Common Solar Faults and Early Warning Signs (Rooftop Solar in India)

Most rooftop solar problems don’t start as “big failures”. They start as small, easy-to-miss symptoms, slightly lower generation, one random inverter trip, a faint burning smell near a connector, then grow into lost units, repeated shutdowns, or (rarely) safety risks.

Catch small solar issues before they become big faults.

This guide covers the most common solar faults seen in Indian homes (on-grid and hybrid), the early warning signs, and the first safe checks you can do before calling a technician.

Safety first (please read): Solar PV has high-voltage DC, which can be dangerous even when the grid is off. Don’t open the inverter/combiner box or unplug MC4 connectors unless you’re trained.

A 60-second solar health check (do this weekly)

1. Inverter status light: Green/Normal? Or red/fault?
2. Today’s generation vs your normal: Compare to a similar sunny day (same season).
3. Shutdown pattern: Does it stop at a specific time daily?
4. Noise/heat: Inverter fan running normally? No unusual buzzing.
5. Smell/visual signs (from a safe distance): No burning smell, melted plastic, or black marks near boxes/cables.

If any item looks off, use the fault list below.

Common solar faults and the early warning signs

1) Dust, bird droppings, and “soft shading” (most common)

Early signs

• Slow, steady drop in units over weeks
• Big difference between “after rain” vs “before rain”
• Panels look dull, patchy, or have stubborn droppings

Safe first checks

• Compare generation for the same weather week-to-week
• If accessible and safe, schedule cleaning (morning/evening, soft water if possible)

Why it matters
Even a small dirty patch can affect an entire string’s output more than people expect.

2) New shading (tree growth, new construction, tank placement)

Early signs

• Generation drops only during certain hours
• Your monitoring graph shows a dip/notch at the same time daily

Safe first checks

• Observe shadows on the array around the problem time
• Look for new tanks, pipes, dish antennas, or nearby construction shadows

Fix
Layout changes, trimming, or module-level optimization (in some cases) helps.

3) Loose/overheated connectors and DC joints (MC4, Y-connectors, junctions)

Early signs (take seriously)

• Burning smell near rooftop cable routes or DC box
• Discoloured/melted connector plastic
• Random inverter trips that “self-recover”
• Faults after hot afternoons (heat expands loose joints)

What to do

• Stop using the system and call service if you smell burning or see melting.
• Ask the technician for a thermal scan of connectors and string joints.

Loose DC connections can cause heating/arcing—this is one of the few issues that can become a fire risk.

4) Inverter faults and frequent shutdowns (grid + ventilation related)

Early signs

• Inverter shows error/warning code
• Frequent “No Grid”, “Grid Over/Under Voltage”, “OV/UV”, “Freq” messages
• Output falls during peak heat (thermal derating)

Safe first checks

• Ensure inverter area has airflow (not boxed in, not in direct sun)
• Check if AC MCB/RCCB is tripping repeatedly (don’t keep resetting blindly)

Common causes in India

• Grid voltage fluctuation (especially afternoons)
• Poor ventilation / clogged fan intake
• Loose AC terminals in the distribution board

5) Isolation / earth leakage / insulation resistance fault (often during rains)

Early signs

• Errors like “Isolation Fault”, “RISO Low”, “Earth Fault”
• Happens early morning, in humid weather, or after rain
• System runs again later when things dry

Likely causes

• Water ingress in junction boxes
• Cable damage (rodents are a big one)
• A nicked DC cable rubbing against metal

What to ask your technician

• Insulation resistance test and documentation (this is part of good PV commissioning and periodic retesting practice).

6) Surge Protection Device (SPD) failure after lightning or switching surges

Early signs

• SPD indicator turns red (many models have a small window)
• Inverter trips after storms
• Unexplained damage to inverter/communication ports

Fix
SPDs are sacrificial. They may need replacement after strong surges. Rooftop technical specs commonly call for proper protections such as earthing/lightning/surge.

7) String mismatch, one weak panel, or module degradation (hotspots / PID / micro-cracks)

Early signs

• One string consistently produces less than the other (if your monitoring shows it)
• Permanent loss that cleaning doesn’t fix
• Visible signs: browning, bubbles, backsheet damage, “snail trails” (not always fatal, but worth checking)

Best diagnostic

• Thermal scan + string I-V checks by a professional
• If under warranty, collect evidence early

Also note: Indian rooftop specs and standards typically reference IEC/BIS safety and performance qualifications for modules (e.g., IEC 61215/IS 14286 and safety series).

8) AC-side issues (MCB/RCCB trips, overheated AC terminals)

Early signs

• Inverter stops and your solar AC MCB is OFF/tripped
• Warm/hot wires near the solar breaker
• RCCB trips especially when heavy loads start

Common causes

• Loose terminals
• Incorrect breaker sizing/quality
• Neutral issues / earthing problems

Because this is electrical safety territory, it’s aligned with broader safety requirements under Indian electricity safety regulations.

 

9) Monitoring/app issues (system is fine, data is wrong)

Early signs

• Inverter display shows normal output but app shows 0
• Data gaps every day at the same time
• Wi-Fi reconnect fixes it temporarily

Fix
Check router placement, Wi-Fi strength, datalogger power, and firmware updates.

 

10) Net meter / export not crediting properly (billing mismatch)

Early signs

• Your plant generates normally, but bill savings don’t match
• Export units not showing as expected
• Meter wiring/CT direction errors (common after maintenance)

What to do

• Compare inverter “total energy” vs net meter export trend
• Raise it with installer/discom with screenshots and dates

 

Quick symptom cheat sheet (safe checks only)

• Sudden drop from yesterday: shading event, AC trip, inverter fault code, loose connection
• Gradual drop over weeks: soiling, seasonal change, partial shading growth
• Trips mostly during heat: inverter overheating/derating, loose terminals expanding
• Faults mostly during rain/humidity: insulation/earth leakage issue
• Burn smell / melted plastic: stop and call service immediately
• App wrong but inverter ok: monitoring/Wi-Fi/logger issue

When to stop troubleshooting and call a technician immediately

Call service (and keep the system off) if you notice:

• Burning smell, smoke, sparks
• Melted connectors, black marks, crackling sounds
• Water inside inverter/combiner
• Repeated MCB/RCCB trips that won’t hold
• Broken glass, severely damaged backsheet, or exposed wiring

Simple preventive maintenance schedule (practical for Indian rooftops)

Monthly

• Visual check for dirt buildup, new shadows, loose conduits
• Check inverter vents/fans aren’t choked with dust

Quarterly

• Cleaning (more frequent in dusty/coastal/industrial areas)
• Review monitoring graphs for new patterns

Yearly (or before summer)

• Tightening/torque check of terminals (by electrician)
• Earthing + SPD inspection
• Insulation resistance test if you’ve had rain-related faults or repeated trips (professional)

What to ask during a service visit (to get real answers)

• String-wise voltage and current readings
• Thermal scan of connectors and hotspots
• SPD status and earthing check
• Inverter event/fault log screenshots
• Insulation resistance test result (especially if “isolation fault” happens)