What are the Differences Between DC Cables and AC Cables? Which Type is Used for Photovoltaic Cables?

What are the Differences Between DC Cables and AC Cables? Which Type is Used for Photovoltaic Cables?

一. What is a Photovoltaic Cable?

Photovoltaic cables are specially designed for use in photovoltaic (solar power) systems. They are mainly used to connect solar panels (photovoltaic modules) to inverters, distribution systems, and other electrical devices. Since photovoltaic systems are typically used outdoors or in harsh environments, photovoltaic cables need to have certain weather resistance, UV resistance, high-temperature tolerance, and mechanical damage resistance properties.

The main features of photovoltaic cables include:

1. UV Resistance: Photovoltaic cables are usually highly resistant to ultraviolet (UV) rays, as they need to be exposed to sunlight for long periods.

2. High-Temperature Resistance: The outer sheath of photovoltaic cables is typically made of high-temperature resistant materials, capable of withstanding high environmental temperatures and preventing aging under high temperatures.

3. Corrosion Resistance: Since photovoltaic cables are often exposed outdoors, the materials must be highly resistant to corrosion, able to withstand factors like rain, humidity, and salt mist.

4. Mechanical Damage Resistance: The design of photovoltaic cables must also take into account external forces, such as handling, installation, wind, and rain. Therefore, they are generally designed to have strong tensile and compressive strength.

5. Safety: Since photovoltaic cables are used for power transmission, they must meet strict safety standards to ensure there are no issues like short circuits or leakage.

Common photovoltaic cable models include TÜV-certified solar cables (such as single-core and multi-core cables), typically made from copper conductors and high-strength insulating materials, in compliance with international standards (e.g., IEC 60216, IEC 60227, UL 4703, etc.).

The outer sheath of photovoltaic cables is often made from materials like XLPE (cross-linked polyethylene) and TPE (thermoplastic elastomer), which offer excellent electrical performance and durability.

二. Are Photovoltaic Cables DC or AC?

Photovoltaic cables are primarily used for Direct Current (DC) circuits.

In a photovoltaic power system, solar panels (photovoltaic modules) generate direct current (DC), which is transmitted via photovoltaic cables to the inverter. The inverter’s role is to convert the DC into alternating current (AC), which is then fed into the grid or used for household and industrial power supply.

Thus, photovoltaic cables mainly carry direct current in the system and are commonly referred to as DC Solar Cables.

However, in some applications, if the connection is from the inverter to the distribution system or load, AC cables may be used. But in a photovoltaic power system, the main cables are generally DC cables.

三. Differences Between DC Cables and AC Cables

The primary differences between DC cables (Direct Current Cables) and AC cables (Alternating Current Cables) lie in their application scenarios, design requirements, and electrical characteristics. Although they share many similarities in basic structure (such as conductors, insulation layers, and outer sheaths), the different characteristics of DC and AC currents require distinct design considerations.

Here are the main differences between DC and AC cables:

1. Current Type

   • DC Cable: Used to transmit direct current (DC). The direction of DC is constant, and the voltage remains stable.
   • AC Cable: Used to transmit alternating current (AC). The direction and magnitude of AC current vary periodically, usually in a sinusoidal waveform, with current direction and amplitude changing over time.

2. Electrical Characteristics

   • DC Cables:
     • Constant Current: DC cables carry unidirectional current, and the voltage is typically stable.
     • Electric Field Distribution: As DC current does not vary periodically, the electric field distribution is simpler, and the cable's insulation design needs to consider uniformity of the DC electric field.
     • Material Requirements: DC cables typically need to be resistant to corona discharge and require superior insulation properties, as DC current places higher demands on insulation.
   • AC Cables:
     • Periodic Variation: AC current varies periodically, with voltage and current reversing direction in each cycle, so AC cables must withstand the reversal of the electric field.
     • Inductance and Capacitance: AC cable design must account for inductive, capacitive effects, and electromagnetic interference (EMI). High-frequency AC currents can produce strong electromagnetic fields, requiring appropriate electromagnetic shielding or sheath designs.
     • Corona Effect: AC currents can sometimes cause corona discharge, so cable design needs to provide enhanced insulation to prevent damage from the corona effect.

3. Conductor Material

   • The conductor materials of both DC and AC cables (typically copper or aluminum) are roughly the same. However, in high-voltage AC cables, more complex techniques like multi-strand wire weaving or shielding are used to reduce current loss and electromagnetic effects.

4. Insulation Layer

   • DC Cables: The insulation material of DC cables must withstand constant voltage, requiring higher voltage resistance and designs that prevent dielectric breakdown due to DC electric fields.
   • AC Cables: The insulation design of AC cables must consider the effects of alternating electric fields and may need better electromagnetic interference (EMI) resistance, especially for high-frequency or high-voltage AC applications.

5. Frequency Response

   • DC Cables: DC cables have no frequency concerns, as the current is unidirectional and the frequency is zero.
   • AC Cables: AC cables must account for frequency effects. High-frequency AC current can induce the skin effect, causing the current to flow along the surface of the conductor, thereby increasing resistance and energy loss.

6. Application Scenarios

   • DC Cables: Primarily used in DC power sources such as photovoltaic power systems, DC transmission systems, and batteries.
   • AC Cables: Primarily used for transmitting alternating current, widely applied in residential, industrial power distribution networks, power systems, and other areas requiring AC current.

7. Outer Sheath and Structure

   • DC Cables: The outer sheath of DC cables typically has higher environmental adaptability requirements, especially for outdoor exposure, and needs to be UV-resistant, high-temperature-resistant, and corrosion-resistant.
   • AC Cables: The outer sheath design of AC cables focuses more on electrical safety, insulation protection, and resistance to electromagnetic interference.

Summary:

• DC Cables: Specifically designed for transmitting direct current, with greater consideration for electric field distribution and insulation requirements. Typically used in photovoltaic systems, electric vehicles, energy storage systems, etc.
• AC Cables: Designed for transmitting alternating current, with attention to frequency variation, skin effect, and electromagnetic interference. Widely used in power systems and residential and industrial power supply.

Therefore, although DC and AC cables may appear similar in structure, their design and use cases are quite different.