Many solar panel manufacturers claim their panels 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 panels, often without the owner of the installation being aware of it. Because of this phenomenon the solar panels degrade faster and therefore don’t achieve the expected return during their lifetime.
Solar panels 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 panels. The test only takes 96 hours, while in practice the lifetime of solar panels 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 panels 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 panels are still considered to be ‘PID free’ although degradation clearly occurs. Therefore, ‘highly PID resistant’ would be a better description for these solar panels than ‘PID free’.
So to be clear, solar panels that are totally ‘PID free’ do not exist!
Since it is impossible to produce ‘PID free’ solar panels, PV manufacturers have been looking for solar panels with different EVA composition (for example delamination or coloration). This is a thermoplastic containing ethylene vinyl acetate which is used to encapsulate the photovoltaic cells. The use of an EVA layer implies a lower electrical conductivity and therefore results in a less significant presence of PID.
In comparison with current PID sensitive solar panels, which are on are rooftops since about 40 years, the solar panel technology with different EVA composition is not yet proven. Therefore unexpected problems might occur in the years after they are installed.
Instead of taking the risk of reducing PID by installing solar panels with unproven EVA technology, one could better invest in PID sensitive solar panels combined with a PID solutions like the PIDbox. This device increases the efficiency of the so-called ‘PID free’ solar panels to approximately their initial value.