Many solar module manufacturers claim their modules are ‘PID free’, which should mean that they will not suffer any efficiency losses due to Potential Induced Degradation. However, in practice ‘PID free’ does NOT mean no degradation will occur.
Potential Induced Degradation (PID) occurs on all photovoltaic modules, often without the owner of the installation being aware of it. Because of this phenomenon the solar modules degrade faster and therefore don’t achieve the expected return during their lifetime.
Solar modules are considered to be ‘PID free’ when they pass the IEC 62804 standard test.
This test is performed under following basic conditions:
- Module-rated system voltage and polarities
- Chamber air temperature 60°C ± 2°C
- Chamber relative humidity 85% ± 5%
- Test duration of 96 hours at above stated temperature and relative humidity with applied stated voltage.
Under the IEC 62804 standard, modules will be deemed to be PID-free if power loss is less than 5% and there is no evidence of any major defect (cf. IEC 61215 clausules 10.1, 10.2, 10.7 and 10.1).
Highly PID resistant
Some critical remarks about the test described above have to be made.
First off all, during this standard test the accelerated PID process is applied on the solar modules. The test only takes 96 hours, while in practice the lifetime of solar modules is about 91.250 hours (10 hours of sun/day x 365 days/year x 25 years). According to PV Magazine, approximately 90 test hours with aluminum foil at 25 °C corresponds to one year under real world conditions in Germany. Therefore the relevance of the IEC 62804 standard test has to be questioned.
Second, solar modules pass the test when the power losses after 96 hours are less than 5%. When efficiency losses are limited to for example 3 or 4%, the modules are still considered to be ‘PID free’ although degradation clearly occurs. Therefore, ‘highly PID resistant’ would be a better description for these solar modules than ‘PID free’.
This statement is increasingly being confirmed in 2020 by solar module manufacturers who no longer label their modules as ‘PID-free’, but as ‘High PID resistant’. So to be clear, solar modules that are totally ‘PID free’ do not exist!