How do I check my solar system is working properly?

The reliable test is a comparison of actual production against a forecast computed for your exact system — location, orientation, tilt, and the day’s real weather. Output tracking the forecast within a few percent means the system is healthy; a persistent gap of 15% or more across different weather is the signal worth investigating.

Why raw numbers mislead

Most owners judge their system by feel — “yesterday was sunny, only 18 kWh?” — but a single day’s total carries no verdict without knowing what that day should have delivered for that roof. Cloud, haze, heat and season move the achievable figure by multiples, so both false alarms and genuinely sick systems hide in raw daily totals. A per-system forecast removes the weather from the question: whatever the sky did, you compare against the same sky.

The daily curve’s shape is the second diagnostic. A healthy system draws a smooth bell (or a two-humped curve on east-west roofs); repeating dents at the same hour betray shading from a chimney or tree, a sagging afternoon can be an overheating inverter, and a flat top is clipping or an export limit — explained in a separate answer.

What to do

1. Run a forecast-vs-actual check over at least a week — one day proves nothing; a stable 15–20% shortfall in all weathers does.
2. Compare string currents in the inverter app — similar strings should track each other closely; one lagging points at a connector, diode or module fault.
3. Read the curve — same-hour dents = shading, afternoon sag = heat, flat top = clipping/export limit, sawtooth = overvoltage tripping (see the inverter shutdown answer).
4. Check the trivial before calling anyone — meter and monitoring online, no new soiling (dust, pollen, bird droppings), no breaker tripped.
5. Call the installer with data — a forecast-vs-actual chart plus string readings turns a vague complaint into a warranty case that is hard to deflect.