We are in October 2020, and a North-American developer is ready to sign a purchase agreement with a South-East Asian manufacturer. The module maker seems serious about quality; they even forwarded the Quality Control Plan (QCP) that they are planning to roll out during production. Nonetheless, the developer is about to sign a contract that will not protect them against receiving up to 1% of “unsafe” modules in their shipment. How is this possible? A “Critical Defect” is, according to STS-STD-PVM1, “a defect that is likely to result in hazardous or unsafe conditions for the individual using the product, likely to cause damages to other products or property (…)”. Let us be clear: it is absolutely unacceptable to have any critical defect in a lot. Yet, the example above is real, and, if not identified on time, the developer may have accepted an Acceptable Quality Level (AQL) of 1.0 for Critical Defect, as boldly stated in the manufacturer’s QCP.
We are now in January 2021, and a North-American asset manager is discovering that a significant portion of their multi-hundred MW plant is affected by soldering defects. The project was developed by a very well-known international player who even hired a consultant (although not ISO 17020-accredited) to perform some quality check during production. The manufacturer was a trusted partner, powering most of the developer’s large fleet in the region. How can this have gone wrong? After a quick enquiry at the manufacturer, the asset manager realized that the manufacturer’s QCP used for this project was permitting up to 7 soldering defects in one module. As a comparison, per STS-STD-PVM1, only one of such defects would have immediately classified the module as defective (“Major Defect”).
The season advances and we are now in March 2021. Yet another North American developer realizes that some of the modules about to ship flash below nameplate. Not much below; just a bit over 1%. Enough to be denting the financial return, but not enough to be filing a warranty claim. These modules were caught on time; but what about the rest of the shipment? The developer did not judge necessary to supervise production 24/7, and most modules are already on the sea. It is in fact very difficult to check the calibration of the measurement tools, if not present during the production shift, let alone after the modules have left the factory. That is one of the reasons why STS recommends 24/7 production supervision for every batch of PV modules manufactured. In fact, STS sees twice as many “findings” during night shifts than during day shifts, and about 80% of STS customers systematically ask for 24/7 production supervision.
And these are just three recent examples… Today, many developers “check the box” of QAQC without realizing that a number of very important variables are hidden in the simple statement “we are using a 3rd party to inspect modules during production”. There are 3 dimensions to take into account when deciding what inspection activity to carry out:
- The qualification of the Inspection Body
- The Quality Control Plan (QCP)
- The scope of control and enforcement of the requirements
For the qualification of the inspection body, the choice is relatively easy. There is a widely accepted international standard that has been specifically designed to ensure qualification, impartiality and independence of the inspection firm. There is today no good reason to hire, for inspection work, a company that is not ISO/IEC 17020-accredited.
For the QCP and the scope of control and enforcement of the requirements, however, there is no ISO nor IEC standard. Module manufacturers may have several dozens of QCPs ready to deploy, depending on the level of scrutiny that the developer will demonstrate during contract negotiation. If the developer is not careful, the manufacturer may put in the contract a QCP that will reduce significantly their reject rate in factory and therefore shave another fraction of a penny per Wp. This is exactly the gap that the Industry Standard STS-STD-PVM1:2018 (“STS-STD-PVM1”) is targeting. STS-STD-PVM1 has been written to provide a non-ambiguous, version-controlled, acceptable quality level for every developer, inspection body and manufacturer using it. Since its publication in 2018, STS-STD-PVM1 has been reviewed, at least in part, by more than 100 stakeholders, and, with GWs of implementation, is today the most common cross-manufacturer QCP used in the solar industry.
STS-STD-PVM1 thoroughly describes requirements, criteria and methods for “Approval of PV modules manufacturing”. It includes, for instance, recommended practices for deploying production supervision, such as incoming quality control (IQC – 65 requirements), in-production quality control (IPQC – 70 requirements) and final quality control (FQC – 23 requirements, 150 criteria). It also describes which elements of the production line need to be verified before production starts, how samples should be selected randomly for pre-shipment inspection, and how to deal with non-conformities in an efficient, impartial manner. Last but not least, it sets the requirements for the inspection body performing the inspection per the Standard to deliver a Certificate of Conformity. This Certificate of Conformity provides assurance that the modules have been built following a given standard of quality for all stakeholders involved in the project: EPC, developer, lender, technical advisor, (tax) equity provider, long-term owner, and even the not-yet-known future owner of the plant.
EL images taken in the field, showing manufacturing defects (“cold soldering”). The QCP used during production would allow for 7 such defects on each module without consequence on rejection of the lot. Per STS-STD-PVM1, only one of such defects would classify the module as defective (“Major Defect”).