Troubleshooting Solar Inverters

Solar Inverter Troubleshooting

In a solar power generation system, the inverter plays a central role as an "energy converter"—it accurately converts the direct current (DC) generated by Photovoltaic Panels into alternating current (AC) that can be fed into the grid or used by loads. A fault inthe inverter can paralyze the entire system, directly impacting power generation efficiency and profitability. For home users, small businesses, and maintenance personnel, mastering basic troubleshooting techniques can not only quickly restore system operations but also reduce unnecessary repair costs. This article will systematically analyze common fault types, causes, and solutions based on the core principles of troubleshooting, helping you easily address unexpected inverter issues.

First, Key Preparations Before Troubleshooting: Safety and Tools First

Safety is always paramount before any troubleshooting begins. Solar systems can generate high voltage even on cloudy days, and improper operation can lead to serious risks such as electric shock and equipment damage. Please ensure the following preparations are complete:

(I) Safety Precautions
Disconnect the AC side switch of the inverter (usually connected to the grid or load), then disconnect the DC side switch (connected to the PV array). Wait 5-10 minutes for the capacitors to fully discharge. Some inverter capacitors can have residual voltages of hundreds of volts, which can be fatal if directly touched.

Wear insulating gloves (rated voltage ≥ 1000V) and insulating shoes. Avoid wearing metal jewelry. Ensure the working environment is dry and free of water.

If you need to climb onto a rooftop to inspect PV panels or wiring, use a non-slip ladder and have someone accompany you for supervision. (II) Essential Tools

Basic troubleshooting doesn't require specialized equipment. The following tools are sufficient for most scenarios:

Digital multimeter (for testing voltage and resistance, with a recommended range of 0-1000V DC/AC);

Phillips/slotted screwdrivers (insulated handles preferred), wire strippers, and crimping pliers (for checking wiring security);

Flashlight (for inspecting wiring inside the device or in dark corners);

Inverter user manual (fault code definitions may vary between brands; the manual is the primary reference).

II. Five Common Fault Types: Symptoms, Causes, and Step-by-Step Solutions

Inverter faults are often indicated by signals such as a flashing warning light, a displayed fault code, or no output voltage. Different symptoms correspond to different root causes. The following are the five most common fault types reported by users in foreign trade scenarios and their troubleshooting methods:

(I) Fault Type 1: Inverter Unresponsive (Indicator Light Off, No Display)

Core Symptoms

After connecting to the DC/AC power supply, the inverter screen is black, all indicators are off, and there is no sign of startup.

Possible Causes

No DC input voltage: The PV array is not generating current, or the DC wiring is loose or broken.

Abnormal AC power supply: The grid is down, the AC switch is not closed, or it is damaged.

Device Fault: The inverter's internal fuse is blown, or the power module is damaged.

Troubleshooting and Solution Steps

Step 1: Check the grid and AC circuit.

Use a multimeter to check the voltage at the AC outlet or terminal blocks to confirm that the grid power is normal. Check that the AC switch (circuit breaker) is in the "closed" position. If the switch is tripped, try resetting it and observe whether the inverter starts. (If it trips repeatedly, check for overload issues and do not proceed.)

Step 2: Check the DC Input Circuit

Disconnect the DC switch and use a multimeter set to the DC range (≥800V) to check the PV array output voltage (refer to the inverter's rated DC input voltage range, e.g., 300-800V). If the voltage is 0, the PV panel wiring may be loose. Check each MC4 connector between the panels, unplug them, re-insert them, and tighten the latches. If the voltage on a particular PV panel is abnormal, it may be a faulty component. Mark the problem and contact customer service.

Step 3: Check the Inverter's Internal Fuses

If both the DC and AC voltages are normal, open the inverter's front cover (make sure the power is off and the inverter is fully charged). Locate the DC input fuse (usually marked "DC FUSE") and check if it's blown. (Glass tube models can be checked directly; ceramic models require a multimeter to verify continuity). If blown, replace the fuse with one of the same specifications (with the same current/voltage specifications as the original fuse; do not replace it with a larger one). If there is still no response after replacing it, the power module may be faulty and you should contact the manufacturer for repair. (II) Fault Type 2: Inverter Displays "Overvoltage/Undervoltage"
Core Symptoms
The screen displays "OV," "UV," or the corresponding fault code. The inverter automatically shuts down, and some models emit a buzzer alarm.
Possible Causes
Overvoltage: The PV array voltage exceeds the inverter's maximum rated DC input voltage (e.g., during strong midday sunlight, too many PV panels in series cause the total voltage to exceed the specified value).
Undervoltage: The PV panel voltage is lower than the inverter's startup voltage (e.g., during low sunlight in the early morning or evening, or too few PV panels in series).
Abnormal Grid Voltage: The AC output side grid voltage exceeds the inverter's tolerance range (e.g., excessive grid fluctuations).
Troubleshooting and Resolution Steps
Step 1: Identify the Fault Type (DC/AC)
Check the fault code description to determine whether it is "DC overvoltage/undervoltage" or "AC overvoltage/undervoltage." DC faults are related to the PV panels, while AC faults are related to the grid.

