RePowering Technical Playbook Part 2: Evaluating and Completing a Repowering Project – Tigo Help Center

Chapters

Chapter	Stage	Purpose
1	ASSESS	Understand the existing system and determine what still has value.
2	DESIGN	Define the project boundary and verify compatibility before selecting replacement equipment.
3	INSTALL	Document the system, correct existing deficiencies, and integrate new and existing equipment.
4	COMMISSION	Verify configuration, communication, Rapid Shutdown, monitoring, and production.
5	EXPAND	Add new capabilities now or prepare the repowered system for future upgrades.

The Repowering Playbook creates and manages the opportunity.

The Repowering Technical Playbook executes it.

How to Use This Playbook

The RePowering Business Playbook explains how to identify, package, sell, and manage a repowering opportunity. This technical companion begins once the opportunity becomes a job. It is written for the point where an installer must evaluate an existing system, decide what can remain, design the replacement, complete the work, and prove the system operates as intended.

The technical workflow is intentionally simple:

ASSESS → DECIDE → DESIGN → INSTALL → COMMISSION → EXPAND

Three Questions for Every Stage

What must be evaluated?
What decision must be made?
Which technical resource supports the next step?

For current product-specific requirements, procedures, compatibility information, and design tools, refer to the Tigo Help Center Repowering Guide and linked technical resources found in the Appendix.

Chapter 1: Assess the Existing System

THE FIRST JOB IS UNDERSTANDING THE EXISTING SYSTEM, NOT REPLACING PARTS.

Repowering rarely begins with a clean slate. The system may be ten, fifteen, or twenty years old. Documentation may be incomplete. Equipment may have been replaced, modified, or abandoned by a previous installer. Before designing anything new, build an accurate record of what is actually on site.

Start with evidence, not assumptions.

1.1 Pre-Site Information

Collect what is available before arriving on site. The goal is not to diagnose the system from the office; it is to arrive with enough context to conduct an efficient assessment.

Reported system problem
When the problem began
Whether the issue is intermittent or consistently reproducible
Available monitoring history
Original plans, permits, and commissioning records
Known inverter, module, MLPE, battery, and monitoring equipment
Previous repairs or equipment changes
Approved project objective from the homeowner or project owner

1.2 Initial Safety Screening

Before testing or modifying the system, determine whether it can be safely inspected and energized.

Visible electrical hazards
Damaged conductors or equipment
Signs of overheating
Corrosion or water intrusion
Damaged connectors or exposed conductors
Conditions that require correction before additional testing

If the site cannot be safely tested, stop, correct the hazard, or escalate the condition before proceeding.

1.3 Verify What Is Installed

Old drawings help, but nameplates, photos, and measurements help more. Document the actual equipment before assumptions about compatibility become part of the new design.

MODULE	INVERTER	INTERCONNECTION
Make / model / ratings	Manufacturer / model / serial	Breaker / panel / point of interconnection

The next design is only as good as the information collected before it.

1.4 Inspect What You Plan to Keep

Repowering is largely an exercise in deciding what still has value. Existing equipment should remain only after its condition, compatibility, and role in the new design are verified.

PV modules: physical condition, ratings, connector type, mixed module types
Array wiring: connectors, homeruns, conductor condition, wire management
Grounding and bonding
Roof penetrations and mounting condition
MLPE type, condition, deployment, and placement
Rapid Shutdown architecture
Breakers, disconnects, service equipment, and conductor pathways
Monitoring and communication equipment

Reuse is a design decision, not a default setting.

1.5 Electrical Evaluation

Perform the electrical checks required to verify that the existing array and balance-of-system behave as expected.

String open-circuit voltage
Polarity
Measured versus expected voltage
Current, where required
Insulation resistance, where appropriate
Grounding continuity
Monitoring and production history
Abnormal or inconsistent string behavior

1.6 The Assessment Must End in a Decision

Use the information collected during the assessment to determine the appropriate technical path forward.

REPAIR Correct a limited failure while retaining the existing system architecture.	REPOWER Replace failed, aging, unsupported, or incompatible equipment.
EXPAND Add storage, PV capacity, monitoring, or other capability.	INVESTIGATE Additional testing or engineering review is required before proceeding.

Pick the technical path before designing the solution.

