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 the AC disconnect FIRST, so the inverter comes up with a grid reference
2. Close the DC disconnect
3. Inverter boots and reads DC input
4. Inverter detects the AC grid and 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):

• Unit is free; the customer pays labor and shipping only, which is usually well under half the out-of-warranty job
• Defective inverter shipped back to the manufacturer

Out of warranty:

• Customer pays parts and labor both. On a residential string inverter the hardware is the larger share, so quote the unit and the labor as separate lines
• This is the moment to price the upgrade path alongside the like-for-like, because the labor is the same either way

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 sustain; there is no zero crossing to snuff them the way there is on AC
• That is exactly why AC comes off FIRST, as in Step 2. Killing the grid makes the inverter stop producing, so the DC disconnect then opens with almost no current through it. Opening DC first means breaking a live DC circuit under load, which is how disconnects get welded and faces get burned
• Verify with a meter before touching wires. The array is still making voltage in daylight no matter what any disconnect is doing

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