Wiring of PV modules

The Wiring of PV modules on the DC side of a commercial photovoltaic system must be carefully calculated, planned and implemented. It has a decisive influence on the Performance and Security of the system. For larger systems in particular, where several hundred or thousands of PV modules are installed, the calculation and composition of the individual strings in conjunction with the inverters is one of the factors that determine the Overall economic efficiency of a solar system. There are also many Legal regulationswhich must be taken into account.

Planning is the key

Before starting to wire the PV modules, always carry out a Careful planning is essential. Not only are the alignment and tilt angle of the PV modules calculated precisely, but the appropriate modules, including the support structure, are also selected. During the calculation phase, all module strings are also calculated with the optimum positions for their Inverter determined according to the structural conditions. Only then can the appropriate cable types, lengths, cross-sections and connectors be selected. Important points that should be considered when selecting cables are

• Efficiency vs. costsThe thicker a cable is, the better it conducts. This means that cables with a larger diameter are more efficient, but they are also more expensive to purchase. The cable cross-section and cable lengths should therefore be calculated precisely.   
• Scalability & flexibilityDue to the long service life of PV modules, which is at least 25 years, a PV system should be installed in a scalable manner so that a company can flexibly expand or modify it. Cable routing is therefore also an essential part of the planning.
• Safety & reliabilityHigh-quality cables with good insulation and the right diameter ensure a reliable power supply in the company, reduce outages and increase safety if they are laid correctly.

Most solar modules are supplied with a cable cross-section of 4 mm². This must be taken into account when calculating the strings and their cable selection. For relatively short strings, cables with the same cross-section are sufficient. For very long strings, losses can be reduced by using distribution boxes.

String layout: Wiring of PV modules in series or parallel connection

The planning of the string design is always based on the requirements of the PV system and the specifications of the inverters. In a Series connection the positive connections of all modules are connected together, as are the negative connections. This increases the voltage of the string while the current remains constant. In a Parallel connection the positive connections and the negative connections are connected separately. This increases the current while the voltage remains constant. This type of string circuit prevents the entire string from failing if an individual module produces less power or is defective.

However, it is also possible to Combination from series and parallel connectionwhich is also known as "stringing" or "array design". It is an important method for optimizing the power and voltage in solar power systems. This type of interconnection makes it possible to connect the individual PV modules together in such a way that the overall output and voltage meet the requirements of the inverter and the system. In order to achieve optimum performance, several strings are connected in parallel. This means that you have several rows of modules that are connected together in series, and these rows are then connected in parallel to each other.  

Specifications for the selection of DC cables and connectors and their installation

Once the data for the PV modules and inverters is available and all the plans for the PV system have been drawn up, you can start selecting the right cables and connectors to connect the PV modules and inverters. In principle, the following must be observed for the entire cable routing Standards DIN VDE 0100-520 and 0100-712 must be observed. For example, the risk of an earth fault or short circuit must be reduced to a minimum through double and reinforced insulation.

In addition, the cables must have sufficient dielectric strength, current carrying capacity and appropriate cross-sections. The laying of PV cables is also governed by the DIN EN 50618 VDE 0283-618 clearly regulated. All plug connections in the DC area must comply with the DIN VDE 0126-3 correspond. The following are also defined String fuses as well as string and bypass diodes to prevent damage to the PV system. These conduct the current around modules that are no longer working efficiently due to shading or other problems. This prevents the entire system from being affected by the power loss of a single module. When laying the cables, bending radii must be observed and cable loops should be avoided.

In general, solar installers must protect the cables from external influences such as wind, rain, snow or ice and lay them in pipes or on cable bridges. It goes without saying that all components must be weatherproof and it is recommended that the positive and negative cables are laid separately. In the DIN DVE 0100-200 and the DIN VDE 0185-305-3 the functional and lightning protection equipotential bonding is also regulated. Once the PV modules have been properly wired with the inverters on the DC side and a corresponding connection on the AC side, even a large commercial PV system is relatively low-maintenance and safe.

Detecting errors in the cabling of PV modules through PV monitoring

The cabling of PV modules is an important step in the installation of a commercial photovoltaic system and should not be underestimated. Careful planning, the selection of the right components and compliance with safety standards are crucial for the long-term high yield of a PV system. For this reason, CUBE CONCEPTS not only checks and documents the correct cabling of all strings with the inverters several times during installation and before commissioning, but also constantly monitors them during operation. This ensures that optimum performance is always achieved and that clean, sustainable energy generation protects the environment and reduces electricity costs.