Chapter 1 Deliverables

Existing-system record
Assessment findings
Safety concerns
Equipment reuse recommendations
Repair, repower, expand, or investigate decision
Information required for system design

Chapter 2: Design the Repowering Solution

WHAT STAYS? WHAT GOES? WHAT GETS ADDED? WHAT IS OUT OF SCOPE?

A repowering design must integrate new equipment with whatever remains from the original system. The design process begins by defining that boundary, then verifying compatibility rather than assuming the old array will simply plug into the new equipment.

Undefined boundaries create expensive surprises.

2.1 Define the Project Boundary

Equipment that will remain
Equipment that will be removed
Equipment that will be replaced
Equipment that will be added
Existing deficiencies that must be corrected
Work specifically excluded from the project

2.2 Will the Existing Array Work With the New Inverter?

This is the design question hiding behind every “simple” inverter replacement. Physical condition determines whether the modules are worth retaining; electrical compatibility determines whether they can be retained.

EXISTING ARRAY	VERIFY	REPLACEMENT INVERTER
Module condition Ratings String configuration	Cold Voc MPPT range Current limits String-to-MPPT assignments	Applicable Tigo EI Inverter Service voltage Interconnection
Click HERE to download the Tigo EI String Sizing Tool

Minimum and maximum string length
Maximum system voltage
MPPT operating range
Cold-temperature open-circuit voltage
Maximum input current
Parallel-string limitations
Existing conductor suitability

Looking good enough to keep is only half the question. Prove the array works electrically with the replacement inverter.

2.3 MLPE and Rapid Shutdown: Rebuild the Architecture on Paper First

Legacy systems may contain older MLPE, no MLPE, or a Rapid Shutdown architecture that no longer fits the repowered design. Identify what exists, then determine what the repowered system must meet.

Determine:

Existing MLPE manufacturer, model, generation, and function
Whether the existing MLPE is required for inverter operation or is independent of the inverter
Whether existing MLPE can remain with the proposed replacement inverter
Whether existing MLPE must be removed or replaced
Whether existing module-level equipment, connectors, or wiring creates compatibility constraints
Whether optimization is required for the new design
Whether module-level monitoring is required or desired
Whether selective or full MLPE deployment is appropriate
Applicable Rapid Shutdown requirements for the repowered system
Whether existing Rapid Shutdown equipment can remain or must be replaced
Required shutdown initiation method
Expected array behavior during shutdown
Labeling, testing, and verification requirements

Refer to Appendix A for an MLPE Decision flowchart.

Do not assume the old Rapid Shutdown design applies to the new system.

2.4 Communication and Monitoring Must Be Designed

Commissioning should confirm the design, not discover it. Know how many devices should be present, where communication equipment will be located, and how monitoring will reach the network before installation begins.

Expected TS4 count
Number of TAPs and TAP placement
TAP-to-CCA assignments
Roof planes, obstructions, and elevation changes
Communication wiring pathways
Internet and network requirements
System ownership and user access
Required site and equipment information

2.5 Can the Existing PV Breaker Stay?

A replacement inverter may have a different output rating than the original equipment. Do not assume that the existing PV breaker must change, and do not assume that it can remain. Evaluate the point of interconnection as part of the design.

Existing PV breaker rating
Panel and bus capacity
Conductor ratings
Interconnection method
Whether changing the inverter output power (IPOC) is applicable
Whether service equipment modifications are required
Required documentation for the AHJ

Existing breaker reuse must be justified by design, configuration, and documentation.

2.6 GO Battery: Now, Later, or Not in Scope?

Repowering is the right time to decide on future expansion. If GO Battery is included now, design the complete system. If deferred, document the technical path so a future installation doesn’t start by undoing today's work. If proceeding with the battery, consult Chapter 5.

A deferred battery still needs a technical plan.

Chapter 2 Deliverables

Final equipment list
String and MPPT design
MLPE and Rapid Shutdown architecture
CCA and TAP design
Electrical integration plan
Monitoring plan
Battery or battery-readiness plan
Installation drawings and project documentation

Chapter 3: Complete the Repowering Installation

THE FASTEST WAY TO LOSE TIME IS TO REMOVE THE ONLY EVIDENCE YOU HAD.

Repowering work is different from new construction because the installer must preserve, identify, and integrate portions of an existing system. Document the original condition before removal, correct deficiencies that should not be carried forward, and use current product manuals for the exact installation procedures.

