One of the major aspects of the product is its ability to deliver the expected power. The maximum power determination is performed according to IEC 60904.
Even though, IEC 61215 requires the output power determination to be performed on class B sun simulators, STS is using AAA Class equipments to obtain the most accurate and reliable results.
The tests are performed in a controlled environment, to guarantee that the tests are performed in conditions as close as possible to the Standard Test Conditions (STC).
During this test STS does not only control the output power, but also check each electrical characteristic as well as the shape of the IV curve to identify any intermittent malfunction of some solar cells.
One guarantee that the modules will perform well in time, is that the solar cells are free from defects such as cracks, pollution and so on.
These defects are invisible to the naked eye.
The most efficient way to detect this type of defect is to use the principle of electro luminescence:
In practice, the solar cells are transforming the light (photons) that they receive into electricity. The solar cells also have the reverse property. When subject to a current, the semi conductors will emit light through the emission of photons.
The electro luminescence equipment is using this property to perform an “x ray” like picture of the module where the dark areas show the less efficient part of the cells.
As a lot of operations remain manual during the production, the quality of workmanship can vary considerably from one module to another.
The quality of workmanship will not only affect the appearance of the module which has become a criterion of choice for the end users, but it can also affect the safety of people installing the products or the reliability of the products in time.
STS performs a thorough inspection of the construction, focusing on the dimensions, the quality of sealing, the components used and the packaging.
IEC 60904: AAA CLASS
IEC 60904-9 defines 3 categories of sun simulators A, B, C (A being the best class) based on 3 different criteria.
In order to be accurate, the measure has to be performed with a stable irradiance (light sent to the module by the simulator) during the whole period of testing (the time to take the entire I-V curve).
The temporal instability refers to the difference between the maximum and the minimum irradiance in percentage. The lower the instability, the better.
The irradiance provided by the sun simulator shall be the same all over the testing area.
The spatial non uniformity refers to the difference of irradiance between different points of the testing area. The lower the non uniformity, the better.
As the natural sunlight is composed of different wavelengths, in order to provide a good evaluation of the behavior of the module in the field, the sun simulator shall be able to recreate the composites of the natural light.
In nature, different wavelengths of light will participate in a certain proportion of the irradiance.
The spectral match is the ability of the sun simulator to provide irradiance similar to the natural light for given wavelength ranges or its deviation from the reference irradiance for different wavelengths.