Low power generation: what have you done to the inverter?

When work resumed after the New Year, we received feedback from an overseas customer that the inverter output was limited and could not be output effectively. After in-depth communication, we understood that there were problems with their inverter and module configurations: the modules were over-matched too much, resulting in excessive working current some of the time, the inverter limited current operation and some power limiting phenomena.

In fact, this situation also happens in China from time to time. Many owners do not understand the operation mechanism of the inverter and do a lot of things that are unpleasant

(1) Making a "shield" for the inverter

Mistake: Previously, when I did research, I found that customers had installed shields to protect the inverter, but this not only did not protect the machine, but also affected the heat dissipation of the machine. Especially in the hot summer, the installation of the shield will easily cause the surrounding working environment to be too hot, resulting in overheating and derating of the inverter, which will limit the output power and affect the power generation income.

Correct: String inverters are all IP65 or above rated and do not require additional overall protection. Therefore, we only suggest two things here: firstly, when installing string inverters, you can install some protective canopy on top of them to avoid direct rainfall; also, when installing multiple string inverters, you should pay attention to the inverter spacing to ensure sufficient space for heat dissipation and follow the installation manual recommendations as far as possible.

(2) Configuring too many components, thinking that the more you have, the more electricity you can generate

There is a saying in the north: "A spoon is too big, but a bowl is too big", which means that a bowl is only this big, so it can't hold more rice. In fact, the same applies to the configuration of inverter components. For example, the maximum output power of a Shengnengjie SE-5kw inverter is 5.5KVA. Even if 6kw of power is input on the input side, its output will not reach 6kw, but only 5.5kw at most, which means that the output power is limited.

Taking into account the impact of system losses, we usually recommend different over-provisioning ratios for different regions. This is because, if the inverter over-provision is too high, it will not only waste the system cost, but also make the inverter overload for a long time, resulting in a lower service life.

(3) Use DC sink boxes for convergence

As we all know, centralised inverters will add a sink box on the DC side, mainly to connect the components of the square array in series and parallel, and add protection devices such as lightning protection, fuses, DC switches, etc., and then unified to the DC cabinet side of the inverter.

In the case of string inverters, the DC sink box is omitted and the lightning protection and overcurrent protection units are placed inside the machine, thus greatly reducing the workload of construction and maintenance. However, we have also found that some users are still configuring with the same old centralised thinking:

Mistake: The number of DC terminals on the input side of the inverter directly determines how many power components can be configured. Some customers ignore the current limit conditions on the input side and connect the modules in parallel before they are connected to the inverter, resulting in excessive input current and burnt fuses, or even damage to the terminals, which affects the income from power generation.

Correct: The power on the input side of the inverter, i.e. the current limit, needs to be fully considered. Generally, the maximum input current of the modules is around 9-10A, and the double-sided modules are slightly larger, but only around 11-12A, while the DC input side current of the inverter is mostly around 12.5A, so extra attention should be paid when configuring.

The above are some of the typical "thankless" construction phenomena I encountered during my research, I hope to give you a reference and avoid similar phenomena.

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