Troubleshooting Solar Inverter Output Voltage Fluctuations

Key Takeaways

• The most likely causes for inverter output voltage fluctuations are an unstable utility grid or an overloaded inverter.
• The first check involves verifying both the incoming grid voltage and the total load connected to your inverter.
• Always disconnect all power sources (PV, battery, grid) before inspecting or tightening electrical connections.
• Stop DIY troubleshooting and contact a qualified technician if internal fault codes appear or if the problem persists after basic checks.

Why is your solar inverter's output voltage fluctuating?

Output voltage fluctuations from your solar inverter are often a sign of instability in your power system. Most commonly, these issues stem from an unstable utility grid supply or an overloaded inverter. It is crucial to identify the root cause quickly to prevent damage to your appliances or the inverter itself.

Diagnosis

Follow these steps to diagnose the cause of your inverter's output voltage fluctuations. Always prioritize safety by ensuring proper personal protective equipment (PPE) and disconnecting power when necessary.

1. Check the Inverter Display for Error Codes:

• • What to look for: Your inverter's display panel or monitoring app may show specific error codes related to voltage or frequency issues.
  • What it means:
  • • Grid Voltage/Frequency Errors: Codes like Solis's OV-G-V01 (Grid voltage exceeds upper range) or UN-G-V01 (Grid voltage exceeds lower range), Deye's F53 (AC line low voltage) or F56 (AC over voltage), Fox ESS's Grid Volt Fault or Grid Freq Fault, and GoodWe's VAC Failure or FAC Failure indicate a problem with the incoming utility grid supply.
    • Overload Errors: Codes such as Solis's Over-Load or OV-ILLC, Axpert VM III's 07 (Overload time out), Deye's F26 (AC over current fault of hardware), Growatt SPF ES's 07 (Overload time out), and Fox ESS's Over Load Fault or Eps Over Load suggest that the inverter is supplying too much power to the connected loads.
    • Internal Inverter Faults: Codes like Axpert VM III's 55 (Over DC voltage in AC output) or Growatt SPF ES's 55 (Over DC voltage in AC output) point to an internal issue within the inverter, requiring professional service.

2. Measure Incoming Grid Voltage and Frequency:

• • What to look for: Use a multimeter to measure the AC voltage and frequency at the point where the utility grid connects to your inverter or main electrical panel.
  • What it means:
  • • Fluctuating Grid Readings: If the voltage or frequency readings are unstable or outside the nominal range (e.g., 220V/230V for voltage, 50Hz/60Hz for frequency), the issue is likely with your utility supply.
    • Stable Grid Readings: If the grid readings are stable and within the acceptable range, the problem is likely internal to your solar system.

3. Measure Inverter Output Voltage and Frequency:

• • What to look for: With the inverter operating, use a multimeter to measure the AC voltage and frequency at the inverter's output terminals.
  • What it means:
  • • Fluctuating Output, Stable Grid: If the output voltage is fluctuating despite a stable grid supply, the inverter itself may be faulty or struggling with the connected load.
    • Output Matches Grid Fluctuations: If the inverter's output mirrors the grid's instability, the inverter is likely passing through the grid's poor quality.

4. Evaluate Connected Load:

• • What to look for: Compare the total power consumption of all appliances connected to the inverter's output with the inverter's rated output power. For example, an Axpert VM III 3KW model has a rated output power of 3KVA/3KW.
  • What it means:
  • • Overload: If the total load exceeds the inverter's continuous rated output power (e.g., 3KW for an Axpert VM III 3KW model) or its surge capacity (e.g., 2 times rated power for 5 seconds for Axpert VM III models), the inverter may struggle to maintain stable voltage. Inductive loads (motors, refrigerators) can cause high startup surges, triggering overload protection even if continuous power is within limits.
    • Balanced Load: If the load is well within the inverter's capacity, the voltage fluctuation is less likely to be load-related.

5. Inspect Wiring and Connections:

• • What to look for: Always disconnect all power sources (PV, battery, grid) before inspecting wiring. Check all AC output wiring connections for looseness, corrosion, or damage. Pay attention to terminal blocks and breaker connections.
  • What it means:
  • • Loose Connections: Loose or corroded connections can cause voltage drops and instability, especially under load. Tighten any loose terminals using insulated tools. A spanner across a battery bank can short hundreds of amps, so ensure tools are insulated and power is off.
    • Damaged Wiring: Damaged wiring can lead to intermittent connections or short circuits, causing voltage fluctuations.

Cause/fix table section

Inverter-Side Checks vs. Grid-Side Checks

When troubleshooting inverter output voltage fluctuations, it's important to distinguish between issues originating from the utility grid and those from your inverter or connected loads.

• Grid-Side Checks: If your inverter displays errors like OV-G-V01 (Solis), F53 (Deye), Grid Volt Fault (Fox ESS), or VAC Failure (GoodWe), the problem is likely with the incoming utility power. You should measure the grid voltage and frequency directly. If these are unstable, the inverter is simply reacting to an external condition. In such cases, the inverter may disconnect from the grid to protect itself and your loads.
• Inverter-Side Checks: If the grid supply is stable but your inverter's output voltage is fluctuating, the issue lies within your solar system. This could be due to an overloaded inverter, loose internal wiring, or an internal component failure. For example, if an Axpert VM III 5KW inverter is consistently drawing more than its 5KVA/5KW rated power, it will struggle to maintain stable output.

Safety

Working with solar inverters and electrical systems carries significant risks. Always observe the following safety precautions:

• Disconnect Power: Before performing any inspections or maintenance on wiring or internal components, always disconnect all power sources including the PV array, battery bank, and utility grid. Verify zero voltage with a multimeter.
• Insulated Tools: Use only insulated tools when working on electrical connections to prevent accidental short circuits or electric shock. A spanner across a battery bank can short hundreds of amps, leading to severe burns or explosions.
• Overload Protection: Inverters have integrated overload protection. For instance, GoodWe ET Series inverters will restart themselves if overload protection is triggered, with preparation time increasing up to one hour if overloads recur. Do not bypass these safety features.
• Breaker Sizing: Ensure all AC and DC breakers are correctly sized for your system. For example, Deye SG03LP1 3.6KW models require a 32A AC breaker for backup load, and Growatt SPF 5000 ES requires a 50A AC breaker. Incorrectly sized breakers can fail to protect equipment or trip unnecessarily.
• Professional Installation: Many inverter models, such as the Solis S5-EH1P-L, require an OCPD (Overcurrent Protection Device) for circuits connected to the inverter and an integrated DC switch. Ensure your system meets all local electrical codes and safety standards.

When to call a technician instead

While many basic troubleshooting steps can be performed by a homeowner, there are clear limits to DIY repairs. You should call a qualified solar technician if:

• Internal Fault Codes: Your inverter displays error codes that indicate an internal hardware failure, such as Axpert VM III's 55 (Over DC voltage in AC output) or Growatt SPF ES's 55 (Over DC voltage in AC output). These issues typically require specialized tools and expertise.
• Persistent Issues: The voltage fluctuations persist even after you have checked the grid, reduced loads, and inspected all accessible wiring connections.
• Safety Concerns: You are uncomfortable or unsure about any step in the troubleshooting process, especially those involving live electrical circuits.
• Warranty: Attempting to open the inverter casing or perform repairs not explicitly outlined in the user manual may void your product warranty. Most manufacturers recommend contacting authorized service personnel for internal repairs.
• Complex Grid Issues: If your utility grid is consistently unstable and causing inverter faults, a technician can help assess the situation and advise on solutions, potentially involving your utility provider.