Common Solar System Issues Diagnostic

Overview

Common problems on residential solar PV systems + their root causes. Diagnostic tree for the most-encountered service calls.

Issue 1: System not producing at all

Cause: Complete shutdown

Check:

1. AC disconnect: open or closed?
2. DC disconnect: open or closed?
3. Inverter display: showing power? error?
4. Service panel breaker: tripped?
5. Grid power: utility on?

Most common: someone manually turned off a disconnect, or breaker tripped.

Fix: close disconnects + breakers; verify safe operation.

Issue 2: Inverter shows red fault light

Cause: Various; check error code

Common faults:

Ground fault:

• DC ground somewhere
• Diagnostic: isolate strings, locate ground

Grid voltage out of range:

• Utility voltage too high or low
• Diagnostic: measure utility voltage
• Fix: contact utility if persistent

Grid frequency out of range:

• Rare; utility issue
• Fix: contact utility

DC overvoltage:

• Panel voltage too high
• Cold weather can cause this
• Diagnostic: measure DC at panel string

DC undervoltage:

• Panel voltage too low
• Cause: poor light, shading, panel issues
• Diagnostic: measure DC

High temperature:

• Inverter overheating
• Cause: hot location, inadequate ventilation
• Fix: improve ventilation

Issue 3: Inverter fan running constantly + loud

Cause: Inverter running hot

• Hot ambient
• Dirty cooling fins
• Failing capacitor

Diagnostic + Fix:

1. Clean dust from cooling fins
2. Verify clear air around inverter
3. Check ambient temp
4. If persistent: schedule replacement

Issue 4: Production well below expected

Cause: see "Diagnose Production Drop" HowTo

Likely:

• Soiling
• Shading
• Component failure
• Monitoring error

Issue 5: Bird droppings causing production loss

Cause: Birds nesting on/near panels

• Solar panels attract birds (warmth, height)
• Droppings shade panels

Mitigation:

• Clean droppings off panels
• Install bird guards (mesh screens at panel edges)
• Some products specifically for solar (PE solar mesh)

Issue 6: Squirrels chewing wiring

Cause: Squirrels living under panels

Common in wooded areas + during nesting season.

Damage:

• Bare DC cables (shock hazard if exposed)
• Reduced production
• Eventual arcing + fire risk

Fix:

• Trim trees overhanging panels
• Bird guards block squirrel access
• Wire mesh around panel perimeter

Issue 7: Monitoring system offline

Cause: Connectivity issue

• WiFi disconnected
• Cellular module failed (some inverters)
• Inverter hardware failure

Diagnostic:

1. Verify inverter is producing (check display, AC at panel)
2. Check WiFi network
3. Restart inverter monitoring module
4. Re-pair to network

Fix:

• WiFi reset
• Range extender if signal weak
• Cellular module replacement if applicable

Issue 8: One string producing less than others

Cause: String-specific issue

• Shading on string panels
• Bad cable in string
• Single bad panel

Diagnostic: measure each panel's voltage; identify outlier.

Fix:

• Single bad panel: replace
• Bad cable: replace
• Shading: trim trees

Issue 9: System produces below expected on bright days

Cause: Inverter clipping (under-sized)

• Panel DC peak exceeds inverter AC rating
• Inverter "clips" at maximum AC output
• Normal at noon on sunny days IF undersized

If happening only at peak sun: normal, expected.

If happening throughout midday: inverter undersized; upgrade if customer requests.

Issue 10: Grid voltage out of tolerance

Cause: Utility voltage variations

• Utility lines undersized for solar
• Long distance from substation
• Solar pushing voltage up further

Symptom: inverter shuts off intermittently.

Fix:

• Contact utility
• Utility may install voltage regulator
• Sometimes requires utility line upgrade

Issue 11: Panel cracked / glass damaged

Cause: Hail, fallen branches, impact

Diagnostic:

• Visual inspection from below + above
• Performance test of suspect panel
• Hot spot check with IR

Fix:

• Replace damaged panel
• Insurance claim (homeowner's policy)
• Manufacturer warranty if defective

Issue 12: System auto-shutdown when utility loses power

Cause: Anti-islanding (this is correct behavior)

• Inverters required to shut down during grid outage
• Prevents back-feed (utility worker safety)
• This is mandatory NEC behavior

Customer who wants power during outage:

• Add battery storage system
• Add transfer-switch + generator
• Otherwise: solar is grid-tied + offline during outages

Issue 13: Smoke or burning smell

Cause: Electrical fault

• Loose connection arcing
• Damaged wire
• Inverter internal failure
• Panel internal short

URGENT: shut down system, locate source, repair.

Issue 14: Battery (if installed) not charging from solar

Cause: Hybrid inverter or charge controller issue

• Battery full (no need to charge)
• Battery management system error
• Inverter battery mode disabled

Diagnostic:

• Check battery state of charge
• Verify hybrid inverter mode (some have grid-charge vs solar-charge modes)
• Review battery error codes

Issue 15: Customer says system has insurance question

For storm-damaged systems:

• Document damage with photos
• Provide repair quote
• Coordinate with insurance company (customer's responsibility primarily)
• Manufacturer warranty for materials, customer's homeowner insurance for damage

Diagnostic equipment checklist

For solar service calls:

• Multimeter (DC + AC capable, 600V+)
• Clamp meter (DC current)
• IR camera (optional but helpful)
• Insulation tester (megger) for diagnosing shorts
• Ground continuity tester
• Pyranometer (irradiance) for performance comparison

Customer maintenance contract value

A monthly or annual maintenance contract:

• Includes annual cleaning + inspection
• Includes diagnostic + minor repair (without parts)
• 80-90% reduction in unexpected failures

Excellent customer retention + revenue stability.

References

• NABCEP troubleshooting curriculum
• Manufacturer service manuals
• NEC Article 690
• Manuall internal: Diagnose Solar Production Drop