In solar system, though the cost of the cable is not high, as the "blood vessel" of the pv system, it plays an important role in connecting pv modules, inverters, distribution boxes and the grid, and also plays an important role in the operation safety of the whole system, which even influences the overall profitability of the power station. Therefore, the cable selection in system design process is very critical.

1. Types of pv cables

From the perspective of different functions, the cables in the pv system can be mainly divided into two types:

DC cables and AC cables.

1.1 DC cable

① Serial cables between pv modules.

② Parallel cables between strings and between strings and DC distribution box (combiner box).

③ Cables between the DC distribution box and the inverter.

The above cables are all DC cables, and they are often laid outdoors. They need to be protected from moisture, sun exposure, cold, heat, and ultraviolet rays. In some special environments, they also need to be resistant to chemical substances such as acids and alkalis.

1.2 AC cable

① Connecting cables from the inverter to the step-up transformer.

② Connecting cables from the step-up transformer to the power distribution unit

③ Connecting cables from the power distribution device to the power grid or users

The above cables are all AC load cable, which are often laid in the indoor environment, and can be selected according to the general power cable selection requirements.

2. Why choose dedicated pv cable?

Under much circumstance, DC cables need to be laid outdoors. The cable materials should be determined according to the resistance to ultraviolet rays, ozone, severe temperature changes and chemical erosion. The long-term use of ordinary material cables in this environment will cause the cable sheath to break and even decompose the cable insulation layer. These conditions will directly damage the cable system, and will also increase the risk of system short circuit. In the medium and long term, the possibility of fire or personal injury is also higher, which greatly affects the lifespan of the system. Therefore, it is very necessary to use dedicate pv cables and modules. Solar-specific cables and modules not only have the best weather resistance, UV and ozone resistance, but also can withstand a wider range of temperature changes.

3. Principles of cable design and selection

① The withstand voltage of the cable should be greater than the maximum voltage of the system. For example, for AC cables with 380V output, 450/750V cables would be selected.

② For the connection inside and between the system arrays, the rated current of the selected cable is 1.56 times the maximum continuous current in the calculated cable.

③ For the connection of AC loads, the rated current of the selected cable is 1.25 times of the calculated maximum continuous current in the cable.

④ For the connection of the inverter, the rated current of the selected cable is 1.25 times of the calculated maximum continuous current in the cable.

⑤ Consider the influence of temperature on the performance of cable. The higher the temperature, the less the current carrying capacity of the cable, and the cable should be installed in a ventilated and heat-dissipating place as much as possible.

⑥ Consider that the voltage drop should not exceed 2%.

4. The DC circuit is often affected by various unfavorable factors during operation and causes grounding, which makes the system unable to work. Such as extrusion, poor cable manufacturing, unqualified insulation materials, low insulation performance, DC system insulation aging, or some damage defects, can cause ground faults or become a grounding hazard. In addition, the intrusion or biting of wild animals in the outdoor environment will also cause a DC ground fault. In this case, armored cables with rodent-proof functional sheaths are generally necessary.

5. Summary: Select the appropriate cable according to the grid form supported by inverter and data of the maximum continuous current in the cable.