My solar inverter won't start: 8 causes and how to diagnose

Your solar inverter won't power on. Before calling a tech ($350) or filing RMA (4 weeks), here are the 8 causes by probability and how to rule them out yourself.

1. Insufficient DC array voltage

Inverter needs a minimum voltage (typical 80-150 V) to start. Measure DC terminals with a multimeter. Lower reading: shaded panels, heavy dust, or a cut series-string panel.

2. Reversed polarity

+ where - should go and vice versa. Some inverters have protection and refuse to start; others burn instantly. Verify with multimeter: red lead to +, black to -. Reversed? Swap them.

3. Blown DC fuse

Between array and inverter or battery and inverter. Multimeter on continuity: if the fuse doesn't show a short, it's blown. Replace with same amperage. Blows again: short somewhere in the system.

4. Battery undervoltage (battery system)

Battery BMS tripped on over-discharge. Measure voltage: <11 V (12V), <22 V (24V), <44 V (48V), battery disconnected. Charge with external charger for hours to wake the BMS.

5. AC breaker tripped

Inverter produces AC but panel breaker is off. Inverter enters 'grid not detected' and shuts down. Check all branch breakers and main breaker.

6. Standby mode by config

Some inverters go to standby if no AC load detected. Plug a test LED bulb; should start on consumption. Find 'standby threshold' parameter in menu.

7. Extreme ambient temperature

Inverters in 122 °F shed go into thermal protection. Same at 14 °F. Move to ventilated spot or thermally isolate. Clean heatsink and verify fan works.

8. Corrupted firmware

After power cut or storm, firmware can corrupt. Soft reset: power off 5 min, on. Hard reset: service menu (manual). Nothing works: contact manufacturer to reflash firmware.

If problem is MPPT, read MPPT not detecting panels.