A brief talk on the structural protection design of photovoltaic inverters

For outdoor photovoltaic inverters, their structural design must meet the IP65 rating standard. Only when this standard is met can our inverters work safely and efficiently. The IP rating is the protection level of the electrical equipment housing against the intrusion of foreign objects. It comes from the International Electrotechnical Commission's standard IEC 60529, which was also adopted as the US national standard in 2004. The IP65 rating we often talk about is the abbreviation of Ingress Protection, where 6 is the dustproof level (6: completely prevent dust from entering); 5 is the waterproof level (5: water spraying will not cause any damage to the product).

In order to meet the above design requirements, the structural design of the photovoltaic inverter is very strict and cautious, which is also where problems are very likely to occur in field applications. So how do we design a qualified inverter product?

Currently, there are two common protection design methods between the inverter cover and the box in the industry: one is to use a silicone waterproof ring, which is generally 2mm thick and is pressed between the cover and the box to achieve a waterproof and dustproof effect. This protection design is limited by the deformation and hardness of the silicone waterproof ring and is only suitable for 1-2KW small inverter boxes. For larger boxes, there are more hidden dangers in its protection effect.

As shown in the following diagram <1>:

The other is to use German RAMPF polyurethane foam for protection. This polyurethane foam is formed by CNC foaming and directly bonded to the upper cover and other structural parts. Its deformation can reach more than 50%, which is particularly suitable for the protection design of our medium and large inverters.

As shown in the following diagram <2>:

At the same time, more importantly, in order to ensure a high-strength waterproof design during structural design, a waterproof groove must be designed between the upper cover and the box body of the photovoltaic inverter chassis to ensure that even if water mist enters the inverter through the upper cover and the box body, the water droplets will be diverted to the outside through the waterproof groove to avoid entering the box body.

In recent years, the photovoltaic market has been highly competitive. In order to control costs, some inverter manufacturers have made some simplifications and substitutions in terms of protection design and material use. For example, as shown in the following diagram <3>:

The left side is a design that reduces costs. The box body has one bend, which controls costs from the aspects of sheet metal materials and processes. Compared with the three-bend box body on the right side, it obviously has one less guide groove, and the strength of the box body is also much lower. These designs bring great hidden dangers to the waterproof performance of the inverter.

In addition, since the inverter box is designed to meet the IP65 protection level, the internal temperature of the inverter will rise when it is working. The pressure difference caused by the high internal temperature and the changing external environmental conditions will cause moisture to enter and damage sensitive electronic components. In order to avoid this problem, we usually install a waterproof breathable valve on the inverter box. The waterproof breathable valve can effectively balance the pressure and reduce condensation in the closed equipment, while blocking dust and liquid from entering. Thereby improving the safety, reliability and service life of the inverter product.

Therefore, we can see that a qualified photovoltaic inverter structure design must be carefully and strictly designed and selected, whether from the chassis structure design or the materials used. Otherwise, blindly lowering the design requirements for the sake of cost control will only bring great hidden dangers to the long-term stable operation of the photovoltaic inverter.