Your app (Enphase, Tesla, SolarEdge, or your PPA provider's) shows production and, with a battery, storage behavior. The one metric that matters: production versus the same period last year. Weather varies, seasons swing — but if production drops significantly in a short window or year-over-year with similar weather, a panel or inverter likely needs service. That's genuinely the only failure mode solar-only systems really have.
Battery acting weird? Check the mode first — standby/backup (saves for emergencies), self-consumption (drains nightly), and time-of-use (follows rate schedules) behave completely differently, and a mode switch is the #1 "my battery is broken" false alarm. Not charging fully or dumping too fast on the right mode? Something's pulling more power than it can serve, or it needs service. Then you call — and if your installer is gone, that's what I'm here for.