Solar technology will become one of the green energy technologies of the future. Solar or photovoltaic (PV) is increasingly widely used in China. In addition to the rapid development of government-supported photovoltaic power plants, private investors are also actively building factories to produce solar modules for global sales.
Cabling systems that connect photovoltaic modules and inverters are not usually seen as key components, but a failure to use dedicated cables for solar applications can affect the life of the entire system.
In fact, solar energy systems are often used in harsh environmental conditions, such as high temperatures and ultraviolet radiation. In Europe, sunny days will result in field temperatures for solar energy systems of up to 100°C. So far, we can use PVC, rubber, TPE and high quality cross-link materials, but unfortunately, the rated temperature of 90°C rubber cable, and even the rated temperature of 70°C PVC cable is often used outdoors, obviously, which will greatly affect the service life of the system.
Environmental stress
For photovoltaic applications, the materials used outdoors should be based on ultraviolet light, ozone, drastic temperature changes, and chemical erosion. The use of low-grade materials under such environmental stress will make the cable sheath fragile and even decompose the cable insulation layer. All of these conditions will directly increase the loss of the cable system, and will also increase the risk of cable short circuit, and in the medium to long term, the possibility of fire or personnel injury is also higher.
Anti-mechanical load
In fact, during installation and maintenance, the cable can be wired on the sharp edge of the roof structure, while the cable must withstand pressure, bending, tension, cross tensile load and strong impact. If the strength of the cable sheath is not enough, the cable insulation layer will be seriously damaged, which will affect the service life of the whole cable, or lead to short circuit, fire and personnel injury risk problems.
Radiation-based cross-linked materials, with a relatively high mechanical strength. The cross-linking process changes the chemical structure of the polymer, transforms the meltable thermoplastic materials into non-meltable elastomeric materials, and the cross-linking radiation significantly improves the thermal, mechanical and chemical characteristics of cable insulation materials.
Contrast the difference
The characteristics of photovoltaic cable are determined by its special insulation material and sheath material, which we call cross-linked PE. After irradiation by the irradiation accelerator, the molecular structure of the cable material will change, so as to provide all aspects of its performance. In fact, during installation and maintenance, the cables can be wired on the sharp edge of the roof structure, while the cables must withstand pressure, bending, tension, cross tensile load and strong impact. If the strength of the cable sheath is not enough, the cable insulation layer will be seriously damaged, which will affect the service life of the entire cable, or lead to short circuit, fire and personnel injury risk problems.
Main performance
Electric performance
1. DC resistance
The DC resistance of the finished cable core at 20℃ is not greater than 5.09 Ω / km.
2. Water-immersed voltage test
The finished cable (20m) was submerged in (20 ± 5) ℃ water for 1h after 5min voltage test (AC 6.5kV or DC 15kV).
3. Long-term DC voltage resistance
The sample was 5m long in (85 ± 2) ℃ of distilled water containing 3% sodium chloride (NaCl) (240 ± 2) h, 30cm exposed at both ends. Add DC 0.9kV voltage between the wire core and water (conductive wire core connected to the positive electrode and water connected to the negative electrode). After removing the test sample, the test voltage is 1kV AC and is not broken down.
4. Insulation resistance
The insulation resistance of the finished cable at 20℃ shall not be less than 1014 Ω · cm,
The insulation resistance of the finished cable at 90℃ is not less than 1011 Ω · cm.
5. Cover surface resistance
The surface resistance of the finished cable sheath shall not be less than 109 Ω.
Selection of cables
In the solar photovoltaic power generation system, the low-voltage DC transmission part of the cable used, because of the use of environment and technical requirements are different requirements, the overall factors should be considered: the insulation performance of the cable, heat and flame resistance, aging performance and wire diameter specifications. The specific requirements are provided as follows:
1. The connection cable between the solar cell module and the module is generally directly connected by the connection cable attached to the module junction box. When the length is not enough, the special extension cable can also be used. According to the different power size of the component, this kind of connection cable has three specifications such as cross-sectional area of 2.5m㎡, 4.0m㎡, 6.0m㎡. This kind of connection cable uses double layer insulation skin, with superior ultraviolet light, water, ozone, acid, salt erosion ability, superior all-weather ability and wear resistance.
2. The connection cable between the battery and the inverter requires to use the multiple cables that have passed the UL test and connect nearby as far as possible. Choosing short and thick cables can reduce the system loss, improve efficiency, and enhance reliability.
3. The connection cable between the battery square array and the controller or DC junction box also requires the use of multiple cables that have passed the UL test. The cross-sectional area specification is determined according to the maximum current output current of the square array.
The cross-sectional area of DC cable is determined according to the following principles: the connecting cable between solar cell components and components, the connecting cable between battery and battery, and the connecting cable of AC load, the rated current of the cable is 1.25 times of the maximum continuous working current of the cable, and the connecting cable between the battery (group) and inverter, the rated current of the cable is 1.5 times of the maximum continuous working current of each cable.
