Solar Cable Guide

Table of Contents

CHAPTER 1:  WHAT ARE SOLAR CABLES?

Solar cables, also known as photovoltaic cables, are those that come into use when installing solar panels and other systems involved in the photovoltaic activity.

Solar panels make use of renewable energy, i.e., these panels capture the heat from the sunlight and convert this energy into electricity employing photovoltaic modules.

This solar energy is created in one place and requires transfer to other sites through the installation of cables. These cables then allow the transmission of electricity.

Thus, those applications which involve the direct exposure of cables to sunlight cannot be carried out with ordinary cables. In such cases, the specialized construction of wires takes place. These are known as solar cables.

Solar Cables have originated as a result of the Renewable Energy initiative of the world. PV Cables are bring designed because of the ever-increasing needs of the solar industry.

PV cables are just the beginning of the development and launch of green technology in wires & cables.

Solar cables have a variety of features. As such, these cables are resistant to UV radiation. Weather resistance is another property of solar cables.

Harsh environmental conditions are no problem for solar cables. This property is because the design is entirely safe, and no degradation takes place during its exposure to UV radiation.

Solar cables are also designed to be very flexible so that they can be useful almost anywhere. Since these cables are mostly useful outside, solar cables can be helpful in a wide range of temperatures.

Solar Cables are abrasion resistant & moisture resistant. The coatings on the top do not allow penetration of foreign objects inside the cables.

PV cables are not only used in solar panels, but these cables are also useful in solar panels wiring, underground service entrances, and service terminal connections.

Solar cables possess excellent operational performance — the initial setup is speedy and efficient. At the same time, the maintenance requirement for solar cables is nearly minimum.

CHAPTER 2: WHAT IS THE STRUCTURE OF SOLAR OR PHOTOVOLTAIC CABLES?

The structure of the solar cables consists of three main parts:

Outer sheath.

CHAPTER 2.1: WHAT IS CONDUCTOR?

There are two common types of conductor materials used. These include:

Copper and aluminum are the two common conductor materials used in residential and commercial solar installations.

Copper has a higher conductivity than aluminum. Thus it carries more current than aluminum at the same size and diameter.

Though the weakening of   Aluminum may occur during installation, especially during bending, it is less expensive than copper wires.

Aluminum is not allowed for interior home wiring since they are useful in larger gauges for underground or overhead service entrances and commercial operations.

CHAPTER 2.2: WHAT IS INSULATION?

Two main types of insulation materials are useful in solar cables :

• XLPE – Cross-linked Polyethylene.
• EPR – Ethylene Propane Rubber.

The insulation that has a cross-linking structure of XLPE is better than the thermoplastic materials such as PVC. XLPE allows the cables to work efficiently under high-temperature conditions.

Insulations made of Cross-linked polyethylene (XLPE) also allow more current to pass through the conductor. XLPE material can allow a conductor temperature up to 250° C.

The insulation is exceptionally weather-resistant, UV resistant, and abrasion-resistant. Furthermore, the insulation also possesses resistance to saltwater, acids, and alkaline solutions.

The design of the insulation is mainly for outdoor use, which means direct sun radiation and air humidity can not deteriorate the cable.

But the cable can also be installed indoors in dry and humid conditions due to the halogen-free and flame retardant cross-linked jacket material (XLPE).

The insulation material enables solar cables to withstand thermal and mechanical loads.

There are other types of insulation materials that are also useful:

• Heat resistant thermoplastic (THHN) used in dry or damp locations.
• THW moisture and heat resistant thermoplastic, used in both dry and wet locations.
• THWN moisture and heat resistant thermoplastic used dry and wet conditions.
• TW moisture-resistant thermoplastic used in dry-wet locations
• UF and US underground feeder and Branch Circuit Cable single conductor, moisture, and heat resistant.
• USE 2 and RHM 2 moisture-resistant thermoplastic
• PV wire thicker insulation or jacket providing additional and more support as compared to other cables

Colour coding is carried out for the insulation to designate its function and uses. Colour coding is essential for future repair and maintenance.

