PV DC Cable Insulation and Sheath Materials: A Technical Guide

When evaluating photovoltaic DC cables, much of the attention is usually placed on the conductor. However, for long‑term outdoor PV applications, the insulation and outer sheath are equally important.

The outer layers of a PV DC cable are generally divided into two main parts:

• Insulation Layer – directly surrounds the conductor and primarily provides electrical insulation.
• Outer Sheath / Jacket – the outermost protective layer, primarily responsible for weather resistance, UV resistance, abrasion resistance, and mechanical protection.

For typical PV cables such as H1Z2Z2‑K, different insulation and sheath materials can be selected according to the required electrical, environmental, mechanical, and safety performance.

1. XLPE – Cross‑Linked Polyethylene

XLPE (Cross‑Linked Polyethylene) is a mature insulation material widely used in power cables.

Through a cross‑linking process, polyethylene forms a more stable molecular structure. Compared with conventional PE, XLPE generally provides improved:

• Heat resistance
• Electrical insulation performance
• Aging resistance
• Chemical resistance
• Dimensional stability

In PV cables, XLPE can be used for both the insulation layer and outer sheath, depending on the cable design and formulation.

However, an important distinction should be made:
XLPE does not automatically mean that a material is specifically formulated for photovoltaic applications.

For long‑term outdoor PV applications, the material formulation should also provide sufficient resistance to:

• UV radiation
• Ozone
• Heat aging
• Humidity
• Temperature cycling
• Outdoor weathering

The actual performance therefore depends not only on the base polymer, but also on the complete material formulation and applicable cable standard.

2. XLPO – Cross‑Linked Polyolefin

For modern photovoltaic cables, XLPO is an important material category.

XLPO stands for Cross‑Linked Polyolefin. Unlike a single specific polymer, XLPO refers to a family of cross‑linked polyolefin‑based materials whose formulations can be engineered for specific cable applications.

For photovoltaic applications, XLPO formulations can be optimized to provide:

• High UV resistance
• Ozone resistance
• Moisture resistance
• Heat resistance
• Low‑temperature resistance
• Good electrical insulation
• Long‑term outdoor weather resistance
• Good flexibility

For this reason, XLPO‑based materials are widely used in modern PV cable designs, including applications associated with PV1‑F and H1Z2Z2‑K cable standards.

A PV cable may be installed in environments such as:
Rooftops → PV mounting structures → Outdoor cable trays → Ground‑mounted solar farms

These installations expose the cable to long‑term:
UV radiation + high temperature + temperature cycling + moisture + ozone + rainwater

One of the advantages of XLPO is that its formulation can be engineered specifically to withstand these environmental stresses.

3. PO – Polyolefin

PO (Polyolefin) is a broader material family that includes polymers such as PE and PP.

In the cable industry, polyolefin‑based materials can be modified and formulated to provide:

• Good electrical insulation
• Low water absorption
• Chemical resistance
• UV resistance
• Good flexibility

However, an important distinction should be made:
Standard PO is not the same as XLPO.

XLPO undergoes a cross‑linking process and can provide improved thermal stability, environmental resistance, and long‑term performance under demanding conditions.

Therefore, when purchasing PV cables, simply seeing the term “Polyolefin” does not necessarily mean that the cable uses a high‑performance photovoltaic‑grade material. The complete material specification and applicable cable standard should always be checked.

4. PVC – Polyvinyl Chloride

PVC (Polyvinyl Chloride) is one of the most widely used insulation and sheath materials in the cable industry.

Its advantages include:

• Relatively low material cost
• Easy processing
• Good flexibility
• Good mechanical performance
• Adjustable flame‑retardant properties through formulation

However, for long‑term outdoor photovoltaic applications, PVC requires careful consideration.

Long‑term exposure to:
UV radiation + high temperature + oxidation + humidity
may cause certain PVC formulations to experience:

• Aging
• Hardening
• Cracking
• Surface degradation

Therefore: Standard PVC is generally not the preferred material for demanding long‑term outdoor PV cable applications. Nevertheless, PVC remains widely useful for indoor cables and applications where environmental requirements are less demanding.

5. EPR – Ethylene Propylene Rubber

EPR (Ethylene Propylene Rubber) is an elastomeric insulation material.

Its major characteristics include:

• Excellent flexibility
• High heat resistance
• Excellent moisture resistance
• Strong electrical insulation performance
• Ozone resistance
• Good environmental aging resistance

EPR is therefore important in certain high‑performance power cables and specialty cable applications.

