Introduction of Common Cables and Materials in Photovoltaic Power Stations
Guide: During the construction process of photovoltaic power stations, in addition to the main equipment such as photovoltaic modules, inverters, and step – up transformers, the photovoltaic cable materials for supporting connections also play a crucial role in the overall profitability, operational safety, and efficiency of the photovoltaic power station.
Cables can be divided into DC cables and AC cables according to the system of the photovoltaic power station. They are classified as follows according to different uses and application environments:
1. DC Cables
1) . Series cables between modules.
2). Parallel cables between strings and from strings to DC distribution boxes (combiner boxes).
3). Cables from DC distribution boxes to inverters.
All of the above cables are DC cables. They are mostly laid outdoors and need to be moisture – proof, anti – exposure, cold – resistant, heat – resistant, and UV – resistant. In some special environments, they also need to be resistant to chemical substances such as acids and alkalis.
2. AC Cables
1). Connection cables from inverters to step – up transformers.
2). Connection cables from step – up transformers to power distribution devices.
3). Connection cables from power distribution devices to the power grid or users.
This part of the cables are AC load cables. They are mostly laid in indoor environments and can be selected according to the general selection requirements of power cables.
3. Special Photovoltaic Cables
A large number of DC cables in photovoltaic power stations need to be laid outdoors, and the environmental conditions are harsh. The cable materials should be determined according to the resistance to ultraviolet rays, ozone, drastic temperature changes, and chemical erosion. If ordinary – material cables are used for a long time in this environment, the cable sheath will be brittle, and even the cable insulation layer will be decomposed. These situations will directly damage the cable system and also increase the risk of cable short – circuit. In the medium – and long – term, the possibility of fire or personal injury is also higher, greatly affecting the service life of the system.
Therefore, it is very necessary to use special photovoltaic cables and components in photovoltaic power stations. With the continuous development of the photovoltaic industry, the market for photovoltaic supporting components has gradually formed. As for cables, a variety of photovoltaic – specific cable products with different specifications have been developed. The recently developed electron – beam cross – linked cable has a rated temperature of 120 °C and can resist harsh climatic environments and mechanical impacts. Another example is the RADOX cable, which is a solar – specific cable developed according to the international standard IEC216. In outdoor environments, its service life is 8 times that of rubber cables and 32 times that of PVC cables. Special photovoltaic cables and components not only have the best weather resistance, UV and ozone resistance, but also can withstand a wider range of temperature changes (for example: from – 40 to 125 °C). In Europe, technicians have measured that the temperature on the roof can be as high as 100 – 110 °C through tests.
4. Cable Conductor Materials
DC cables used in photovoltaic power stations usually work outdoors for a long time in most cases. Due to the limitations of construction conditions, cable connections mostly use connectors. Cable conductor materials can be divided into copper – core and aluminum – core. Copper – core cables have better antioxidant capacity than aluminum, long service life, better stability, small voltage drop, and small power loss. In construction, due to the good flexibility of the copper core, the allowed bending radius is small, so it is convenient to turn and easy to pass through pipes. Moreover, the copper core is resistant to fatigue, and it is not easy to break when bent repeatedly, so it is convenient to wire. At the same time, the copper core has high mechanical strength and can withstand large mechanical tension, which brings great convenience to construction and laying and also creates conditions for mechanized construction. On the contrary, for aluminum – core cables, due to the chemical properties of aluminum materials, oxidation phenomena (electrochemical reactions) are prone to occur at the installation joints, especially the creep phenomenon is likely to occur, which easily leads to failures.
Therefore, copper cables have outstanding advantages in the use of photovoltaic power stations, especially in the field of cable power supply by direct burial. It can reduce the accident rate, improve the reliability of power supply, and be convenient for construction, operation, and maintenance. This is the reason why copper cables are mainly used in underground cable power supply in China at present.
5. Cable Insulation Sheath Materials
The DC circuit is often affected by various unfavorable factors during operation, resulting in grounding and making the system unable to operate normally. Problems such as squeezing, poor cable manufacturing, unqualified insulation materials, low insulation performance, insulation aging of the DC system, or the existence of certain damage defects can all cause grounding or become a hidden danger of grounding. In addition, the invasion or biting of small animals in the outdoor environment can also cause DC grounding faults. Therefore, in this case, generally armored cables with anti – rat – agent – functional sheaths are used.