However, wiring labels are different for AC or DC:

• Alternating Current: (AC)
• Black or red: Used for ungrounded applications.
• White: Used as a grounded conductor.
• Green or bare: Used in ground equipment.
• Direct Current: (DC)
• Red:
• White: Negative or grounded Conductor.
• Green or Bare: Equipment ground.

CHAPTER 2.3: WHAT IS THE OUTER SHEATH OR PROTECTIVE JACKET:

Sheaths are the outer coating in medium voltage underground cables, which protect the cables from environmental conditions and faults. The sheath comes in two colors, black and red.

The sheath performs several functions, such as :

• The sheath provides protection from flames, which means it is flame retardant.
• Another essential feature is the UV resistance of the sheath, which enables the cable to work in harsh environments.
• It also provides insulation to wires from the ground.
• The sheath protects the metal elements from humidity.
• The cables get protection from the mechanical stresses that it faces during installation and service.
• The sheath can also be designed to withstand termite attacks, resistance to hydrocarbons, etc.

CHAPTER 2.4 (1): MATERIALS USED FOR CABLE SHEATHS:

Two primary substances are useful for cable sheaths:

• Poly-Vinyl Chloride (PVC), Polyethylene (PE) :
• The PE material used for sheaths can be of medium density (MDPE) or Linear low density (LLDPE) or high density (HDPE).
• PVC is softer than PE. Thus, it is used mainly in solar cables.
• PVC has several advantages. It is fire resistance.
• However, it emits toxic gases after catching fire, which acts as a drawback when using PVC for cables.
• HFFR (HalogenFree Fire Retardant) materials :
• HFFR (HalogenFree Fire Retardant) materials are useful when the installation of cables is in confined places.
• These materials are fire-resistant and emit no harmful gases.
• Because of this, these cables are safer to use than PVC or PE.
• However, the mechanical properties of the HFFR materials are not as better as PVC or PE.
• These cables are also costly.
• But you can make use of these cables in places where fire protection is the priority since these cables have excellent functionality.

CHAPTER 3:  WHAT IS THE WIRING CONSIDERATION YOU SHOULD MAKE FOR SOLAR CABLES?

A wire is a single conductor that is either made of aluminum or copper. This wire can transfer electric current from the solar panel. Thus, you are going to need these wires to be able to connect the system.

But before the process of making renewable energy, you need to make sure that correct wiring and connections are selected.

However, you are required to give special consideration to safety. It should be your top priority. The kind of wiring you select should be according to national standards. Generally, these wirings are of two types:

• Single or solid wire:
• The individual or solid wire consists of a single conductor, which is either left bare or is either insulated by a protective sheath.
• It is useful for different applications, such as electrical wiring in homes, where the plastering takes place on the inside.
• Solid wires are cheaper than stranded wires.
• These wires also have a more compact diameter for the same ability of current-carrying as stranded wires.
• However, the solid wires are only available in small gauges.
• Stranded wire:
• Stranded wires are those which are composed of multiple thin strands of wires twisted together to form one single wire core.
• Stranded wires are useful in applications where there is frequent movement or even vibrations (i.e., robotics or vehicular applications).
• However, stranded wires have a larger diameter for the same carrying capacity as solid wires.
• Another drawback of stranded wires is that these wires are more expensive than solid wires.

CHAPTER 4: WHAT ARE THE DIFFERENT TYPES OF SOLAR CABLES USED?

A cable is the combination of two or more wires that are insulated and enveloped together in one jacket.

The number of conductors inside a cable and the cable diameter also vary. There may be one conductor or more, depending upon the requirement.

