Understanding the variations of production on solar panel quality
Understanding the variations of production on solar panel quality
PV modules are a product of a careful selection of materials and a PV module manufacturing process. They must be compliant with that of what was IEC61215 and IEC61730 certification to meet minimal quality and safety requirements. Small variations in the storage, handling, and processing of these can ultimately lead to solar panel efficiency performance, reliability, and durability issues. Inspections, factory audits, and production monitoring not only try to assure that the solar PV panel is compliant but also execute best practices to provide zero risk PV projects. All in undertaking steps to help solar plants that generate the most kWh yield possible. This article explores a typical assembly line, and informs the reader of the different phases of production and what issues can arise.
Difference between yearly IEC61215 and IEC61730 and third party inspection
A condition of IEC certification is that technically an accredited auditor from the certifying body does annual inspections for a period of 5 years. These inspections are to review that the manufacturer has not deviated from what was initially documented and is doing so in a safe manner. This includes looking at if the solar PV panel producer is using the same materials as stated in the Construction Design Form (CDF), using the same machines and procedures. This is to ensure the certificate is valid and any departures from what was initially certified are then noted. Any major issues can lead to the certificate being pulled until rectified. Minor issues usually are noted and typically addressed by the next solar audit.
Third party quality assurance and quality control inspections go much further. Building on the certification audits, the inspector will not only check compliance but also dive into how materials are stored (if they meet supplier and best practice standards), handling thereof, and expiration of these materials. Moreover, taking best practices for each of the equipment and comparing those procedures to that of is used as a standard by the manufacturer and how these machines are calibrated & maintained. The investigator may note, watch, and discuss with operators, quality managers, shift leaders, and production managers their level of training, experience & knowledge, and their application thereof. Revising the latest quality, production, and maintenance reports of the different machines in the assembly line.
Table 1. Manufacturing audit: IEC audits vs third party inspections
Understanding purchase orders, factory locations, quality, and OEM
When providing a purchase order, it can go to different factory locations. Different factories have a few operating workshops and production lines. The quality can vary depending on the level of operator training or turnover, the maintenance of machines, the type of technology being produced, pass/fail quality criteria, level of automation and calibration thereof, procedures, storage, and handling of materials seen in Figure 1.
An original equipment manufacturer (OEM) is a secondary manufacturer that specializes in making specific products on behalf of brands. As such, due to capacity constraints or other reasons, a solar module company may opt to outsource their production to OEMs. It is a strategy often employed to reduce costs through economies of scale, avoiding factories from being outdated - solar panel manufacturers can leverage updates and innovations offered by their OEM partners and help bring new products to a market more quickly. Nonetheless, even OEM locations can differ and their resulting quality.
Independent Power Producers or developers keen to ensure that modules are made of sound condition often opt for factory auditing or production monitoring to ensure modules are compliant and meet performance and reliability expectations. Optionally, but often also chosen for an environmental, social, and governance (ESG) criteria are checked of that site too.
The four levels of industry automation
As mentioned in Figure 1, but visualised in Figure 2 a site may have different levels of automation which play a significant role in the overall quality of a PV module.
Solar panel manufacturer lines may have various levels of automation. The more outdated lines may be largely a combination of industry 2.0 and 3.0. Newer lines are more often a combination of Industry 2.0, 3.0, and largely 4.0. The general rule of thumb is the higher the automation and removal of human interaction, the higher the quality. However, this is not completely true.
How materials are handled and introduced, but above how these machines are calibrated & maintained can greatly impact the end product quality. More so, how the data is monitored and used to optimize lines also plays a role. In particular, the manufacturing execution system (MES) and its use thereof. The MES is a software designed to optimize the production process by not only monitoring but also tracking, documenting and controlling the entire manufacturing lifecycle. A trifecta of visual inspection, MES, and random testing is required to find the balance in and optimization of these lines that is often overlooked.
Typical Assembly Line (Glass - Glass or Glass - Foil half cut TOPCON/PERC)
Figure 3 gives some insight into the production flow of a half cut glass - foil half cut TOPCON module. Though a critical point is also testing solar panels, storage, and handling of incoming goods. Suppliers have specific storage, handling, and expiration criteria with regard to cells, glass, backsheets, and encapsulants. The humidity and temperature of manufacturing halls can also impact the overall reliability of a module in the long run.
