Micro-cracks represent a form of solar cell degradation and can affect both energy output and the system lifetime of a solar photovoltaic (PV) system.
The silicon used in solar PV cells is very thin (in the range of 180 +/- 20 microns) and hence is susceptible to damage easily if the PV module's production and handling are not up to the required standards.
Even slight imperfections in the PV cell can lead to large micro-cracks once it is incorporated into the PV module.
The length of micro-cracks can vary; some span the whole cell, whereas others appear in only small sections of a cell.
How do micro-cracks occur?
Cell fractures at any stage from wafer processing right up to installation and after that.
During manufacturing defects can be attributed mainly to poor quality of raw material, defective or lack of process control, and incorrect handling.
Mechanical stress in the supply chain and logistics processes can be caused by:
Incorrect packaging and storage
Unsuitable transportation methods
Incorrect handling techniques
During the installation of a solar PV system, mechanical stress can be caused by:
Piling modules on top of one another, or resting other equipment on top of the modules
Bumping or dropping modules as they are lifted onto the roof
Installation on a nonplanar surface, may cause twisting of the mounting frame and place stress on the module
Dragging modules along while carrying them
One person instead of two carrying a module
Sitting on the module edge of modules while installing them
After installation, the environmental conditions that can cause micro-cracks in solar PV systems include:
Thermal cycling (variation of temperature between night and day), and seasons
Humidity and Freezing
Cyclic (or dynamic) pressure loads and wind loads
Heavy snowfall
Hail
How to detect micro-cracks?
Manufacturers need to work mindfully to prevent micro-cracks in cells and modules during manufacturing and assembly.
Several quality tests are performed before and after lamination to identify micro-cracks. Manufacturers perform incoming and outgoing inspections, such as electroluminescence (EL) or electroluminescence crack detection (ELCD) testing.
EL testing is a process that makes use of image analysis and measurement, which enables sight directly into the solar cells to locate inherently potential defects. EL testing can detect hidden defects that were not found by other testing methods, such as infrared imaging with thermal cameras, flash testing, and V-A characteristic. The information gathered from these tests produces an image, which can provide evidence of any faults or variations within a cell, including micro-cracks.
EL testing is necessary to ensure that solar panels of the highest quality are shipped.
RenewSys has invested in state-of-the-art equipment to test modules under accelerated, extreme climatic, and environmental conditions. Read more
With the help of an EL test, a PV manufacturer can evaluate the structural quality of solar cells and any other possible defects caused by improper handling of photovoltaic panels.
Integrating the EL test into the production line, as we have done at RenewSys is key to ensuring high-quality output.
What defects can the EL test detect?
With the help of the EL test, a manufacturer can detect defects that are normally not visible. Defects that can be found with an EL test are:
Broken cells and micro-cracks in the cells
Detection of bus bar contact defects
Detection of missing or interrupted screen-printed fingers
Detection of no homogeneity and foreign matter in the crystalline silicon
RenewSys has devoted resources to deploy a robust ML + AI (Machine Learning + Artificial Intelligence) software in EL Testing to further bolster traditional EL testing, thus ensuring high performance of solar modules- Read more here
What are the consequences of micro-cracks?
According to research, micro-cracks have the potential to create an electrical separation, resulting in inactive cell parts. However, determining the power loss caused by these micro-cracks is difficult because some micro-cracks can have varied to minimal effects depending on the location and size of the crack.
Micro-cracks also have the potential to produce hot spots. These occur when the internal resistance of the damaged cell rises and causes an increase in cell temperature as the current passes through. Hot spots have been shown to cause further damage to a cell.
Solar Panel Handling, Installation, and Cleaning - Good Practices - Click Here
How to prevent micro-cracks?
Three key areas must be addressed to effectively prevent solar panel micro-cracks: manufacturing, transportation/installation, and environment.
Selecting a solar panel manufacturer that acknowledges the prevention of micro-cracks is a critical part of the solution.
Minimal human intervention, appropriate training, and guidelines for unpacking and repacking modules are all crucial to preventing micro-cracks.
Data Credits:
https://www.aig.com