Thus, the classification of cables depends upon the number of conductors and the external diameter of the wires. Ranking includes:

CHAPTER 4.1:  SOLAR DC CABLES:

Solar DC cables are of two types:

• Module cables or string cables.
• DC main cables.

CHAPTER 4.2: MODULE CABLES OR STRING CABLES:

The module or string cables consist of suitable connectors integrated into the PV solar panels. In this type, you have very little influence on the type of cable used.

CHAPTER 4.3: DC MAIN CABLES:

DC cables are mainly useful for outdoor applications. In DC cables, special extension cables are used to connect the positive and negative wires from strings to the generator connection box.

The DC cables come with the cross-sectional areas of 2.5mm², 4mm², and 6mm², which depends upon the power output of the modules.

To make sure that there are no short circuits, do not lay the positive and negative wires together in the same cable. Single-wire cables with double insulation are a great solution and provide high reliability.

Those DC cables found between the modules and the generator connection box are two core cables. The double core cables consist of a negative blue wire and a current-carrying red wire.

An insulation layer surrounds both these wires. Furthermore, two designs are useful in connecting the PVC strings to the inverter of the solar system:

• System of node string.
• And the provision of a direct connection.

CHAPTER 4.4:  AC CONNECTION CABLES:

Alternating current (AC) connection cable is the solar cable that connects the solar power inverter to the electricity grid. It makes use of protective equipment.

Five core AC cables are useful in the case of three-phase inverters for connection to the low voltage grid.

The Alternating current (AC) connection cable links the solar power inverter to the electricity grid through the use of the protection equipment.

There is a construction of Three live wires for the three phases that carry the current. It consists of a neutral wire which carries current away from the device.

And a ground wire, also known as the safety wire that connects the casing of the device to the ground.

Three core cables are useful in the case of single-phase inverters. Three core cables consist of a neutral wire, one live wire, and a ground wire.

CHAPTER 5: WHAT ARE THE IMPORTANT FEATURES OF SOLAR CABLES?

Solar cables posses innumerous features:

• Solar cables are fast & Easily installed
• Solar cables possess color identification.
• The construction of solar cables follows new environmental regulations.

Some other properties of solar cables include:

CHAPTER 5.1: ELECTRICAL CHARACTERISTICS:

• Solar cables are designed to have a rated AC Voltage of 0.6/1 kV.
• The Rated DC Voltage of solar cables is 1.5 kV.
• Solar cables possess a maximum allowed DC Voltage of 1.8 kV.
• The maximum permitted AC voltage of solar cables is 0.7/1.2 kV.
• The working Voltage of the solar cables is DC 1000 V.
• The Insulation Resistance of solar cables is somewhere at 1000 MW-km.
• Spark Test for solar cables shows 6000 Vac (8400 Vdc).
• Solar cables can withstand a voltage of 6500 V for 5 minutes.
• The ampacity of the solar cables is as per the requirements for Photovoltaic system cables.

CHAPTER 5.2 THERMAL CHARACTERISTICS:

• The ambient temperature range of solar cables is -40 °C to +90 °C ambient,  and 120 °C on the conductor.
• Ambient temperature and conductor temperature is from the Arrhenius law. According to Arrhenius law, the aging of polymers doubles for every 10 °C rises.
• Solar cables can reach a maximum conductor temperature of 120°C (20000h).
• The short circuit temperature of the solar cables is 200°C.
• The thermal endurance test shows a temperature index of +120°C.
• Solar cables can also withstand high-Temperature Pressure.
• Damp – Heat Resistance Test for solar cables shows 1000 hrs. At 90°C with 85% humidity.
• The phase to ground DC voltage for solar cables is Uo1.5kVDC.