Each step has defined standard operating procedures (SOP), minimal quality standards it must meet, and cleaning & maintenance logs that help give an indicator of the condition of that segment. Some manufacturers meet IEC62941 best practices for product design, manufacturing, processes, and selection and control of materials in a PV module. This means each machine may have a failure mode effect analysis (FMEA). The FMEA is an overview if one thing is a variable that changes the impact it will have on the machine, but also the complete process as a whole.
Additionally, the production line should undergo frequent quality checks and comparisons with either an internal or external lab. Such Solar PV testing includes: gel content tests, peel tests, laminator temperature uniformity with a PT1000, testing comparison of power of modules, random climate chamber tests, and many more.
An important but often overlooked process is the packaging and transportation of the made modules. The IEC62759 methods of transportation of complete package units of modules can help.
Sinovoltaics with its 17.6GW of experience executing quality assurance inspections of PV solar panels closely inspects and monitors each segment. Reviewing the documentation on site and jointly monitoring how these are implemented. Sinovoltaics' team of solar auditors compares those with its own best practices to ensure its clients get zero risk projects if so contractually stated and allowed.
Quality Pass Fail Criteria
Module manufacturers may have different grading systems in place, it is therefore important to start the discussion with your supplier and review the requirements. Sinovoltaics has an in-house standard with which it can be compared with and reviewed. The criteria touch upon testing and ergo the pass/fail of incoming goods, the storage of materials, processes, training, calibration, maintenance, and use of the different machines in the production line.
The three most known quality criteria at the end of the production line are; Hi-Pot testing, Electroluminescence (EL), Visual Inspection, and IV curves generated on the solar simulator. This is based on the minor, major, and critical of IS2859 AQL as seen in Figure 4.
As it's not practical to inspect 100% of the modules, IS2859 sampling procedures for inspection give an overview of how many samples must be tested for a given project size. It also gives an indicator when a batch fails. Level 1 inspections have a smaller sampling base and indicate trust, going down the scale to Level 3 the sample amount increases as there could have been an earlier quality issue. Levels S1 to S4 are special tests that are often destructive and have a lower sample base.
EL images show cracks, cell deformities, or soldering issues that aren't visible to the human eye. More insights on EL testing can be seen in our earlier blog on the topic. As according to IS2859 sampling procedures for assurance quality level (AQL) there is more often an insight into what is a minor, major, and critical failure as seen in Figure 4. The operator or EL tester (depending on the level of automation) will determine the soldering issues, cell material issues, and amount of type and amount of cracks - determining if the module has minor, major, or critical issues (fail). The calibration and/or training of this operator(s)/test machine is critical and so is the quality of the pictures. Customers always have the right to ask (and is highly recommended) that the serial code related HD EL images are also sent.
The Hipot test measures the withstand voltage capacity of the module. It involves applying a high voltage to the module's terminals and checking for any electrical leakage or breakdown. This PV test ensures that the module can handle the voltage stress it will experience throughout its lifetime. This is typically 3 times the system voltage for a 5 second duration.
IV testing is mapping the current, voltage, and power (power is voltage x current) of the module. Again the calibration, upkeep, and use of the solar simulator can yield different results. All in all, the solar simulator is not only used to measure power but is more often used to optimize the production and detect small variations.
Visual inspection is done in combination with the IV, EL, and Hi-pot results - revising if the module has any dried encapsulant on the back or frontside, silicon spillage, broken cells, scratches, and all. This is usually done in 20 - 40 seconds. Therefore typically the site quality manager does random sampling to double check dimensions and the operator's observations.
Effect of production variations on lifetime and degradation of the solar modules
The non-compliance of modules to that of the certified product can raise concerns with regard to their initial 5 - 10 year performance. As IEC61215 and IEC61730 goals are to ensure the modules will suffer minimal from infancy failure events.
Earlier research has shown that even between batches module degradation can vary greatly, more so that modules produced around Chinese New Year show a higher frequency of issues than the rest of the year - as do modules made at night.
Conclusion
Sinovoltaics is your Third Party Solar Inspection Services partner for zero risk solar PV projects. Sinovoltaics has 17GW of experience in independent factory PV audits and production monitoring to mitigate non-compliant products and increase the overall quality level of the modules being procured by your team. Third party inspections are critical as small variations in training, personnel loss, machine upkeep, and use of materials can impact the overall kWh yield the module can produce over its lifetime. For further information contact us.