Photovoltaic modules play a vital role in the generation of renewable energy. However, over time, PV modules can experience performance degradation due to various factors, one of which is Potential Induced Degradation (PID). In order to ensure the life and efficiency of the photovoltaic system, Potential Potential Induced Degradation (PID) Tester from Millennial Solar came into being. This article will deeply explore the Potential Induced Degradation (PID) performance evaluation of the transparent backsheet of the photovoltaic module and introduce its importance.

PID performance evaluation of transparent backplane

Transparent backsheets are currently a viable alternative to glass when building bifacial modules, with their main advantages being lower cost than glass, significantly lower weight, better transparency and better protection of the module from hail. In addition, because it does not contain sodium, the transparent backplane can also reduce the occurrence of PID and reduce the risk of PID on the back of the cell. The experiment examined the stability of photovoltaic modules constructed with transparent backsheets by exposing them to extended potential-induced decay (PID) stress.

The photovoltaic module used in the test is a P-PERC glass backsheet module, and its main properties are listed in the table below.

Test process

Five modules (one set of reference module, one set of 0V polarized module Mod1, one set of +1500V polarized module Mod2, and two sets of -1500V polarized module) were pretreated by current injection within 486 hours at 75°C. module Mod3&4), conduct current-voltage measurement control every 162 hours, and avoid light-induced degradation (LID) and light and high temperature-induced degradation (LeTID) during the test phase.

PID testing per IEC 61215 standard (MQT 21) at 85°C, 85% RH for up to 576 hours instead of the 96 hours required in the standard (voltage monitoring every 96 hours or 192 hours). Use a cutting wheel to cut two complete samples on the -1500V polarization module, and then use a diamond wire saw to cut one sample into small pieces of 1 cm × 1 cm.

Finally, the encapsulated samples were cut out and photoluminescence (PL) measurements were performed using BT imaging and finally transmission electron microscopy (TEM) measurements.

Test Results

Current-Voltage (I-V) Figures 1 and 2 plot the performance evolution of the module front and back through PID testing respectively.

Figure 1. Performance evolution of module front in extended PID test

Figure 2. Performance evolution on the back of the module during extended PID testing

 As shown in Figure 1, the module performance on the front side is not affected by the applied positive or neutral voltage. After the test, all electrical parameters of the module are similar to those of the untested reference module. In contrast, applying a negative voltage, after 576 hours of PID, the power on the front dropped by nearly 8%, the performance on the back dropped three times more severely (25%), and the current varied significantly, as shown in Figure 2.

Electroluminescence and Photoluminescence Characterization

To better understand the reasons for the performance degradation, EL and PL detection was performed on module Mod3. The EL imaging of module Mod3 and the PL imaging of the cut sample are shown in the figure below.

a) EL imaging of Mod3 after pretreatment; b) EL imaging after 576 hours of PID testing; c) Top: EL and PL imaging after magnification; Bottom: EL and PL imaging in dark areas

Since the PL measurement uses cells cut out of the module, glass cracks can be seen in the picture. EL imaging shows a general decrease in signal and the appearance of some dark areas, with some "light trails" also visible on most cells with locally higher EL intensity. These dark areas and light trails were also confirmed by PL imaging and pointed to potential local passivation changes.

A double-sided module with a transparent backsheet was subjected to extended PID stress testing, and current-voltage, EL and PL measurements showed the presence of two types of PID effects in the module: PID potential type (PID-p) and corrosion type (PID-c). The type of shunting of PID-s is generally associated with the migration of sodium ions from the glass into the cell, and the current-voltage changes did not show any significant Voc fill factor drop. Even if no direct evidence is observed using TEM measurements, the observed localized depassivation may be related to PID-c.

Potential Induced Degradation Tester

E-mail: market@millennialsolar.com

Introduce:

Long-term current leakage will cause changes in the state of the cell carriers and depletion layer, corrosion of the contact resistance in the circuit, and electrochemical corrosion of the packaging materials.

This results in cell power attenuation, increased series resistance, reduced light transmittance, delamination and other phenomena that affect the long-term power generation and life of the module.

Fulfill the standard:

Meets the MQT21 clauses in the IEC61215 standard and the IEC62804 standard

Features:

•The frame end of the module is grounded, which not only simulates the actual situation, but also prevents potential dangers caused by high voltage on the frame;

•Using a 2-wire test method, the positive and negative electrodes are short-circuited and connected to the positive electrode, and the negative electrode is connected to the equipotential hole of the frame;

•Each channel is independent of each other, and the voltage size, polarity and time of multiple channels can be set independently;

•Multiple voltages, leakage current, and insulation resistance are displayed simultaneously;

•Real-time monitoring of voltage, leakage current, and insulation resistance curves;

In the rapidly growing solar industry, the reliability and efficiency of photovoltaic systems are critical. Potential Induced Degradation Tester from Millennial Solar follows IEC standards and helps manufacturers maintain high standards of quality and performance in their projects, playing a vital role in ensuring that modules reach their full potential and deliver expected performance over the long term, serving global customers. Contributing to the growth of renewable energy.