3.1 Document First. Disconnect Second.

Before equipment removal, capture both the detail and the context of the existing installation.

DETAIL	CONTEXT
Photograph conductor terminations, labels, grounding, communications, and landed conductors.	Photograph equipment locations, conduit routing, disconnects, service equipment, and the overall BOS layout.

Before disconnecting: document conductor terminations, equipment locations, and conduit routing.

Confirm the approved design
Verify equipment and materials
Label conductors and circuits
Record inverter settings and monitoring information
Confirm shutdown and lockout procedures
Protect equipment that will remain

3.2 Remove Existing Equipment Safely

Follow the required shutdown sequence
Account for stored energy
Verify de-energization before removal
Preserve reusable conductors and equipment
Document unexpected site conditions
Follow disposal, recycling, or return requirements where applicable

3.3 Correct Existing Deficiencies

A REPOWER IS AN OPPORTUNITY TO CORRECT EXISTING DESIGN PROBLEMS, NOT REPRODUCE THEM.

A repowering project should not inherit unsafe or noncompliant conditions simply because they existed before the new work began.

Damaged conductors
Improper wire management
Grounding or bonding problems
Connector issues
Unsupported equipment combinations
Incorrect breaker sizing
Inadequate Rapid Shutdown architecture
Water intrusion or corrosion

Correct existing deficiencies before incorporating existing equipment into the repowered system.

3.4 Use the Playbook for Sequence, the Manuals for Procedure

The playbook should guide the order of work and the decisions that belong to a repowering project. It should not duplicate current installation manuals.

SAFE REMOVAL → CORRECT DEFICIENCIES → INSTALL → INTEGRATE → QUALITY REVIEW

Tigo EI Inverter
TS4 MLPE
CCA
TAP
Rapid Shutdown components
Monitoring equipment
ATS
GO Battery, when included

3.5 Integrate Existing and New Equipment

Conductor identification and polarity
String and MPPT assignments
Breaker and disconnect ratings
Grounding and bonding
Communication wiring
Equipment labeling
Required clearances
Torque requirements

3.6 Installation Quality Review

Before energizing, compare the completed installation with the approved design.

Inspect all terminations
Confirm required labels
Verify clearances
Confirm conductors are protected and supported
Confirm communication connections
Record model and serial numbers
Photograph the completed installation
Document any as-built changes or unresolved issues

Common Repowering Installation Mistakes

Assuming the existing design is correct
Failing to label conductors before equipment removal
Reusing equipment without verifying compatibility
Treating the project exactly like new construction
Overlooking legacy MLPE
Incorrect MPPT assignments
Inadequate TAP placement
Reusing breakers or conductors without verification
Skipping corrections because the condition existed before the repower

Chapter 3 Deliverables

Installed system
Updated equipment record
As-built changes
Installation photographs
Pre-commissioning inspection results
List of unresolved issues

Chapter 4: Commission and Verify the System

INSTALLED IS NOT THE SAME AS OPERATIONAL.

Commissioning proves that the repowered system is configured correctly, communicates as designed, performs the required safety functions, and produces as expected. The goal is not simply to get the inverter to turn on.

PRE-CHECK → POWER UP → CONFIGURE → DISCOVER → TEST RSD → VERIFY PRODUCTION

4.1 Pre-Energization Checks

Mechanical installation
Conductor terminations
Polarity
String voltage
Grounding and bonding
Breaker and disconnect positions
Communication wiring
Battery connections, where applicable
ATS wiring, where applicable

4.2 Follow the Required Power-Up Sequence

Use the current product documentation for the required startup sequence. The technical playbook should show the sequence at a high level and point to the exact procedure.

AC power
DC power
CCA
EI Inverter
ATS
GO Battery
Monitoring devices

4.3 Verify Firmware and Configuration

Current required firmware
Grid profile
System operating mode
Export or power-control settings
Battery settings
Meter and CT configuration
Monitoring configuration

4.4 Discovery and Communication: Know What You Expect to Find

A successful discovery should confirm the design. If the design calls for 32 TS4 devices and the system discovers only 31, commissioning is incomplete.

