Look for a screen light or status LED on the inverter/battery. If blank, check the solar/battery switches & the relevant circuit breaker in the switchboard.
This test is performed by connecting a DC clamp meter around one of the string conductors, or by momentarily connecting the multimeter (set to the DC amperage range) across the terminals, provided the meter's rating exceeds the panel's $I_ {sc}$.
This includes an initial voltage check after charging, investigating individual cell groups, assessing cell health, testing under load conditions, and monitoring self-discharge. You can also use a multimeter to check internal resistance.
You can know how much electricity your solar panels are generating by using a solar power meter or monitor, which measures the kilowatt-hours of your solar system's production.