What is PID?
PID (Potential Induced Degradation), also known as Potential Induced Decay, is caused by a high potential difference between the semiconductor material and the other components of the solar panel. Simply put, it is current leakage that causes negative and positive ions to migrate outward. Negative ions flow out from the aluminium bracket, positive ions flow to the solar cell, a large number of charges gathered on the surface of the battery cell, so that the battery surface passivation effect is intensified, which leads to a reduction in the fill factor of the battery cell, the open-circuit voltage and the short-circuit current, and the battery cell power attenuation, PID phenomenon is serious, it may be up to more than 50% of the degree of attenuation.
PID formation causes
External reasons: PID is easy to occur in high temperature, humid environment, with the temperature, humidity increases, the current leakage rate is also accelerated, thereby accelerating the PID effect on the damage to the photovoltaic module. At the same time, the surface of the module is contaminated by conductive, acidic, alkaline and ionic substances, all of which are related to the PID phenomenon.
Such as high temperature, high humidity, high salinity areas, especially in coastal areas, PID phenomenon is more obvious.
Internal reasons: solar panels in the encapsulation process, because the EVA material cannot ensure 100 percent insulation, coupled with the humid environment, water vapor can enter the internal components, so that the insulation system of photovoltaic panels there is leakage phenomenon, with the loss of electrons in the P-N junction, the conductive performance is getting worse and worse. And the high open-circuit voltage of the system will increase the bias voltage of the circuit and the aluminium frame, exacerbating the PID effect.
In addition, PID is also related to changes in the internal structure of the solar panel, such as changes in the semiconductor structure, shunt, resulting in a large series resistance, will also exacerbate the PID effect
How to detect PID?
Cell PID Tester: Rapidly detects important parameters that determine the performance of a cell, without the need for an environmental chamber, predicts the effects of PID in advance, and monitors the PID decay and recovery process.
Electroluminescence: EL test utilizes a high-resolution infrared camera to capture near-infrared images of the components, to obtain and determine the defects of the components, with high sensitivity and intuitive image of the results, but the cost is expensive, and the site requirements are strict.
IV curve tracing: It can test the output voltage and current of single or multiple solar panels with protection function to protect the monitoring personnel and equipment safety. And IV curve tester also has high precision, automation and high stability.
How to deal with it?
PID is generally a reversible surface polarization phenomenon, but some types of PID effects may be irreversible due to damage caused by the physical level. So, in practice, most individuals or businesses choose prevention over remediation.
PID prevention: When selecting PV solar panels, prioritizing materials with anti-PID templates or using improved encapsulated adhesive films can effectively inhibit the PID effect, thus maintaining the long-term stability and efficiency of PV modules. In the later stage of the solar system power generation process, you can choose the above detection methods for timely detection of the PID effect, reduce the possibility of PID occurrence.
PID night repair: the main reason for the PID effect is that a large number of conductive ions flow out of the PV module, so that the PV module power generation capacity has decreased significantly. PVOB equipment at night between the module and the earth to apply a positive voltage (1000V) so that during the day from the loss of conductive ions in the PN junction back to the PN junction, thus restoring the power generation capacity of the battery module to repair the PID effect of the module.
Summarize
PID is a common problem in sola power system, but through the above methods to carry out reasonable preventive measures and repair methods, can effectively reduce the incidence of PID, improve the power generation efficiency and lifespan of solar energy system.
