Solar energy technology will become one of the green energy technology in the future. Solar energy or photovoltaic (PV) is widely used and photovoltaic power plant is developing rapidly. The construction of cost-effective and profitable photovoltaic power plants represents the most important goal and core competitiveness of all solar manufacturers. In fact, profitability depends not only on the efficiency or high performance of the solar panel itself, but also on the associated system components, high quality components ensure efficient, stable and long term operation of the photovoltaics.
In the photovoltaics power generation system, the amount and cost of the cable is the basis of the matching electric equipment, which is more than the general power generation system, and is also one of the major factors affecting the efficiency of the whole system.
In photovoltaic power generation projects, the construction cost of solar cable projects is generally relatively large, and the reasonable selection of cable type and laying method directly affects the construction cost, so reasonable planning and correct selection of cable type and laying method, is the first step in cable design. In photovoltaic power generation system, the selection of positive cable is an important link to reduce the cost of power generation.
In the photovoltaics power generation system, the amount and cost of the cable is the basis of the matching electric equipment, which is more than the general power generation system, and is also one of the major factors affecting the efficiency of the whole system.
In photovoltaic power generation projects, the construction cost of solar cable projects is generally relatively large, and the reasonable selection of cable type and laying method directly affects the construction cost, so reasonable planning and correct selection of cable type and laying method, is the first step in cable design. In photovoltaic power generation system, the selection of positive cable is an important link to reduce the cost of power generation.
01
Solar Basic principles of cable selection
The selection of cables for photovoltaic power generation follows the general requirements for cable selection, that is, according to the voltage level, to meet the continuous work of the allowable current, short-circuit thermal stability, allowable voltage drop, economic current density and laying environmental factors such as selection.
At the same time, photovoltaic power generation has its own 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 PV system should consider the following factors:
(1) insulation performance of cables;
(2) heat resistance and flame retardancy of cables;
(3) the cable's moisture-proof, light-proof (anti-radiation) ;
(4) the way in which the cables are laid;
(5) cable conductor material (copper core, aluminum alloy core) ;
(6) specifications for cable sections.
02
cable selection
2.1 type of solar cable
Photovoltaic power system cables, according to the photovoltaic power system can be divided into DC cables and AC cables, among which the components in series, and groups in series and parallel DC cables occupy more than half of the cable volume, after the inverter for the use of AC cable.
According to the application environment, the cables of photovoltaic power generation system can be divided into:
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Direct current cable
(1) a series cable between the modules, where a dedicated PV certified cable should be used.
(2) parallel cables between groups and between groups to DC distribution box (bus box) , rare earth aluminum alloy conductor cable can be used.
(3) cable between DC distribution box and inverter, this part can also be selected with rare earth aluminum alloy conductor cable.
(2) parallel cables between groups and between groups to DC distribution box (bus box) , rare earth aluminum alloy conductor cable can be used.
(3) cable between DC distribution box and inverter, this part can also be selected with rare earth aluminum alloy conductor cable.
-
AC cable
(1) connection cable from inverter to step-up transformer.
(2) connection cable from booster transformer to distribution unit.
(3) the connection cable from the distribution unit to the power grid or to the customer.
(2) connection cable from booster transformer to distribution unit.
(3) the connection cable from the distribution unit to the power grid or to the customer.
2.2 Problems needing attention in cable selection of photovoltaic projects
▼Why use photovoltaic special cable
A large number of DC cables in photovoltaic power plants 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, severe temperature changes and chemical erosion. The long-term use of ordinary material cables in this environment will cause the cable sheath to be fragile, and even decompose the cable insulation. These conditions will directly damage the cable system, but also increase the risk of short-circuiting the cable. In the medium and long term, the possibility of fire or personal injury is also higher, which greatly affects the service life of the system.
Therefore, it is very necessary to use photovoltaic special cables and components in photovoltaic power plants. At present, various specifications of photovoltaic professional cable products have been developed in the market. For example, the rated temperature of the electron beam cross-link cable is 120 °C, which can withstand harsh weather environments and mechanical shocks; another example is the RADOX cable, which is a special solar cable developed according to the international standard IEC216. In outdoor environments, the service life is the rubber cable. 8 times that of PVC cables and 32 times that of PVC cables. Photovoltaic special cables and components not only have the best weather resistance, UV resistance and ozone erosion resistance, but also can withstand a wider range of temperature changes (for example: from -40°C to 125 °C). In Europe, technicians have passed tests, and the temperature value that can be measured on the roof is as high as 100 to 110 °C.
