In recent years, the technology of the photovoltaic industry has developed faster and faster. The power of single modules has become larger and larger, and the current of the string has also become larger and larger. The current of high-power modules has reached more than 17A. In terms of system design, the use of high-power components and reasonable reserved space can reduce the initial investment cost and kilowatt-hour cost of the system. The cost of AC and DC cables in the system is not low. How should design and selection be carried out to reduce costs?
1. Selection of DC cables
The DC cable is installed outdoors. It is generally recommended to choose special photovoltaic cables that have been cross-linked by radiation. After high-energy electron beam irradiation, the molecular structure of the cable insulation layer material changes from linear to three-dimensional network molecular structure, and the temperature resistance level increases from non-cross-linked 70°C to 90°C, 105°C, 125°C, 135°C, Even up to 150°C, the current carrying capacity is 15-50% higher than that of cables of the same specifications. It can withstand severe temperature changes and chemical erosion and can be used outdoors for more than 25 years. When choosing DC cables, choose products from regular manufacturers with relevant certifications to ensure long-term outdoor use.
Currently, the most commonly used photovoltaic DC cable is the PV1-F1*4 4 square meter cable. However, with the increase in the current of photovoltaic modules and the increase in the power of a single inverter, the length of the DC cable is also increasing. 6 square meters The use of DC cables is also increasing.
According to relevant specifications, it is generally recommended that the loss of photovoltaic DC should not exceed 2%. We use this standard to design how to choose DC cables. The line resistance of PV1-F1*4mm² DC cable is 4.6mΩ/meter, and the line resistance of PV6mm² DC cable is 3.1 mΩ/meter, assuming that the DC module working voltage is 600V, 2% voltage drop loss is 12V, assuming that the module current is 13A, using 4mm² DC cable, the distance between the farthest end of the module and the inverter is recommended not to exceed 120 meters (single string, (excluding positive and negative poles), if the distance is greater than this distance, it is recommended to choose a 6mm² DC cable, but it is recommended that the distance between the farthest end of the component and the inverter should not exceed 170 meters.
2. Photovoltaic cable loss calculation
In order to reduce system costs, the components and inverters of photovoltaic power stations are rarely configured in a 1:1 ratio. Instead, certain over-configurations are designed based on lighting conditions, project needs, etc. For example, for a 110KW module and a 100KW inverter, calculated based on 1.1 times the AC side overmatching of the inverter, the maximum AC output current is approximately 158A. The AC cable can be selected based on the maximum output current of the inverter. Because no matter how many components are configured, the AC input current of the inverter will never exceed the maximum output current of the inverter.
3. Inverter AC output parameters
Commonly used AC copper cables for photovoltaic systems include BVR and YJV. BVR means copper core PVC insulated flexible wire, YJV cross-linked polyethylene insulated power cable. When selecting, pay attention to the voltage level and temperature level of the cable. , to choose the flame-retardant type, the cable specification is expressed by the number of cores, nominal cross-section and voltage level: Single-core branch cable specification representation, 1*nominal cross-section, such as: 1*25mm 0.6/1kV, means a 25 square meter of cables. Multi-core twisted branch cable specification representation, the number of cables in the same circuit * nominal cross-section, such as: 3*50+2*25mm 0.6/1KV, which means three 50 square live wires, one 25 square neutral wire and A 25 square ground wire.
Post time: Mar-20-2024