Solar panel quality testing: 5 common defects to avoid

Regardless in which country your solar panels are produced, solar panel defects occur on a regular basis. The payback performance of a solar PV systems is based, besides FITs and irradiation, on the initial power output, power degradation and the lifetime of the pv module(s). Needless to say that solar PV system installers and end-users need to be entirely assured about the quality of the solar panels purchased. Sinovoltaics specializes in independent solar quality consultancy and quality testing of PV inverters, mounting racks and modules on-site in the Greater China region. In this article we discuss how solar panel testing is performed and what are the common defectives found.

Certified solar panels

When reviewing manufacturers for solar products, first determine if the manufacturer is producing solar panels according to industry standards. This can easily be found out by requesting the common pv product certifications. After receiving the certifications, verify the authenticity of the pv certificate on-line at for instance TUV Rheinland.

Defect – Poor sealing pv module

Certifications on your solar panels provide the standards for the profitability and security of your investment. All standard solar panels should be certified. Common solar panel (pv) certifications are IEC 61215 / EN 61215 IEC 61215 Ed. 2, IEC61646, IEC 61730 / EN 61730, IEC 60364-4-41, IEC 62108 and IEC 61701.

More information regarding solar panel certifications, have a look at our Guide to Solar Panel (PV) Certifications.

Basically, on-site solar panel quality inspection consists of minimum two basic parts: the visual inspection and the flash test.

Visual inspection

During the visual inspection each solar panel is reviewed by an independent certified testing agency for defectives, including scratches, glue marks, montage frame and anything that is deviant.

Defect – Excessive glue mark

Flash test

Most manufacturers use what is called the I-V (Current-Voltage) data measurement test, sun simulation test or most commonly: flash test. During a flash test, the pv module is exposed to a short (1ms. to 30 ms.), bright (100 mW. per sq. cm.) flash of light from a xenon filled arc lamp. The output spectrum of this lamp is as close to the spectrum of the sun as possible. The output is collected by a computer and the data is compared to a reference solar module. The reference module has its power output calibrated to standard solar irradiation. The results of the flash test are compared to the specifications of the pv module datasheet and the numbers printed on the label on pv module’s back.

Even though every manufacturer (should) provide(s) the flash test of all solar panels ordered, we always decide to perform our own flash test and confirm if all quality criteria are met.

Standard test conditions

Module parameters are measured at standard test conditions (STC). STC specifies a temperature of 25 °C and an irradiance of 1000 W/m2 with an air mass 1.5 (AM1.5) spectrum. These correspond to the irradiance and spectrum of sunlight incident on a clear day upon a sun-facing 37°-tilted surface with the sun at an angle of 41.81° above the horizon. This condition approximately represents solar noon near the spring and autumn equinoxes in the continental United States with surface of the cell aimed directly at the sun.

Defect – Scratch on glass pv module

Why use standard test conditions?

Temperature has a significant effect on the PV Module Performance. As the temperature of a module increases two things happen. One, the voltage output of each cell decreases, and two, the current output of each cell increases slightly. The used standards do not necessarily reflect actual operating conditions. Apart from Standard Test Conditions (STC), there are other testing condition standards about which you can find more details in our learning center or in our article here

Standard pv testing parameters:

With the use of the flash test, the following parameters are tested.

1. VOC (V), open-circuit voltage, PV Modules are rated at two voltage levels: the first is called ‘Open Circuit Voltage (Voc)’. The voltage output of the module is measured with the module disconnected from any load.

2. VMP (V), voltage at maximum power point, the second voltage rating point is called ‘Voltage at maximum power point (Vmp)’ and is the voltage at which the module puts out the most power. All voltage measurements are made at the module’s electrical terminals mounted on the module’s back. These measurements are made with a highly accurate voltmeter.

3. ISC (A), the short-circuit current, current is also rated at two important levels: The first is called ‘Short Circuit Current (Isc)’ and is the amount of current that the pv module supplies into a dead short.

4. Imp (A), Current at maximum power point, the second current rating is called ‘Current at maximum power point (Imp)’ and is the number of Amperes delivered by the module at its maximum power point.

5. Pm (W), Maximum Power and Maximum Power Point, power is equal to Amperes times Volts (P=IE, or Watts=Amperes X Volts). Every module has a specific point on its power curve where the product of Amps times Volts yields the greatest Wattage. This is the Maximum Power Point, and the module’s wattage output is rated at this point’s voltage and current. In order to find the module’s maximum power point, the flash test takes data over the entire range of voltage and current. This way the wattage for each Current and Voltage data point can be calculated. By doing this we can find the Maximum Power Point in the sea of Current versus Voltage data.

6. FF (%), Fill Factor, the Fill Factor is defined as the maximum power produced (at MPP) divided by the product of Isc and Voc. One can see that the Fill Factor will always be less than 1. Due to the difficulties in measuring conversion efficiency quickly, it is common to measure the fill factor instead.

Five common solar panel defects

The following defects are common when testing solar panels:

1. Scratches on frame / glass
2. Excessive or uneven glue marks / Glue marks on glass
3. Gap between frame and glass due to poor sealing
4. Lower output than stated in data sheet (we require positive tolerance on each solar panel)
5. Lower FF than stated in requirements

Other defects that we find are dirt marks on the pv module, gaps on the corner of the pv frame, poor quality labels and solar panels that do not meet the requirement of positive tolerance.

The rubbing test makes sure that the label at the back of the solar panel will still be readable after 25 years. It includes 15 seconds of rubbing on the label, with a mix of water and alcohol. The PV rubbing test is important, as the serial number is directly linked to the solar manufacturer’s guarantees.

Conclusion

The above defectives can be avoided by following certain steps that will allow you to replace defective solar panels before shipment.

A first step is to select a solar panel manufacturer that produced certified solar panels. This is a first simple step to be sure that the solar manufacturer produces solar panels according to the quality standards. I recommend to verify the authenticity of each certification.

Secondly it is important to know what determines the quality of a solar panel, to present these quality requirements to the solar panel manufacturer and to agree on these requirements by both parties. The pv quality requirements need to be included in the contract.

Finally, after the solar panel manufacturer has produced the solar panels according to your quality requirements, independent testing needs to be performed. Solar panel quality testing includes an on-site visual test and a flash test.

I recommend to be present at the solar manufacturer’s factory at the time of price negotiation, solar panel testing and the loading of the solar panels.

Assure pv quality before shipment

By identifying the defective solar panels straight after production, the defective solar panels can be replaced or repaired before they will be shipped. This is the only approach that will ensure that your solar panels will perform at 100% and are perfect in appearance as well. This approach helps solar panel system installers to prevent time consuming problems when defective solar panels are identified after arrival.

Solar panel quality inspections

Are you purchasing solar panels, inverters or mounting racks in the Greater China region? Sinovoltaics performs independent quality inspections on-site at solar manufacturers.

Advantages:

1. Replace defects prior to shipment
2. Independent testing report
3. 100% certainty about product quality
4. International testing crew specialized in solar PV panels, inverters and mounting racks

Learn more about Sinovoltaics and its PV quality inspection and consultancy services