One of its key advantages is its ability to maintain good performance under:
High temperature + moisture + demanding flexibility requirements

However, EPR is generally less common than polyolefin‑based materials in standard PV DC cable applications.

6. TPU – Thermoplastic Polyurethane

TPU (Thermoplastic Polyurethane) is a particularly interesting material for cable sheathing.

Its main advantages are related to mechanical protection, including:

• Excellent abrasion resistance
• Tear resistance
• Oil resistance
• Chemical resistance
• High flexibility
• Mechanical damage resistance
• Good low‑temperature flexibility

TPU can therefore be advantageous for cables exposed to repeated movement, dragging, bending, or mechanical friction.

Typical applications may include:

• Mobile equipment
• Robotic systems
• Solar tracking systems
• Specialized outdoor equipment

However, TPU is not necessarily the standard sheath material for every PV cable design.

7. LSZH / LS0H – Low Smoke Zero Halogen

LSZH (Low Smoke Zero Halogen), also written as LS0H, is better understood as a material performance category rather than one specific plastic.

Its primary objective is to reduce:
Smoke generation
Halogen‑containing gas emissions
during a fire.

LSZH materials can be particularly relevant for:

• Buildings
• Indoor electrical systems
• High‑occupancy areas
• Tunnels
• Data centers
• Specialized industrial facilities

Typical LSZH formulations focus on:
Low smoke + zero halogen + flame retardancy
rather than simply minimizing material cost.

What Functions Does the “Outer Layer” of a PV Cable Perform?

A simple way to understand a PV cable is:
The conductor carries electrical current, while the cable insulation and sheath protect the electrical system.

The insulation and sheath perform several critical functions.

1. Electrical Insulation

   The insulation layer separates the conductor from the external environment and helps prevent:
   Conductor‑to‑conductor short circuits, Contact with equipment, Accidental human contact, Leakage current and ground faults

2. Withstanding System Voltage

   For example, a 1500V DC PV cable must maintain stable electrical insulation performance under long‑term DC voltage stress. Therefore, material selection should consider parameters such as: Dielectric strength, Insulation resistance, Volume resistivity, Long‑term electrical aging performance. Mechanical strength alone is not sufficient to determine whether a material is suitable for a high‑voltage PV cable.

3. UV Resistance

   UV exposure is one of the major differences between conventional cables and photovoltaic cables. A conventional cable may be installed: Indoors / inside conduits / in protected cable trays. A PV cable, however, is often installed directly under sunlight. Long‑term exposure can create a combination of: UV radiation → heat → oxidation → material aging. Therefore, PV cable materials normally require formulations specifically designed for long‑term UV and outdoor weather resistance.

4. Resistance to Temperature Cycling

   A PV cable can experience: Low temperature in the morning → high temperature at midday → cooling at night. This thermal cycling may occur thousands of times over the service life of a solar installation. Therefore, cable materials should provide suitable: Thermal stability, Heat aging resistance, Low‑temperature flexibility.

5. Water and Moisture Resistance

   This is particularly important for: Agricultural PV systems, Ground‑mounted solar farms, Coastal projects, High‑humidity environments, Rooftop PV systems. PV cables can be exposed to: Rainwater + humidity + condensation. Therefore, water absorption and long‑term moisture resistance are important material considerations.

6. Ozone and Environmental Aging Resistance

   Outdoor PV cables are exposed not only to UV radiation, but also to ozone and other oxidative environmental factors. Over time, unsuitable materials may experience: Surface cracking → crack propagation → reduced insulation performance. For this reason, ozone resistance and environmental aging resistance are important parameters for long‑term outdoor PV cable applications.

7. Mechanical Protection

   During installation and operation, PV cables may experience: Pulling, Bending, Abrasion, Compression, Friction against mounting structures, Accidental stepping or impact. The outer sheath therefore provides more than simple insulation. It also serves as an important mechanical protection layer.

A Practical Way to Understand PV Cable Material Selection

For technical content aimed at EPC companies, PV module manufacturers, cable harness manufacturers, distributors, and solar project developers, it is better not to simply state that one material is “the best.”

A more professional approach is to evaluate the complete application:

The appropriate insulation and sheath material depends on the installation environment, system voltage, temperature range, mechanical stress, required service life, and applicable cable standard.

For PV cable procurement, it is therefore important to evaluate not only the polymer name, but also the complete material formulation, cable construction, test requirements, certification, and intended application environment.