CHAPTER 5.3: MECHANICAL CHARACTERISTICS:

• Solar cables possess a minimum Bending Radius of 5 x OD when fixes and 15 x OD in occasional flexing.
• Tensile Strength of solar cables is 6.5 N/mm2 for insulation and 8 N/mm2 for sheathing.
• Elongation of Insulation and sheathing for solar cables is 125%.
• Solar cables are designed to have a life period of more than 25 years, even under harsh environmental conditions.
• The shrinkage test shows that solar cables shrink 2% at 120°C.
• The cables are RoHS, which means there is a restriction of certain Hazardous Substances for solar wires.

CHAPTER 5.4: CHEMICAL CHARACTERISTICS:

• Solar cables are mineral Oil Resistant.
• Ozone Resistance is another feature of solar cables.
• Solar cables are weather and UV Resistant.
• Solar cables are Ammonia resistant until 30 days in a saturated ammonia atmosphere.
• Solar cables possess excellent resistance to oil and chemicals.
• Solar cables can withstand loads and are abrasion-resistant.
• Acid & Alkaline Resistance is another property of solar cables.
• The types of insulation and outer sheathing makes solar cables flame retardant.
• In the case of fire, solar cables produce Low smoke emission, less than 20%.
• Solar cables are Halogen free.
• The acid gas emission of solar cables is not more than 0.5%.

CHAPTER 6: WHAT ARE THE DIFFERENT APPLICATIONS OF SOLAR CABLES?

There are a variety of applications for solar cables. These applications depend upon the type of insulation carried around the cable:

• For dry and indoor locations, THHN is useful.
• For wet outdoor applications in conduit, THW, THWN, and TW can be useful.
• For moist or underground applications UF and USE work efficiently.
• In outdoor conditions that are incredibly harsh and wet, PV Wire, USE-2, and RHW-2 cables are the best choices available.
• PV wire, USE-2, and THW-2 cables are also sunlight and UV radiation resistant. Thus widely used for outdoor applications.

Other applications of the solar cables include:

• For connecting the photovoltaic/solar power supply systems, solar cables are beneficial.
• The solar cables also possess great flexibility, which makes them extremely handy. Thus they can be used on the rooftops, on walls, etc.

Furthermore, in grounded PV systems, only USE-2 Solar wire is helpful. Use-2 power cables possess excellent resistance to crushing and impact.

But the photovoltaic wires are better than USE-2 cables since they offer great flexibility in terms of temperature resistance, sunlight resistance, and flame resistance.

The outer jacket or sheath of the photovoltaic wires is also thicker and better insulated than USE-2 power cables. Thus, in comparison, photovoltaic cables are better.

The THNN wire is mainly useful in solar industrial applications. But special consideration needs to be given when installing THNN wires.

THNN wires don’t have the additional strength like the specialized solar power cables, because of which these wires can fail. Thus, the THNN wires should not be put to use in main solar applications.

CHAPTER 7: HOW TO SELECT THE CORRECT SIZE OF SOLAR WIRES AND CABLES FOR YOUR SOLAR SYSTEM?

Selecting the correct cable size is of the utmost importance. You have to be extremely careful during the size selection of the solar cable.

This care is required because the correct selection of solar cables will ensure that there is no overheating, and the loss of energy is very less.

If you make use of the wrong size for solar cables, it will ultimately lead to dysfunction, such as short circuits or the production of fire.

CHAPTER 8: WHICH FACTORS DETERMINE THE SIZE OF SOLAR WIRES?

The size of the wire for solar cables depends upon two aspects:

• The generating capacity of the Solar Panel: This means that the higher the current produced, the more significant is the size of the cable.
• The distance of the solar panel system from the loads, meaning the higher the range, the more prominent will be the size of your cable.

You can choose a thinner wire for installation since it may cost less. But using a thicker wire size can benefit you in the longer run, since:

Thicker wire will provide additional safety and protection for your system.

You will not be worrying about the short circuits for a significant time.

Your solar cable will work efficiently, even in a very harsh environment, without you having to worry about its deterioration.

Furthermore, you can make use of a wire size calculator. The wire size calculator will allow you to figure out which size of solar cable will be best suited for your system.