How do we evaluate the quality of the modules?

 

Performance, Cells quality and workmanship: these 3 different aspects of quality are evaluated by STS during the products assessment to define completely how good a PV module is, but also how a manufacturer is able to produce good PV modules on a large scale in mass production.

 

1. Performance [weight 34%]

Performance shows mainly the power output of a module, but power alone is not entirely representative of a module performance.

A module with higher efficiency will reduce the cost of the BOS (Balance Of System) by reducing the land use and the number of structure elements.
Under this category is evaluated the power output of each module, based on the result of a flash test at the Standard Testing Conditions (STC) but also at low irradiance to evaluate the power output in less sunny day.

In addition, STS evaluates the lot tested as a whole or lot homogeneity as PV modules in the field will be grouped together to produce electricity and the weaker one will affect the power output of all the other PV modules.

Also evaluated under this category is the ability for the manufacturer to provide PV modules with positive tolerance on power, appreciated by the buyers.

 

2. Cells quality [weight 30%]

The performance is evaluated at the time of testing, but users of PV modules want to get a high power output from their modules for the longest time possible.

A solar cell containing cracks may perform correctly at the moment, but with transportation, mechanical stress and climate constraints, cracks and other cell defects will spread in the cell with time and result in a cell that does not produce any more electricity.

Under this category, STS evaluates the quality of the cells themselves or more exactly their electroluminescence picture.

 

3. Workmanship [weight 36%]

Under this category is grouped the quality related to the making of the PV modules. Assessment includes the visual appearance of the PV modules but also the safety to the user and the packaging as well as the quality of the sealing, construction and other parameters.
The workmanship score indicates the quality of the work that has been performed to produce the PV modules.

 

Evaluating step by step: the details

 

The mark we give for each panel is the result of a thorough and detailed testing, during which we check all the following factors.

 

Positive tolerance [weight 5%]

A higher score is given to manufacturers providing PV modules with a positive tolerance for their PV modules.
This seems to be easy, but the output will later be evaluated against this positive tolerance.

Output against nominal value [weight 12%]

The power output is determined by flash test under STC (25°C, AM=1.5, 1000W/m2).
To show the ability of the manufacturer to produce quality PV modules on a mass production scale, are taken into account the average power of the lot, the minimum and the consistency (homogeneity in power) of the whole lot.

Efficiency [weight 6%]

In order to save cost of system and space, the PV modules need to provide the maximum of power on the smaller area. A higher score is given to modules with a higher efficiency.

Efficiency at low light [weight 6%]

Modules are expected to perform well in shiny weather but also during less sunny days. The power output is therefore determined under low irradiance (25°C, AM=1.5, 400W/m2) to evaluate its performance under these conditions.

Inefficient Area [weight 10%]

Appearing as black area under EL test, these areas of the cells do not produce power and reduce the power output of the module. Another risk is heating of these areas resulting in hotspot (burns on the modules)

IV curve appearance [weight 6%]

When natural sunlight is simulated through a flash test machine, the response from the module in terms of current and voltage is well defined. Bumps and accident in that curve show some problems in the function of the solar cells or the module itself.

Cracks [weight 10%]

Crack in solar cells are a threat to the reliability of the PV modules with time. Cracks in cell are identified under electroluminescence test.

Pollution [weight 5%]

Processing issues during solar cells manufacturing might result in less efficient area which in turn can results in hotspot problem or lower output of the cells. These defects are identified under electroluminescence test.

Soldering defects [weight 5%]

Processing issues during solar cells manufacturing might result in less efficient area which in turn can results in hotspot problem or lower output of the cells. These defects are identified under electroluminescence test.

Packing [weight 5%]

If packing is not always considered as a major item by manufacturers, it crucial to protect the PV modules during long transportation and, of course, user-friendly.

Marking [weight 3%]

Required by IEC standards and mandatory to enter European or US market, marking must include specific information and be legible.

Construction [weight 3%]

Under this category are taken into account both the design of the PV modules construction and the quality of the assembly.

Dimensions [weight 5%]

Installers are basing their structure and installation on the dimensions of the PV modules. Dimensions such as length, width, skew and compliance of mounting holes are measured.

Frame assembly [weight 5%]

Poor docking of the frame elements can result in sharp edges putting the user at risk. The presence of these sharp edges and quality of the work is evaluated.

Sealing [weight 5%]

In order for the PV module to perform for more than 20 years, the encapsulation of the cells and the sealing must be waterproof to prevent moisture from entering and corrode the inner elements.

Cells layout [weight 3%]

Spacing between cells and between strings is important to avoid any risk of short circuit inside the modules. A minimum distance between the electrical conductors and the frames must be respected as well to avoid electrical shock risks.

Stringing [weight 2%]

In order to perform correctly, the cells must be correctly connected to each other. The conductors have to be well soldered and properly laid to ensure good conductivity in time.

Component appearance [weight 3%]

As end users are more and more concerned with the visual appearance of the products they buy, cosmetic defect are taking a higher importance in the choice of the PV modules. Components such as glass, frames, junction box and cables are evaluated.

Components usage and function [weight 2%]

When tested against IEC standards, the PV modules are a combination of different components. Taken separately, some components might seem equivalent, however, the combination of all these components might not work properly. This is the reason why it is mandatory for the manufacturers to respect the use of the specified components. The function of these components such as connecting function of connectors is also evaluated.