September 6, 2019

Wet environment PV systems

In some wet environment PV systems, a frequently mentioned problem is that after a period of operation of the photovoltaic power generation system, the power generation volume drops significantly, resulting in a significant reduction in power plant revenue, which seriously damages the interests of the c channel steel suppliers. After field testing, it was found that after one to two years of completion of several photovoltaic power generation systems, the power of some backplane components was greatly attenuated, and the power attenuation of some backplane components was as high as 50% or more, and the power attenuation of the components caused the power generation of the photovoltaic system to decrease. One of the important reasons. Just like humans have rheumatism?

Why does the photovoltaic system get “rheumatism”?

Component power attenuation has a great impact on system power generation, and there are many reasons for component power attenuation, such as photo-attenuation, aging attenuation, cracking, cell rupture, etc. One of the important reasons is component PID effect, component PID effect is Because the voltage of the negative pole to ground is less than 0, the electron loss of the component causes the component power to decay, which makes the photovoltaic power generation system suffer from “rheumatism”.

It is understood that there are many reasons for the component PID, which is more likely to occur in humid and high temperature environments. The greater the humidity and the higher the temperature, the more likely the PID effect will occur. Therefore, the humidity and temperature in the eastern roof and water surface are high. In the application scenario, the impact of component PID on the power generation of photovoltaic power plants is more obvious.

Experts in the industry pointed out that whether PV system will suffer from “rheumatic disease” is mainly affected by two factors: one is whether the PV module is strong enough to resist high humidity and high temperature environment; the other is whether the electrical environment of PV module works Catalysis. If both “causes” are met at the same time, it will lead to “rheumatism”. As long as any of the “causes” are not satisfied, they will not get sick.

Common prescription for the treatment of rheumatism in photovoltaic power generation systems

To solve the component PID, it is necessary to solve the problem that the component’s negative pole to ground voltage is less than 0. According to the “cause”, the medicine can be taken from the following two directions.

The first type of prescription is to make PV modules stronger. Component manufacturers have done a lot of work on materials, structures and other aspects and made some progress. For example, double-glass components have very strong anti-PID characteristics.

The second type of prescription is to eliminate the electrical environment that catalyzes “rheumatism.” In order to eliminate the electrical environment that catalyzes “rheumatism”, many inverter manufacturers have introduced solutions, and the commonly accepted schemes include a negative direct grounding scheme and a PID night compensation solution.

Vaccination “vaccination” to prevent work

When constructing a photovoltaic power generation system, if the “vaccine” is inoculated to prevent the rheumatism from being “vaccinated”, it can be done once and for all. From sino east steel group co ltd the perspective of improving the electrical environment of the inverter, experts suggest that the following two schemes can be used for prevention.

Option 1: Negative direct grounding scheme

The direct grounding scheme of the negative pole is to directly ground the negative pole of the panel or inverter through a resistor or a fuse, so that the voltage of the negative pole to ground is greater than 0. This scheme is mostly used for a centralized inverter.

Option 2: String type negative virtual grounding scheme

Due to the different networking forms of the string type and the centralized inverter, the two types of inverter negative virtual grounding schemes differ in the way of preventing the AC access point of the PID device, the installation position, and the method of obtaining the negative pole to ground voltage. In the string system, a unit array inverter will be equipped with a PID protection device. The principle of the scheme is consistent with the principle of the centralized negative grounding scheme. Through the PID protection device, the negative electrode potential of all components in the square matrix is ​​raised, and the negative electrode voltage of the component with the lowest negative electrode potential is higher than the ground voltage, achieving the purpose of virtual grounding of the negative electrode.

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