What exactly is Potential Induced Degradation in PV panels?

Question

Can someone explain Potential Induced Degradation? I've been looking over the internet but a lot of the explanations go into too much detail.

Answer 1

In very simple terms, current leaks from the solar cells to the structure of the panel. This happens when a combination of heat, water and the generated electricity cause the material the panel is made of to break down at a very low level, and start conducting electricity where we don't want them to.

It's hard to balance "how, exactly" with "not too detailed" in an answer to your question. Going beyond "very simple" above means talking about ions (atoms that have more or fewer electrons than normal), crystal structure (where those ions should be) and ion channels (where the ions move to). The explanation below is one fairly simple technical one I found online.

From Advanced Energy (pdf):

Potential Induced Degradation, as the designation implies, occurs when the module’s voltage potential and leakage current drive ion mobility within the module between the semiconductor material and other elements of the module (e.g. glass, mount and frame), as shown in Figure 1, thus causing the module’s power output capacity to degrade. The ion mobility accelerates with humidity, temperature and voltage potential. Tests have revealed the relationship of mobility to temperature and humidity: “Planar contact with the panel surface also causes a capacitive coupling to the cells, resulting in a capacitive leakage current of varying strength.” 1

The PV system and environment interact to cause PID. The conditions necessary for the occurrence of PID involve (i) environmental factors, as well as factors involving (ii) the system, (iii) the module, and (iv) the cells.2 3 “While the environment is set for each individual installation, it is possible to prevent PID by properly controlling only one of the factors

Answer 2

Technical explanations aside, here is an example from sunny Florida.

You would think that more sunlight equals more power output, but that isn't the case. It is easily possible, especially in South Florida, that the temperature of the panel can exceed the effective operating range of the solar module materials. At which point the power output drops precipitously!

It is very important to select solar modules that are designed to operate in the environment in which they will be used.

In the case of this example, a small amount of the power generated was used to pump water from a cool reservoir to run down the faces of the panels to assist in keeping them cool, thus maintaining maximum power output on especially hot days. This was very effective and resulted in a net increase in power output. The water was collected, filtered, and used again.