Solar cable

Solar cable is the interconnection cable used in photovoltaic power generation. A solar cable interconnects solar panels and other electrical components of a photovoltaic system. Solar cables are designed to be UV resistant and weather resistant. It can be used within a large temperature range and are generally laid outside.

Features

One common factor for most of the photovoltaic power systems is outdoor use, characterized by high temperatures and high UV radiation. Single-core cables with a maximum permissible DC voltage of 1.8 kV Umax. The phase to ground DC voltage rating must be Uo1.5kVDC and a temperature range from -40 °C to +90 °C ambient, 120 °C on the conductor for 25 year service life against thermal ageing. Ambient temperature and conductor temperature is derived from the Arrhenius law for ageing of polymers - ageing of polymers doubles for every 10 °C rise.

DC string cables must be class II double insulated to protect against short circuits and ground faults.

Small Scale systems with String Inverters 

A three-core AC cable is used for connection to the grid if a single-phase inverter is used, and a five-core cable is used for three-phase feed-in.[1]

Large Scale System Wiring with Central Inverters

Referred to as the Main DC, larger power collector cables are used to interconnect from the Generator box also referred to as the DC combiner to the central inverter. These cables must be shielded when over 50m in length (IEC62548). Central inverters are large frequency converters and unshielded cables would cause EMC issues throughout the whole solar farm which can behave like a capacitor.

Insulation

The cable's insulation must be able to withstand thermal and mechanical loads. As a consequence, plastics which have been cross-linked using an electron beam are increasingly used today. The insulation and jacket materials are extremely resistant to weathering, UV-radiation and abrasion . Additionally, it is salt water resistant and resistant to acids and alkaline solutions. It is suitable for fixed installation as well as for moving applications without tensile load. It is especially designed for outdoor use, which means direct sun radiation and air humidity, but due to the halogen free flame retardant cross-linked jacket material the cable can also be installed in dry and humid conditions indoors.[2]

DC connection

Individual modules are connected using cables to form the PV generator. The module cables are connected into a string which leads into the generator junction box, and a main DC cable connects the generator junction box to the inverter. In order to eliminate the risk of ground faults and short circuits, the positive and negative cables, each with double insulation, are laid separately.

Loss minimization

The cross-section of the cables should be proportioned such that losses incurred in nominal operation do not exceed 1%. String cables usually have a cross-section of four to ten square millimeters.

UL4703 standard

In 2005 the American Underwriters Laboratories (UL) published the UL subject 4703 Photovoltaic Wire. It covers singleconductor, insulated and integrally or non-integrally jacketed, sunlight resistant, photovoltaic wire in several temperature and voltage ratings for interconnection wiring of grounded and ungrounded photovoltaic power systems. The standard UL 4703 is based on the service entry cords USE-2 and specifies some additional requirements for photovoltaic cables. It applies for solar cables in North America.

References

  1. ↑ "Inverter and PV System Technology - Cables and Connectors". pv-system-tech.com. Retrieved 2011-06-20.
  2. ↑ "Cables for Photovoltaic Applications" (PDF). iwcs.omnibooksonline.com. Retrieved 2011-06-20.

3. EN50618 http://shop.bsigroup.com/ProductDetail/?pid=000000000030320864

4. In the U.K. DC string cable installation must observe the recommendations of the IET Code of Practice. Connectors used must be from the same manufacturer. https://www.bre.co.uk/filelibrary/nsc/Documents%20Library/Presentations/The-IET-solar-PV-code-of-practice-what-this-means-for-you.pdf

Further reading

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