How to effectively protect a photovoltaic installation against PID?
Dodane przez: admin June 10, 2021
Companies involved in the production of PV panels are very intensively focused on increasing not only the efficiency of these devices, but also their overall efficiency. One of the activities performed in this area is the elimination of cases that could lead to loss of power. One example of such a situation is the so-called PID effect, i.e. degradation by induced voltage. What exactly is this phenomenon, and how to counteract it, is described below.
What is the PID effect and how does it affect the performance of PV panels?
Induced voltage degradation is also called an electrical leakage and can translate into very significant losses in the power generated by the device. The PID effect is a consequence of the potential differences between the semiconductors contained in the cells, which may have a voltage of, for example, 600V, and the grounded aluminum frame of zero-voltage modules. The most common phenomenon occurs in the case of cells located a short distance from the negative pole. Due to the large potential difference, damage to the photovoltaic panels occurs. An intermediary electrostatic field is generated, first in the transport of electrons to the glass of the module, and then in their movement to the aforementioned grounded aluminum frame.
When it comes to PID, photovoltaics as an industry discovered the problem relatively recently – it has been in the minds of producers only for a few years and, interestingly, was much less common in panels produced in the past than in much cheaper ones available on the market today. The phenomenon affects thin-film modules and modules made of crystalline silicon. The intensity of the induced voltage degradation taking place in a given case may be additionally worsened when the area is characterized by high temperature and high air humidity. Particularly important information to remember is the fact that while a one-off occurrence of the problem, when polarization occurs, is fully reversible, its systematic recurrences can cause serious failures of the photovoltaic installation in the form of electrochemical corrosion, and thus degradation of p-n junctions.
Solar panel test for PID
Before we get to the stage where we will be forced to look for an answer to the question of how to repair a photovoltaic panel, it is worth realizing that the basis for the protection of PV installations is, of course, professional diagnostics of photovoltaic panels. It is worth doing even when their manufacturer declares that the devices he produces are free from degradation by induced voltage. In practice, however, very often such assurances are not true and can be trusted only if they have been provided with an appropriate, official certificate. Control tests of photovoltaic panels performed by independent, specialized laboratories in their field clearly show the susceptibility to the described phenomenon (to a greater or lesser extent) of many of the PV modules available on the market – including those advertised as protected against PID.
The institutions involved in carrying out this type of control tests include the TÜV Rheinland certification body, and other important ones in the industry include, among others, The Fraunhofer Society or the American Renewable Energy Laboratory NREL. Obtaining the IEC 62804 standard through the photovoltaic panel test is the official and, most importantly, fully reliable confirmation of the PID resistance of the modules – in the event of degradation, there are no damage to the photovoltaic panels, and power losses are below 5%. The conditions for carrying out the test necessary to obtain a certificate of compliance with the IEC 62804 standard are determined primarily by:
• voltage – 1000 V, • temperature – 60 degrees Celsius with a permissible fluctuation of 2 degrees, • air humidity – 85% with an acceptable margin of 5%.
If someone thinks that the above conditions in which the diagnostics of photovoltaic panels are carried out are very restrictive, it is worth paying attention to the fact that the models of PV panels of some manufacturers pass the tests under even less favorable circumstances. An example can be a panel made in the Riecium technology from the Chinese company JA Solar, which was tested by the TÜV SÜD institute coming from beyond our western border. This device successfully passed the 500-hour PID test, achieving a degradation level of less than 2% at 85 degrees Celsius, a voltage of 1000 V, and an air humidity of 85%.
How to fix a solar panel that turned out to be insufficiently protected against PID?
There are a number of different methods to avoid the PID effect. Photovoltaics understood as a sector of the Polish market experiences this problem so often that nowadays it is not difficult to have access to specialists who will help us in obtaining increased resistance to the described problem. The solutions most frequently recommended by them include:
- replacement of anti-reflective layers with higher quality variants,
- the use of other types of encapsulants,
- changing the composition of the glass, e.g. to those with a lower sodium content, which favors the PID effect,
- the use of professional devices dedicated to counteracting PID, which automatically restore the proper distribution of loads when the panel parameters drop below a certain level is detected.
If you want to avoid a situation in which serious failures of the photovoltaic installation will occur, it is definitely worth considering using one of the options mentioned above.