Step 2: Addressing DC Overvoltage/Undervoltage

Overvoltage: Disconnect the DC switch and reduce the number of PV panels in series (recalculate the total voltage to ensure it is below the inverter's maximum input voltage). If adjusting the number of panels is impossible, check for obstructions that may be causing voltage fluctuations on some panels. Remove the obstruction and restart the system.

Undervoltage: Increase the number of PV panels in series (ensure the total voltage is above the inverter's startup voltage, typically ≥100V). Insufficient sunlight is normal and requires no action; the problem will recover automatically with increased sunlight.

Step 3: Addressing AC Overvoltage/Undervoltage

Use a multimeter to check the grid voltage. If it exceeds the range of 220V ± 10% (single-phase) or 380V ± 10% (three-phase), contact the local power company for repairs. If the grid voltage is normal, the inverter's AC voltage detection module may be faulty, requiring manufacturer technical support. (III) Fault Type 3: Inverter Displays "Overload"
Core Symptoms
The inverter suddenly shuts down while operating under load, displaying "OL" or "Overload." It restarts after disconnecting the load, but the fault re-occurs upon re-connection.
Possible Causes
The actual load power exceeds the inverter's rated output power (e.g., multiple high-power appliances connected);
The load is short-circuited or leaking: for example, an internal short circuit in the appliance causes excessive transient current;
The inverter's output current detection module is generating a false alarm.
Troubleshooting and Resolution Steps
Step 1: Calculate Load Power
List the power of all appliances connected to the inverter. The total must be ≤ 80% of the inverter's rated power (allowing a safety margin). If overloaded, shut down some high-power devices (e.g., air conditioners, electric water heaters), leaving only essential loads. Restart the inverter to see if the inverter recovers.
Step 2: Check for short circuits/leakages in the load circuit
Disconnect all loads and connect a single low-power appliance (e.g., a desk lamp). If the inverter operates normally, the original load has a problem. Connect each appliance one by one to identify the "faulty load" and repair or replace it if found. If the overload persists even with a low-power load, use a multimeter to measure the resistance between the inverter output terminal and the ground wire. If the resistance is close to 0, the output wiring may be short-circuited. Check for damaged or exposed wiring.

Step 3: Troubleshoot the device itself

If the overload indication persists even when unloaded, the inverter's internal IGBT module may be damaged or the current detection is faulty. This requires professional inspection and repair; do not disassemble the inverter yourself.

(IV) Fault Type 4: Inverter Displays "Ground Fault"

Core Symptoms

The screen displays "GF" or "Ground Fault." Some models automatically trip the AC side switch, preventing grid connection.

Possible Causes

PV panel or DC line grounding: Module glass breakage, resulting in backplane grounding, or DC cable insulation damage contacting the metal bracket;

Poor internal inverter grounding: The ground terminal is not securely connected or the ground resistance exceeds the specified value;

Abnormal AC side grounding: The grid ground wire is loose or the grounding system is faulty.

Troubleshooting and Solution Steps

Step 1: Check the Inverter Ground Connection

Confirm that the inverter ground terminal (marked "PE") is connected to the ground electrode with a ground wire. Ensure that the ground wire is not broken or loose. Use a ground resistance tester to check the ground resistance (should be ≤4Ω, ≤10Ω in humid areas). If the resistance exceeds the specified value, re-make the ground electrode (for example, by increasing the length of the grounding element or adding a resistance-reducing agent).

Step 2: Check the DC Grounding

Disconnect the DC switch and remove the inverter DC input cable. Use a multimeter with the resistance range (megohm range) to check the resistance between the positive and negative terminals of the PV panel and the grounding bracket. Normally, it should be ≥10MΩ. If the resistance is too low, inspect the DC cables section by section: strip the cable insulation to check for exposed copper wire contacting metal. Inspect the PV panel backsheet for damage; any damaged modules should be replaced.

