This checklist is a companion article to the more detailed information found here:
Repowering a PV System with a Tigo Inverter: The Definitive Guide
Project Intake
Every repowering project begins with understanding the homeowner's concern before evaluating the existing equipment. Gathering this information helps confirm the reported issue, identify the customer's goals, and ensure the subsequent assessment focuses on the appropriate solution.
Complete the following before beginning the system assessment:
☐ Interview the homeowner.
☐ Document the reported symptoms. Record when the problem first occurred.
☐ Determine whether the issue is intermittent or continuous.
☐ Review system monitoring history (if available).
☐ Ask about any recent changes (roof work, electrical work, severe weather, utility outages, service visits, or equipment replacement).
☐ Confirm the homeowner's objective (restore operation, replace failed equipment, improve performance, add battery storage, expand the system, etc.).
☐ Photograph the existing installation before beginning work.
☐ Record the system make and model information, if readily accessible.
☐ Note any obvious safety hazards before proceeding with the assessment.
1. Assessment of Existing System
- Inspect the condition of the existing solar modules for physical damage (cracks, delamination, discoloration).
- Check wiring for wear, loose connections, or corrosion.
- Verify module degradation—calculate expected performance loss based on age.
- Identify any changes in shading (grown trees, new structures, etc.).
- Check the grounding configuration of the old inverter (transformer-based vs. transformerless).
- Determine if the existing array meets updated code requirements.
- Identify the number of strings, module ratings, and array configuration.
- Note the existing inverter’s max voltage, current, and MPPT specs for comparison.
2. Voltage and Current String Checks
- Measure and record each string's open-circuit voltage (Voc) during the coldest part of the day.
- Ensure string Voc does not exceed the Tigo inverter’s maximum DC input voltage (550V), even under cold temperatures.
- Measure and record the short-circuit current (Isc) under sunny conditions.
- Confirm Isc does not exceed the inverter’s max input current (16.9A).
- Verify the temperature coefficient impact on voltage and current readings.
- Ensure the string Vmp falls within the Tigo inverter’s MPPT range (80-550V).
- Check that all strings are producing similar voltage and current values.
3. Compatibility with the Tigo Inverter
- Check that the EI Inverter has sufficient MPPT terminals for the string configuration.
- Assign strings logically to MPPT inputs (e.g., different orientations).
- Decide if Module-Level Power Electronics (MLPE) like TS4 optimizers are needed for shading/mismatch.
4. Regulatory and Code Compliance
- Check if the jurisdiction requires NEC 2017+ module-level rapid shutdown.
- If rapid shutdown is required, install Tigo TS4 units.
- Verify that all disconnects, breakers, and fuses meet the latest NEC and local codes.
- Confirm that the system is compliant with utility interconnection standards.
- Check the existing labels and replace or update system placards as needed.
- Ensure the system is permitted and interconnection agreements are updated.
5. System Efficiency and Performance Gains
- Compare the efficiency ratings of the old and new inverters.
- Ensure the system is appropriately utilizing multi-MPPT inputs for optimization.
- If applicable, recommend DC oversizing to increase production (up to 200% DC:AC).
- Enable and test module-level monitoring if TS4 optimizers are installed.
- Verify that the existing array voltage allows for early-morning and low-light operation (80V).
6. Removal and Replacement Best Practices
- Shut down AC and DC power, and verify zero voltage before handling wiring.
- Remove old inverter carefully, labeling wires as needed.
- Reference the Tigo EI Inverter quick start guide (included in packaging) during this process.
- Mount the new Tigo inverter securely, ensuring adequate ventilation and clearances (>12 inches).
- Properly land and tighten DC input wiring, checking polarity before connecting.
- Connect AC wiring to the correct terminals (L1, L2, Ground, Neutral).
- If using TS4-O/S units, install the TAP (Tigo Access Point) in the center of the array. Multiple
- TAPs may be necessary, depending on the roof layout.
- Ground all components correctly, ensuring a continuous ground path.
- Install surge protection devices (SPDs) if necessary.
- Check DC disconnect placement and operation.
- Ensure conduit and wire management is neat, secure, and code-compliant.
7. Warranty and Manufacturer Support
- Register the Tigo EI inverter for warranty coverage.
- Confirm the warranty claim process and installer support options.
- Inform the customer about warranty coverage and service procedures.
- Ensure all installation and commissioning records are documented.
8. Final Testing and Commissioning
- Test and confirm internet connectivity for remote monitoring. Strong internet is required!
- Perform a final wiring check, ensuring all terminations are torqued to spec.
- Energize the DC input first, verifying proper startup sequence.
- Close the AC breaker and allow the inverter to sync with the grid.
- Use the Tigo EI app to configure and commission the inverter.
- Verify power production and MPPT tracking in the monitoring portal.
- Conduct a rapid shutdown test by cutting AC power and checking voltage drop.
- Walk the customer through inverter operation and monitoring access.
- Document and submit any required paperwork to AHJ and utility.
9. Next Step: Design
You should now have the information necessary to determine whether the existing system can be repaired or whether repowering is the preferred solution.
If repowering is appropriate, continue with the design process using the guidance provided in the Repowering a PV System with a Tigo Inverter: The Definitive Guide to:
Evaluate system compatibility.
Select an appropriate replacement inverter.
Identify any required electrical modifications.
Complete the installation and commissioning process.