Signs Your Solar System Is Underperforming
Last updated: 2026-04-06 · Solar Benchmark
Signs Your Solar System Is Underperforming
The clearest sign of solar underperformance is a production shortfall against a physics-based benchmark for your system size and location. Seven other signs are more practical to spot without a benchmark tool: your electric bill hasn't changed since installing solar, production has declined year-over-year faster than expected, your monitoring app shows unexplained gaps, or a summer month produced less than a spring month with no storm to explain it.
Seven Signs to Watch For
| Sign | What It Looks Like | Likely Cause |
|---|---|---|
| 1. Electric bill unchanged after solar | Billing shows same usage as before installation | System not producing or not properly interconnected |
| 2. Production declines faster than 1%/year | Year 3 shows 8% less than year 1 | Accelerated degradation, wiring issue, or panel failure |
| 3. Monitoring shows production gaps | Zero or near-zero output during daylight hours | Inverter fault, tripped breaker, disconnect open |
| 4. Summer month below spring month with no weather explanation | August produces less than April | New shading, inverter clipping, or panel failure |
| 5. Specific yield 20%+ below regional benchmark | Boston 6kW system producing 5,900 kWh vs. 7,450 benchmark | Multiple causes; needs full investigation |
| 6. Inverter fault codes recurring | Same fault code appears monthly | Hardware fault, grid connection issue, wiring problem |
| 7. Sudden step-change drop after a storm | Post-hailstorm production permanently 10% lower | Panel physical damage |
Sign 1: Your Electric Bill Hasn't Changed
A new solar system that doesn't reduce your electric bill requires immediate investigation. Possible causes:
- Interconnection not complete: The utility interconnection approval is separate from installation. Some systems are installed but not legally permitted to export energy for weeks or months. Check your utility account for net metering enrollment confirmation.
- Inverter not operating: New inverter installations sometimes require configuration. Check the inverter display or monitoring app on a sunny day to confirm it's producing.
- Usage offset: If your electricity consumption increased significantly after installation (new EV, added HVAC, new occupants), solar production may be masking usage growth. Calculate production in kWh and subtract from your consumption to verify.
Sign 2: Year-Over-Year Production Decline Above 1%
Calculate annual production in kWh for each full year the system has been operating. Normal PERC panel degradation is about 0.5%/year. If your year-over-year decline averages above 1%, something is reducing output beyond normal aging.
Faster-than-expected decline causes:
- Accumulated soiling that goes without cleaning for multiple years
- Increasing tree shading as trees grow
- Microinverter failures that aren't triggering visible alerts (common after year 5–7)
- Panel degradation accelerated by heat in high-temperature climates
Sign 3: Production Gaps in Monitoring Data
Pull 90 days of hourly production data. Any period showing zero or near-zero production during daylight hours is a gap event. One gap event may be a transient fault that self-corrected. Multiple gap events suggest a recurring problem:
- String inverter trips: Multiple gap events from a string inverter typically indicate a grid frequency or voltage issue, or a hardware fault reaching its tolerance threshold.
- Microinverter outages: Panel-level monitoring showing one panel at zero output for multiple days indicates a failed microinverter, not a panel problem.
Sign 5: Specific Yield 20%+ Below Regional Benchmark
Calculate specific yield by dividing annual kWh by system size in kW. Compare to the regional benchmark in the table on the solar production by system size page. A 20%+ shortfall is significant and warrants a full site inspection.
Typical regional benchmarks for a 6kW system:
- Arizona: ~11,200 kWh/year (specific yield ~1,867 kWh/kW)
- California coast: ~9,430 kWh/year (~1,572 kWh/kW)
- Texas: ~9,440 kWh/year (~1,573 kWh/kW)
- Mid-Atlantic: ~8,040 kWh/year (~1,340 kWh/kW)
- New England: ~7,450 kWh/year (~1,242 kWh/kW)
What Data to Collect Before Calling Your Installer
Documenting the problem before calling saves time. Collect:
- Monthly production data for the last 24 months (from your monitoring app or utility bill)
- Any inverter fault codes visible on the physical display or in the app
- The date any production change began
- Any recent events near that date: major storms, construction nearby, new trees or structures
- Your system's installed specifications (system size in kW, panel model, inverter model)
An installer who can't explain a 20%+ underperformance gap with specific data is not doing a complete diagnosis.
Frequently Asked Questions
Q: How do I know what my solar system should produce so I can tell if it's underperforming?
A: The benchmark depends on your system size and location. A physics-based model using actual hourly weather data at your address calculates expected monthly production. Compare that to your monitoring app's actual production. The gap between expected and actual is the diagnostic number. Learn how proper benchmarks are calculated at /resources/methodology.
Q: My installer says my system is performing normally but I think production is low. What now?
A: Ask your installer for a specific comparison: actual production vs. expected production using actual weather data at your address, not a TMY estimate or the original proposal estimate. If they can't provide weather-corrected expected production, the "performing normally" claim isn't based on complete data.
Q: Can underperformance void my warranty?
A: No. Underperformance doesn't void a warranty; it may trigger it. Panel warranties typically cover output degradation exceeding 0.5–0.7%/year. If your panels show accelerated degradation, document it with annual production data and submit a warranty claim with specifics. Most claims fail because homeowners can't demonstrate the baseline.
Q: How long should I wait before concluding a new system is underperforming?
A: Wait 12 months to have a full seasonal cycle for comparison. A system that seems low in month 2 may be fine over the full year. If after 12 months your specific yield is 15%+ below the regional benchmark, investigate. Don't wait for year two.
Data: pvlib physics modeling + Open-Meteo ERA5 weather data | Last updated: 2026-04-06 | Solar Benchmark