Nowadays, with the exponential growth of utility-scale photovoltaic solar plants, ensuring a good performance throughout the entire operating life of a plant is more important than ever. For an independent power producer (IPP) that operates and maintains its assets over the long term, ensuring quality in the earliest stages of the project is essential.
The photovoltaic module is a fundamental part of the photovoltaic solar plant. In my experience, not only does it represent approximately 40% of a solar plant construction price, but it also is the element in charge of generating electricity. Since it impacts the production of the PV solar plant, ensuring good performance throughout its life span is a primary task in any photovoltaic project.
Studies such as one conducted by the International Energy Agency show these are the most typical failures that occur in a PV module throughout its life.
We can ensure maximum performance throughout the module life span by ensuring quality from the acquisition process. When purchasing the module for a photovoltaic project, it is important to pay attention to prestigious reports, such as the tier 1 list from BNEF. Additionally, we must ensure the quality of the module expressly manufactured for our project.
Recognized companies dedicated to performance quality inspections on-site at the factories show in their reports the most recurring failures or issues during module production. During a Sinovoltaics webinar, I learned that the most common defects identified during PV modules inspection carried out by the company in 2019 alone included:
• Cell-Inherent Defects: These defects are invisible to the naked eye and require electroluminescence imaging in order to detect them. Cell-inherent defect types include micro-cracks, solder faults, finger breaks and wafer impurities. The consequences of cell-inherent defects, which are subjected to environmental and mechanical stress, can potentially grow over time, result in issues like reduced yield and overall module life span.
• Workmanship Defects: These are visual defects that can be detected with the naked eye, such as scratches, chipped cells, broken contact fingers and encapsulant cross-linking issues, as well as aesthetic defects such as cell color deviations. Many workmanship defects result from lower-grade primary materials and may affect the overall performance of a PV system.
• Uncertified Materials: These are materials assembled in a module that has not been tested according to the applicable international (IEC) and national or regional (e.g., UL) standards. Noncompliance of materials and/or material combinations not only renders a module effectively uncertified, but also risks affecting the overall life span of a module. It is not rare that manufacturers modify primary materials, components and even design details without updating or catching up on the certification of such modification.
• Equipment Calibration: The improper setup of I-V measurement (i.e., flash testing), including inaccurate calibration of the measurement equipment by the manufacturer, damaged measurement devices (reference modules) and improper preparation of the samples to be tested, is widespread. The consequences involve a power output not matching to the rating label and, thus, potential underperformance from the start.
How do factories ensure quality?
Quality assurance at the factories reduces risk and ensures downstream project stakeholders maximize the energy output of their systems. The main tests and inspections carried out in a factory occur at each of these stages:
• Before the production starts, there is an inspection through an on-site factory audit, including a revision of the factory’s management system certifications (e.g., ISO, OHSAS standards), change control management, customer complaints management and employee management, as well as product certifications, quality and reliability policies and practices, manufacturing process setup, facility logistics, and environment policies and practices.
• Once the production starts, there is monitoring and supervision of the manufacturing of modules, including verification of BOM/CDF and compliance to certification, incoming quality controls, materials storage, expiry and preparation controls, cell soldering quality, cell defect/crack screening, cell bow and warp monitoring, gel content and peel strength results, equipment calibration, equipment maintenance, equipment cleaning, material and/or equipment contamination, frame application, frame sealing, frame curing, junction box application, junction box soldering, and junction box curing.
• Once the modules have been produced, there is an inspection on a sample basis to release modules for shipment, which includes I-V measurement to check for power and resistance defects, electroluminescence (EL) imaging to check for cell defects, and a visual inspection to check module component integrity.
Also, it is recommended to conduct performance module reliability testing at the laboratory. Such tests include maximum power determination (STC), EL analysis for micro-cracks and impurities, wet leakage current test, potential-induced degradation (PID) test (85 degrees Celsius with 85% relative humidity for 48 hours), light-induced degradation (LID) preconditioning test (5% at 5kWh/m2), low irradiance measurements, and EVA gel content and peel tests. Agreed-upon inspection criteria and defect rate thresholds will be applied, commonly using acceptance quality limits (AQLs) according to ISO 2859-1:1999. Defect rates that exceed the acceptance thresholds may result in additional inspection or rejection of the product as part of the agreed-upon process to control quality.
• Loading of modules into containers confirms that the pallets of modules being loaded come exclusively from inspected and approved lots, assuring proper packing, loading, container and seal information, and product.
What can we achieve with this?
The benefit of quality inspection is directly related to the minimization of defects in the modules within our construction projects, which may result in significant additional revenue for project owners.
POST WRITTEN BY
Joern Hackbarth
EVP, Global Head of Engineering and Construction, Sonnedix, overseeing the design and construction of assets for global solar PV platform.
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