Guide
A diagnostic decision tree for production drops, from normal weather variance to inverter replacement.
Low solar production is a symptom, not a diagnosis. The right next step depends on whether output is zero, lower than seasonal expectation, isolated to one panel, or only visible on the utility bill. This guide walks through a decision tree before you pay for cleaning, service, or replacement.
Solar ROI Explained
Expected solar production
NREL PVWatts
Used as the benchmark framework for monthly expected production by system size, tilt, azimuth, weather, and location.
Monitoring diagnostics
Enphase and SolarEdge monitoring documentation
Used for panel-level, string-level, communication, and inverter-status troubleshooting concepts.
Maintenance and safety
NREL PV O&M resources and NEC Article 690
Used to separate homeowner observation from qualified electrical diagnostics.
Utility billing context
EIA and utility net-metering/net-billing tariffs
Used to distinguish actual production loss from billing, rate, or export-credit changes.
Data Sources Related Guides Next Steps FAQ Related Links
Compare production kWh, not just bill dollars. Utility bills can rise because rates changed, household use increased, export credits fell, or billing periods shifted. Open the monitoring portal and compare daily and monthly kWh with the same period last year. If the monitoring data is unavailable, check whether the gateway or internet connection has failed before assuming the solar system is underperforming.
Shorter winter days, cloudy periods, smoke, storms, and high module temperatures can lower output without any equipment fault. Use PVWatts or the original installer estimate to compare against expected monthly production, not the best summer month. A 20% month-to-month change can be normal across seasons. A persistent 20% gap against the expected month after weather adjustment deserves investigation.
Zero production points toward inverter, breaker, AC disconnect, grid, or monitoring issues. A smooth but lower curve suggests weather, soiling, shade, clipping changes, or degradation. A sudden midday drop can point to string or inverter behavior. One panel or one optimizer underperforming points toward module-level hardware, shade, or wiring. A normal production curve with a higher bill points toward consumption or tariff changes.
Look from the ground for new shade, heavy soiling, snow, visible debris, or damage. Trees and neighboring construction can create a new shade profile after installation. Soiling usually affects the whole array or a visible portion of it. Snow can block output until it slides off. Do not climb on the roof or open equipment; collect photos and monitoring screenshots for the installer.
Call the installer or a licensed solar electrician if production is zero on clear days, the inverter shows red or fault status, the solar breaker trips repeatedly, arc-fault messages recur, or panel-level monitoring shows one device offline for several days. If the inverter is near its planning-life window, estimate replacement cost and check warranty coverage before approving paid work.
Diagnose before paying for service