Expected TS4 count
TAP communication
CCA communication
EI system communication
Battery communication
ATS communication
Internet connectivity
Portal visibility

4.5 Test Rapid Shutdown

Initiate shutdown using the designed method
Verify inverter response
Verify TS4 response
Verify CCA or transmitter behavior
Confirm required voltage reduction
Restore operation and verify recovery
Confirm final Rapid Shutdown labeling

Rapid Shutdown is not verified until it is tested.

4.6 Verify Production

String voltage
String current
MPPT behavior
Inverter production
Monitoring data
Module-level data, where applicable
Alarms and warnings
Comparison with expected system behavior

A green light is not a commissioning test.

4.7 Complete the Technical Handoff

Keep this handoff technical. The Business Playbook already covers customer relationship strategy and ongoing service.

Demonstrate system operation
Confirm monitoring access
Explain shutdown and restart procedures
Explain backup behavior, where applicable
Provide manuals and system documentation
Record commissioning results
Identify deferred work or known limitations

Chapter 4 Deliverables

Commissioning record
Verified device counts
Rapid Shutdown test result
Production verification
Monitoring confirmation
Final system configuration
Technical handoff documentation

Chapter 5: Expand the Repowered System

THE REPOWER IS THE RIGHT TIME TO MAKE THE FUTURE-EXPANSION DECISION.

Some projects end with restored operation. Others create a platform for storage, additional PV, improved monitoring, or future household loads. Treat expansion as a technical design decision, not an afterthought.

5.1 Add Tigo GO Battery During Repowering

Battery sizing and quantity
EI Inverter compatibility
ATS requirements
Backup-load design
Equipment location and clearances
Communication requirements
Commissioning sequence
Permitting requirements

5.2 Prepare for Future GO Battery Installation

If battery storage is deferred, make reasonable accommodations during the repower so the future installation does not require unnecessary rework.

Select compatible replacement equipment
Reserve battery installation space
Plan conduit pathways
Plan communication pathways
Reserve electrical capacity
Identify future backup loads
Document proposed equipment locations
Record deferred design recommendations

DESIGN TODAY’S SYSTEM WITH TOMORROW’S BATTERY IN MIND.

5.3 Add PV Capacity

Inverter capacity
MPPT availability
String compatibility
Module compatibility
Conductor capacity
Interconnection limits
Monitoring and MLPE requirements
Permitting implications

5.4 Upgrade or Add MLPE

Legacy TS4 compatibility
Mixed-device limitations
Monitoring additions
Optimization additions
Rapid Shutdown implications
Discovery and commissioning requirements

5.5 Upgrade Monitoring

Existing monitoring limitations
CCA and TAP additions
Network requirements
Module-level visibility
Account and ownership transfer
Portal configuration

5.6 Document Deferred Expansion

Equipment selected for future compatibility
Reserved spaces
Planned pathways
Electrical limitations
Future design assumptions
Additional equipment required
Conditions that must be reevaluated before expansion

Chapter 5 Deliverables

Expansion design
Compatibility confirmation
Updated system drawings
Updated equipment record
Revised commissioning documentation
Future-expansion recommendations

The Technical Repowering Mindset

1. Do not assume the existing system is correct.

2. Do not reuse equipment until compatibility is verified.

3. Do not leave until safety, communication, and production are verified.

Technical Resources

Use the resources below for detailed procedures, product-specific instructions, and information that may change over time. Linking to the current source keeps this guide focused while ensuring you always have the latest requirements and instructions.

Appendix A: MLPE Decision Flowchart

APPENDIX B: REPOWERING FIELD ASSESSMENT WORKSHEET

Optional field resource for documenting the existing system and on-site assessment.

PROJECT INFORMATION

Project / Site		Assessment Date	________________
Site Address		Installer / Company	____________________________
Primary Contact		System Age /	________________
Reported Problem	________________________________________________________________________________________
Project Objective	________________________________________________________________________________________

EXISTING SYSTEM

Equipment	Manufacturer / Model	Rating / Qty.	Serial / Notes
PV Modules	________________________	____________	________________________
Inverter	________________________	____________	________________________
MLPE / RSD	________________________	____________	________________________
Monitoring / CCA / TAP	________________________	____________	________________________
Battery / ATS	________________________	____________	________________________
Other	________________________	____________	________________________
PV Breaker	________ A	Service Voltage	____________
Main Breaker	________ A	Bus Rating	________ A
Point of Interconnection	________________________	Monitoring History	☐ Reviewed ☐ Unavailable

