Development of photovoltaic cable technology and its standards

All solar cells generate direct current and need to convert alternating current
.
With a certain capacity of optical power supply, it is necessary to be composed of many thousands of unit modules, and each unit module is regularly connected, and it is conceivable that the PV cable structure includes a lot of insulated thin wires
.
In the early research of photovoltaic cells, the main focus was on the components and their combinations, and the current research on PV cables is also on the agenda
.
In the past decade, the global solar power generation market has grown rapidly, and photovoltaic cables still have no international standards, so the standards and tests that can be used for reference need to be adjusted, such as life cycle tests, etc.
, especially attention should be paid to the aging problem
of cables exposed to strong ultraviolet rays for a long time.

Photovoltaic cells from large to small, the small PV on the roof of the general residence is a few kilowatts peak (kWp-Kilowatt peak), the medium PV for industrial use is a few megawatt peak (MWp), and the PV of large power plants is 2 gigawatt peak (2GWp).

The global PV market for newly installed systems was 5.
6 GW in 2008, and most people predict about 8~10GW of capacity
per year.
PV cables are usually considered only in the DC part of the system, excluding gate wiring, system control cables, and other connecting wires
.
The relationship between PV cable and PV installation capacity is roughly as follows: 1 MW is equivalent to 40~60km PV cable, which is directly related to the arrangement and number of crystal and thin-film components, and its connection principle is shown in Figure 1, and the converter is not drawn in the figure
.

Figure 1 Principle of connecting thin wire cable and module cable to module

PV cables are exposed to sunlight for a long time, or immersed in water for a long time, and there are sharp changes in ambient temperature, so users are concerned
about the life of the cable.
Because there is no international standard (such as IEC standards), manufacturers also feel that there is no basis, so PV cable in the process of development, its quality and life issues have been debated, but most experts agree.

UL-4703 (and its related standards and benchmarks) published and distributed by UL; In addition, the "Requirements for cables used in photovoltaic systems" 2Pfg-1169" (and its related standards and benchmarks), printed by TÜV (German Technical Inspection Agency), has become the main reference document
at present.
It may become the accepted standard
in the future.

The cable conductors consist of very fine tin plating in accordance with IEC 60228 class, with mostly cross-sections of 4.
00 mm2 and 6.
00 mm2, consisting of 56 and 84 single wires respectively; The insulation sheath meets TüV and UL requirements, can be used in thermoplastic or crosslinking, these are conventional, and the insulation thickness is curved 0.
5 mm
.

The cable sheath needs to have sufficient mechanical strength to prevent damage to the sheath during laying
.
In addition, mice and termites should have a protective function, sometimes it is necessary to add a steel wire braid layer (as armor), the DC part of the PV system is an ungrounded system, metal weaving Some people are opposed, in addition, metal weaving produces anti-corrosion problems
.

As for the electrical performance of photovoltaic cables, the authors believe that there are no big requirements
.
The use of cables in the 90s of last century, the use time is not long, the sheath appears ring cracking, cracking near the connection box is more significant, it is believed that the quality of the cable at that time is poor, perhaps the temperature around the connection box is higher, may be caused by
thermal stress.

Sheath liquid should have the ability to resist various chemical agents, such as photovoltaic cell cleaning fluid, lubricating oil, acid gas, acid rain, salt spray, mold and other grease fog smoke
.

From the perspective of investment and return, the service life of PV cable is 25 years, which should be considered a reasonable requirement
.
Examination using existing test standards may not necessarily lead to such precise conclusions
.
Since PV cables are becoming household commodities, there are certain uncertainties in terms of quality compared with other industrial cables, and so far, the debate between design and manufacturing has not been resolved
about how long the service life should be guaranteed.
The cable sheath needs to have sufficient mechanical strength to prevent damage to the sheath during laying
.
In addition, mice and termites should have a protective function, sometimes it is necessary to add a steel wire braid layer (as armor), the DC part of the PV system is an ungrounded system, metal weaving Some people are opposed, in addition, metal weaving produces anti-corrosion problems
.

As for the electrical performance of photovoltaic cables, the authors believe that there are no big requirements
.
The use of cables in the 90s of last century, the use time is not long, the sheath appears ring cracking, cracking near the connection box is more significant, it is believed that the quality of the cable at that time is poor, perhaps the temperature around the connection box is higher, may be caused by
thermal stress.
Sheath liquid should have the ability to resist various chemical agents, such as photovoltaic cell cleaning fluid, lubricating oil, acid gas, acid rain, salt spray, mold and other grease fog smoke
.
From the perspective of investment and return, the service life of PV cable is 25 years, which should be considered a reasonable requirement
.
Examination using existing test standards may not necessarily lead to such precise conclusions
.

Since PV cables are becoming household commodities, there are certain uncertainties in terms of quality compared with other industrial cables, and so far, the debate between design and manufacturing has not been resolved
about how long the service life should be guaranteed.

Figure 2 Laying a 4.
00 mm2PV cable with a long length Figure 3 Laying a 4.
00 mm2PV cable with a shorter length