Two effects affecting the normal operation of photovoltaic modules

- Jan 03, 2019-

Photovoltaic modules are the most important equipment in photovoltaic power generation. If special conditions occur during daily installation and operation and maintenance, the hot spot effect and potential induced decay effect (PID) of photovoltaic modules will be caused, causing losses for the majority of owners, so we should Care should be taken to control the PV plant during installation and routine maintenance of the plant to avoid these two effects.

 

First, the hot spot effect

The solar cell module that is shielded in a series branch will be used as a load to consume the energy generated by other illuminated solar cell components. The shaded solar cell component will heat up at this time, which is the hot spot effect.

This effect can seriously damage the solar cell. Part of the energy generated by a solar cell with light may be consumed by the obscured battery. The hot spot effect may be just a piece of bird droppings.

In order to prevent the solar cell from being damaged by the hot spot effect, it is preferable to connect a bypass diode between the positive and negative terminals of the solar cell module to prevent the energy generated by the illumination component from being consumed by the shielded component. When the hot spot effect is severe, the bypass diode may be broken down, causing the component to burn out, as shown below:

 

Second, the PID effect

The potential-induced attenuation effect is that the battery assembly has a long-term under high voltage, causing leakage current between the glass and the packaging material, and a large amount of electric charge is struck on the surface of the battery sheet, so that the passivation effect on the surface of the battery is deteriorated, resulting in lower than the design standard. When the PID phenomenon is serious, it will cause a component to attenuate more than 50% of the power, thus affecting the power output of the entire string. High temperature, high humidity, high salinity coastal areas are most prone to PID phenomenon.

After the PID effect occurs, some of the batteries appear to have high resistance and cause component PID phenomenon. There are three main reasons:

First, the system design reason: the lightning protection grounding of the photovoltaic power station is realized by grounding the component frame at the edge of the square array, which causes a bias voltage to be formed between the single component and the frame. The higher the bias voltage of the component occurs, the PID phenomenon occurs. The more serious it is. For the P-type crystalline silicon component, the anode of the inverter with the transformer is grounded, and the forward bias of the component frame relative to the cell is eliminated, which effectively prevents the occurrence of the PID phenomenon, but the grounding of the negative pole of the inverter increases the corresponding system construction. cost;

The second reason is the photovoltaic module: the high temperature, high humidity environment causes leakage current between the cell and the ground frame, and a leakage current channel is formed between the package material, the back plate, the glass and the frame. By using the modified insulating film ethylene vinyl acetate (EVA) is one of the ways to achieve component anti-PID, the component's anti-PID performance will be different under different EVA encapsulation film conditions. In addition, the glass in the photovoltaic module is mainly calcium soda glass, and the influence of glass on the PID phenomenon of the photovoltaic module is still unclear;

The third reason is the battery piece: the uniformity of the cell sheet resistance, the thickness of the anti-reflection layer and the refractive index has different effects on the PID performance. Among the three aspects of the above-mentioned PID phenomenon, the component PID phenomenon caused by the potential difference between the component frame and the component in the photovoltaic system is recognized by the industry, but the mechanism of the PID phenomenon generated by the component in both the component and the battery is not yet Clearly, the corresponding measures to further improve the anti-PID performance of components are still unclear.