What your inverter actually does
Solar panels produce direct current (DC). Your inverter converts this to alternating current (AC) — the form of electricity used in your home and exported to the grid. The inverter also monitors and records system performance, which is why it is the first place to check when something seems wrong.
Most modern inverters have a small display showing live and historical data. Many also connect to an app or web portal (SolarEdge, SMA Sunny Portal, Enphase Enlighten, Growatt ShinePhone, GivEnergy) which gives richer historical views and alerts.
The key readings and what they mean
Current output (W or kW). This is what your panels are generating right now. On a clear summer afternoon, a 4 kW system should be producing 3,000–4,000 W. On a cloudy winter morning, 200–500 W is normal. What matters is whether the reading makes sense given the current weather conditions.
Today's yield (kWh). The total electricity generated since midnight. Compare this to previous clear days at the same time of year — your inverter or app will usually show historical comparisons. A sudden unexplained drop on a clear day is the earliest warning sign of a problem.
Total yield (kWh). Cumulative generation since installation. Useful for calculating how much the system has saved, and for checking annual totals against expected performance for your location and system size.
Fault or error codes. These appear as F-codes, E-codes, or status messages depending on the manufacturer. A brief fault that clears itself is often harmless (a brief grid voltage fluctuation, for example). A persistent fault code, or one that appears repeatedly, needs investigation.
Spotting genuine underperformance
The most reliable diagnostic is consistent output below what you would expect on clear days. Most inverter apps allow you to overlay weather data on output graphs — if your system is generating significantly less than comparable clear days in the same month last year, something has changed.
Common causes in order of likelihood: panel soiling (the cheapest fix), partial shading from a new obstruction, a failing or degraded panel, a loose DC connector or cable fault, an ageing inverter.
Start with the cheapest intervention: a professional panel clean removes soiling as a variable. If output does not recover after a clean, the next step is a visual inspection of the panels from the ground for obvious damage, followed by a qualified solar engineer if no cause is visible.
When to call someone
Call your installer or a solar engineer if: a fault code persists for more than 24 hours; output is more than 25% below expected levels on multiple clear days in a row after panels have been cleaned; the inverter display is blank or unresponsive; you hear unusual sounds from the inverter unit; or the inverter is more than 10 years old and output has declined steadily.
Solar cleaners are not electricians and cannot diagnose inverter faults or panel electrical issues. If your inverter is showing a fault code, that is a job for an MCS-certified solar installer or electrician — not a cleaning visit.