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GoodWe Bus Voltage High

Updated June 2026 · Reviewed for technical accuracy · ~3 min read

Bus Voltage High (error 21) means the internal DC bus voltage inside your GoodWe rose above its safe limit, so the inverter shut down to protect its electronics. It very often tracks a PV string voltage that is too high, which is why it is closely related to PV Over Voltage. High voltage stresses components, so do not keep resetting it.

What causes it

  • A PV string that is too long. Too many panels in series, especially once the cold-weather voltage rise is counted, pushes the bus over the limit.
  • Cold, bright mornings. Panels make more voltage when cold, so the peak appears at the start of a clear cold day.
  • A sudden load or grid change that briefly spikes the bus.
  • An internal fault, if the strings are correctly sized and it still happens.

What to do, safely

Do not just keep clearing it Repeated overvoltage stresses the inverter. The right move is to find why the voltage is high, which usually means checking the string design.
  1. Note the conditions. If it appears on cold or very bright mornings, that strongly suggests string voltage rather than an inverter fault.
  2. Do not repeatedly reset. Let your installer look before clearing it again and again.
  3. Have the string sizing checked. Your installer compares the string's cold open-circuit voltage against the GoodWe's maximum DC input for your climate.
  4. If the string is within spec and it still trips, it is an internal fault for GoodWe service.

Quick decision flowchart

Bus Voltage High appears
↓ when does it happen?
❄️ Cold or bright mornings → likely string voltage. Have the string design checked.
🔁 Any conditions, string is correct → likely an internal fault.
↓
Either way, stop resetting and let your installer or GoodWe assess it.

Related GoodWe codes

PV Over Voltage Isolation Failure Over Temperature

FAQ

Bus Voltage High happens on cold mornings.

That fits a string that is borderline too long. Solar panels produce a higher open-circuit voltage when they are cold, so on a clear, cold morning the string voltage peaks and can push the DC bus over the limit. Your installer should check the string size against the inverter's maximum DC input for your lowest expected temperature.

Is my string too big?

It may be. If Bus Voltage High appears in cold or bright conditions, the number of panels in series could exceed what the GoodWe allows once the cold-weather voltage rise is included. Only an installer should re-check the string design and adjust it.

Helpful guides

Error codes explained How to safely restart your inverter Inverter overheating

Sources

  • GoodWe inverter user manual and error-message list (Bus Voltage High / error 21 = internal DC bus overvoltage; check PV string voltage and sizing).
  • General PV string-sizing and cold-temperature open-circuit voltage guidance.
⚠️ Safety disclaimer. Solar inverters carry lethal DC and AC voltage even when "off", and PV strings are live in daylight. This guide is educational only. String sizing changes and any wiring work must be done by a licensed installer or electrician.