Replace a Failed Solar Inverter

Goal

Replace a failed grid-tied solar inverter cleanly + safely, restore system to production. Most string inverters need replacement at 10-15 years; planning for this is part of every solar system lifecycle.

Prerequisites

• New inverter (matching or upgraded model)
• Licensed electrician (legally required)
• DC + AC voltage testers
• Conduit fittings (sometimes needed)
• 3-6 hours per replacement
• Permit (if AHJ requires)

Procedure

Step 1: Verify diagnosis (before order)

Confirm inverter is the failure point:

• Display shows fault / nothing
• DC input present (panels working)
• No AC output
• Error codes / warranty support contacted

Order replacement model:

• Same brand + model when possible (same install)
• Same output rating
• Newer revision OK (firmware compatible)

Step 2: Shut down + verify isolation (30 min)

1. Open AC disconnect at panel
2. Open DC disconnect at inverter
3. Verify no voltage at AC + DC sides with meter
4. Wait for inverter capacitors to discharge (10 min for high-voltage models)
5. Tag-out/lock-out where appropriate

Step 3: Remove existing inverter (1 hour)

1. Disconnect AC wiring (mark each lead with tape)
2. Disconnect DC wiring (mark each lead with tape)
3. Disconnect grounding
4. Disconnect monitoring / communication cables
5. Unmount from wall (typically 4 lag bolts into stud)
6. Remove inverter from premises

Step 4: Install new inverter (1-2 hours)

1. Mount new inverter in same location (if dimensions match)

• Or relocate if needed; ensure adequate clearance

1. Mount per manufacturer spec (clearances, heat dissipation)
2. Connect AC wiring per labels + manufacturer diagram
3. Connect DC wiring per labels + manufacturer diagram
4. Connect grounding (per NEC)
5. Connect monitoring / communication

Step 5: Configure new inverter (30 min)

1. Set utility parameters (voltage, frequency tolerance)
2. Set grid connection profile (per utility requirements)
3. Configure WiFi/network connectivity
4. Pair with manufacturer monitoring portal
5. Customer signs into app + verifies access

Step 6: Energize + verify (30 min)

1. Close DC disconnect first (allows panel voltage to inverter)
2. Inverter boots; reads DC input
3. Close AC disconnect
4. Inverter detects AC grid, synchronizes
5. After 5-15 minutes: inverter begins producing
6. Verify DC input voltage matches expected
7. Verify AC output voltage + frequency
8. Verify monitoring online

Step 7: Customer walkthrough (30 min)

1. Show new inverter operating
2. Walk through new monitoring app (if different)
3. Discuss new warranty terms
4. Provide receipt + documentation
5. Schedule next inspection

Step 8: Inspection (if AHJ requires)

• Some jurisdictions require inspection of inverter replacements
• Schedule via permit
• Generally simple inspection

Different inverter brand (upgrade path)

If customer wants to switch inverter brand (e.g., string to microinverter):

Considerations:

• More complex install (per-panel installation)
• Panel-level DC wiring changes
• Different combiner / junction box requirements
• Cost: 50-100% premium over like-for-like

Procedure differs significantly:

• Microinverter install: separate SOP

When to upgrade vs replace

Replace like-for-like:

• Inverter failed within warranty: warranty replacement
• Inverter failed after warranty: cost-effective replacement
• Customer happy with current performance

Upgrade considerations:

• Battery storage interest → hybrid inverter
• Monitoring upgrade → newer inverter + better app
• Multiple shading issues → microinverter or optimizers
• Older string inverter + system is shaded → DC optimizer retrofit

Warranty replacement vs out-of-warranty

Manufacturer warranty (typically 10 years):

• Free replacement
• Customer pays labor only ( typical)
• Defective inverter shipped to manufacturer

Out of warranty:

• Customer pays full replacement
• for parts + labor

Verify warranty before quoting.

Common pitfalls

• Wrong polarity on DC: damages inverter immediately (some have reverse protection)
• Wrong AC phase connection: inverter doesn't synchronize
• Loose connections: voltage drop, inverter shutdown
• Grounding wrong: NEC violation, safety hazard
• Skipping firmware update: new inverter ships with old firmware
• Not configuring monitoring: customer can't see production
• Permit not pulled: legal issue

DC disconnect handling

The DC side requires special care:

• DC voltages typically 200-600V
• DC arcs (won't extinguish like AC)
• Always isolate at DC disconnect FIRST
• Verify with meter before touching wires

DC disconnect failure modes:

• Stuck open
• Stuck closed (worse - assumed dead, isn't)
• Internal arcing

Replace DC disconnect if it has any history of issues.

Inverter monitoring during transition

• Old inverter offline: customer loses monitoring data temporarily
• Manufacturer can usually preserve historical data
• New inverter monitoring resumes when paired

Set customer expectations.

Customer communication

Before service:

• Confirm inverter being replaced
• Confirm timing (some installs need multi-day if scheduling permits)
• Confirm payment plan if out-of-warranty

During:

• Update customer on progress
• Show before/after photos

After:

• Walk through new system
• Confirm satisfaction
• 30-day check-in call

Permit requirements

Some jurisdictions:

• Permit required for any electrical equipment swap
• Sometimes streamlined for like-for-like
• Always check + comply

Documentation

For each inverter swap, retain:

• Old inverter serial + failure documentation
• New inverter serial + installation date
• AHJ permit + inspection
• Warranty paperwork
• Photos
• Customer signoff

References

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