Solis Seminar, Episode 24: PV Panel Micro-Crack Problems and Identification Methods

The last Solis Seminar introduced the problem of PID effect and its solutions. This seminar will give details on the causes of cell micro-cracks, how to identify them and ultimately prevent them.

PID effect, micro-cracks, and hot spots are three important factors that can affect the performance of crystalline silicon photovoltaic modules. Among them, PID effect and hot spots usually appear after installation and operation of PV panels for a period of time. Micro-cracks are a common problem associated with solar photovoltaic modules and they are difficult to detect with the eyes. In view of these potentially hidden problems, how we identify and rectify them is important.

What is a “Micro-Crack” and what are its possible causes?

Micro-cracks are a relatively common defect of crystalline silicon photovoltaic modules, which mainly refers to some small cracks that are not easily detectable by the human eye. Due to the characteristics of its own crystal structure, crystalline silicon modules are very prone to cracking.

In the process flow of crystalline silicon panel production, many parts of the process could cause the cell to crack. But the root cause is usually one of three types:

Mechanical Stress: This is when the cell is exposed to external forces such as welding, lamination, framing, installation, construction, etc., and when the parameters are set incorrectly, equipment fails or there has been improper operation which has caused micro-cracks.

Thermal Stress: Mainly caused when the cell swells and ruptures after being exposed to sudden high temperature, such as the welding or lamination temperature are too high, and other parameter settings are not correct.

Raw Material Defects: The sourcing of poor raw materials or materials that are not properly handled will result in material defects.

The Influence of “micro-crack” on the Performance of Photovoltaic Modules:

The current of the cell is mainly collected and led out by the main grid lines and the thin grid lines whose surfaces are perpendicular to each other. Therefore, when the micro-cracks (mostly parallel to the bus bars) cause the thin grid lines to break, the current will not be effectively transported to the bus bars, which will lead to partial and even the entire cell failure, and may also cause fragments, Hot spots, etc., at the same time cause power attenuation of the components.

How to identify “micro-crack”:

EL Equipment: EL (Electroluminescence) equipment is solar cell or panel internal defect detection equipment which uses the electroluminescence principle of crystalline silicon to capture near-infrared images of components through high-resolution infrared cameras. This equipment obtains and determines component defects.

However, this method has several drawbacks in micro-crack recognition of installed photovoltaic panels:

1. The equipment is expensive
2. Long detection time, usually several weeks or even months for large systems
3. Professional personnel are required for on-site operation, and the labour costs is high

I-V Curve Scanning Method:

For PV panels that have been installed and connected to an intelligent monitoring platform, the
I-V curve scanning function can be used to quickly scan and categorize the PV panels with micro-cracks.