The construction cost of cable projects in PV power generation projects is generally large, and the reasonable selection of cable type and laying method directly affects the construction cost. Therefore, reasonable planning and correct selection of cable type and laying method is the first link of cable design work. In a photovoltaic power generation system, the cable selection that is taken is an important link to reducing the cost of power generation.
1. The basic principle of cable selection
Photovoltaic power generation cable selection follows the general requirements of cable selection, that is, according to the voltage level, to meet the continuous working current, short-circuit thermal stability, allowable voltage drop, economic current density, and laying environmental conditions factors for selection. At the same time, photovoltaic power generation has its characteristics, solar energy systems are often used in harsh environmental conditions, such as high temperature, cold and ultraviolet radiation.
Therefore, the selection of cables in photovoltaic systems needs to consider the following factors.
1.1. the insulation performance of the cable.
1.2. The heat and flame resistance of the cable.
1.3. the cable’s moisture-proof, and light-proof (anti-radiation).
1.4. the way the cable is laid.
1.5. the material of the cable conductor (copper core, aluminum core).
1.6. the specifications of the cable cross-section.
2. Cable selection
2.1 Photovoltaic power generation cable type Photovoltaic power generation system cable, according to the system of photovoltaic power generation can be divided into DC cable and AC cable, which is connected in series between the components, and parallel DC cable between the string occupies more than half of the cable volume, after the inverter for the use of AC cable.
Depending on the application environment, the cables of photovoltaic power generation systems can be divided into.
1. DC cables
1.1. series cables between modules and components, this part should use special cables with PV certification.
1.2. Parallel cables between strings and between strings to DC distribution box (sink box), rare earth aluminum alloy conductor cables can be used.
1.3. The cable between DC distribution box and inverter, this part can also choose to use rare earth aluminum alloy conductor cable.
All the above cables are DC cables, which are more often laid outdoors and need to be moisture-proof, sunlight-proof, cold-proof, heat-proof, UV-proof, and in some special environments, acid and alkali-proof chemicals. Among them, the connection cable between the component and the component is usually supplied in sets with the component.
2. AC cable
2.1. Connection cable from the inverter to the step-up transformer.
2.2. Connection cable from the step-up transformer to the power distribution unit.
2.3. Connection cable from the distribution unit to the grid or the consumer.
The focus here is on the selection and laying of DC cables in grid-connected photovoltaic power generation, the principles of which are also applicable to some other types of photovoltaic power generation projects.
3. PV special cables
A large number of DC cables in photovoltaic power generation systems need to be laid outdoors under harsh environmental conditions, and their cable materials should be determined according to the resistance to ultraviolet light, ozone, severe temperature changes, and chemical erosion.
Common material cable in this environment for a long time will lead to the cable sheath being fragile, and even decomposing the cable insulation layer.
These conditions will directly damage the cable system, but also increase the risk of short-circuiting the cable, and in the medium and long term, the possibility of fire or injury to personnel is also higher, greatly affecting the service life of the system.