INITIAL SITE & SAFETY CHECK

☐ Visible electrical hazards ☐ Damaged/exposed conductors ☐ Overheating ☐ Water intrusion/corrosion ☐ Damaged/mismatched connectors
☐ Grounding/bonding concerns ☐ Roof/mounting concerns ☐ Damaged modules ☐ Poor wire management ☐ Correct hazard before testing

Safety concerns / notes: ________________________________________________________________________________________________________

ARRAY & STRING MEASUREMENTS

Str.	Mods.	Module Model	Expected Voc	Measured Voc	Current*	Polarity	Notes
1	____	____________	_____ V	_____ V	_____ A	☐ + / −	____________
2	____	____________	_____ V	_____ V	_____ A	☐ + / −	____________
3	____	____________	_____ V	_____ V	_____ A	☐ + / −	____________
4	____	____________	_____ V	_____ V	_____ A	☐ + / −	____________
5	____	____________	_____ V	_____ V	_____ A	☐ + / −	____________
6	____	____________	_____ V	_____ V	_____ A	☐ + / −	____________

*Current where required or appropriate. Additional checks may include insulation resistance, grounding continuity, and abnormal string behavior.

Additional strings / measurements: ________________________________________________________________________________________

REPOWERING FIELD ASSESSMENT WORKSHEET — PAGE 2

EQUIPMENT CONSIDERED FOR REUSE

Item	Acceptable	Concern	Replace	Notes
PV modules	☐	☐	☐	________________________________
Module connectors	☐	☐	☐	________________________________
Array wiring / homeruns	☐	☐	☐	________________________________
Grounding / bonding	☐	☐	☐	________________________________
Racking / mounting	☐	☐	☐	________________________________
Roof penetrations	☐	☐	☐	________________________________
MLPE	☐	☐	☐	________________________________
Rapid Shutdown equipment	☐	☐	☐	________________________________
Breaker / disconnects	☐	☐	☐	________________________________
Existing conductors	☐	☐	☐	________________________________
Monitoring / communications	☐	☐	☐	________________________________

Insulation resistance performed, where appropriate: ☐ Yes ☐ No ☐ N/A Grounding continuity verified: ☐ Yes ☐ No

EXISTING MLPE / RAPID SHUTDOWN

MLPE Mfr. / Model	________________________	Existing MLPE Qty.	________
MLPE Function	☐ Optimization ☐ Monitoring	Rapid Shutdown	☐ Yes ☐ No ☐ Unknown
Inverter-dependent MLPE?	☐ Yes ☐ No ☐ Unknown	Expected to Remain?	☐ Yes ☐ No ☐ Review

Existing shutdown initiation method: ________________________________________________________________________________

Architecture / compatibility observations: ________________________________________________________________________________

MONITORING & COMMUNICATION

☐ Existing monitoring operational ☐ Internet/network available ☐ CCA identified ☐ TAP(s) identified ☐ Existing TS4 count documented
☐ System/account ownership identified ☐ Communication pathway documented

Concerns / notes: ________________________________________________________________________________________________

DOCUMENTATION CAPTURED

☐ Inverter nameplate ☐ Module model/nameplate ☐ MLPE/RSD equipment ☐ Electrical/service equipment ☐ Breaker / POI
☐ Conductor terminations ☐ Array/roof condition ☐ Monitoring equipment ☐ Equipment locations/conduit routing ☐ Existing labels ☐ Overall installation

ON-SITE ASSESSMENT

Equipment suitable for reuse: ________________________________________________________________________________

Equipment requiring replacement: ________________________________________________________________________________

Existing deficiencies requiring correction: ________________________________________________________________________________

Additional testing / engineering review required: ________________________________________________________________________________

PRELIMINARY TECHNICAL PATH

☐ REPAIR Correct a limited failure while retaining the existing system architecture.	☐ REPOWER Replace failed, aging, unsupported, or incompatible equipment.
☐ EXPAND Add storage, PV capacity, monitoring, or other capability.	☐ INVESTIGATE Additional testing or engineering review is required before proceeding.

Recommended next action / preliminary scope:

Installer / Assessor

____________________________

Date

________________

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