Signs Your Solar
Inverter Is Failing

If your monitoring app shows strong morning production that drops sharply between 1–4 PM — especially on hot days — your inverter may be thermally throttling. This is the most common inverter symptom in the Central Valley. String inverters mounted in garages can reach 130°F+ in Fresno summers, triggering thermal protection that reduces or halts output.

Modern inverters (SolarEdge, Enphase, SMA, Fronius, Growatt) display error codes when something is wrong. Common codes include: Grid Fault (utility voltage or frequency out of range), Ground Fault (insulation failure in DC wiring), Arc Fault (DC arc detected — fire risk, requires immediate attention), Isolation Fault (ground fault in panels or wiring), and Temperature Fault (inverter overheating). Any error code should be investigated — even if the system appears to be producing power.

If your inverter frequently disconnects from the grid and reconnects — visible as gaps in your monitoring data — it may be detecting grid voltage or frequency fluctuations that are outside its operating range. This can be caused by a failing inverter, a loose AC connection, or actual grid instability. It can also be caused by a failing capacitor bank inside the inverter that causes the inverter to lose its grid reference.

A healthy inverter produces a faint, steady hum. Unusual sounds — buzzing, clicking, rattling, or high-pitched whining — indicate internal component failure. Buzzing often indicates a failing capacitor. Clicking may indicate relay failure. Rattling suggests a loose internal component. These sounds should be investigated promptly — a failing inverter can cause a fire if the failure involves the DC side of the system.

Inverters generate heat during operation and are designed to dissipate it through their housing. A warm inverter is normal. A hot inverter — one that is uncomfortable to touch — is not. Excessive heat indicates either that the inverter is working harder than it should (possible internal fault) or that its cooling system has failed (blocked vents, failed fan). Either condition accelerates component degradation.

If your panels are clean, there's no new shading, your monitoring is working, and your production is still 15–30% below expected — the inverter is the most likely culprit. Inverter efficiency degrades over time, particularly in the capacitor bank and MPPT (Maximum Power Point Tracker) circuits. A degraded MPPT may fail to find the optimal operating point for your panels, leaving significant production on the table.

String inverters are typically warranted for 10–12 years and have a realistic service life of 10–15 years. Microinverters (Enphase, APsystems) have a longer service life — typically 20–25 years — but individual units can fail earlier. If your inverter is approaching or past its warranty period, proactive replacement is worth considering — especially before adding battery backup or expanding your system.