Step 3: Check the AC Grounding

Check the connection between the grid ground wire and the ground electrode to ensure they are secure. Poor grounding of other devices in the grid-connected system (such as the distribution box) may also trigger an inverter ground fault. Therefore, thoroughly inspect the grid grounding loop. (V) Fault Type 5: Significant Decrease in Inverter Power Generation
Core Symptoms
The inverter is operating normally (no fault code), but power generation has decreased by more than 20% compared to the same period in the past, or is significantly lower than similar systems in the same region.
Possible Causes
PV Panel Shading: Leaves, dust, or bird droppings cover the panel surface, affecting light absorption;
Inverter Efficiency Degradation: Aging internal capacitors and poor heat dissipation lead to reduced conversion efficiency;
Module Performance Degradation: PV panels are too old (over 10 years) and hot spots are present;
Loose Wiring: Poor contact between DC/AC wiring leads to power loss.
Troubleshooting and Resolution Steps
Step 1: Clean the PV Panels and Check for Obstructions
Rinse the panel surface with clean water (avoid using a high-pressure water gun) to remove obstructions such as dust and bird droppings. Check for new buildings or trees blocking sunlight. If so, remove any obstructions or adjust the panel angle.

Step 2: Check the PV panels and wiring.

Use an infrared thermometer to check the surface temperature of the PV panels. If one panel is significantly hotter than the others (a difference of ≥5°C), this could be a hot spot (caused by hidden cracks or obstructions) and the panel should be replaced. Check all wiring connectors and re-tighten any loose connections to reduce contact resistance.

Step 3: Check the inverter's heat dissipation and parameters.

Ensure that the inverter is clear and the cooling fan is operating properly (no abnormal noise or stalling). If the fan is faulty, replace it. Check the "Conversion Efficiency" parameter on the inverter's backend or app. If the efficiency is below 85% (normally ≥90%), it could be due to aging internal components and require contacting the manufacturer for inspection.

III. Advanced Troubleshooting: Fault Code Query and Manufacturer Support

Fault code definitions vary between inverter brands. If the general methods above don't cover all situations, you can use the following methods to accurately locate the problem:

(I) Fault Code Query Tips

First, consult the user manual: The manual will detail the meaning of all fault codes (e.g., "0102" for the Huawei SUN2000 series indicates a DC overvoltage, or "E006" for the GoodWe GW10K-MT indicates a ground fault) and provide specific solutions.

Visit the brand's official website support page: Most brands will update their fault code manuals under the "Technical Support" section of their official website. A PDF version can be downloaded for easy reference.

Using the inverter app/backend: Smart inverters allow you to view fault details via the mobile app or monitoring backend. Some platforms support a "one-click diagnosis" feature that automatically analyzes the cause of the fault.

(II) When should I contact the manufacturer's customer service? In the following situations, do not attempt to disassemble or repair the inverter yourself. Contact the brand's foreign trade after-sales team immediately:

The inverter emits smoke, has a burning smell, or shows obvious physical damage (such as a deformed casing or leaking liquid);

The fault recurs after replacing the fuse or adjusting the wiring;

The fault code is not listed in the manual, or the cause cannot be determined after troubleshooting;

The device is still under warranty (self-disassembly may void the warranty).

When contacting after-sales service, please provide the following key information: inverter model, serial number, fault code, installation date, troubleshooting steps, and results, so the manufacturer can quickly provide a solution.

IV. Daily Maintenance and Prevention: Four Key Points to Reduce Failure Rate

Compared to post-failure troubleshooting, daily maintenance can significantly reduce the probability of inverter failure and extend the life of the device:

Regular Cleaning and Inspection (once a month)

Clean dust from the inverter surface and ensure that the heat dissipation holes are unobstructed. Check the wiring connectors for looseness and oxidation (apply conductive paste if oxidation occurs) and check that the DC/AC switch is flexible. Pay attention to the operating environment.
The inverter should be installed in a well-ventilated, dry, and cool location (avoid direct sunlight and maintain an ambient temperature ≤ 40°C). Outdoor installations require a rain cover to prevent water from seeping in.
Monitoring system operating data
Check parameters such as power generation, input and output voltages, and conversion efficiency daily via the app. If any abnormalities occur (such as a sudden drop in power generation or excessive voltage fluctuations), investigate the cause immediately.
Regular firmware updates
Manufacturers use firmware updates to fix device bugs and optimize performance. Check the app or official website regularly to update the inverter firmware. (Be sure to power off the device before updating to avoid upgrade failures.)