How to choose cables reasonably in photovoltaic system
In recent years, the technological development of the photovoltaic industry has become faster and faster, the power of a single module has become larger and larger, and the current of the string has also increased. The current of high-power modules has reached more than 17A. In terms of system design, the use of high-power components and reasonable over-configuration can reduce the initial investment cost of the system and the cost of electricity per kilowatt-hour. The cost of AC and DC cables in the system is not low, how should the design and selection to reduce the cost?
1. Selection of DC cable
DC cables are installed outdoors. It is generally recommended to select special photovoltaic cables that have been cross-linked by irradiation. After high-energy electron beam irradiation, the molecular structure of the insulating layer material of the cable changes from linear to three-dimensional network molecular structure, which is temperature resistant. The grade is increased from the non-cross-linked 70℃ to 90℃, 105℃, 125℃, 135℃, or even 150℃. Compared with the cable of the same specification, the current carrying capacity is increased by 15-50%. It can withstand severe temperature changes and chemical attack. Used outdoors for more than 25 years. When selecting the DC cable, it is necessary to choose a product with relevant certification from a regular manufacturer to ensure long-term outdoor use.
▲Calculation of line loss of photovoltaic cable
What is the difference between a single-core cable and a multi-core cable?
Single-core cable means that there is only one conductor in one insulation layer. Multi-core cables refer to cables with more than one insulated core. In terms of insulation performance, both single-core and multi-core cables must meet national standards.
The difference between a multi-core cable and a single-core cable is that the two ends of a single-core cable are directly grounded, and the metal shielding layer of the cable may also generate circulating currents and cause loss; multi-core wires are generally three-core wires, because in the operation of the cable, the sum of the current flowing through the three cores is zero, and there is basically no induced voltage at both ends of the metal shielding layer of the cable.
In terms of circuit capacity, single-core and multi-core cables have the same cross-section, and the rated ampacity of single-core cables is greater than that of three-core cables; the heat dissipation performance of single-core cables is greater than that of multi-core cables, at the same load or short circuit in this case, the heat generation of single-core cables is less than that of multi-core cables, which is safer;
From the point of view of cable laying, the laying of multi-core cables is simpler and more convenient. The cables have inner layer and multi-layer protection for safer; single-core cables are easier to bend when laying, but long-distance cables are more difficult to lay. Single-core cables are more difficult than multi-core cables. From the installation of the cable head, the single-core cable head is easier to install and easy to split. In terms of price, the unit price of multi-core cables is slightly higher than that of single-core cables.
Photovoltaic system wiring skills
The line of the photovoltaic system is divided into a DC part and an AC part. The two parts of the line need to be wired separately, the DC part is connected to the module, and the AC part is connected to the grid. There are many DC cables in medium and large power stations. In order to facilitate future maintenance, the wire numbers of the cables must be affixed firmly. Separate strong and weak wires. If there are signal wires, such as 485 communications, they must be routed separately to avoid interference. Wire pipes and bridges should be prepared for routing, and try not to expose the wires. When routing the wires horizontally and vertically, it will look better. Try not to have cable joints in the threading pipes and bridges, because maintenance is inconvenient. If there is a scenario where aluminum wire replaces copper wire, reliable copper-aluminum transfer terminals must be used.
In the entire photovoltaic system, the cable is a very important component, and the cost of the system is increasing. When we design the power station, we need to save the system cost as much as possible under the premise of ensuring the reliable operation of the power station. Therefore, the design and selection of the AC and DC cables of the photovoltaic system are particularly important.