During the installation, operation and maintenance of the photovoltaic power generation system, the cables may be wired in the soil below the ground, in the overgrown rocks, or on the sharp edges of the roof structure, or exposed in the air. The cables must be subjected to pressure and bending. Folding, tension, cross tensile load and strong impact. If the cable jacket is not strong enough, the cable insulation will be damaged, affecting the life of the entire cable, or causing problems such as short circuits, fire and personal injury hazards. Cable scientific research and technical personnel found that the material cross-linked by radiation has higher mechanical strength than before radiation treatment. The cross-linking process changes the chemical structure of the polymer of the cable insulation jacket material, the fusible thermoplastic material is converted into a non-fusible elastomeric material, and the cross-linking radiation significantly improves the thermal, mechanical and chemical properties of the cable insulation characteristic.
▼Copper core VS aluminum core
The copper core cable has the characteristics of better oxidation resistance than aluminum, long life, better stability, low voltage drop and low power loss; in construction, due to the good flexibility of the copper core, the allowable bending radius is small, so it is convenient to bend and pass through the tube. It is easy; and the copper core is fatigue-resistant and not easy to break after repeated bending, so the wiring is convenient; 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 .
Due to the chemical properties of aluminum, the installation joints of aluminum core cables are prone to oxidation (electrochemical reaction), especially creep, which can easily lead to failures. Calculated according to IEC287, under the same laying conditions, in order to obtain the same current carrying capacity, the cross-section of aluminum should be larger than the second gear, which will increase the cable laying channel, and it may be necessary to adopt a special laying channel and increase the investment cost.
Therefore, copper cables have outstanding advantages in the use of photovoltaic power stations, especially in the field of direct buried cable power supply. It can reduce the accident rate, improve the reliability of power supply, and facilitate construction, operation and maintenance. This is the reason why copper cables are mainly used in underground cable power supply in China.
A large number of DC cables in photovoltaic power plants 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, severe temperature changes and chemical erosion. The long-term use of ordinary material cables in this environment will cause the cable sheath to be fragile, and even decompose the cable insulation. These conditions will directly damage the cable system, but also increase the risk of short-circuiting the cable. In the medium and long term, the possibility of fire or personal injury is also higher, which greatly affects the service life of the system.
Therefore, it is very necessary to use photovoltaic special cables and components in photovoltaic power plants. At present, various specifications of photovoltaic professional cable products have been developed in the market. For example, the rated temperature of the electron beam cross-link cable is 120 °C, which can withstand harsh weather environments and mechanical shocks; another example is the RADOX cable, which is a special solar cable developed according to the international standard IEC216. In outdoor environments, the service life is the rubber cable. 8 times that of PVC cables and 32 times that of PVC cables. Photovoltaic special cables and components not only have the best weather resistance, UV resistance and ozone erosion resistance, but also can withstand a wider range of temperature changes (for example: from -40°C to 125 °C). In Europe, technicians have passed tests, and the temperature value that can be measured on the roof is as high as 100 to 110 °C.
During the installation, operation and maintenance of the photovoltaic power generation system, the cables may be wired in the soil below the ground, in the overgrown rocks, or on the sharp edges of the roof structure, or exposed in the air. The cables must be subjected to pressure and bending. Folding, tension, cross tensile load and strong impact. If the cable jacket is not strong enough, the cable insulation will be damaged, affecting the life of the entire cable, or causing problems such as short circuits, fire and personal injury hazards. Cable scientific research and technical personnel found that the material cross-linked by radiation has higher mechanical strength than before radiation treatment. The cross-linking process changes the chemical structure of the polymer of the cable insulation jacket material, the fusible thermoplastic material is converted into a non-fusible elastomeric material, and the cross-linking radiation significantly improves the thermal, mechanical and chemical properties of the cable insulation characteristic.
▼Copper core VS aluminum core
The copper core cable has the characteristics of better oxidation resistance than aluminum, long life, better stability, low voltage drop and low power loss; in construction, due to the good flexibility of the copper core, the allowable bending radius is small, so it is convenient to bend and pass through the tube. It is easy; and the copper core is fatigue-resistant and not easy to break after repeated bending, so the wiring is convenient; 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 .
Due to the chemical properties of aluminum, the installation joints of aluminum core cables are prone to oxidation (electrochemical reaction), especially creep, which can easily lead to failures. Calculated according to IEC287, under the same laying conditions, in order to obtain the same current carrying capacity, the cross-section of aluminum should be larger than the second gear, which will increase the cable laying channel, and it may be necessary to adopt a special laying channel and increase the investment cost.
Therefore, copper cables have outstanding advantages in the use of photovoltaic power stations, especially in the field of direct buried cable power supply. It can reduce the accident rate, improve the reliability of power supply, and facilitate construction, operation and maintenance. This is the reason why copper cables are mainly used in underground cable power supply in China.
For more information on solar cable, please feel free to call Slocable at 86-769-22010201. You can also email us at pv@slocable.com.cn.
