module testing, it cannot be performed with any Tigo MLPE attached. If it is necessary to test the PV-Module, the I-V Curve Tracer can be run on the module(s), without the MLPE connected.

Please see this video on YouTube as an example
https://www.youtube.com/watch?v=69PGz7bvets

 

Earth Resistance Test

An Earthing Tester measures the resistance of the earth/ground by employing a constant current generator which injects current into the earth between electrode spikes in the ground.

  • Requires an earth tester, spikes, hammer and a measuring tap.
  • Has several different methods of testing suggested (different numbers of spikes and distances).

This test is for the general grounding of a system and does not affect the Tigo MLPE's in any way. 

 

Insulation Test

Commonly referred to as a Megger test, it measures the resistance of the insulation around a cable or connector. This can confirm that a wire sheathing has become damaged, dried out or compressed (pinched). 

  • Requires an Insulation (megger) tester
  • Shows megaohm values for resistance between conductors and other surfaces (grounds, conduit, racking, etc).

Note: Before running an insulation test, make sure to read the voltage rating written on the output cable of the MLPE as there are 1000V and 1500V versions. The Insulation Tester's output voltage should not exceed the rated voltage of the equipment/cables when testing. 

 

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If you require any assistance or information regarding testing and/or system design, please contact Tigo's Sales Engineering team at: se@tigoenergy.com or you can fill out a Sales Contact Form.

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