PV Testing: How to and Why Is It Important?
Underperforming solar photovoltaic (PV) modules result in lost revenue for asset owners. Solar system owners must invest in module testing plans that will eventually generate enough revenue to justify their costs.
To maintain smooth PV system operation, installers are encouraged to regularly inspect and test the solar modules.
What Is PV Testing?
Photovoltaic (PV) testing can be divided into two categories: visual inspection and a testing procedure.
Visual Inspection During Solar PV Testing
A visual inspection is done before and after a PV module has undergone environmental, electrical, or mechanical stress testing in the lab to ensure that the module is in good condition.
A visual inspection should take place, not only at commissioning but also, during routine testing.
The British standard BS EN 62446’s checklist is a great technique to ensure that all critical DC system components are evaluated and taken into consideration during the visual inspection. Below is a checklist example shared by NREL.
Getting Started With Testing
System performance testing comes after the inspection phase. For the DC side, the following test list is provided in BS EN 62446 (for the DC side):
Continuity testing is frequently performed to check electrical system connections, the proper process of disconnecting mechanisms, grounding, and the performance of overcurrent protection devices. PV system equipment grounding is particularly difficult; mounting configurations offered by different manufacturers frequently need specific hardware and grounding procedures.
To ensure correct equipment grounding procedures, be careful to adhere to the company’s instructions for the module and mounting system.
PV Modules Polarity Testing
The polarity of array wire and other dc components should be carefully considered in PV systems, as it is with all dc circuits. Arrays with reversed polarity are capable to serve as loads, which can have drastic consequences and harm PV modules or the wiring of the source circuit.
The 2011 NEC states that all PV components must be clearly recognized by marking, grouping, or tags at all terminations, connections, or splices in order to clear up ambiguities and encourage improved wire management techniques.
Voltage and Current Testing
Before closing disconnects and starting system operations, basic voltage and current checks are carried out on both dc and ac circuits in PV systems to verify that these parameters are within acceptable ranges.
Open-circuit Voltage (Voc) and Short-circuit Current (Isc)
The short-circuit current (Isc) and open-circuit voltage (Voc) test values are used for particular module functionality. Both these values should be within design specifications. Open-circuit voltage (Voc) and short-circuit current (Isc) values from either the Nominal Operating Cell Temperature (NOCT) table or the Standard Test Conditions (STC) table should be valid.
Insulation Resistance Testing
According to the NEC [110.7], an insulation resistance test is used to confirm and show the integrity of electrical equipment and system wiring. Measurement of insulation resistance is performed between the test conductors and the ground, or between other conductors.
System Functional Testing
Functional testing of systems ensures that they operate as intended during startup, shutdown, and normal process settings. This testing process is developed to verify system’s operating parameters are within nominal and intended bounds.
System Performance Testing
Performance tests are used for the verification of system power output and energy production. Performance tests can also be useful to identify issues that need maintenance, as well as to estimate system revenue and warranty terms.
These tests generally include voltage and current measurements and may also entail I-V curve tracing.
Special tests are performed for preventive maintenance or troubleshooting specific problems.
These tests are as follows:
An electroluminescence (EL) is identical to an X-ray. EL images show microcracks and defects in the inner layers of solar cells.
This technology helps the solar owner and manufacturing companies to detect cell damage which can be responsible for hot spots and underperformance in the future.
The shading effects on PV arrays are evaluated and assessed using a shading analysis. Any obstruction close to PV arrays that block the solar window could result in shading.
Power Quality Analysis
Power quality analysis, inverters efficiency, and ac module testing can be done with the help of power analyzer tools available in the market.
These tools can be used to monitor power factors, voltage surges and sags, harmonics, and other conditions with time.
Periodic inverters testing is as important as module testing for solar system safety and reliability. However, these inverter tests are not addressed in this article.
Success in the Solar Industry Starts With Testing and Certification
A certification list for quality assurance has been proposed by the International Electrotechnical Commission (IEC), and these international standards are largely acknowledged throughout the solar sector. This certification list is effective at revealing system design verification, and material faults that can lead to premature field failures.
Expertise and Experience Count in Solar PV Testing
The individual responsible for conducting the test must be aware of the purpose of each test, expected outcomes, and test instruments used. Although it may seem simple, even a tiny error when entering numbers might result in a significant risk to the project.
One of the sales arguments used over the years to market PV panels goes like this: “It has no moving parts, it requires no maintenance, and it is an “install and forget solution”.
Yes, solar PV is a reliable and simple solution but it requires maintenance and testing just like any other electrical system. Therefore, an “install and forget” solution can leave you on the road sooner rather than later.