Troubleshooting
Solar inverter fault finder
Pick what your inverter is doing to see the likely causes, the checks you can make safely from outside the equipment, and the point where it becomes a job for a qualified installer.
Before you touch anything
- Solar panels produce DC voltage whenever light reaches them. Switching off the DC isolator does not make the cable between the panels and the isolator safe.
- String voltages are commonly several hundred volts DC, and a DC arc does not go out by itself the way an AC arc can.
- Batteries in hybrid systems can deliver very large fault currents even when everything is switched off.
- Shut the system down using the sequence in your inverter's manual. Only a qualified installer should open the inverter, disconnect DC connectors or test insulation.
Inverter is off, blank, or will not start
Common alarm names: No display, Waiting, PV voltage low, No PV input. Names and codes differ by manufacturer, so match yours against your inverter's manual.
Likely causes
- Not enough light: inverters need a minimum DC voltage to start, so they stay off at night and can be slow to start at dawn or under heavy cloud.
- The DC isolator is switched off.
- A blown string fuse or an open connection somewhere in a string.
- The AC side is isolated or its breaker has tripped. Many grid-tie inverters will not start without grid power.
- An internal inverter fault.
Safe checks you can make
- Check it is daylight and the panels are not shaded or covered.
- Check the DC isolator and the AC isolator and breaker are on.
- If the inverter shows per-string readings (on screen or in its app), see whether one string reads zero while others read normally.
When to stop and call an installer
If a string reads zero volts in full sun, there is an open circuit or blown fuse in it. Finding it means working on live DC cabling: call your installer.
Checking whether output is really low? The solar panel output calculator estimates what your array should produce.