Earth Rod

Grounding in PV systems is one of the most frequently overlooked issues by PV installation personnel, especially in small-capacity PV systems where grounding and lightning protection are not given much attention.

However, if grounding is not done, errors can occur due to low insulation resistance to ground or excessive leakage currents, affecting power generation and potentially endangering personal safety. Additionally, unshielded or elevated metal parts are more susceptible to lightning strikes. Without grounding, equipment may be struck by lightning, causing significant damage to the PV power generation system.

Grounding in PV systems mainly includes grounding on the solar component side, inverter side, and distribution cabinet side. Proper grounding not only enhances the safety of the solar system but also extends its lifespan.

Galvanized steel is cheaper, but it has many welded joints, resulting in lower construction efficiency and higher construction costs. Pure copper has excellent conductivity but is expensive. Copper-bonded steel, however, only costs 9.4% more than galvanized steel and offers a much longer service life. Therefore, copper bonded steel electric earth rods are typically chosen as the primary grounding material in solar power systems.

Copper-bonded Steel

In photovoltaic power systems, the horizontal grounding body of copper-bonded steel grounding materials commonly uses Φ10-Φ12 copper-bonded round steel, with a manufacturing length typically of 100 meters per reel. The grounding electrodes use Φ14 or Φ17.2 copper-bonded steel rods.

Connection method: Thermite welding (no external power or acetylene needed), using pure copper for joint materials, with no need for anti-corrosion measures at the welding points.

Galvanized Steel

In traditional grounding grids, horizontal grounding bodies made of hot-dip galvanized steel are generally designed with specifications of 50X5 or 60X6 galvanized flat steel, with a manufacturing length of 6 meters per piece. Vertical grounding electrodes use 50X5 hot-dip galvanized angle steel or Φ50 galvanized steel pipes, with a grounding electrode length of 2.5 meters per piece.

Connection method: Electric welding, with the welding points needing anti-corrosion treatment, such as two coats of anti-rust paint and one coat of asphalt paint.

Bare Copper

For pure copper grounding materials, the horizontal grounding body usually uses 25×4, 40×4, 50×5, or 60×6 mm copper strips, or S70/S95/S120/S150/S185/S240 mm bare copper wires. The vertical grounding body typically uses 16×2500 mm or 20×2500 mm copper rods, or 50×3000 mm or 55×2500 mm pure copper electrolytic ion grounding electrodes.

Connection method: Thermite welding, fire mud melting welding, or hot-melt welding.

During construction, installing a ground rod is very flexible and can be adapted to the specific conditions on site. Various methods can be used, such as directly driving the electric ground rods into the soil with heavy hammers or electric hammers. In complex soil conditions where the rod cannot be driven in, a hole can be drilled first before installing the ground rod.

In uniform soil conditions, if using a heavy hammer for installation and driving a single rod, it is advisable to install a drill bit (impact-resistant bolt) on the pointed end of the rod to prevent damage to the copper layer when the rod is driven deep. For deeper grounding, multiple rods can be connected using connectors to achieve the desired length, ensuring good electrical connection.

In cases where deep drilling is difficult or impossible, drilling tools can be used to penetrate rocks. After drilling, there are two methods for installing the earth rods:
1. Connect the rods to the desired length using connectors. Once drilled to the intended depth, fill the hole with a resistivity-reducing agent and add water until the hole is filled.
2. Connect the rods to the desired length using connectors. After drilling to the intended depth, mix the resistivity-reducing agent with water and pour it into the hole to fully envelop the rod.

Component-side Grounding:

• Module Frame Grounding: The aluminum frame of the module contacting the mount does not mean effective grounding. The grounding hole of the module needs to be connected to the mount for effective grounding. The grounding holes of the modules are typically used for string connections, with the grounding holes at both ends connected to the metal mount.
• Mount Grounding: Usually, round steel, galvanized steel rods, or copper-bonded steel rods are used for grounding, with the grounding resistance required to be no greater than 4Ω.

Inverter-side Grounding:

• Operational Grounding: The PE terminal of the inverter is connected to the PE busbar in the distribution box, which is grounded through the distribution box.
• Protective Grounding: The grounding hole of the inverter chassis is used for repeated grounding to protect the inverter and the safety of operators. The protective grounding of the inverter chassis can either use a separate grounding electrode or share one with the distribution box.

Distribution Box-side Grounding:

• Lightning Protection Grounding: AC-side lightning protection consists of fuses or circuit breakers and surge protection devices (SPD). The lower end of the SPD is connected to the grounding busbar of the distribution box.
• Box Grounding: According to regulations, the metal frame and base steel of the distribution box must be grounded or connected to neutral. The cabinet door and the cabinet body need cross-connection to ensure reliable grounding.